an introduction using the renesas rx62n microcontroller

an introduction using the renesas rx62n microcontroller
EMBEDDED
SYSTEMS
AN INTRODUCTION USING THE
RENESAS RX62N MICROCONTROLLER
James M. Conrad
University of North Carolina at Charlotte
Alexander G. Dean
North Carolina State University
Micri␮m Press
1290 Weston Road, Suite 306
Weston, FL 33326
USA
www.micrium.com
Designations used by companies to distinguish their products are often claimed as trademarks. In all instances where
Micri␮m Press is aware of a trademark claim, the product name appears in initial capital letters, in all capital letters, or
in accordance with the vendor’s capitalization preference. Readers should contact the appropriate companies for more
complete information on trademarks and trademark registrations. All trademarks and registered trademarks in this book
are the property of their respective holders.
Copyright © 2011 by James M. Conrad and Alexander G. Dean except where noted otherwise. Published by Micri␮m
Press. All rights reserved. Printed in the United States of America. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of
the publisher; with the exception that the program listings may be entered, stored, and executed in a computer system, but
they may not be reproduced for publication.
The programs and code examples in this book are presented for instructional value. The programs and examples have
been carefully tested, but are not guaranteed to any particular purpose. The publisher and content contributors do not
offer any warranties and does not guarantee the accuracy, adequacy, or completeness of any information herein and
is not responsible for any errors or omissions. The publisher and content contributors assume no liability for damages
resulting from the use of the information in this book or for any infringement of the intellectual property rights of
third parties that would result from the use of this information.
Library of Congress subject headings:
1. Embedded computer systems
2. Real-time data processing
3. Computer software—Development
For bulk orders, please contact Micrium Press at: ⫹1 954 217 2036
ISBN: 978-1-935772-99-6
Please report errors or forward any comments and suggestions to [email protected]
Preface
This book is the results of a long relationship the authors have enjoyed with Renesas
Electronics America, Inc. (and one of its predecessors, Mitsubishi Electronics). We originally worked with this company because of their commitment to providing a low-cost evaluation board and free development software that students could purchase and use in classes
and senior design projects. Over the years the boards have remained as affordable (and
popular) as ever, and the software development tools available have added more functionality while still remaining available for free to our students.
We have been teaching embedded systems courses for over twelve years (and working
in the field even longer). We had not been able to find a book suitable for using in an undergraduate course that would lend itself to the theoretical and applied nature of embedded
systems design. Renesas had been asking us to create a book for several years, and the introduction of the new RX62N microcontroller offered a wonderful opportunity to work
with this powerful device and integrate it into our classes.
This book also has a radical feature not seen in many books currently on the market
(if any). It is freely available for download and is also provided with the Renesas RX62N
evaluation board. It is also available for purchase in hardcopy form for a modest price.
This book can be used on its own for an Introduction to Embedded Systems class or an
Introduction to Microprocessors/Microcontrollers. It can also be used as a supplement in
many different types of classes.
This book would not have been possible had it not been for the assistance of numerous
people. Several students and educators contributed to some of the chapters, including: Adam
Harris (1, 2), Suganya Jebasingh (2, 6), Vikram Gill (3,4), Archana Subramanian (4), Onkar
Raut (5, 7), Steven Erdmanczyk (8,9), Sunil Gurram (8,11), Aswin Ramakrishnan (11),
Vivek Srikantan (12), and Paul Mohan Das (12). Stephanie Conrad heavily edited versions
of the chapters. Michael McLain helped create the solutions for the homework assignments.
Thanks go to the compositor, Linda Foegen, and especially to June Hay-Harris, Rob Dautel,
and Todd DeBoer of Renesas for their help in getting this book produced and published (and
for their patience!). Many, many thanks go to the reviewers who offered valuable suggestions to make this book better, especially Jerry Zacharias, Mitch Ferguson, Mike Wilkinson,
and students from my UNC Charlotte Embedded Systems course.
Jim Conrad: I would like to personally thank my parents, the Conrads, and my in-laws,
the Warrens, for their continued assistance and guidance through the years while I worked
on this and other books. Also, I would especially like to thank my children, Jay, Mary Beth,
and Caroline, and my wife Stephanie, for their understanding when I needed to spend more
time on the book than I spent with them.
iii
iv
PREFACE
Alex Dean: I would like to thank Bill Trosky and Phil Koopman for opening the doors
into so many embedded systems through in-depth design reviews. I would like to thank my
students in my NCSU embedded systems courses for bringing their imagination, excitement, and persistence to class projects. I would also like to thank my wife Sonya for sharing her passion of seeking out and seizing opportunities, and our daughters Katherine and
Jacqueline for making me smile every time I leave work to head home.
James M. Conrad and Alexander G. Dean
September 2011
Foreword
The world of MCU-based embedded designs can be divided into those that take advantage
of existing code and MCUs, and those that require leading edge MCU architectures and
implementations. Dr. Conrad, with assistance from Dr. Dean, spent more than a year internalizing the inner workings and surrounding ecosystem of the newly-developed RX architecture, and have generated a book showcasing the RX line which has a level of peripheral
integration that has not been seen before. Indeed, by taking the best DNA of both CISC and
RISC architectures, and combining them into a new breed of MCU, the RX line enables
design approaches that were previously spread across the CISC and RISC camps and inaccessible in one device line.
The authors leverage the capabilities of the RX and demonstrate their own expert grasp
of all the dynamics that differentiate successful end solutions from those of the “me-too”
variety. They recognize that successful embedded systems require more than just good
hardware and software engineering. Jim and Alex have masterfully applied RX capabilities
to real world challenges using examples, applications, and approaches that will surely empower individuals and teams of designers.
Readers aspire to find books that have the right balance between depth and breadth.
Where there is too much detail, the relevance can be obscured; while a broad brush approach may trivialize the essence of key topics. This is especially true of books relating to
embedded designs that must achieve a utilitarian purpose. Here, Jim and Alex skillfully
navigate from topic to topic, knowing exactly when to throttle for maximum utility.
Whether you are a university student preparing for the real world, a design engineer
looking for leading edge approaches to time-critical processes, or a manager attempting to
further your risk management techniques, you will find their approach to embedded systems to be stimulating and compelling.
Ali Sebt
Renesas
September 8, 2011
v
Contents
Preface
iii
Foreword
v
CHAPTER ONE
Introduction to Embedded Systems
1
1.1
Learning Objectives
1
1.2
Concepts
1
1
2
1.2.1
1.2.2
1.3
Economics and Microcontrollers
Embedded Networks
Typical Benefits of Embedded Systems
1.3.1
1.3.2
1.3.3
1.3.4
Greater Performance and Efficiency
Lower Costs
More Features
Better Dependability
2
3
3
4
4
1.4
Embedded System Functions
4
1.5
Attributes of Embedded Systems
5
1.6
Constraints on Embedded Systems
6
1.7
Designing and Manufacturing Embedded Systems
6
1.8
An Example of an Embedded System: The EIN GreenEval Zigbee Module
7
1.9
Summary of Book Contents
8
1.10
Recap
9
1.11
References
9
CHAPTER TWO
Concepts of Microcontrollers
11
2.1
11
Learning Objectives
vii
viii
2.2
CONTENTS
Interfacing with Digital Signals
2.2.1
2.2.2
2.2.3
2.2.4
2.3
12
Data Register (DR)
13
Port Register (PORT)
14
Check State of Switch1 (Port 4 bit 0) and Turn On LED1
(Port D bit 0)
15
Input Buffer Control Register (ICR)
15
Open Drain Control Register (ODR)
15
Pull-Up MOS Control Register (PCR)
Example 1: Reading Switches to Control LEDs
16
16
Using LEDs as Outputs
16
Using Switches as Inputs
Driving Motors and Coils
Scanning Matrix Keypads
17
20
22
Analog to Digital Converters
Analog Comparator
Digital to Analog Conversion
24
24
25
26
Resistor Networks
26
Binary Weighted DACs
26
R-2R DAC
27
Pulse Width Modulation
28
Infrastructure: Power, Clock, and Reset
2.4.1
2.4.2
2.4.3
11
11
Data Direction Register (DDR)
Interfacing with Analog Signals
2.3.1
2.3.2
2.3.3
2.4
General Purpose Digital I/O
Power Supply
Clock Signal Generation
Reset Circuit
28
28
30
31
2.5
Recap
32
2.6
References
32
2.7
Exercises
32
CONTENTS
ix
CHAPTER THREE
Organization and Architecture of the Renesas
RX62N Microcontroller Board
35
3.1
Learning Objectives
35
Basic Concepts
35
35
38
3.2
3.2.1
3.2.2
Introduction to Computer Organization & Architecture
Architecture of the Renesas RX62N
CPU
3.2.3
3.2.4
3.2.5
3.2.6
Register Set
Data Types
Endianness
Data Arrangement
Bus Specification
42
42
52
55
56
57
Description of Buses
58
Bus Error Monitoring Section
63
Types of Bus Error
63
3.3
Basic Examples
64
3.4
Advanced Concepts
3.4.1
Pipelining
65
65
3.4.2
3.4.3
Pipeline Basic Operation
Operating Modes
Memory Organization
67
71
75
3.4.4
3.4.5
Byte Addressing vs. Word Addressing
Memory Map
I/O Registers
75
76
76
3.5
Advanced Examples
79
3.6
References
81
3.7
Exercises
82
x
CONTENTS
CHAPTER FOUR
Software Development Tools
85
4.1
Learning Objectives
85
4.2
Basic Concepts
4.2.1
4.2.2
4.2.3
Compilation Mechanism
Compilers for Embedded Systems
RX Compiler Package
85
85
87
87
4.2.4
4.2.5
Features of RX Family C/C⫹⫹ Compiler
Debugging Tools
Introduction to HEW
88
89
89
4.2.6
4.3
4.4
4.5
Creating or Opening a Project in HEW-IDE
90
Windows in HEW
92
Concept of Configuration and Session
93
Configuration
94
Session
Concepts of Header Files
94
94
Header Files Used in RX Family C/C⫹⫹ Compiler
95
Header Files Associated with RX62N
95
Basic Examples
Advanced Concepts
96
4.4.1
4.4.2
Advanced Debugging Concepts
The J-Link Debugger
106
106
117
4.4.3
Features
Description of the Header Files Used in the RX Family
118
118
Advanced Examples
130
Window Configuration
130
Changing the Register Display Radix
131
Setting the Layout
131
Choosing a Register to be Displayed
133
Modifying the Register Contents
133
Setting the Flag Value
134
CONTENTS
xi
Screenshot
134
Saving Register Contents
135
4.6
References
136
4.7
Exercises
137
CHAPTER FIVE
Software Engineering for Embedded Systems
141
5.1
Learning Objectives
141
5.2
Introduction
141
141
5.2.1
5.3
Risk Reduction
Software Development Stages
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
Development Lifecycle Overview
Requirements
Design Before Coding
Peer Reviews of Design Artifacts
System Architecture and Design Approach
Time-Critical Processing
5.3.6
5.3.7
5.3.8
5.4
Safety-Critical Processing
Detailed Design
Implementation
Software Testing
148
149
149
151
152
Do We Know How the System is Built?
153
How Many Modules Do We Test at a Time?
153
How Do We Keep from Breaking Old Bug Fixes?
154
Software Development Lifecycle Models
5.4.1
5.4.2
5.4.3
5.4.4
5.4.5
142
142
145
146
147
147
Waterfall Process
Iterative Process
Spiral Process
Agile Development Methods
Prototyping
155
155
156
156
157
158
xii
CONTENTS
5.5
Recap
158
5.6
References
158
5.7
Exercises
159
CHAPTER SIX
Converting Between the Analog and Digital Domains
161
6.1
Learning Objectives
161
6.2
Basic Concepts
161
163
165
165
6.2.1
6.2.2
6.2.3
6.3
Basic Examples
6.3.1
6.3.2
6.3.3
6.4
Analog to Digital Conversion by Successive Approximation
Conversion Speed
Transfer Function Calculation
Conversion Speed
Digital Value for a Given Analog Value
Step Size
Advanced Concepts
6.4.1
6.4.2
12-Bit A/D Converter
167
167
167
168
168
168
Registers
170
A/D Data Registers n (ADDRn) (n ⫽ A to H)
170
A/D Control Register (ADCSR)
170
A/D Channel Select Register (ADANS)
171
A/D-Converted Value Addition Mode Select Register (ADADS)
171
A/D-Converted Value Addition Count Select Register (ADADC)
172
A/D Control Extended Register (ADCER)
173
A/D Start Trigger Select Register (ADSTRGR)
173
Operation
175
Single-Cycle Scan Mode
175
Continuous Scan Mode
10-Bit A/D Converter
178
178
Registers
178
A/D Data Register (ADDRn) (n ⫽ A to D)
178
CONTENTS
6.4.3
6.5
xiii
A/D Control/Status Register (ADCSR)
178
A/D Control Register (ADCR)
180
A/D Data Placement Register (ADDPR)
181
A/D Self-Diagnostic Register (ADDIAGR)
181
Operation
D/A Converter
182
183
D/A Registers
183
D/A Data Register (DADRm) (m ⫽ 0, 1)
184
D/A Control Register (DACR)
184
D/A Data Placement Register (DADPR)
184
Operation
184
Advanced Examples
6.5.1
12-Bit ADC
186
186
6.5.2
Output
10-Bit ADC
188
188
6.5.3
Output
DAC
190
190
6.6
Recap
191
6.7
References
192
6.8
Exercises
192
CHAPTER SEVEN
Serial Communications
193
7.1
Learning Objectives
193
7.2
Basic Concepts of Serial Communications
193
7.2.1
7.2.2
Terminologies
Introduction to the RX62N Serial Communication Interfacing
Universal Asynchronous Receiver and Transmitter
194
196
198
Registers Related to the SCI in UART Mode
200
Serial Mode Register (SCIX.SMR)
201
Serial Control Register (SCIx.SCR)
202
xiv
CONTENTS
7.2.3
7.2.4
Serial Status Register (SCIx.SSR)
203
Bit Rate Register (SCIx.BRR)
204
Transmit Data Register (SCIx.TDR)
205
Receive Data Register (SCIx.RDR)
205
Variations to the UART
Renesas Serial Peripheral Interface
General Working of SPI Modules
207
Configurations of the Renesas SPI
208
Registers Related to the Renesas Serial Peripheral Interface
208
Configuring the RSPI to Function in Single Master Single Slave Mode
Renesas Inter Integrated Circuit Bus
I2C Bus Protocol
2
7.3
7.3.2
7.3.3
7.4
7.4.2
221
222
Registers Related to the RIIC Interface
224
Basic Transmission/Receiving of Serial Data via UART
236
236
Explanation of Initialization Code
239
Explanation of Transmission Code
240
Explanation of Reception Code
241
Explanation of Main Program
Basic Transmission of Data Using Serial Peripheral Interface Bus
241
242
Explanation of Initialization Code
244
Transmission Code
246
Explanation of Transmission Code
246
Main Code
247
Explanation of Main Code
Basic Transmission and Reception of Data Using the Renesas I2C Bus
Advanced Concepts
7.4.1
220
221
I C Communication Modes
Basic Examples
7.3.1
205
205
Applying FIFO Data Structures for Transmission and Reception
Using the UART Serial Communications Interface
Multiprocessor Communication Using the Renesas Serial
Peripheral Interface
247
248
262
262
264
Master Algorithm
266
Slave Algorithm
267
CONTENTS
7.4.3
7.5
Transfer of Data Between Peripherals Connected
on the I2C Bus Using FIFOs
Advanced Examples
7.5.1
FIFO Data Structures for Transmission and Reception Using
the UART Serial Communications Interface
Setting Up Interrupt Service Routines
7.5.2
7.5.3
Main Program
Multiprocessor Communication Using Queues and the Renesas
Serial Peripheral Interface
xv
268
276
276
276
279
280
Setting Up Interrupt Service Routines
280
Setting Up Function Definitions for Operating on the Queues
281
Setting Up All the Function Details Related to the Functioning
of the UART and FIFO Queues
282
Main Program
Transfer of data between peripherals connected
on the I2C bus using FIFOs
285
286
7.6
Recap
297
7.7
References
299
7.8
Exercises
299
CHAPTER EIGHT
Event Counters, Timers, and the Real Time Clock
301
8.1
Learning Objectives
301
8.2
Basic Concepts
301
301
8.2.1
Timer and Event Counter
Timer
8.2.2
8.2.3
8.3
Event Counter
Cascading Timers
Pulse Output Operation
Real Time Clock
8.3.1
8.3.2
8.3.3
RTC Registers
Setting the RTC
Reading the RTC
301
302
310
311
313
314
321
322
xvi
CONTENTS
8.4
Basic Examples
8.4.1
8.4.2
8.4.3
8.5
Advanced Concepts
8.5.1
8.5.2
8.5.3
8.6
Setting Up Cascaded Timers
Setting Up a Timer for Pulse Output
Setting and Reading from the Real Time Clock
Using a Cascaded Timer with 16-Bit Timer Constant Registers
Calculating and Programming Pulse Frequency and Duty Cycle
in Pulse Output Mode, and Controlling a Servo Motor
Using the Real Time Clock’s Alarm and Periodic Interrupts
Advanced Examples
8.6.1
8.6.2
8.6.3
Using a Cascaded Timer with 16-Bit Timer Constant Registers
Setting Up Pulse Output Mode to Control a Servo Motor
Using the Real Time Clock’s Alarm and Periodic Interrupts
323
323
327
328
333
333
334
336
337
337
340
343
8.7
Recap
347
8.8
References
347
8.9
Exercises
347
CHAPTER NINE
Using Interrupts with Peripherals
349
9.1
Learning Objectives
349
9.2
Basic Concepts
349
349
9.2.1
9.3
Using Interrupts for Tasks versus Other Methods
Interrupts
350
Interrupt Request Register n (IRn) (n ⫽ interrupt vector number)
351
IR Flag (Interrupt Status Flag)
354
Interrupt Priority Register m (IPRm) (m ⫽ 00 to 8Fh)
355
Fast Interrupt Register (FIR)
356
Software Interrupt Activation Register (SWINTR)
356
IRQ Control Register i (IRQCRi) (i ⫽ 0 to 15)
357
Non-Maskable Interrupt Enable Register (NMIER)
357
Non-Maskable Interrupt Status Register (NMISR)
358
CONTENTS
Non-Maskable Interrupt Clear Register (NMICLR)
9.3.1
9.3.2
NMI Pin Interrupt Control Register (NMICR)
Interrupt Vector Table
Interrupt Operation
Edge Detection
9.3.3
Level Detection
Setting Up an Interrupt for a Peripheral
Setting Up an Interrupt
9.3.4
9.4
Basic Examples
9.4.1
9.4.2
9.5
Polling a Switch for Input versus Using an Interrupt
Setting up the ADC with an Interrupt
Advanced Concepts
9.5.1
9.5.2
9.5.3
9.6
Registers Set in the ICU for an Interrupt
How an Interrupt Operates
Minimizing the Amount of Code in Interrupts
Brief Introduction to State Machines
State Machines and Using Them with Interrupts
Advanced Examples
9.6.1
9.6.2
Using an ADC Interrupt with Flags to Process Data
A Simple State Machine Controlled by Interrupts
xvii
359
360
360
360
361
362
363
363
365
369
370
370
373
377
377
378
379
380
380
383
9.7
Recap
389
9.8
References
389
9.9
Exercises
389
CHAPTER TEN
Floating Point Unit and Operations
391
10.1
Learning Objectives
391
10.2
Basic Concepts
391
391
10.2.1 Floating Point Basics
Floating Point Representation
391
IEEE 754 Floating Point Standard
392
xviii
CONTENTS
The IEEE 754 Floating Point Standard
393
Single Precision (32 bits)
393
Double Precision (64 bits)
10.2.2 Pipelining Basics
Instruction Fetch
397
Instruction Decode
398
Execution
398
Memory Access
398
Write-Back
10.2.3 Floating Point in RX62N
10.3
398
398
Floating Point Unit
399
Floating Point Registers
399
Floating Point Instructions
401
FADD
401
FSUB
401
FCMP
403
Floating Point Exceptions
403
Overflow
403
Underflow
404
Inexact
404
Divide-By-Zero
404
Invalid Operation
404
Basic Examples
10.3.1 Operations Explaining Floating Point Exceptions
10.4
395
397
Advanced Concepts of RX62N Floating Point Unit
10.4.1 FPSW in Detail
404
404
408
408
Rounding-Modes
409
Cause Flags
409
Exception Flags
410
Exception Handling Enable Bits
410
Denormalized Number Bit
410
Floating Point Error Summary Flag
411
Reserved Bits
411
CONTENTS
10.4.2 Floating Point Exception Handling Procedure
10.5
xix
411
Acceptance of the Exception
411
Hardware Pre-Processing
412
Processing of User-Written Program Code
412
Hardware Post-Processing
414
Advanced Examples
10.5.1 Fixed-Point and Floating-Point Operation Time Calculation
414
414
Int
417
Float
417
Double
10.5.2 Matrix Multiplication Time Calculation
417
418
Int
422
Float
422
Double
422
10.6
Recap
422
10.7
References
423
10.8
Exercises
423
CHAPTER ELEVEN
Watchdog Timer and Brown-Out Detector
425
11.1
Learning Objectives
425
11.2
Basic Concepts of Watchdog Timer
425
426
426
11.2.1 Watchdog Timer (WDT)
11.2.2 Register Descriptions
Timer Counter Register (TCNT)
428
Explanation of the Code
428
Timer Control/Status Register (TCSR)
428
Bit Description of TCSR
429
Explanation of the Code
431
Reset Control/Status Register (RSTCSR)
431
xx
CONTENTS
Bit Description of RSTCSR
11.3
Explanation of the Code
11.2.3 Operation of WDT
432
432
Basic Code Examples
11.3.1 Example 1: Setting Up Watchdog Timer Mode
434
434
Explanation of the Code
11.3.2 Example 2: Application of a Watchdog Timer
434
434
Explanation of the Code
11.4
Advanced Concepts of the Watchdog Timer
11.4.1 Interval Timer Mode
11.4.2 Independent Watchdog Timer (IWDT)
11.5
435
436
436
436
Bit Description for IWDTCR
438
Bit Description of IWDTSR
441
Operation of Independent Watchdog Timer
441
Complex Examples
11.5.1 Example 1: Interval Timer Mode of a Watchdog Timer
443
443
Explanation of the Code
11.5.2 Example 2: Setting Up of IWDT
443
444
Explanation of the Code
11.6
431
Brownout Condition
444
11.6.1 How Brownout Occurs
11.6.2 Automatically Detecting a Brownout Condition
444
444
444
11.7
Recap
445
11.8
References
445
11.9
Exercises
445
CHAPTER TWELVE
Designing Responsive and Real-Time Systems
447
12.1
Learning Objectives
447
12.2
Motivation
447
12.3
Scheduling Fundamentals
449
CONTENTS
12.3.1
12.3.2
12.3.3
12.3.4
12.3.5
12.3.6
12.4
Task Ordering
Task Preemption
Fairness and Prioritization
Response Time and Preemption
Stack Memory Requirements
Interrupts
Task Management
12.4.1 Task States
12.4.2 Transitions between States
12.4.3 Context Switching for Preemptive Systems
12.5
Sharing Data Safely
12.5.1
12.5.2
12.5.3
12.5.4
12.6
Data Shared Objects
Function Reentrancy
High-Level Languages and Atomicity
Shared-Data Solutions and Protection
xxi
449
451
452
453
454
455
456
456
457
458
460
460
461
462
464
Disable Interrupts
464
Use a Lock
465
RTOS-Provided Semaphore
466
RTOS-Provided Messages
467
Disable Task Switching
467
Nonpreemptive Dynamic Scheduler
12.6.1 Concepts
12.6.2 Implementation
467
467
470
Task Table
470
Managing Tasks
471
Tick Timer Configuration and ISR
473
Scheduler
12.6.3 Example Application using RTC Scheduler
474
474
12.7
References
475
12.8
Exercises
476
Appendix A
479
Index
487
Chapter One
Introduction to Embedded Systems
1.1
LEARNING OBJECTIVES
In this chapter the reader will learn:
䡲
䡲
䡲
䡲
1.2
What an embedded system is
Why to embed a computer
What functions and attributes embedded systems need to provide
What constraints embedded systems have
CONCEPTS
An embedded system is an application-specific computer system which is built into a
larger system or device. Using a computer system rather than other control methods (such
as non-programmable logic circuits, electro-mechanical controls, and hydraulic control)
offers many benefits such as sophisticated control, precise timing, low unit cost, low development cost, high flexibility, small size, and low weight. These basic characteristics can
be used to improve the overall system or device in various ways:
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Improved performance
More functions and features
Reduced cost
Increased dependability
Because of these benefits, billions of microcontrollers are sold each year to create embedded systems for a wide range of products.
1.2.1
Economics and Microcontrollers
Microcontrollers are remarkably inexpensive yet offer tremendous performance. The microprocessor for a personal computer may cost $100 or more, while microcontrollers typically cost far less, starting at under $0.25. Why is this so?
1
2
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Microcontrollers provide extremely inexpensive processing because they can leverage
economies of scale. MCUs are programmable in software, so a chipmaker can design a
single type of MCU which will satisfy the needs of many customers (when combined with
their application-specific software). This reduces the per-chip cost by amortizing the design costs over many millions of units.
The cost of an integrated circuit (such as a microcontroller or a microprocessor)
depends on two factors: non-recurring engineering (NRE) cost and recurring cost. The
NRE cost includes paying engineers to design the integrated circuit (IC) and verify
through simulation and prototyping that it will work properly. The recurring cost is incurred by making each additional IC, and includes raw materials, processing, testing, and
packaging.
The IC’s area is the major factor determining this recurring cost. The smaller the IC,
the more will fit onto a silicon wafer and the lower the recurring cost. Microcontrollers are
much smaller than microprocessors for personal computers, so they will cost less (given
the same number of ICs sold). The NRE cost must be divided across each IC sold. As the
number of ICs sold rises, the NRE adder falls, and so each IC’s price falls as well. Lowvolume chips are more expensive than high-volume chips.
1.2.2
Embedded Networks
Some embedded systems consist of multiple embedded computers communicating
across an embedded network, and offer further benefits. Each computer on the network
uses a communication protocol to share the same set of wires to communicate, rather than
dedicating one set for each possible communication route. Several advantages come from
having fewer wires:
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Lower parts cost, as fewer wires are needed
Lower labor costs, as it is faster to assemble
Greater reliability, as it has fewer connections to fail
Other advantages come from allowing separate nodes to share information. New features
may be possible, or the system efficiency may be improved through better coordination of
activities among different nodes.
1.3
TYPICAL BENEFITS OF EMBEDDED SYSTEMS
As an example, let’s examine how embedded systems have affected automobiles. A typical
modern car has dozens of microcontrollers embedded within it. Let’s see why.
CHAPTER 1 / INTRODUCTION TO EMBEDDED SYSTEMS
1.3.1
3
Greater Performance and Efficiency
Computer control of automobile engines lowers pollution and increases fuel efficiency, reducing operating costs.
Burning gasoline with air in spark ignition engines is a tricky business if we want to maximize efficiency, yet minimize pollution. The main factor affecting emissions is the ratio of
air mass to fuel mass. The ideal ratio is 14.7 to 1, and the catalytic converter is designed to operate most efficiently at this ratio. If there is too little air (a rich mix), then excessive carbon
monoxide (CO) and hydrocarbons (HC) will be produced. If there is too much air (a lean
mix), then large amounts of oxides of nitrogen (called NOx) will be created. So we would like
for each fuel injector to add just the right amount of fuel. This depends on the mass of the air
inside the cylinder, which depends on factors such as air temperature and air pressure. These
in turn depend on altitude and weather, as well as whether the engine is warmed up or not.
Another factor is the timing of the sparkplug firing. If it fires early, then there is more
time for combustion within the cylinder before the exhaust valve opens. This raises the average temperature within the cylinder and changes the combustion process, affecting CO,
HC, and NOx concentrations.
It would be quite impractical to design a mechanical control system to consider all of
these factors and squirt the fuel injectors at just the right instant for the right amount of
time. Thankfully, an inexpensive microcontroller is quite effective at these kinds of calculations and control.
1.3.2
Lower Costs
There are various ways in which an embedded system can reduce the costs associated with
a device.
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Component costs: Embedded software can compensate for poor signal quality, allowing the use of less-expensive components. For example, a low-cost pressure
sensor may be very temperature-dependent. If ambient temperature information is
already available, then it is a simple matter to compensate for the temperatureinduced error.
Manufacturing costs: Many vehicles use the Control Area Network (CAN) protocol to communicate across an in-car network. The embedded network reduces
assembly and parts costs because of the simpler wiring harness.
Operating costs: As mentioned above, an embedded system enables automobile
engines to operate more efficiently, reducing the amount of gasoline needed and
hence lowering operating costs.
Maintenance costs: Some vehicles predict oil life by monitoring engine use history, notifying the driver when an oil change is needed.
4
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
1.3.3
More Features
An MCU running application-specific software offers tremendous opportunities for features and customization. These features can make your company’s products stand out from
the competition.
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1.3.4
Cruise control keeps the car running at the same speed regardless of hills, wind,
and other external factors.
Smart airbags reduce injuries by adjusting inflation speed based on passenger
weight.
Power seats move to each driver’s preferred position automatically, based on
whose keyless entry fob was used to open the car.
Headlights and interior lights shut off automatically after a time delay if the car
is not running and prevents the lights from draining the battery.
Better Dependability
Embedded systems and networks offer many opportunities to improve dependability.
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1.4
An engine controller (and other controllers) can provide various “limp-home
modes” to keep the car running even if one or more sensors or other devices fail.
A warning of an impending failure can be provided.
Diagnostic information can be provided to the driver or service personnel, saving
valuable trouble-shooting time.
EMBEDDED SYSTEM FUNCTIONS
There are several common functions which embedded systems typically provide.
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Control systems monitor a process and adjust an output variable to keep the
process running at the desired set point. For example, a cruise control system may
increase the throttle setting if the car’s speed is lower than the desired speed, and
reduce it if the car is too fast.
There is often sequencing among multiple states. For example, a car engine goes
through multiple states or control modes when started. During Crank and Start,
the fuel/air mix is lean and depends on the engine coolant temperature. Once the
engine has started, the controller switches to the Warm-Up mode, in order to raise
the engine and exhaust system temperatures to their ideal levels. Here the fuel/air
CHAPTER 1 / INTRODUCTION TO EMBEDDED SYSTEMS
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1.5
5
mixture and ignition timing are adjusted, again based in part on the engine coolant
temperature. When the engine has warmed up it can switch into Idle mode. In this
mode the controller seeks to minimize the engine’s speed, yet still run smoothly
and efficiently despite changes in loads due to air conditioning, power steering,
and the electrical system.
Signal processing modifies input signals to eliminate noise, emphasize signal
components of interest, and compensate for other factors. For example, a handsfree speakerphone interface may use multiple microphones, beam-forming, and
active noise cancellation to filter out low-frequency road noise. Other sensors may
have spark-plug noise filtered out.
Communications and networking enable different devices on the same network
to exchange information. For example, the engine controller may need to send a
message indicating speed. To do this, the speed value must be formatted according
to the communication protocol and then loaded into the network interface peripheral for transmission.
ATTRIBUTES OF EMBEDDED SYSTEMS
Embedded systems are designed so that the resulting device behaves in certain desirable
ways.
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Embedded systems need to respond to events which occur in the environment,
whether a user presses a button or a motor overheats. A system which is not sufficiently responsive is not likely to be a successful product. For example, when we
press a channel select button for the radio, we would like for it to respond within
some reasonable time.
For real-time systems, the timing of the responses is critical because late answers
are wrong answers. Igniting the fuel in a cylinder is time-critical because bad timing can damage or destroy engine components (to say nothing of reducing power,
or the efficiency and pollution concerns mentioned previously).
Embedded systems typically require sophisticated fault handling and diagnostics to enable safe and reliable operation. Often the fault handling code is larger
and more complex than the normal operation code. It is easy to design for the
“everything goes right and works fine” case. It is far more difficult to determine
methods to handle the exceptional cases. What is likely to fail? Which failures
can lead to dangerous conditions? How should the system handle failures? How
will you test that the system handles the failures correctly?
Embedded systems may be expected to operate independently for years without operator attention such as adjustment or resetting. The system is expected to
6
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
operate robustly and always work. Given that it is very difficult and expensive to
write perfect, bug-free software, developers build in mechanisms to detect faulty
behavior and respond, perhaps by restarting the system.
1.6
CONSTRAINTS ON EMBEDDED SYSTEMS
Embedded systems often have constraints which limit the designer’s options, and can lead
to creative and elegant solutions. These constraints are typically different from those for
general-purpose computers.
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1.7
Cost is a common constraint. Many applications which use embedded systems are
sold in very competitive markets, in which price is a major factor. Often a manufacturer will hire subcontractors to design and build individual sub-systems. This
allows the manufacturer to pit potential subcontractors against each other, keeping
prices down.
There may be size and weight limits for portable and mobile applications. An embedded system for an automotive remote keyless entry transmitter must fit into a
small fob on a key ring which fits easily into a pocket. Similarly, the receiver must
not be too heavy. A heavier car will have worse acceleration, braking, cornering,
and fuel efficiency. Aircraft and spacecraft are especially sensitive to weight since
a heavier craft requires more fuel to achieve the same range.
There may be limited power or energy available. For example, a battery has a limited amount of energy, while a solar cell generates a limited amount of power.
High temperatures may limit the amount of cooling available, which will limit the
power which can be used.
The environment may be harsh. Automotive electronics under the hood of a car need
to operate across a wide range of temperatures (⫺40°C to 125°C, or ⫺40°F to 193°F),
while withstanding vibrations, physical impact, and corroding salt spray. Spark plugs
generate broadband radio frequency energy which can interfere with electronics.
DESIGNING AND MANUFACTURING EMBEDDED SYSTEMS
Embedded systems are designed with a central microcontroller and other supporting electronic components mounted on a printed circuit board (PCB). PCBs provide the means to
connect these integrated circuits to each other to make an operational system. The PCB provides structural support and the wiring of the circuit. The individual wires on the PCB are
called traces and are made from a flat copper foil. While many circuit designs may use the
same standard components, the PCB is often a custom component for a given design.
Designing a PCB requires a completed schematic for the circuit. This schematic is
sometimes different than the schematic seen in textbooks. It often contains extra informa-
CHAPTER 1 / INTRODUCTION TO EMBEDDED SYSTEMS
7
Figure 1.1 EIN GreenEval Zigbee Module.
tion about the components and construction of the board. For example, a textbook
schematic may only show a battery for the power supply, while the production schematic
would show the battery case, the number of cells, the rating of the battery, and the manufacturers of the components.
From the schematic, a designer will use their computer-aided design tools to identify
the size of the PCB, and then place the electronic components on their board drawing. The
designer will also place the wiring between the components on the PCB.
The physical PCB is manufactured from a fiberglass-resin material that is lightweight
and inexpensive. A manufacturer will add copper wiring traces to the surfaces of the board
and the appropriate insulation and white silk screening. The final manufacturing steps are
applying solder, placing the components, and heating/cooling the solder. Figure 1.1 shows
an example of a finished board.
The completed boards are electrically tested for functionality. Any board failing the
test is inspected in more detail to find the problems. These boards are repaired to increase
the passing rate acceptable to the manufacturer. The boards are wrapped in anti-static materials and shipped to the next location for the next stage of production, or immediately installed in a mechanical enclosure (like the mechanical shell of a mobile phone).
1.8
AN EXAMPLE OF AN EMBEDDED SYSTEM:
THE EIN GREENEVAL ZIGBEE MODULE
The EIN GreenEval Zigbee (Envisionnovation, http://www.eininc.net/products.html) module is one example of a Renesas MCU-based embedded system. This device has thirty-four
digital I/O lines that are controlled by a Zigbee radio.
8
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Figure 1.1 shows the main board of the EIN GreenEval Zigbee Module. As seen in this
example, taking off the shielding provides a good look at the internal circuitry. Six of the
main components are visible. Starting from left to right; the large cylindrical device hanging off the left edge of the board is an antenna for the 2.4 GHz radio.
The chip labeled 5PE20V (http://www.micron.com//get-document/?documentId=
5965&file=M25PE20_10.pdf) (the small 8-pin chip at the top left of the image) is a pageerasable serial FLASH chip. This chip communicates with the Renesas MCU through the
SPI bus. This chip is also used to hold more data than the MCU. Since the MCU can only
handle 8 k of data, it is quickly filled. This extra FLASH chip can hold an additional
2 Mbits.
The square chip on the lower left is a Skyworks 2.4 GHz Front-End Module (FEM)
(SKYWORKS Solutions, Inc., http://www.skyworksinc.com/Product.aspx?ProductID⫽752),
which simply boosts radio signals sent from the MCU. It is controlled by three output pins of
the MCU. One pin controls putting the FEM to sleep to save power, another pin selects
whether the FEM will send or receive data, and the last pin actually transmits and receives data
to and from the FEM.
The large chip in the center is a Renesas R5FF36B3 from the M16C family of chips
with 256 K ⫹ 24 K of ROM, 20 k RAM, and 8 k of data (Renesas Electronics America,
Inc., RENESAS MCU: M16C Family/M16C/60 SERIES, http://am.renesas.com/products/
mpumcu/m16c/m16c60/m16c6b/m16c6b_root.jsp). Thirty-four I/O pins are used to interface with external pins on the module. This processor is running at 4 MHz (controlled by
the small metal chip which is actually a temperature compensated crystal oscillator). This
chip has an RF radio built in.
The pins at the far right are a programming and interface header. They are used to communicate with and program the Renesas MCU.
1.9
SUMMARY OF BOOK CONTENTS
This book is structured as follows:
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Chapters 2 and 3 present basic microcontroller concepts and the specifics of the
RX62N.
Chapters 4 and 5 show how software is built. At the low level they show how programs are compiled and downloaded. At the high level they show software engineering concepts and practices.
Chapters 6 through 8 present how to use peripherals to interface with the environment and simplify programs.
Chapter 9 presents how to use interrupts to improve response times and program
structure.
CHAPTER 1 / INTRODUCTION TO EMBEDDED SYSTEMS
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1.10
9
Chapter 10 presents how to use the floating-point math support in the RX62N.
Chapter 11 presents how to increase system robustness using the watchdog timer
and voltage brownout detector.
Chapter 12 presents how to structure multi-threaded software so the resulting system is predictably responsive.
RECAP
An embedded system is an application-specific computer system which is built into a
larger system or device. Using a computer system enables improved performance, more
functions and features, lower cost, and greater dependability. With embedded computer
systems, manufacturers can add sophisticated control and monitoring to devices and other
systems, while leveraging the low-cost microcontrollers running custom software.
1.11
REFERENCES
Envisionnovation. EININC Products. Ontario: Envisionnovation, 2010. Web. Accessed at http://www.eininc.
net/products.html
Numonyx MP25PE20 datasheet http://www.micron.com//get-document/?documentId=5965&file=M25PE20_
10.pdf
RENESAS MCU: M16C Family/M16C/60 SERIES. Renesas Electronics America, Inc., 2010. Web. Accessed
at http://am.renesas.com/products/mpumcu/m16c/m16c60/m16c6b/m16c6b_root.jsp
SKYWORKS Solutions, Inc. SKYWORKS Products: SKY65352–11. Woburn, MA: SKYWORKS Solutions,
Inc., 2009. Web. Accessed at http://www.skyworksinc.com/Product.aspx?ProductID⫽752
Chapter Two
Concepts of Microcontrollers
2.1
LEARNING OBJECTIVES
Embedded systems consist of computers embedded in larger systems. Additional circuitry
such as power supplies, clock generators, and reset circuits, is required for the computer to
work. Transducers (devices that convert one type of energy into another) are also used to
connect microcontrollers to the outside world. There are two classes of transducers: inputs
and outputs. Inputs are also known as “sensors” and contain such things as switches, keypads, and buttons. Output transducers include devices such as LEDs, motors, and coils.
In this chapter the reader will learn general information about:
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Connecting LEDs
Connecting motors and coils
Connecting switches and buttons
Connecting keypads
Analog to digital conversion
Digital to analog conversion
Power supplies for embedded systems
Clock generation options
Reset circuitry
2.2
INTERFACING WITH DIGITAL SIGNALS
2.2.1
General Purpose Digital I/O
Embedded systems consist of computers embedded in larger systems. The processor needs
to sense the state of the larger system and environment, and control output devices. The
most basic way to do this is through one or more discrete signals, each of which which can
be in one of two states (on or off). General purpose digital I/O ports are the hardware
which can be used to read from or write to the system outside the microcontroller.
11
12
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The RX62N has eleven I/O ports (Port 0 to 5, A to E). Each port has eight pins, and on
most ports all eight pins can be selected as inputs or outputs. However, on some ports some
pins are reserved. The reserved pins cannot be configured as I/O pins. Each port has a
Data Direction Register (DDR), Data Register (DR), Port Register (PORT), and Input
Buffer Control Register (ICR). The pins of a port may serve several purposes; for example,
Port 4 pin 0 can be used as a general purpose I/O pin, as an A/D converter input, or as an
interrupt input. Depending on the purposes these pins serve, they might have extra registers. Ports A through E have an extra register called the Pull-up MOS Control Register
(PCR), and Ports 0 to 3 (P30 to P34) and C have Open Drain Control Register (ODR). All
of these registers are 8 bits long.
Certain other registers called Port Function Registers are also present. These registers
are associated with special features of the RX62N board such as USB, CAN, etc.
Data Direction Register (DDR)
This register, as the name suggests, is used to set the data direction (input or output) of a
pin. DDR is a read/write register. Each bit of the Data Direction Register represents a pin.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
0
0
0
0
0
0
0
0
Figure 2.1 Data Direction Register. Source: Kuphaldt, T. R. “Successive Approximation ADC,” in All about
Circuits, page 765.
The ‘iodefine_RX62N.h’ file has C code constructs that make it easy to access each port
with C code. Each port is defined as a structure and each register of the port is defined as a
union of variables within that structure. An example of how the DDR is defined inside a
port structure follows:
1. struct st_port4 {
2.
union {
3.
unsigned char BYTE;
4.
struct {
5.
unsigned char B7:1;
6.
unsigned char B6:1;
7.
unsigned char B5:1;
8.
unsigned char B4:1;
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
9.
10.
11.
12.
13.
14.
15. }
unsigned
unsigned
unsigned
unsigned
} BIT;
} DDR;
char
char
char
char
13
B3:1;
B2:1;
B1:1;
B0:1;
Line 1 shows that port0 has been defined as a structure. Lines 2 to 14 suggest that Data
Direction Register (DDR) has been defined as a union with the variable BYTE and a structure called BIT. This organization helps in easy access of the bits of the DDR. Unsigned
char Bn:1(n 0 to 7) indicates that the character variable is assigned one bit.
To select a particular pin as the input pin, the corresponding bit of the DDR has to be
set to ‘0’; and to select a pin as output, the corresponding bit of the DDR has to be set to
‘1.’ The general syntax to set a bit of the DDR is PORTx.DDR.BIT.Bn (x 0 to 5, A to E;
and n 0 to 7) since ports are defined as structures and accessing structure members is
done so this way. To configure multiple pins at the same time, the char variable BYTE can
be used. All pins are configured as inputs at reset, by default.
EXAMPLE 1
Set Switch 1 (Port 4 bit 0) as Input
PORT4.DDR.BIT.B1 = 0;
When a pin is selected as an input from a peripheral, the Input Buffer Control Register
(ICR) has to be enabled. The ICR will be explained a little later.
Selecting a pin as an output involves setting the Data Register (DR) and the Data
Direction Register (DDR).
Data Register (DR)
The Data Register is used to store data for pins that have been configured as output
pins. This register is similar to the DDR in that each bit of the register represents a pin and
certain bits of certain ports are reserved.
14
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
0
0
0
0
0
0
0
0
Figure 2.2 Data Register.
The Data Register (DR) is also defined as a union of variables inside the port structure,
in the ‘iodefine_RX62N.h’ file. It is presented just like the DDR. Unsigned char: 1 is used
to represent reserved pins.
The syntax to access the bits of the Data Register (DR) is PORTx.DR.BIT.Bn (x 0 to 5,
A to E; and n 0 to 7). To select a pin as an output pin, first set the Data Register (DR) to
a known value, preferably 0, so that changes in the output can be easily observed. The char
variable BYTE can be used to set multiple pins as output at the same time.
EXAMPLE 2
Set LED1 (Port D bit 0) as Output
1. PORTD.DDR.BIT.B0 = 1;
2. PORTD.DR.BIT.B0 = 0;
Line 1 sets LED1 as an output and line 2 switches on the LED.
Sets LEDs 1, 2, and 3 (Port D bit 0, 1, and 2) as Outputs
1. PORTD.DDR.BYTE = 0x07;
2. PORTD.DR.BYTE = 0xF8;
Line 1 sets LED1, 2, and 3 as outputs and line 2 switches on the LEDs.
Port Register (PORT)
Port register is also defined as a union of variables inside the port structure in the
‘iodefine_RX62N.h’ file. PORTx.PORT.BIT.Bn (x 0 to 5, A to E; and n 0 to 7) is used
to read the state of a pin and the state is stored in the Port Register regardless of the value
in the Input Buffer Control Register (ICR). This register also has some reserved bits. These
bits are read as 1 and cannot be modified.
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
x
x
x
x
x
x
x
x
15
Figure 2.3 Port Register.
Check State of Switch1 (Port 4 bit 0) and Turn On LED1 (Port D bit 0)
1. if(PORT4.PORT.BIT.B0 == 1){
2.
PORTD.DR.BIT.B0 = 1;
3. }
Input Buffer Control Register (ICR)
This register is used to buffer the input values for pins that have been configured as input
from peripheral modules.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
0
0
0
0
0
0
0
0
Figure 2.4 Input Buffer Control Register.
Before configuring a pin as an input from a peripheral, the ICR must be enabled. To enable
the ICR set PORTx.ICR.BIT.Bn (x 0 to 5, A to E; and n 0 to 7) to 1. If a pin has to be
configured as an output pin, set PORTx.ICR.BIT.Bn (x 0 to 5, A to E; and n 0 to 7) to
0. Setting ICR to 0 disables the ICR. While setting the ICR, make sure that the corresponding pin is not in use. For example, when setting IRQi (i 0 to 15) as input, first disable
the interrupts, next enable ICR and then enable interrupts. It is necessary to follow the
above steps to avoid unintended operations from taking place.
Open Drain Control Register (ODR)
Most output pins function as CMOS but some output pins can operate as CMOS or NMOS
open-drain pins. Since NMOS circuits are faster compared to the CMOS circuits, which
consist of the slower p-channel transistors, using NMOS open-drain pins as outputs
would be similar to a wired-OR connection. All of the pins of port 0, 1, 2, C and pins
0 to 4 of port 3 are capable of functioning as NMOS open-drain output pins. Setting
PORTx.ODR.BIT.Bn (x 0 to 5, A to E; and n 0 to 7) to 1, selects the pin as an
NMOS open-drain pin.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Pull-Up MOS Control Register (PCR)
Some devices have limited signal swing. When such a device is interfaced with the
RX62N board, the signal from the device has to be pulled up so that it is in the valid
voltage range of the board (this is not the typical usage, the typical usage is the external device is only capable of pulling down; or there is nothing attached and you do not want the
port to float). To simplify this kind of interfacing, pull-up MOS circuitry is available for
ports A to E. To enable pull-up MOS for a particular pin of a port, set PORTx.PCR.BIT.Bn
(x 0 to 5, A to E; and n 0 to 7) to 1. To disable pull-up MOS, set PORTx.PCR.BIT.Bn
(x 0 to 5, A to E; and n 0 to 7) to 0. The PCR is automatically disabled for
pins configured as outputs. To enable or disable pull-up MOS for multiple pins use
PORTx.PCR.BYTE command. The value of the PCR after reset is 0x00.
Example 1: Reading Switches to Control LEDs
Using LEDs as Outputs
LEDs require a current-limiting resistor so that they do not draw too much current from the
I/O pin to which they are connected. Most microcontrollers can sink more current than they
can supply, so generally LEDs are connected with the cathode to the microcontroller pin,
and a current-limiting resistor between the anode and supply voltage. Formula 2.1 shows
how to calculate the value of the current limiting resistor. Figure 2.5 shows the two ways of
connecting LEDs to a microprocessor.
R (VOutput VLED)/ILED
Formula 2.1
R5F211A1DD
VSS/AVSS
P1_0/AN9/KI01/CMP0_0
P1_1/AN8/KI0/CMP0_0
P1_2/AN10/K12/CMP0_2
P1_3/ANN11/KI3/TZOUT
P1_4/TXD0
P1_5/RXD0/CNTR01/INI11
P1_6/CLK0/SSIO1
P1_7/CNTR00/INI10
P3_3/TCIN/INI3/SSI00/CMP1_0
5
LED2
18
17
15
14
13
12
11
10
R2
GND
2.2.2
19
Figure 2.5A The microprocessor is sourcing current to an LED. Turning on this LED requires a
logical HIGH signal on the output pin. If the LED is attached to Port D, Pin 0, and that pin is set
to an output; then the code needed to turn the LED on would be: PORTD.DR.BIT.B0 = 1;
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
17
R5F211A1DD
P1_0/AN9/KI01/CMP0_0
P1_1/AN8/KI0/CMP0_0
P1_2/AN10/K12/CMP0_2
P1_3/ANN11/KI3/TZOUT
P1_4/TXD0
P1_5/RXD0/CNTR01/INI11
P1_6/CLK0/SSIO1
P1_7/CNTR00/INI10
P3_3/TCIN/INI3/SSI00/CMP1_0
5
R2
18
17
15
14
13
12
11
10
VCC
VSS/AVSS
LED1
19
Figure 2.5B The microprocessor is sinking current from the LED. Turning on the LED requires
a logical LOW on the output pin. If the LED is attached to Port D, Pin 0, and that pin is set to
an output; then the code needed to turn the LED on would be: PORTD.DR.BIT.B0 = 0;
Using Switches as Inputs
A simple interfacing design can include using a pull-up resistor on a pin that is also connected to ground through a button or switch. The resistor will pull the voltage on that pin to
logic HIGH until the button connects to ground. When the button is pressed, the voltage at
that pin will drop to zero (logic LOW). Figure 2.6 shows a schematic of this approach. If the
switch in Figure 2.6 is connected to Port D pin 0, the code to check this switch would be:
1. if(PORTD.PORT.BIT.B0 == 0){
2.
//Conditional code goes here
3. }
18
17
15
14
13
12
11
10
19
P3_3/TCIN/INI3/SSI00/CMP1_0
20
P3_4/SCS/SCA/CMP1_1
S1
P1_0/AN9/KI01/CMP0_0
P1_1/AN8/KI0/CMP0_0
P1_2/AN10/K12/CMP0_2
P1_3/ANN11/KI3/TZOUT
P1_4/TXD0
P1_5/RXD0/CNTR01/INI11
P1_6/CLK0/SSIO1
P1_7/CNTR00/INI10
5
2
VSS/AVSS
1
R5F211A1DD
R19
VCC
GND
Figure 2.6 Basic button connection to a microprocessor input pin.
18
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Contact bounce is a worry with any mechanical switch. When the switch is closed, the
mechanical properties of the metals in the switch cause the contacts to literally bounce
off of one another. This can cause false signals to be read as inputs. Your design should
take this into account with either a hardware or software debouncing solution. Hardware debouncing circuits often require digital logic as well as some resistors and capacitors. Hardware debouncing circuits are very useful for interrupt pins. Software debouncing is accomplished by setting up a timer to check the state of the switch at a set
interval, such as every 1 ms. If the value of the input has been the same for the duration
of the timer (1 ms in this case) the input can be considered valid. This method helps to
ignore false input values.
To better understand configuring I/O pins let us look at an example. The RX62N board
has three push buttons and twelve LEDs (six red and six green). Switches and LEDs are
simple I/Os and in the following program we will see how to set up switches as inputs and
LEDs as outputs. According to this program, when switch1 is pressed, green LEDs will
glow, when switch2 is pressed, red LEDs will glow, and when switch3 is pressed, all the
LEDs will glow.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
#include “iodefine_RX62N.h”
#ifdef YRD_RX62N
#define LED1
PORTD.DR.BIT.B0
#define LED2
PORTD.DR.BIT.B1
#define LED3
PORTD.DR.BIT.B2
#define LED4
PORTD.DR.BIT.B3
#define LED5
PORTD.DR.BIT.B4
#define LED6
PORTD.DR.BIT.B5
#define LED7
PORTD.DR.BIT.B6
#define LED8
PORTD.DR.BIT.B7
#define LED9
PORTE.DR.BIT.B0
#define LED10
PORTE.DR.BIT.B1
#define LED11
PORTE.DR.BIT.B2
#define LED12
PORTE.DR.BIT.B3
#define LED1_DDR
PORTD.DDR.BIT.B0
#define LED2_DDR
PORTD.DDR.BIT.B1
#define LED3_DDR
PORTD.DDR.BIT.B2
#define LED4_DDR
PORTD.DDR.BIT.B3
#define LED5_DDR
PORTD.DDR.BIT.B4
#define LED6_DDR
PORTD.DDR.BIT.B5
#define LED7_DDR
PORTD.DDR.BIT.B6
#define LED8_DDR
PORTD.DDR.BIT.B7
#define LED9_DDR
PORTE.DDR.BIT.B0
#define LED10_DDR
PORTE.DDR.BIT.B1
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
19
#define LED11_DDR
PORTE.DDR.BIT.B2
#define LED12_DDR
PORTE.DDR.BIT.B3
#define LED_ON
1
#define LED_OFF
0
#define ALL_LEDS_ON
{LED1 = LED2 = LED3 = LED4 = LED5 = LED6 =
LED7 = LED8 = LED9 = LED10 = LED11 = LED12 = LED_ON;}
#define ALL_LEDS_OFF
{LED1 = LED2 = LED3 = LED4 = LED5 = LED6 =
LED7 = LED8 = LED9 = LED10 = LED11 = LED12 = LED_OFF;}
#define ENABLE_LEDS
{LED1_DDR = LED2_DDR = LED3_DDR = LED4_DDR =
LED5_DDR = LED6_DDR = LED7_DDR = LED8_DDR = LED9_DDR =
LED10_DDR = LED11_DDR = LED12_DDR = 1;}
#endif
#define SW1
PORT4.PORT.BIT.B0
#define SW2
PORT4.PORT.BIT.B1
#define SW3
PORT4.PORT.BIT.B2
#define ENABLE_SWITCHES
{PORT4.DDR.BIT.B0 = PORT4.DDR.BIT.B1 =
PORT4.DDR.BIT.B2 = 0;}
void main(void){
ENABLE_LEDS;
ENABLE_SWITCHES;
while(1){
if(SW1 == 0){
LED12 = LED11 = LED10 = LED6 = LED5 = LED4 = LED_ON;
} else if(SW2 == 0){
LED9 = LED8 = LED7 = LED3 = LED2 = LED1 = LED_ON;
} else if(SW3 == 0){
ALL_LEDS_ON;
} else {
ALL_LEDS_OFF;
}
}
}
In line 1, the file ‘iodefine_RX62N.h’ has been included. It is a custom header file created
by Renesas for easy access and manipulation of data. The RX62N board has two sets of
LEDs: RSK_RX62N LEDs which are used to indicate basic functions like power on, and
YRD RX62N LEDs which are used to simulate a motor. This program uses the
YRD RX62N LEDs to demonstrate the use of digital I/O pins. Line 2 and line 32 are
used to indicate that the statements between them should be executed only for
YRD RX62N LEDs. All pins of Port D and pins 0 to 3 of Port E are the LED pins. The
three switches are at Port 4 bits 0 to 2.
20
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
In main, first the LEDs have been enabled (line 38). ENABLE_LEDS is a macro defined earlier in the program (line 31) to set the Data Direction Register (DDR) of the
LEDs to 1; i.e., set up the LED pins as output pins.
Next, the switches have been enabled (line 39). ENABLE_SWITCHES is another
macro defined earlier (line 36) to set the Data Direction Register (DDR) of the switches
to 0; i.e., set up the switch pins as output pins.
The next part of the program is an important part of many embedded systems—the while
(1) loop (line 40). This loop makes the microcontroller execute all the statements within the
loop repeatedly until the microcontroller is stopped by an external force (e.g., power off). In
this program, the conditions for LED operation are given within the while (1) loop using ifelse statements (lines 41 to 47). Even though use of the switch statement will result in much
better code, the if-else statement has been used for easy understanding.
䡲
䡲
䡲
䡲
2.2.3
If switch 1 is pressed (state of switch 1 is low), all the green LEDs are turned on
(line 42). The state of the switch is checked using the macro defined in line 33 using the PORT register. From the schematic of the board it can be seen that green
LEDs are LED 12, 11, 10, 6, 5, and 4. They are turned on by setting the Data
Register (DR) of the LED pins to 1 (active high) which has been defined using the
macro LED_ON in line 27.
If switch 2 is pressed (state of switch 2 is low), all the red LEDs are turned on
(line 44). The state of the switch is checked using the macro defined in line 34 using the PORT register. From the schematic of the board it can be seen that red
LEDs are LED 9, 8, 7, 3, 2, and 1. They are turned on by setting the Data Register
(DR) of the LED pins to 1 (active high) which has been defined using the macro
LED_ON.
If switch 3 is pressed (state of switch 3 is low), all the LEDs are turned on (line 46)
using the macro LED_ON.
If none of the switches are pressed (line 47) all the LEDs are turned off using the
macro LED_OFF (line 48).
Driving Motors and Coils
Input/Output (I/O) pins on a microcontroller have specific limits to the amount of current
each pin can sink or source. These limits are found in the datasheet. Voltage levels can also
be different between sensors and the microcontroller. Both of these constraints must be
taken into account when designing interfaces for the actuator.
Because of their large coils, motors draw a lot of current. For Direct Current (DC) motors, simple transistor drivers or H-bridges (shown in Figure 2.7) can be used to interface
them with a microcontroller. If the left input of the circuit in Figure 2.7 is connected to
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
21
Port D pin 0 and the right input of this circuit is connected to Port D pin 1, the code to turn
the motor one direction would be:
1. PORTD.DDR.BYTE = 0x03;
2. PORTD.DR.BYTE = 0x02;
//Sets pins 0 and 1 on Port D as outputs
//Sets one pin as HIGH and the other as LOW
Stepper motors can use transistors or stepper motor driver ICs. Some ICs such as the
L293 or the 754410 are specifically designed to drive the DC motors and interface directly
with a microcontroller. Servos are gearboxes that have motor control circuitry built in.
These devices can often connect their control pins directly to a microprocessor as their internal circuitry handles driving the motor itself. Other large coils such as relay coils should
be treated similarly to motors. Figure 2.8 shows a basic coil driving circuit. Code to drive
the coil is the same as it is to drive an LED.
Vout
R17
Q4
2N3906
Q2
2N3906
R18
MOTOR
1
Q1
2N3904
Q3
2N3904
GND
Figure 2.7 H-bridge motor driver. Two if the microprocessor’s outputs are connected to the
resistors. Note: Both inputs should not be the same value for the motor to turn.
22
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
R20
Vout
R5F211A1DD
P1_0/AN9/KI01/CMP0_0
P1_1/AN8/KI0/CMP0_0
P1_2/AN10/K12/CMP0_2
P1_3/ANN11/KI3/TZOUT
P1_4/TXD0
P1_5/RXD0/CNTR01/INI11
P1_6/CLK0/SSIO1
P1_7/CNTR00/INI10
5
18
17
15
14
13
12
11
10
D1
1N4004
VSS/AVSS
L1
2
T2
2N3904
1
R16
19
P3_3/TCIN/INI3/SSI00/CMP1_0
20
P3_4/SCS/SCA/CMP1_1
1
P3_5/SSCK/SCL/CMP1_2
2
P3_7/CNIR0/SSO/IXD1
GND
Figure 2.8 A simple coil driver.
There are other methods of controlling large loads with a microprocessor, such as using relays or triacs. The overall concept with all load driving circuits is to keep the source and
sink currents of the microprocessor within the manufacturer’s recommendations.
Some sensors may require different voltages than what the microprocessor requires.
Care should be taken when interfacing these sensors. If the microprocessor runs at 5 V and
the sensor runs at 1.8 V, the microprocessor will not be able to read a HIGH logic signal on
the sensor output. Circuits for interfacing with higher voltage sensors can be designed using transistors or by using level converter ICs, which convert the signals between the microcontroller and the sensor either uni-directionally or bi-directionally (in case the microprocessor needs to communicate to the sensor.) The use of a flyback diode is very
important when interfacing inductive loads, to safely dissipate the voltage spike when the
voltage to the load is removed.
2.2.4
Scanning Matrix Keypads
Keypads work as a matrix of buttons. For instance, Figure 2.9 shows an example keypad
matrix. The top three output pins are used as the columns of the matrix. The three pins connected as the rows of the matrix are all input pins. A button is placed in the circuit at each
intersection of a column and row. One at a time, the output pins turn on and each of the input pins is read. If an input is detected, the microprocessor can determine which button on
the keypad had been pressed. For example, if the microprocessor noted an input on the
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
23
middle row pin at the time in which the middle output was logic HIGH, then the center
button must have been pressed. If the columns in Figure 2.9 are connected to Port D bits
0, 1, and 2 respectively, and the rows are connected to Port E bits 0, 1, and 2 respectively;
code to read the keypad values of the first column would be:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
PORTD.DR.BIT.B0 = 1;
PORTD.DR.BIT.B1 = 0;
PORTD.DR.BIT.B2 = 0;
//Set the output of the first column to 1
//Set the output of the second column to 0
//Set the output of the third column to 0
if(PORTE.PORT.BIT.B0 == 0){
//Conditional code for Row 0
}
if(PORTE.PORT.BIT.B0 == 0){
//Conditional code for Row 1
}
if(PORTE.PORT.BIT.B0 == 0){
//Conditional code for Row 2
}
R5F211A1DD
VSS/AVSS
P1_0/AN9/KI01/CMP0_0
P1_1/AN8/KI0/CMP0_0
P1_2/AN10/K12/CMP0_2
P1_3/ANN11/KI3/TZOUT
P1_4/TXD0
P1_5/RXD0/CNTR01/INI11
P1_6/CLK0/SSIO1
P1_7/CNTR00/INI10
5
18
17
15
14
13
12
11
10
19
P3_3/TCIN/INI3/SSI00/CMP1_0
20
P3_4/SCS/SCA/CMP1_1
1
P3_5/SSCK/SCL/CMP1_2
2
P3_7/CNIR0/SSO/IXD1
P4_2/VREF
P4_5/INI0/HXD1
P4_6/XIN
P4_7/XOUT
16
9
6
4
1
1
S2
2
1
1
S7
2
1
1
S8
2
1
1
S3
2
1
1
S6
2
1
1
S9
2
1
1
S4
2
1 1
S5
2
1
1
S10
2
MODE 8
Figure 2.9 Keypad button matrix.
24
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
2.3
INTERFACING WITH ANALOG SIGNALS
The world is not digital; it is analog. Microphones, thermometers, speakers, light sensors,
and even video cameras are all analog sensors. As a result, the signals from these sensors
must be converted to digital values so that the microcontrollers can process them.
Analog to Digital Converters
To read the value of an analog sensor, Analog to Digital Converters (also referred to as ADC,
A/D, A-to-D, and A2D) are used. This circuit produces a multi-bit binary number based on a
voltage scale. The number of bits in the multi-bit binary number helps determine the resolution
or precision of the reading; 8-bit, 10-bit, and 12-bit converters are commonly used. ADCs also
require a reference voltage. This is a stable voltage to which the current reading will be compared to produce the binary output. The analog reference voltage is scaled by the resolution.
Most ADCs use linear scales, so converting the values is straightforward. Figure 2.10 shows
the transfer function which is used to convert an analog voltage (measured on the horizontal
axis) to its digital output code representation (on the vertical axis). Each step on the transfer
function represents one least-significant bit. Figure 2.11 shows an example input analog voltage which is sampled over time.
The resolution of the conversion is determined by Formula 2.2.
Resolution VLSB Vref /2Nbits
“3.0V”
4.0V
00
1.0V
“0.0V”
01
3.0V
“1.0V”
1 LSB
10
2.0V
“2.0V”
Formula 2.2
11
Output Code
2.3.1
Input Voltage
Figure 2.10 2-bit ADC conversion chart. The stair step line shows the ADC’s output code.
25
Digital Value
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
Time
Figure 2.11 ADC readings over time.
If Vref 5 V, and there is an 8-bit resolution, the volts per ADC raw value step 5 V/256 0.01953 V/step.
To determine the value of the conversion, Formula 2.3 can be used:
ADC output code int (((2Nbits 1) * (Vin /Vref)) 1/2)
Formula 2.3
For example:
Vref 5 V, Vin 2.26295 V, with a 10-bit resolution;
int ((1023 * (2.26295 V/5 V)) 1/2) 463 ADC raw value steps.
Once the raw ADC value is known, the application software should reverse the formula to
calculate the actual voltage on that pin. Since the datasheet for most sensors provides a formula for converting the voltage to the unit the sensor is measuring (be it degrees Celsius,
distance in centimeters, pressure in kilopascals, etc.), this formula can be inserted into the
firmware to make sense of the data.
More advanced sensors use a communication protocol such as RS-232, RS-485,
I2C, and SPI. These sensors generally take an analog value, convert it to digital, and
then send it to the microcontroller for processing using a communication protocol.
These protocols sometimes allow for multiple sensors to be connected to the same pins
of the microcontroller.
2.3.2
Analog Comparator
Some microcontrollers may contain one or more comparator circuits. This circuit can be
thought of as a simple 1-bit analog to digital converter. It compares an analog voltage input
with an analog reference voltage, and then determines which is larger.
26
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
2.3.3
Digital to Analog Conversion
Just as we must convert analog signals to digital to process them, sometimes there is a need
to convert digital signals to analog. In systems that control audio, speed, or even light levels; digital output from a microprocessor must be converted into an analog signal. There
are several different methods for converting digital signals to analog.
Resistor Networks
Resistor networks allow a very simple solution for converting digital signals to analog.
There are many methods of using resistor networks for DACs, but two designs are predominantly used.
Binary Weighted DACs
Resistor networks are another simple method for DAC conversion. Several different
methods are available for using resistor networks, and again it is up to the designer to
R5F211A1DD
P1_0/AN9/KI01/CMP0_0
P1_1/AN8/KI0/CMP0_0
P1_2/AN10/K12/CMP0_2
P1_3/ANN11/KI3/TZOUT
P1_4/TXD0
P1_5/RXD0/CNTR01/INI11
P1_6/CLK0/SSIO1
P1_7/CNTR00/INI10
5
18
17
15
14
13
12
11
10
19
P3_3/TCIN/INI3/SSI00/CMP1_0
20
P3_4/SCA/SCD/CMP1_1
1
P3_5/SSCK/SCL/CMP1_2
2
P3_7/CNIR0/SSO/IXD1
P4_2/VREF
P4_5/INI0/HXD1
P4_6/XIN
P4_7/XOUT
R4
R5
Vout
VSS/AVSS
R6
R7
16
9
6
4
MODE 8
RESET 3
VCC/AVCC 7
IC5
Figure 2.12 4-bit binary weighted network DAC design. Source: Kester, W. A., and Analog Devices,
Inc., Data Conversion Handbook, 2005, page 153–159.
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
27
decide which method is best for a particular design. Voltage-Mode Binary Weighted
DACs are commonly used with microcontroller circuits. In this design, resistors are
connected together on one end (the analog output), and the other ends are connected directly to the pins of a microcontroller port. The values of the resistors are based on binary bit place-values (R, 2R, 4R, 8R, etc.; with R being the least significant bit or LSB).
When the pins of the microcontroller are set to HIGH, then the sum voltage of the analog output are related to the value on that port. Figure 2.12 shows an example of a 4-bit
Binary Weighted DAC.
R-2R DAC
Another method of using resistor networks to design a DAC is called the R-2R or R/2-R Network. It consists of resistors of only two values. One value is twice the value of the other.
For instance, if the R resistors are one kilo-ohm, then the 2R resistors must equal two kiloohms. Figure 2.13 shows an example R-2R network (Kuphaldt, T. R., “The R2-R,”).
GND
R5F211A1DD
P4_2/VREF
P4_5/INI0/HXD1
P4_6/XIN
P4_7/XOUT
R15
R10
R12
R14
Vout
19
P3_3/TCIN/INI3/SSI00/CMP1_0
20
P3_4/SCS/SCD/CMP1_1
1
P3_5/SSCK/SCL/CMP1_2
2
P3_7/CNIR0/SSO/IXD1
R8
R9
18
17
15
14
13
12
11
10
R11
P1_0/AN9/KI01/CMP0_0
P1_1/AN8/KI0/CMP0_0
P1_2/AN10/K12/CMP0_2
P1_3/ANN11/KI3/TZOUT
P1_4/TXD0
P1_5/RXD0/CNTR01/INI11
P1_6/CLK0/SSIO1
P1_7/CNTR00/INI10
5
R13
VSS/AVSS
16
9
6
4
MODE 8
RESET 3
VCC/AVCC 7
IC6
Figure 2.13 R-2R network. R9, R11, and R13 are considered “R” resistors and all 1kohm
while R8, R10, R12, R14, and R15 are considered “2R” and all 2kohm. Source: “The R2-R,” in
Kuphaldt, T. R., All about Circuits, http://www.allaboutcircuits.com/vol_4/chpt_13/2.html
28
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Figure 2.14 An example PWM signal. If this were controlling an active-high LED, the
LED would be brighter during the first half of the graph, and dimmer over the second half.
As with the binary weighted DAC, the output voltage corresponds to the binary value on
the port. The following example is valid for both R-2R as well as Binary Weighted DACs:
If the Vref is 5 V and there is a 4-bit binary value 1001 (decimal number 9) on the microcontroller pins, we would expect the output voltage to be:
Vout (Vref /(2N)) * (binary value of microcontroller output)
Formula 2.4
For example:
(5 V / 16 bits) * (9) 2.8125 V.
Pulse Width Modulation
A common method for controlling the speed of a simple DC motor or the brightness of an
LED is Pulse Width Modulation. Pulse Width Modulation works as a DAC by changing the
duty cycle of an oscillating digital output as shown in Figure 2.14. In the case of an LED,
the more time the duty cycle is HIGH, the brighter the LED. This method works in cases
where the oscillating frequency is so fast that the resulting output seems smooth. The
LED is actually turning on and off several times per second; however, the human eye cannot detect the independent flashes of the LED due to their speed. Motor speed can be controlled this way because the inertia of the spinning armature carries the motor forward
through the moments when no power is applied.
2.4
INFRASTRUCTURE: POWER, CLOCK, AND RESET
2.4.1
Power Supply
When designing the power supply for an embedded system, the designer must determine
how to power peripherals and whether or not they will use a separate supply. This decision
will affect the overall design requirements of the power supply. This chapter only addresses the power supply for the microprocessor itself.
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
29
Voltage and current ratings for the microprocessor can be found in the manufacturer’s
datasheet for the chip, often under the title of Recommended Operating Conditions
or Electrical Characteristics. Another section in the datasheet also shows Absolute
Maximum Ratings, which should be considered but not confused with the recommended
values. To be assured that the chip will operate as expected, a system should never be
designed to operate too close to the absolute maximum or minimum power ratings. Fluctuations in the power supply may cause the values to go over the absolute maximum
ratings of the chip, which can damage the microprocessor. The power supply should be
designed with a safety factor to account for these fluctuations, hence the recommended
values.
Once the requirements are determined, the source of the power must be determined.
Whether the design plugs into the wall or if it uses batteries will determine the type of
power supply circuit.
If the design uses mains power, then a standard design method for a power supply circuit can be used. This design will require a transformer to drop the voltage to an acceptable
range for a voltage regulator chip. Capacitors will be required to smooth out any ripple or
noise.
If batteries are to be used, then the type of battery (NiCad, NiMH, LiPo, etc.) must be
selected based on the current rating each battery type can supply, and whether the design
will need to be rechargeable.
The length of time a battery will last can be calculated based on the capacity of the battery and the amount of current the circuit uses using Formula 2.5.
Battery Life (hours) Capacity (amp-hours) / current (amps)
Formula 2.5
An 800 mAh battery will power a device that draws 200 mA for;
800 mAh / 200 mA 4 hours
Putting batteries in parallel adds their current capacities. Putting them in series adds their
voltages.
For two batteries with each 1.5 V and 2000 mAh:
Series: 1.5 V 1.5 V 3.0 V at 2000 mAh
Parallel: 2000 mAh 2000 mAh 1.5 V at 4000 mAh
If the batteries need to be recharged, then a battery charging circuit as well as battery level
monitor will also need to be designed.
Regardless of which batteries are chosen, a voltage regulator of some type is generally
required. The use of linear or switch-mode voltage regulator integrated circuits (ICs) is a
standard practice.
30
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
2.4.2
Clock Signal Generation
Microprocessors are synchronous circuits that require a clock to work. This clock allows
data to be pushed through the stages of the instruction pipeline and helps the microprocessor coordinate tasks. When selecting a clock generator, the microcontroller datasheet must
be used. This datasheet gives the values of the different clocks that a particular microprocessor can accept.
There are two major types of clock signal generators: those that work on purely electrical
principles, and those that work on mechanical vibration (resonance of a quartz element). The
signal generators for the electrical driven clock can be simple resistor-capacitor (RC) or
inductor-capacitor (LC) circuits. Generally, these clocks aren’t very accurate on their own, and
their design can become quite complicated when precision is required. Many microprocessors
offer signal generators with an internal clock that consists of an RC circuit inside the chip,
which can be configured. These clocks should not be used when precision is required. Figure
2.15 shows the connection of an RC oscillator to the clock input of a microprocessor.
P4_2/VREF
P4_5/INI0/HXD1
P4_6/XIN
P4_7/XOUT
16
9
6
4
VCC
R3
19
P3_3/TCIN/INI3/SSI00/CMP1_0
20
P3_4/SCS/SCA/CMP1_1
1
P3_5/SSCK/SCL/CMP1_2
2
P3_7/CNIR0/SSO/IXD1
C1
MODE 8
RESET 3
VCC/AVCC 7
U3
GND
Figure 2.15 RC clock generator.
Clock signal generators that are mechanically driven use a quartz crystal to produce a
steady signal. These oscillators rely on the piezoelectric effect of the crystal. This method
of clocking is accurate (around 30 parts per million or about 0.003% error), cheap, and
widely available. Generally, two small load capacitors are required between each lead of
the crystal and ground. The values of these capacitors are based on the crystal characteristics and are listed in the crystal’s datasheet.
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
31
GND
GND
MODE 8
RESET 3
VCC/AVCC 7
C3
16
9
6
4
Y1
P4_2/VREF
P4_5/INI0/HXD1
P4_6/XIN
P4_7/XOUT
C2
19
P3_3/TCIN/INI3/SSI00/CMP1_0
20
P3_4/SCS/SCA/CMP1_1
1
P3_5/SSCK/SCL/CMP1_2
2
P3_7/CNIR0/SSO/IXD1
U4
Figure 2.16 Connection of a crystal clock generator chip.
Ceramic resonators are growing in popularity for use as a clock generator. The resonators use a piezoelectric ceramic element that is not as accurate as quartz, yet more accurate than RC circuits. They also contain the appropriate load capacitors built in so they
do not require any additional components to work.
External clock generator integrated circuit chips can also be used. These clocks use a
quartz or RC circuit as a resonant oscillator, but also contain an amplifier. The frequency
can be changed by reprogramming the clock generator. The duty cycle is also selectable for
use in cases where a 50 percent duty cycle cannot be used. These circuits are usually more
expensive when compared to other oscillators.
2.4.3
Reset Circuit
Resetting a microprocessor starts the processor off in a predictable state. When a reset is
detected, the microprocessor loads predefined values into the system control registers.
These registers are useful in case of a catastrophic event, such as if the power supply were
to drop below a certain threshold. All microprocessors designate a pin that is solely used
for resetting the chip. A reset circuit controls this pin to assure a reset is valid if it is used.
The requirements of a reset circuit is specific to the microprocessor being used and can be
found in the manufacturer’s datasheet. Some microcontrollers contain reset logic internally; however, the manufacturer’s datasheet should be consulted to make sure it meets the
specifications for your application. Alternatively, reset controller chips can be used which
contain all the parts necessary for the circuit. Even though they are generally more expensive in some cases, such as low-volume productions, it may be best to use reset controller
chips.
32
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
2.5
RECAP
It should now be easier to understand how the embedded systems you encounter in your
everyday life actually operate and communicate with the outside world. It should also be
easier to break some of these systems down into their component parts, given the knowledge of sensor and actuator interfacing presented in this chapter.
2.6
REFERENCES
Kester, W. A., and Analog Devices, Inc. Data Conversion Handbook. Lawrence, KS: Newnes, 2005:
pp. 153–159. Print.
Kuphaldt, T. R. “Successive Approximation ADC,” in All about Circuits. Electronic publication. Accessed at
http://www.allaboutcircuits.com/vol_4/chpt_13/6.html
“The R2-R,” in Kuphaldt, T. R., All about Circuits. Electronic publication. Accessed at http://www.
allaboutcircuits.com/vol_4/chpt_13/2.html
2.7
EXERCISES
1. Name ten devices that use an embedded system.
2. Write the C code to set port 4, bits 0 through 3 to be input pins, and port 4, bits
4 through 7 to be output pins.
3. Write the C code to read the data on port 4, bits 0 through 3 and write the read
data to port 4, bits 4 through 7.
4. How long will a 2500 mAh battery last if the circuit using it runs at 600 mA?
5. You have a wireless sensor node whose current drain is 50 mA for one minute
6.
7.
8.
9.
every one hour and 0.001 mA the rest of the time. I am using a single 5000 mAh
cell as the power supply for this device. How long will my device run in hours,
days, and years?
What are the different kinds of clock generators? Define their base technologies.
What resistor value should be used to connect an LED with a forward voltage of
3.1 volts and a forward current of 20 mA to the input pin of a microcontroller that
outputs 5 volts?
Is it generally safe to connect a coil or motor directly to a microcontroller
I/O pin? Why or why not?
Is it generally safe to connect a servo control input directly to a microcontroller
I/O pin? Why or why not?
CHAPTER 2 / CONCEPTS OF MICROCONTROLLERS
33
10. How many volts per ADC step are in a system with an ADC resolution of 10-bits,
and a reference voltage of 3.3 V?
11. How many volts per ADC step are in a system with an ADC resolution of 12-bits,
and a reference of 5 V?
12. An analog input has a voltage of 1.37860. What value will the ADC return if it
has an 8-bit resolution and a reference of 4.25 volts?
13. An analog input has a voltage of 7.61245. What value will the ADC return if it
has a 12-bit resolution and a reference of 10 volts?
14. Using a binary-weighted DAC, using 8 bits and a reference of 4.35 volts, what is
the voltage of the output if the 8-bit value is 01011010?
Chapter Three
Organization and Architecture of the Renesas
RX62N Microcontroller Board
3.1
LEARNING OBJECTIVES
In this chapter the reader will learn about:
䡲
䡲
䡲
䡲
Basic organization of computers
Architecture of the Renesas RX62N board
Endianness, data arrangement, and bus specification in RX62N CPU
Date types, operating modes, and memory map of RX62N CPU
3.2
BASIC CONCEPTS
3.2.1
Introduction to Computer Organization & Architecture
A computer is a complex digital system. The best way to look at it is by looking at its hierarchical nature. Hierarchical systems are best described as a series of subsystems that are interconnected at various levels to form a complete computer system. At each level is a set of
components whose behavior depends on the characteristics and functions of the next lower
level. A designer focuses on structure and function within each level. The computer has four
basic functions to perform (see Figure 3.1):
1.
2.
3.
4.
Data processing
Data storage
Data movement
Data control
Computers process data with the help of the data processing facility. During and after processing, storage is required for this data. During processing, the data needs a temporary or
short term storage area. After processing, the data will be stored in long-term storage area.
The Data Movement Block provides a data path between the outside environment and the
computer. This block is also responsible for the data flow between various subcomponents
35
36
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Data storage
facility
Data source
&
destination
Control
mechanism
Data
movement
Data processing
facility
Figure 3.1 A generalized view: Building blocks of a computer.
within the computer. The Control Mechanism takes care of controlling and managing various subcomponents and their interactions with each other.
Computers have four basic structural components (See Figure 3.2):
1.
2.
3.
4.
CPU: Processes the data and controls the operation of computer.
Memory: Stores data.
I/O: Moves the data between the computer and the external environment.
System Interconnection: Provides a mechanism for transferring data or communicating between components such as the CPU, main memory, and I/O.
I/O
Memory
System
interconnection
CPU
Figure 3.2 A top level view of a computer.
The Central Processing Unit (CPU) is the most complex component out of the four basic
components. The structure of the CPU is illustrated in Figure 3.3. The components that make
up a CPU are:
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
37
1. Control Unit: Controls the operation of the CPU.
2. Arithmetic and Logic Unit (ALU): Performs the computer’s data processing
functions.
3. Registers: Provides internal storage for the CPU. They store ALU operands.
4. Interconnections: Provides a mechanism for transferring data or communicating
between components such as the Control Unit, ALU, and registers.
ALU
Registers
Interconnection
Control
unit
Figure 3.3 A top level view of a CPU.
The IAS* computer, which is a prototype of general-purpose computers, is based on the
stored-program concept. This idea was developed by John von Neumann and is known as
the von Neumann Machine. As shown in Figure 3.4, the von Neumann machine has a main
CPU
ALU
I/O
Main
memory
Control
unit
Figure 3.4 Structure of a von Neumann machine.
*
Institute for Advanced Study, Princeton, NJ
38
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
memory for storing the instructions and data the same as an IAS computer. It also has an
ALU, which processes the binary data. A control unit decodes the instructions and forwards
them to the ALU for execution. The Input/Output unit interacts with the external environment and is controlled by the Control Unit.
3.2.2
Architecture of the Renesas RX62N
The RX62N microcontroller architecture has the following components:
1. CPU: The CPU contains two main modules or functions:
䡲 CPU: It is a 32-bit RX CPU with maximum operating frequency of 100 MHz.
䡲 Floating Point Unit (FPU): This unit is a single precision (32-bit) floating
2.
3.
4.
5.
6.
7.
point unit which supports data types and floating-point exceptions in conformance with IEEE 754 standard.
Memory: The Memory contains three main modules:
䡲 ROM: Its capacity is 512 Kbytes (max) and it supports two on-chip programming modes and one off-chip programming mode.
䡲 RAM: Its capacity is 96 Kbytes (max).
䡲 Data Flash: Its capacity is 32 Kbytes.
Clock generation circuit: The clock generation circuit consists of two circuits,
namely a main clock oscillator and a sub clock oscillator. The CPU and other bus
masters run in synchronization with the system clock (ICLK): 8 to 100 MHz; the
peripheral modules run in synchronization with the peripheral module clock
(PCLK): 8 to 50 MHz; while devices connected to the external bus run in synchronization with the external bus clock (BCLK): 8 to 50 MHz.
Reset: There are various reset sources available for different modules in the MCU
such as pin reset, power-on reset, voltage-monitoring reset, watchdog timer reset,
independent watchdog timer reset, and deep software standby reset.
Voltage detection circuit: When the voltage available on VCC falls below the
voltage detection level (Vdet), an internal reset or internal interrupt is generated.
External bus extension: The external address space is divided into nine areas:
CS0 to CS7 and SDCS. The capacity of each area from CS0 to CS7 is 16 Mbytes,
and for SDCS the capacity is 128 Mbytes. A chip-select signal (CS0# to CS7#,
SDCS#) can be output for each area. Each area is specifiable as an 8-, 16-, or
32-bit bus space; however, only 176-pin versions support 32-bit bus spaces.
Direct Memory Access (DMA): The DMA system consists of three different
controllers which are explained below. The activation sources for all three controllers are software trigger, external interrupts, and interrupt requests from peripheral functions:
䡲 DMA controller: It has four channels and three transfer modes. These modes
are normal transfer, repeat transfer, and block transfer.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
䡲
39
EXDMA controller: It has two channels and four transfer modes. These
modes are normal transfer, repeat transfer, block transfer, and cluster transfer.
䡲 Data transfer controller: It has three transfer modes. These modes are normal
transfer, repeat transfer, and block transfer.
8. I/O ports: The main modules of I/O ports are programmable I/O ports. There are
several I/O ports available on the 176-pin LFBGA, 145-pin TFLGA, 144-pin
LQFP, 100-pin LQFP, and 85-pin TFLGA packages.
9. Timers: There are seven timer units available for controlling the sequence of an
events or processes.
䡲 Multi-function timer pulse unit: It has two units each supporting six channels
and each channel has 16 bits. It provides time bases for the twelve 16-bit
timer channels by way of up to 32 pulse-input/output lines and six pulseinput lines.
䡲 Port output enable: It controls the high-impedance state of the MTU’s waveform
output pins.
䡲 Programmable pulse generator: It has two units, each supporting four groups
and each group has four bits. It outputs MTU pulse as a trigger. The maximum output possible is 32-bit pulse output.
䡲 8-bit timers: It has two units, each supporting two channels and each channel has
8 bits. The clock signal can be selected from seven internal clock signals (PCLK,
PCLK/2, PCLK/8, PCLK/32, PCLK/64, PCLK/1024, and PCLK/8192) and one
external clock signal. These are capable of outputting pulse trains with desired
duty cycles or of PWM signals.
䡲 Compare match timer: It has two units, each supporting two channels and
each channel has 16 bits.
䡲 The clock signal can be selected from four internal clock signals (PCLK/8,
PCLK/32, PCLK/128, and PCLK/512).
䡲 Watchdog timer: It has one channel of 8 bits. The clock signal can be selected
from eight counter-input clock signals (PCLK/4, PCLK/64, PCLK/128,
PCLK/512, PCLK/2048, PCLK/8192, PCLK/32768, and PCLK/131072). It is
switchable between watchdog timer mode and interval timer mode.
䡲 Independent watchdog timer: It has one channel of 14 bits. It requires
counter-input clock which is available from dedicated on-chip oscillator.
10. Communication function: For communicating with the outside world, the
MCU provides several controllers:
䡲 Ethernet controller: The data rate it supports is either 10 or 100 Mbps. It supports both full and half duplex modes.
䡲 DMA controller for Ethernet: It supports transmission and reception FIFO of
2 Kbytes each.
䡲 USB 2.0 host/function module: It includes a USB device controller and transceiver for USB 2.0. It incorporates 2 Kbytes of RAM as a transfer buffer and
supports data rate of 12 Mbps.
40
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Data Flash
WDT
IWDT
CRC
SCI 3 6 ch
USB (up to 2 ports)
RSPI (unit 0)
RSPI (unit 1)
CAN
MTU 3 6 channels (unit 0)
MTU 3 6 channels (unit 1)
Internal main bus 1 to 6
Port 2
Port 3
PPG (unit 0)
PPG (unit 1)
TMR 3 2 channels (unit 0)
TMR 3 2 channels (unit 1)
EDMAC
Internal main bus 2
Port 1
POE
ETHERC
ROM
Port 0
CMT 3 2 channels (unit 0)
ICU
CMT 3 2 channels (unit 1)
DTC
Port 4
Port 5
Port 6
Port 7
Port 8
Port 9
RTC
RAM
DMACA
RIIC 3 2 channels
12-bit A/D converter 3 8 channels
RX CPU
MPU
10-bit A/D converter 3 4 channels (unit 1)
Internal main bus 1
Clock
generation
circuit
10-bit A/D converter 3 4 channels (unit 0)
10-bit D/A converter 3 2 channels
Port A
Port B
Port C
Port D
Port E
Port F
EXDMAC
External bus
Port G
BSC
Figure 3.5 Block diagram. Source: Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series, Renesas
Electronics America, Inc., 2010, Figure 1.2, page 1–12.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
41
䡲
Serial communication interfaces: It has six channels and supports several
serial communication modes such as asynchronous, clock synchronous,
and smart-card interface. The desired baud rate is selected by on-chip baud
rate generator.
䡲 I2C bus interfaces: The communication formats supported are I2C bus format/SMBus format and Master/slave selectable.
䡲 CAN module: It supports one channel and 32 mailboxes.
䡲 Serial peripheral interfaces: It supports two channels and MOSI (master out,
slave in), MISO (master in, slave out), SSL (slave select), and RSPI clock
(RSPCK) signals. They enable serial transfer through SPI operation (four
lines) or clock-synchronous operation (three lines). It is capable of handling
serial transfer as a master or slave.
11. A/D converter: MCU supports two A/D converters, specifically 12-bit and
10-bit. The conversion time is 1.0 ms per channel. The selectable operating
modes are single mode and scan mode.
12. D/A converter: It supports two channels and 10-bit resolution. The output voltage ranges from 0V to Vref.
13. CRC calculator: CRC code generator generates code for arbitrary amount of
data in 8-bit units. It is capable of selecting any of three generating polynomials:
X8 X2 X 1, X16 X15 X2 1, or X16 X12 X5 1.
One can also generate CRC codes for use with either LSB-first or MSB-first
communications.
DEFINITION OF TERMS:
ETHERC:
Ethernet Controller
WDT:
Watchdog timer
EDMAC:
DMA controller for Ethernet controller
IWDT:
Independent watchdog timer
ICU:
Interrupt control unit
CRC:
Cyclic redundancy check calculator
DTC:
Data transfer controller
MPU:
Memory-protection unit
DMACA:
DMA controller
SCI:
Serial communications interfaces
EXDMAC:
EXDMA controller
USB:
USB 2.0 host/function module
BSC:
Bus controller
RSPI:
Serial peripheral interfaces
42
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
DEFINITION OF TERMS:
CAN:
CAN module
TMR:
8-bit timer
MTU:
Multi-function timer pulse unit
CMT:
Compare match timer
POE:
Port output enable
RTC:
Real time clock
PPG:
Programmable pulse generator
RIIC:
I2C bus interface
CPU
The RX CPU being used in RX62N/RX621 group of MCU’s supports high-speed and
high-performance.
The instruction set architecture (ISA) of RX CPU has a variable-length instruction format. The most commonly used instructions have been allocated shorter instruction lengths,
making it possible to develop efficient programs that occupy less memory. The ISA of
RX62N/RX621 group has ninety instructions, out of which seventy-three are basic instructions, eight are floating-point operation instructions, and nine are DSP instructions. It
achieves high-speed operation by executing instructions in a single cycle. It includes an internal multiplier and divider for high speed multiplication and division. These operations
now take less time and hence add to the efficiency of the processor. The RX CPU has a
five-stage pipeline for processing instructions.
1.
2.
3.
4.
5.
Instruction fetching stage
Instruction decoding stage
Execution stage
Memory access stage
Write-back stage
In cases where pipeline processing is drawn-out by memory access, subsequent operations
may in fact be executed earlier. By adopting “out-of-order completion” of this kind, the execution of instructions is completed in fewer clock cycles.
Register Set
The RX CPU has sixteen general-purpose registers, nine control registers, and one accumulator used for DSP instructions.
General-Purpose Registers (R0 to R15): The RX CPU has sixteen general-purpose registers (R0 to R15). R0 can function as a stack pointer (SP) and R1 to R15 can be used as
data or address registers. The stack pointer can be made to operate either as an Interrupt
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
TABLE 3.1
FEATURES
43
Features of CPU.
DESCRIPTION
High instruction execution rate
One instruction in one clock cycle.
Address space
4-Gbyte linear address space.
Register set of the CPU
There are sixteen 32-bit general purpose registers and nine
32-bit control registers. It has a 64-bit register accumulator.
Basic instructions
It has seventy-three basic instructions such as arithmetic/logic
instructions, data-transfer instructions, branch instructions,
bit-manipulation instructions, string-manipulation instructions,
and system-manipulation instructions.
Floating-point operation
instructions
It is an optional function that can be used. There are eight such
operations.
DSP instructions
It is an optional function that can be used. There are nine such
instructions. It supports 16-bit 16-bit multiplication and
multiply-and-accumulate operations. It rounds the data in the
accumulator.
Addressing modes
There are ten addressing modes.
Five-stage pipeline
It has a five-stage pipeline and allows out-of-order
completion.
Processor modes
A supervisor mode and a user mode are supported.
Floating-point operation unit
It supports single-precision (32-bit) floating point operations
and supports data types and exceptions in conformance with
the IEEE 754 standard.
Data arrangement
The data can be selected either as little endian
or big endian.
stack pointer (ISP) or user stack pointer (USP). The required stack pointer can be selected
by the value of the stack pointer select bit (U) in the processor status word (PSW).
Control Registers: This CPU has the following nine control registers:
1. Interrupt stack pointer (ISP)
2. User stack pointer (USP)
44
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
General-purpose register
b31
b0
R0 (SP)
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R11
R12
R13
R14
R15
Control register
b31
b0
ISP (interrupt stack pointer)
USP (User stack pointer)
INTB (Interrupt table register)
PC (Progam counter)
PSW (Process status word)
BPC (Backup PC)
BPSW (Backup PSW)
FINTV (Fast interrupt vector register)
FPSW (Floating point status word)
DSP instruction register
b63
b16
b15
b0
ACC (Accumulator)
Figure 3.6 Register set of CPU. Source: Hardware Manual, Figure 2.1, page 2–2.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
45
Interrupt table register (INTB)
Program counter (PC)
Processor status word (PSW)
Backup PC (BPC)
Backup PSW (BPSW)
Fast interrupt vector register (FINTV)
Floating-point status word (FPSW)
3.
4.
5.
6.
7.
8.
9.
The section below explains each control register briefly. It mainly focuses on the bit configuration and the functionality of each register.
1. Interrupt Stack Pointer (ISP)/User Stack Pointer (USP): After reset, all the bits
of the register hold the value zero. The register is configured with 32 bits. The register can be made to operate either as Interrupt stack pointer (ISP) or user stack
pointer (USP). The decision is made by the value of the stack pointer select bit
(U) in the processor status word (PSW). Depending on the value of the bit, the
stack pointer operates either as ISP or USP. Setting the value of ISP or USP to a
multiple of four reduces the numbers of cycles required to execute interrupt sequences and instructions.
2. Interrupt table register: The interrupt table register (INTB) points to an address
where the relocatable vector table starts and is configured with 32 bits. After reset,
value of the register is Undefined.
3. Program counter: Value after reset: Contents of addresses FFFFFFFCh to
FFFFFFFFh. The program counter (PC) points to the address of the instruction that
will be executed next. As soon as that instruction’s execution starts, PC value is incremented and it points to the next instruction. The PC is configured with 32 bits.
4. Processor Status Word (PSW):
b31
b30
b29
b28
b27
b26
b25
—
—
—
—
b15
b14
b13
b12
b11
b10
b9
—
—
—
—
—
—
—
b24
b23
b22
b21
b20
b19
b18
b17
b16
—
—
—
PM
—
—
U
I
b8
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
—
O
S
Z
C
IPL[2:0] IPL[2:0] IPL[2:0] IPL[2:0]
Figure 3.7 PSW. Source: Hardware Manual, page 2–5.
46
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
After reset, all the bits of the register hold the value zero.
䡲
䡲
䡲
䡲
䡲
䡲
䡲
䡲
C Flag (Carry Flag): Whenever an operation results in a carry, borrow, or shift-out,
this flag is set. The bit position of the carry flag is b0 and when it is set as 1, it
means a carry has occurred. When it is 0, it means no carry has occurred. The symbol of the flag is C and it can be read and written by the CPU.
Z Flag (Zero Flag): Whenever an operation results in a zero, this flag is set. The bit
position of the zero flag is b1 and when it is set as 1, it means the result of an operation is zero. When it is 0, it means the result is non-zero. The symbol of this flag
is Z and it can be read and written by the CPU.
S Flag (Sign Flag): This flag indicates that the result of an operation was negative.
The bit position of the sign flag is b2 and when it is set as 1, it means the result of
an operation is negative. When it is 0, it means the result is non-negative. The symbol of this flag is S and it can be read and written by the CPU.
O Flag (Overflow Flag): This flag indicates that an overflow occurred during an
operation. Whenever an operation results in an overflow, this flag is set. The bit position of the overflow flag is b3 and when it is set as 1, it means the result of an operation resulted in an overflow. When it is 0, it means there was no overflow. The
symbol of this flag is O and it can be read and written by the CPU.
I Bit (Interrupt Enable): Whenever this bit is set, an interrupt can occur. If this bit
is disabled, then even if an interrupt occurs an exception will not be accepted. The
bit position of interrupt enable is b16 and when it is set as 1, it means interrupt is
enabled which means interrupt requests will be accepted. When it is 0, then interrupt requests will not be accepted. The symbol of this flag is I and it can be read
and written by the CPU.
U Bit (Stack Pointer Select): This bit specifies the stack pointer as either the ISP or
USP. When an interrupt occurs and the interrupt enable bit is set to 1, an exception
request is accepted. When this happens this bit is set to 0 and then this register acts
as an interrupt stack pointer. When the processor mode is switched from supervisor mode to user mode, this bit is set to 1. Now the register acts as a user stack
pointer. The bit position of the stack pointer select is b17. The symbol of this flag
is U and it can be read and written by the CPU.
PM Bit (Processor Mode Select): This bit specifies the processor mode. When an
interrupt occurs and the interrupt enable bit is set to 1, an exception request is accepted. When an exception is accepted, supervisor mode is selected and the bit is
set as 0. When user mode is selected then this bit is selected as 1. The bit position
of the processor mode select is b20. The symbol of this flag is PM and it can be
read and written by the CPU.
IPL [3⬊0] Bits (Processor Interrupt Priority Level): The IPL [3⬊0] bits specify
the processor interrupt priority level. There are in total sixteen levels from
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
47
zero to fifteen, wherein priority level fifteen is the highest. When the priority
level of a requested interrupt is higher than the processor interrupt priority
level, the interrupt is enabled; and when the priority level of a requested interrupt is lower than the processor interrupt priority level then the interrupt request
is not accepted. So if the IPL [3⬊0] bits is set to a level fifteen (Fh) then it will
disable all interrupt requests. The only case where IPL [3⬊0] bits are set to
level fifteen (Fh) is when a non-maskable interrupt is generated. When interrupts in general are generated, the bits are set to the priority levels of accepted
interrupts. The bit positions of the processor interrupt priority level are from
b27 to b24. The symbol of this flag is IPL [3⬊0] and it can be read and written
by the CPU.
The following list shows sixteen priority levels.
b27
b26
b25
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
b24
0: Priority level 0 (lowest)
1: Priority level 1
0: Priority level 2
1: Priority level 3
0: Priority level 4
1: Priority level 5
0: Priority level 6
1: Priority level 7
0: Priority level 8
1: Priority level 9
0: Priority level 10
1: Priority level 11
0: Priority level 12
1: Priority level 13
0: Priority level 14
1: Priority level 15 (highest)
Reserved Bits:
The following bits are reserved in the PSW register. These bits are always read
as 0. The write value should be 0.
b15 to b4; b19, b18; b23 to b21; b31 to b28
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
5. Backup PC (BPC): After reset, the value of the register is Undefined. The register
is configured with 32 bits. The Backup PC (BPC) register assists in speeding up
the response to interrupts. After a fast interrupt has been generated, the contents of
the program counter (PC) are saved in the Backup PC register.
6. Backup PSW (BPSW): After reset, the value of the register is Undefined. The
register is configured with 32 bits. After a fast interrupt has been generated, the
contents of the processor status word (PSW) are saved in the Backup Processor
status word (BPSW) register. The allocation of bits in the BPSW register corresponds to that in the PSW register.
7. Fast Interrupt Vector Register (FINTV): After reset, the value of the register is
Undefined. The register is configured with 32 bits. As the name suggests, this register assists in speeding up the response to interrupts. As soon as a fast interrupt is
generated, the FINTV register specifies a branch destination address.
8. Floating-Point Status Word (FPSW):
b31
b30
b29
b28
b27
b26
b25
b24
b23
b22
b21
b20
b19
b18
b17
b16
FS
FX
FU
FZ
FO
FV
—
—
—
—
—
—
—
—
—
—
b15
b14
b13
b12
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
—
EX
EU
EZ
EO
EV
—
DN
CE
CX
CU
CZ
CO
CV
RM[1:0] RM[1:0]
Figure 3.8 FPSW. Source: Hardware Manual, page 2–9.
After reset, all the bits of the register hold the value zero.
The floating-point status word (FPSW) indicates the results of floating-point operations. The register can be broadly classified into three types of bit configuration.
One type is enable bits, another type is flag bits, and the third type is cause bits. So
for every exception that occurs, there exists an enable bit (Ej), a flag status bit (Fj),
and an exception cause bit (Cj). When an exception handling enable bit (Ej) is enabled, which means when Ej 1, corresponding Cj flag indicates the cause. If the
exception handling is masked (Ej 0), then the state of the Fj flag at the end of a
series of instructions indicates whether an exception occurred. The Fj flag is the
accumulation type flag where j represents X, U, Z, O, or V.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
TABLE 3.2
BIT
SYMBOL
b1, b0
RM
[1⬊0]
Description of FPSW
BIT NAME
Floating-Point
Rounding-Mode
Setting
49
DESCRIPTION
R/W
b1 b0
0 0 : Rounding to the nearest value.
R/W
0 1 : Rounding to 0.
1 0 : Rounding to ⬁.
1 1 : Rounding to ⬁.
b2
CV
Invalid Operation
Cause Flag
0 : No invalid operation has been
encountered.
R/W*1
1: Invalid operation has been encountered.
b3
b4
b5
b6
b7
CO
CZ
CU
CX
CE
Overflow Cause
Flag
0 : No overflow has occurred.
Division-by-Zero
Cause Flag
0 : No division-by-zero has occurred.
Underflow Cause
Flag
0 : No underflow has occurred.
Inexact Cause
Flag
0 : No inexact exception has been generated.
Un-Implemented
Processing Cause
Flag
0 : No un-implemented processing has been
encountered.
R/W*1
1: Overflow has occurred.
R/W*1
1: Division-by-zero Overflow has occurred.
R/W*1
1: Underflow has occurred.
R/W*1
1: Inexact exception has been generated.
R/W*1
1: Un-implemented processing has been
encountered.
Source: Hardware Manual, page 2–9.
Notes:
1. Writing 0 to the bit clears it. Writing 1 to the bit does not affect its value.
2. Positive denormalized numbers are treated as 0, negative denormalized numbers as 0.
3. When the EV bit is set to 0, the FV flag is enabled.
4. When the EO bit is set to 0, the FO flag is enabled.
5. When the EZ bit is set to 0, the FZ flag is enabled.
6. When the EU bit is set to 0, the FU flag is enabled.
7. When the EX bit is set to 0, the FX flag is enabled.
8. Once the bit has been set to 1, this value is retained until it is cleared to 0 by software.
(Continued)
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
50
TABLE 3.2
BIT
SYMBOL
b8
DN
Description of FPSW—Continued
BIT NAME
DESCRIPTION
0 Flush Bit of
Denormalized
Number
0: A denormalized number is handled as a
denormalized number.
R/W
R/W
1: A denormalized number is handled as 0.*2
b9
—
(Reserved)
This bit is always read as 0. The write value
should be 0.
R/W
b10
EV
Invalid Operation
Exception Enable
0: Invalid operation exception is masked.
R/W
Overflow
Exception Enable
0: Overflow exception is masked.
Division-by-Zero
Exception Enable
0: Division-by-zero exception is masked.
Underflow
Exception Enable
0: Underflow exception is masked.
Inexact Exception
Enable
0: Inexact exception is masked.
(Reserved)
These bits are always read as 0. The write
value should be 0.
R/W
Invalid Operation
Flag
0: No invalid operation has been
encountered.
R/W
b11
b12
b13
b14
EO
EZ
EU
EX
b25
to b15
—
b26
FV*3
1: Invalid operation exception is enabled.
R/W
1: Overflow exception is enabled.
R/W
1: Division-by-zero exception is enabled.
R/W
1: Underflow exception is enabled.
R/W
1: Inexact exception is enabled.
1: Invalid operation has been
encountered.*8
b27
FO*4
Overflow Flag
0: No overflow has occurred.
R/W
8
1: Overflow has occurred.*
b28
b29
5
FZ*
FU*6
Division-by-Zero
Flag
0: No division-by-zero has occurred.
Underflow Flag
0: No underflow has occurred.
R/W
1: Division-by-zero has occurred.*8
1: Underflow has occurred.*8
R/W
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
TABLE 3.2
BIT
b30
SYMBOL
7
FX*
51
Description of FPSW—Continued
BIT NAME
Inexact Flag 0: No
DESCRIPTION
0: No inexact exception has been
generated.
R/W
R/W
1: Inexact exception has been generated.*8
b31
FS
䡲
Floating-Point
Flag Summary
This bit reflects the logical OR of the FU, FZ,
FO, and FV flags.
R/W
RM [1⬊0] bits:
These bits specify the floating-point rounding-mode.
Explanation of Floating-Point Rounding Modes
▫ Rounding to the nearest value (the default behavior):
An inaccurate result is rounded to the available value that is closest to the result which would be obtained with an infinite number of digits. If two available values are equally close, rounding is done to the even alternative.
▫ Rounding towards 0:
An inaccurate result is rounded to the smallest available absolute value.
▫ Rounding towards ⬁:
An inaccurate result is rounded to the nearest available value in the direction
of positive infinity.
▫ Rounding towards ⬁:
An inaccurate result is rounded to the nearest available value in the direction
of negative infinity.
The default mode is to round off to the nearest value in order to return the most accurate
value. The other modes, such as rounding towards 0, rounding towards ⬁, and rounding
towards ⬁, are used to ensure precision.
䡲
䡲
䡲
Cj (Cause flag): The five floating-point exceptions based on IEEE 754 standard are
overflow, underflow, inexact, division-by-zero, and invalid operation. The bit is set
to 1 until and unless FPU instruction is executed. After that the bit is set to 0. When
instructions like MVTC and POPC instructions write 0 to the bit, the bit is set
to 0; and when they write 1, the bit retains the previous value.
DN Flag: When this bit is set to 0, a denormalized number is handled as a denormalized number; and when this bit is set to 1, a denormalized number is handled as 0.
Ej (Exception handle bit): When any of the five floating-point exceptions is generated by the FPU instruction, this bit then decides whether the CPU will handle the
exception or not. When the bit is set to 0, the exception handling is masked and the
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
CPU will not handle the exception; when the bit is set to 1, the exception handling
is enabled and CPU will handle the exception.
Fj: While the exception handling enable bit (Ej) is 0 (exception handling is masked),
if any of the five floating-point exceptions specified in the IEEE 754 standard is
generated, the corresponding bit is set to 1. When Ej is 1 (exception handling is enabled), the flag retains its value. When the corresponding flag is set to 1, it remains 1
until it is cleared to 0 by software. (Accumulation flag)
FS bit (Floating-point flag summary bit): This bit reflects the logical OR of the
FU, FZ, FO, and FV flags.
Accumulator (ACC):
Range for reading by MVFACMI
b63
b48
b47
Range for reading and writing by
MVTACHI and MVFACHI
b32
b31
b16
b15
b0
Range for reading by MVTACLO
Figure 3.9 ACC. Source: Hardware Manual, page 2–12.
This register is configured with 64 bits and is mainly used for DSP instructions. It is also
used for the multiply and multiply-and-accumulate instructions, where the prior value in
the accumulator is modified by the execution of instruction. The examples of such instructions are EMUL, EMULU, FMUL, MUL, and RMPA. To write to the accumulator,
MVTACHI and MVTACLO instructions are used. These instructions write data to the
higher-order 32 bits (bits 63 to 32) and the lower-order 32 bits (bits 31 to 0). To read from
the accumulator, MVFACHI and MVFACMI instructions are used. The MVFACHI and
MVFACMI instructions read data from the higher-order 32 bits (bits 63 to 32) and the
middle-order 32 bits (bits 47 to 16), of the accumulator.
3.2.3
Data Types
The RX CPU supports four types of data: integer, floating-point, bit, and string.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
53
1. Integer:
b7
b0
b7
b0
Signed byte (8-bit) Integer
Unsigned byte (8-bit) Integer
b15
b0
b15
b0
Signed word (16-bit) Integer
Unsigned word (16-bit) Integer
b31
b0
b31
b0
Signed longword (32-bit) Integer
Unsigned longword (32-bit) Integer
Figure 3.10 Integer. Source: Hardware Manual, Figure 2.2, page 2–14.
2. Floating-Point:
The IEEE standard defines four different types of precision for floating point
operations. They are single precision, double precision, single-extended precision,
and double-extended precision. Most of the floating-point hardware follows
IEEE 754 standard’s single and double precision for floating point computations.
RX family supports single precision floating-point computation. There are in total
eight operations that can be done with such floating-point operands: FADD,
FCMP, FDIV, FMUL, FSUB, FTOI, ITOF, and ROUND.
b31
b0
S
E
F
Figure 3.11 Floating point. Source: Hardware Manual, Figure 2.3, page 2–14.
Single-precision floating-point
S: Sign (1 bit)
E: Exponent (8 bits)
F: Mantissa (23 bits)
Value (1)S (1 F 223) 2(E127)
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The floating-point format supports different values for exponent and mantissa.
When the value of E is between 0 and 255 (i.e., 0 E 255), then the number is
considered as a normal number. For a signed zero number, the value of E and
F should be 0. For denormalized numbers, the value of E is 0 and the value of F is
greater than 0. When the value of E is 255 and the value of F is 0, then the number
is considered as infinity. When the value of E is 255 and the value of F is greater
than 0, then the number is not a number.
NOTE:
The number is treated as 0 when the DN bit in FPSW is 1. When the DN bit is 0, an
unimplemented processing exception is generated.
3. Bitwise Operations:
There are five different types of bit-manipulation instructions for bitwise operations: BCLR, BMCnd, BNOT, BSET, and BTST. The register is a 32-bit register so
the bits range from 0 to 31. In the Figure 3.12, notation looks like “#bit, Rn”;
which means ‘corresponding bit in register n.’ Here the value of ‘n’ ranges from
0 to 15. So notation “#30, R1” suggests 30th bit in R1 register. For bitwise operation in memory, the notation is “#bit, mem.” For instance, #2, [R2] means address
[R2] and bit 2. The bit value ranges from 0 to 7. The addressing modes available to
specify addresses are register indirect and register relative.
Register
b31
b0
#bit, Rn
(Bit:31 to 0, n:0 to 15)
Example
#30, R1
(register R1, bit 30
Memory
Example
#bit, mem
(Bit:7 to 0)
b7
#2, [R2]
(address [R2], bit 2)
b0
Figure 3.12 Bitwise Operation. Source: Hardware Manual, Figure 2.4, page 2–15.
4. Strings:
The string data type consists of an arbitrary number of consecutive byte (8-bit),
word (16-bit), or longword (32-bit) units. To work with strings there are seven
string manipulation instructions: SCMPU, SMOVB, SMOVF, SMOVU, SSTR,
SUNTIL, and SWHILE.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
55
String of byte (8-bit) data
8
String of word (16-bit) data
16
String of longword (32-bit) data
32
Figure 3.13 Strings. Source: Hardware Manual, Figure 2.5, page 2–15.
3.2.4
Endianness
Endianness refers to the arrangement of sub-units such as bytes within a longer data word,
while storing it in memory. Basically there are two types of endianness: big endianness and
little endianness.
䡲
䡲
Big endian: The most significant byte (MSB) is stored at the lowest byte address of
the memory.
Little endian: The least significant byte (LSB) is stored at the lowest address of the
memory.
As arrangements of bytes, the RX62N/RX621 Group supports both big endian, where the
most significant byte (MSB) is stored at the lowest byte address of the memory; and little
endian, where the least significant byte (LSB) is stored at the lowest address of the memory. For the RX CPU, instructions are always little endian, but the way the user wants to
handle data decides endianness. Therefore, if a programmer wants to change the endianness, it can be changed.
56
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Register
AB CD EF 12
Memory
A
AB
A11
CD
A12
EF
A13
12
Big endian
Register
AB CD EF 12
Memory
A
12
A11
EF
A12
CD
A13
AB
Little endian
Figure 3.14 Endianness: Arrangement in memory.
3.2.5
Data Arrangement
1. Data Arrangement in Registers:
Figure 3.15 shows the relation between the sizes of registers and bit numbers.
2. Data Arrangement in Memory:
Data in memory have three sizes: byte (8-bit), word (16-bit), and longword
(32-bit). According to the requirement, the data arrangement can be selected as little or big endian.
Figure 3.16 shows the arrangement of data in memory.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
57
b7
b0
Byte (8-bit) data
b15
b0
Word (16-bit) data
b31
b0
Longword (32-bit) data
MSB
LSB
Figure 3.15 Data arrangement in registers. Source: Hardware Manual, Figure 2.6, page 2–21.
Data type
Address
Little endian
Big endian
b7
1-bit data
Address L
7
Byte data
Address L
MSB
Word data
b0
6
Address M
Address M 1 1
4
3
2
1
0
7
LSB
MSB
LSB
MSB
b0
6
5
4
3
2
MSB
Address N
Longword data
5
b7
1
0
LSB
LSB
LSB
MSB
Address N 1 1
Address N 1 2
Address N 1 3
MSB
LSB
Figure 3.16 Data arrangement in memory. Source: Hardware Manual, Figure 2.7, page 2–21.
3.2.6
Bus Specification
In total, there are five different types of buses in RX62N microcontroller board. The following section lists various bus specifications. It describes whether the bus operates in synchronization with a clock or not.
1. CPU bus:
䡲 Instruction bus:
It is connected to the CPU and to the on-chip memory such as on-chip
RAM and on-chip ROM. It operates in synchronization with the system
clock (ICLK).
58
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
2.
3.
4.
5.
Operand bus:
It is connected to the CPU and to the on-chip memory such as on-chip RAM and
on-chip ROM. It operates in synchronization with the system clock (ICLK).
Memory bus:
䡲 Memory bus 1: It is connected to on-chip RAM.
䡲 Memory bus 2: It is connected to on-chip RAM.
Internal main bus:
䡲 Internal main bus 1: It is connected to the CPU and operates in synchronization with the system clock (ICLK).
䡲 Internal main bus 2: It is connected to the DMACA, DTC, and EDMAC. Also,
it is connected to on-chip memory, namely on-chip RAM and on-chip ROM.
It operates in synchronization with the system clock (ICLK).
Internal peripheral bus:
䡲 Internal peripheral bus 1: It is connected to peripheral modules and operates in
synchronization with the system clock (ICLK).
䡲 Internal peripheral bus 2: It is connected to peripheral modules, on-chip ROM
(for programming and erasure), and data-flash memory. It operates in synchronization with the peripheral-module clock (PCLK).
䡲 Internal peripheral bus 3: It is connected to peripheral modules (USB) and it
operates in synchronization with the peripheral-module clock (PCLK).
䡲 Internal peripheral bus 4: It is connected to peripheral modules (EDMAC and
ETHERC) and it operates in synchronization with the system clock (ICLK).
䡲 Internal peripheral bus 5: It is connected to peripheral modules and it operates
in synchronization with the system clock (ICLK).
䡲 Internal peripheral bus 6: It is connected to on-chip ROM (for programming
and erasure) and data-flash memory. It operates in synchronization with the
peripheral-module clock (PCLK).
External bus:
䡲 CS area: It is connected to the external devices and it operates in synchronization with the external-bus clock (BCLK).
䡲 External bus SDRAM area: It is connected to the SDRAM and it operates in
synchronization with the SDRAM clock (SDCLK).
Description of Buses
1. CPU Buses:
The CPU buses consists of instruction and operand buses, which are connected to
internal main bus 1 as shown in Figure 3.17. The instruction bus is used to fetch instructions for the CPU, while the operand bus is used for operand access. These
buses are connected to on-chip RAM and on-chip ROM and therefore the CPU can
directly access these areas. Direct access refers to that access which is not by way
of internal main bus 1. In contrast to access through internal main bus 1, direct ac-
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
59
cess allows only reading the on-chip ROM by the CPU. Programming and erasure
are handled by way of an internal peripheral bus. Internal main bus 1 handles bus
requests for instruction fetching and operand access. The operand access has a
higher priority than instruction fetching. The bus-access operations can proceed simultaneously, irrespective of whether the instruction fetching and operand access
need different buses or not. For example, parallel access to an on-chip ROM and
on-chip RAM or to an on-chip ROM and external space is possible.
2. Memory bus:
There are two memory buses; namely memory bus 1 and memory bus 2. On-chip
RAM is connected to memory bus 1 and on-chip ROM is connected to memory bus
2. Bus requests from the CPU buses and internal main bus 2 are handled through
memory buses 1 and 2. Internal memory bus 2 has a higher priority than the CPU bus.
3. Internal main bus:
The internal main bus consists of two buses; one is internal main bus 1, which is
used by the CPU; and internal main bus 2, which is used by the other bus-master
modules such as the DTC, DMACA, and EDMAC. Bus requests for instruction
fetching and operand access are handled through internal main bus 1. Operand access has higher priority than instruction fetching. Bus requests from the DTC,
DMACA, and EDMAC are handled by internal main bus 2. The order of priority is
EDMAC, DMACA, and then DTC, as shown in Table 3.3. The bus access operations can proceed simultaneously. For instance, if the CPU and another bus master
are requesting access to different buses; in this case, the respective bus-access operations will take place simultaneously. Internal main bus 2 has a higher priority
than internal main bus 1. However, when the CPU executes the XCHG instruction,
the only request that can access bus is the request from CPU, until and unless data
transfer for the XCHG instruction is completed. If data transfer for the XCHG is
completed, requests for bus access from other masters will be accepted. Furthermore, during reading and writing back of control information, the only bus master
which has access is DTC. Bus requests from other masters are not accepted.
TABLE 3.3
Priority of Bus Masters.
PRIORITY
BUS MASTER
High
EDMAC
DMACA
DTC
CPU
Low
Source: Hardware Manual, Table 12.3, page 12–5.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
ICLK Synchronization
CPU
Instruction bus
Operation bus
Onchip
RAM
Onchip
ROM
Bus error monitoring
section
Internal main bus 1
DTC
EDMAC
DMACA(m)
Internal main bus 2
PCLK
Synchronisation
1*
2*
3*
4*
EXD
MAC
Peripheral
module
D
M
A
C
A
Peripheral
module
Peripheral
module
Peripheral
module
Peripheral
module
On-chip
ROM
BCLK
Synchronisation
External bus control
Write buffer
SDCLK
Synchronisation
BCLK
Synchronisation
SDRMAC
1: Internal peripheral bus 1
2: Internal peripheral buses 2 and 3
3: Internal peripheral buses 4 and 5
4: Internal peripheral bus 6
CSC
External bus
Figure 3.17 Bus Configuration. Source: Hardware Manual, Figure 12.1, page 12–2.
Data Flash
Memory
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
61
NOTES:
BCLK (external-bus clock): The maximum frequency of the clock is 100 MHz. The
CSC (CS area controller) and the EXDMAC operate in synchronization with the
BCLK.
SDCLK (SDRAM clock): The maximum frequency of the clock is 50 MHz. The
SDRAMC (SDRAM area controller) operates in synchronization with the SDCLK.
BCLK: The frequency is the same as the BCLK as default. 1/2 BCLK can be
supplied by setting the BCLK pin output select bit (BCLKDIV) in the system
clock control register (SCKCR).
The BCLK and the SDCLK should be operated with the same frequency (50 MHz as
a maximum) when the SDRAM is in use.
4. Internal peripheral buses:
The following table lists various peripheral buses and the peripheral modules to
which they are connected:
TABLE 3.4
Connection of Peripheral Modules.
TYPES OF BUS
Internal peripheral bus 1
PERIPHERAL MODULES
DMACA
EXDMAC
Interrupt controller
Bus error monitoring section
Internal peripheral bus 2
Peripheral modules other than those connected
to internal peripheral buses 1, 3, 4, and 5
Internal peripheral bus 3
USB
Internal peripheral bus 4
EDMAC and ETHERC
Internal peripheral bus 5
Reserved area
Internal peripheral bus 6
Data flash memory
Source: Hardware Manual, Table 12.4, page 12–5.
Bus mastership requests from the CPU (internal main bus 1) and other bus masters
(internal main bus 2) are handled through internal peripheral buses 1 to 6. Internal
main bus 2 has higher priority than internal main bus 1.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
5. External Bus:
This section lists various specifications of the external bus. Bus masters such as internal main bus 1, internal main bus 2, and EXDMAC keep requesting bus mastership. In such a scenario, the external bus controller arbitrates various requests and
decides the master. The order of priority determines which bus master will handle
mastership first, if all of them request at the same time. The order of priority is
EXDMAC, internal main bus 2, and then internal main bus 1. The various areas of
external bus and their specifications are as follows:
䡲 External address space:
An external address space is divided into two specific areas. One area is further divided into eight areas (CS0 to CS7) and the other area is the SDRAM
area (SDCS). This is how external address space is organized for better management. For each area the chip select signals can be output, an 8/16/32-bit
bus space can be selected, and an endian mode can be specified.
䡲 CS area controller:
The CS area controller deals with the read and write controls associated with
CS areas (CS0 to CS7). In the controller, recovery cycles can be inserted. In
read recovery up to fifteen cycles, and in the write recovery up to fifteen cycles
can be inserted. The cycle wait function can wait up to thirty-one cycles. In the
page access, wait function takes up to seven cycles. The controller uses wait
control to set up timing of assertion and negation for chip-select signals (CS0#
to CS7#) and for read signal (RD#) and write signals (WR0# to WR3#). It also
sets up the timing with which data output starts and ends. It has two write access modes; one is single write strobe mode and other is byte strobe mode.
䡲 SDRAM area controller:
The SDRAM Controller is a part of external bus. Several features are available
in the SDRAM area controller. The SDRAM controller is capable of self-refresh
and auto-refresh. It supports multiplexing output of row address/column address
(8, 9, 10, or 11 bits). The CAS latency can be specified from one to three cycles.
䡲 Write buffer function:
Write buffer function is used when there is data to be written to a buffer. When
write data from the bus master has been written to the write buffer, the write
access by the bus master is completed.
䡲 Frequency:
As mentioned earlier, the CS area controller (CSC) operates in synchronization with the external-bus clock (BCLK), while the SDRAM area controller
(SDRAMC) operates in synchronization with the SDRAM clock (SDCLK).
NOTE:
When different bus-master modules request access to different slave modules, then all of the
different masters can be given access to different peripheral modules. This is known as parallel operation as all of the accesses are taking place at the same time. Consider the case where
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
63
the CPU is fetching an instruction from on-chip ROM and at the same time an operand is
needed from on-chip RAM. What will happen in such a scenario? Here the master module
CPU wants to gain access to on-chip ROM as well as on-chip RAM. The DMACA simultaneously handles transfer between a peripheral bus and the external bus. In this example, the
CPU uses instruction and operand buses for simultaneous access to on-chip ROM and RAM,
respectively. So, with the help of instruction bus and operand bus, the CPU is able to fetch instructions and access an operand, both at the same time. Moreover, the DMACA simultaneously uses internal main bus 2 or the external bus to achieve parallel operation.
Bus Error Monitoring Section
Whenever an error occurs in a bus, the bus-error monitoring system comes into play. It
monitors each individual area and whenever it detects an error, it generates an interrupt.
Usually, two types of error occur in a bus, illegal address access error and timeout error.
Whenever the bus-error monitoring system detects illegal access to an area, an illegal address access error is said to have occurred. Similarly, when the bus-error monitoring system detects any bus-access operation that is not being completed within 768 cycles, then a
time out error is said to have occurred.
Types of Bus Error
As said earlier, there are mainly two types of error that can occur in a bus. The following
section explains them briefly.
1. Illegal Address Access:
To detect illegal access to an area, first of all a bit in a register has to be set up. The
bit is called an illegal address access detection enable bit (IGAEN) and is usually
set to 1 in the bus error monitoring enable register (BEREN). If that happens, accesses of the following types lead to illegal address access errors:
䡲 Access to those external areas for which operation has been disabled. The
space area is disabled by setting up the value of registers CSnCNT.EXENB
and SDCCR.EXENB as ‘0.’
䡲 With respect to areas other than those described above, access to illegal address ranges.
2. Time out:
To detect time out error, first of all a bit in a register has to be set up. The bit is
called a timeout detection enable bit (TOEN) and is usually set to 1 in the bus error monitoring enable register (BEREN). After setting up that bit, if any bus access
is not completed within 768 cycles, then it leads to a timeout error. In the
RX62N/RX621, a timeout error occurs only for access to CS areas. During access
to any of the CS areas from CS0 to CS7, it might lead to timeout error if bus access
is not completed (the WAIT# signal is not negated) within 768 external bus clock
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
(BCLK) cycles from the start of the access. When timeout error occurs, accesses to
bus are prohibited. In fact, accesses from the bus master are rejected for
256 BCLK cycles. If a single bus request from bus master also contains generated
multiple external bus accesses, then the bus access cannot be stopped by the timeout. At this time, timeout errors may occur repeatedly. The CPU is aware of the errors that are occurring in the bus section and whenever an error occurs the CPU is
informed. The CPU does not poll for errors on the bus. Whenever there is an error,
an interrupt is generated. The interrupt generated gives an indication to CPU that
there is an error in the bus section. The IEN register in the ICU decides whether to
generate an interrupt in the case of a bus error or not.
3.3
BASIC EXAMPLES
EXAMPLE 1
What is the difference between computer organization and architecture?
A computer’s architecture is its abstract model and is the programmer’s view in terms
of instructions, addressing modes, and registers. A computer’s organization expresses the
realization of the architecture. Architecture describes what the computer does and organization describes how it does it. The architecture is like a blue print which mentions all the
components and how they are connected, while the organization is an implementation of
that blue print. Each vendor will have their own version of organization, and their own way
of implementing the blue print.
Computer architecture computer organization (what the machine looks like) instruction set architecture (how you talk to the machine).
EXAMPLE 2
What is the difference between a microcontroller and a microprocessor?
The main difference is that a microcontroller incorporates features of a microprocessor
(CPU, ALU, Registers) along with the presence of added features like RAM, ROM, I/O ports,
counter, etc. In addition, microcontrollers are usually designed to perform a small set of specific functions; for example, the case of a Digital Signal Processor which performs a small set
of signal processing functions, whereas microprocessors tend to be designed to perform a
wider set of general purpose functions.
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EXAMPLE 3
1. Can you, the user, store a value at memory location 0008 C067h? Why or why not?
No, because address 0008 C067h corresponds to the memory area that stores special function registers. In the RAM, the memory addresses from 0000 0000h to 0001 8000h are reserved for special function registers and cannot be used by the user to save his data.
2. What area of Flash is available for the user program on the RX62N board? List the
range of addresses and the exact size in bytes (not Kbytes).
In RX62N, the memory addresses of the on-chip ROM or data flash ranges from
0010 0000h to 0010 8000h.The total number of bytes available for user program is
32768 bytes.
3.4
ADVANCED CONCEPTS
3.4.1
Pipelining
Pipelining is an important technique used to make fast CPUs. It is implemented to increase
the instruction throughput (i.e., the number of instructions that can be executed in a unit of
time) but it does not reduce the time taken to execute an individual instruction. The execution time of an individual instruction actually increases due to overhead caused by implementing the pipeline. The overhead in the pipeline is from register delay (setup time) and
clock skew. Improvement in instruction throughput means programs run faster and have
lower execution time, though no single instruction runs faster. The performance will be reduced if there is an imbalance between the stages. For instance, if execution stage takes
more time than memory access stage or, in other words, an instruction stays in execution
stage longer than memory access stage, then the performance degrades because the clock
cannot be faster than the slowest stage. Pipelining would provide optimal CPU performance CPU if every instruction was independent of every other instruction but, unfortunately, most of the instructions are dependent on each other.
The RX CPU is based on the classical five-stage pipeline. During the execution of an
instruction, it is converted into various micro-operations. The five stages of the pipeline are
described below. Only the Instruction Fetch (IF) stage is executed in the terms of instructions while others are executed in terms of micro-operations.
The operation of pipeline and respective stages is described as follows:
1. Instruction Fetch Stage (IF Stage):
In the IF stage, the CPU fetches 32/64 bit instructions from the memory. The
Program counter (PC) fetches the instruction and then the PC is incremented by
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
2.
3.
4.
5.
4 or 8 since the instructions are 4 or 8 bytes long. The RX CPU has four 8-byte instruction queues. The RX CPU keep fetching instructions until the queues are filled.
Instruction Decode Stage (ID Stage):
The main function of this stage is decoding. Instructions are decoded in the
ID stage and are converted into micro-operations. In addition to the decoding of
the instructions, the values of registers (operands) are also read from the register
file. If the value of a register needed is the result of the preceding instruction,
then the CPU executes a bypass process (BYP). This process is also called
forwarding.
Execution Stage (E Stage):
Two main types of calculation take place in this stage. One is normal ALU operations and the other is memory address calculations for memory access stage.
Normal ALU operations are register to register operations which includes add,
subtract, compare, and logical operations. The other calculations are memory reference operations which includes all load operations from the memory. During the
execute stage, the ALU adds the two arguments; i.e., a register and a constant offset given in the instruction to produce an address by the end of this stage.
Memory Access (M Stage):
Memory is accessed either for fetching an operand from the memory or storing an
operand in the memory. The address of an operand is calculated in the precious execution stage. This stage (M Stage) is divided into two sub-stages, M1 and M2.
The RX CPU enables respective memory accesses for M1 and M2.
䡲 M1 stage (memory-access stage 1):
In this sub-stage, operand memory accesses OA1 and OA2 are processed.
A store operation is processed when a write request is received via the bus.
During the Load operation, the operation proceeds to the M2 stage only when
a read request is received via the bus. In addition to the request, if the load data
is received at the same timing (i.e., no-wait memory access), then the operation proceeds to the WB stage.
䡲 M2 stage (memory-access stage 2):
In this sub-stage operand memory access OA2 is processed. In this sub-stage
the CPU waits for the load data, and once received the operation proceeds to
the WB stage.
Write-back stage (WB stage):
The last stage of the pipeline writes data into the register file. In this stage, the operation result calculated in the execution stage and the data read from memory in
the memory access stage are written to the register (RW). The data read from
memory and the other type of data, such as the operation result, can be written to
the register in the same clock cycles.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
67
One cycle
Pipeline stage
IF stage
D stage
E stage
M stage
M1 stage M2 stage
WB stage
BYP
Execution processing
IF
DEC
OP
RF
Figure 3.18 Pipeline Configuration and its Operation.
OA1
RW
OA2
Source: Hardware Manual, Figure 2.10,
page 2–26.
Pipeline Basic Operation
Ideally, each pipeline stage should take the same amount of time to process the instruction.
Unfortunately, ideal conditions are hard to achieve and hence stalls are created in the
pipeline and performance is degraded. The slowest stage which takes the maximum
amount of time becomes the bottleneck. Once the pipeline is filled, each instruction will
come out of the pipeline after one clock cycle. In a non-pipelined processor, if there are
n tasks to handle and each task takes m clock period , then total time taken to process
n tasks is n*m clock periods. In a pipelined processor, when it has m stages, ideally n tasks
will take (m (n 1)) clock periods. So, if we calculate the speed-up gained in this scenario, it will be n * m/{m (n 1)}.
Hazards prevent the next instruction from executing at the next cycle. They reduce the
performance and speed-up gained by pipelining. There are three types of hazards:
1. Structural hazard:
It arises from resource conflicts when the hardware is not capable of supporting
multiple instructions simultaneously in an overlapped manner.
2. Data hazard:
It arises when an instruction depends on the result of previous instruction. For instance, in the pipeline, an instruction I 1 depending on the result of instruction
I will cause a data hazard because one of the operands of the instruction I 1 is the
result of instruction I. In such a case, instruction I 1 cannot execute, as the data
is not available.
3. Control hazard:
It arises from pipelining of branches and other instructions that change the program counter; i.e., when a set of instructions are control dependent on the branch
condition, and what value the PC will take is not known until the execution stage
or decode stage.
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Hazards in the pipeline cause stalls in the pipeline which simply means stalling the pipeline.
Allowing some instructions to proceed and delaying other instructions helps in avoiding the
stall. When an instruction is stalled, the instructions issued (from the instruction stream)
later than the stalled one are also stalled. And the ones which were issued earlier than the
stalled instruction are allowed to proceed, so that the hazard goes away with time.
The following figures show typical cases that can occur in the pipeline. (In the following section, the abbreviation “mop” stands for micro-operations.)
1. Pipeline flow with stalls:
In Figure 3.19 the first instruction is a division operation and its execution stage takes
more than one cycle to complete. The other instructions, such as the ‘ADD’ instruction, if allowed to execute will complete execution before the division operation.
Since out of order completion might create a problem, the pipeline has to be stalled.
DIV R1, R2
IF
ADD R3, R4
D
E
E
......
E
WB
IF
D
stall
......
stall
E
WB
IF
stall
......
stall
D
E
ADD R5, R6
(mop) div
(mop) add
WB
(mop) add
Figure 3.19 Stalls created due to an Instruction that requires multiple cycles to execute in
the E Stage. Source: Hardware Manual, Figure 2.20, page 2–32.
In Figure 3.20, the first instruction is a load instruction which takes more than one
cycle to complete its operand access from memory. Again since in-order completion is important, therefore the later instructions have to be stalled and no more
fetching of instructions takes place. As soon as the memory access completes, the
pipeline is no longer stalled and instructions are passed to their next stage.
Other than no-wait
memory access
MOV [R1], R2
MOV [R3], R4
ADD R5, R6
IF
D
E
M
M
......
M
WB
IF
D
E
stall
......
stall
M
WB
(mop) load
IF
D
stall
......
stall
E
WB
(mop) add
(mop) load
Figure 3.20 Stalls created due to an Instruction that requires more than one cycle for its
operand access to execute in the E stage. Source: Hardware Manual, Figure 2.21, page 2–32.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
69
Figure 3.21 shows how control dependencies in the code cause stalls in the
pipeline. For instance, consider a simple “if statement.”
Branch instruction is executed
Branch
instruction
IF
D
(mop) jump
E
Branch penalty
Two cycles
IF
D
E
WB
Figure 3.21 Stalls created due to control dependency on a Branch Instruction.
Source: Hard-
ware Manual, Figure 2.22, page 2–33.
Code0
.......
.......
if(Cond1){
Code1
}
Code2
.........
..........
Code1 is control dependent on cond1. Code1 will only execute if Cond1 becomes
true or is satisfied. Code2 is also control dependent on Cond1. When this code is
converted into assembly code, a branch instruction such as jump executes. As the
branch instruction goes into the instruction decode stage, it’s time to fetch the next
instruction. But which instruction should be fetched, Code1 or Code2? Since the
decision is dependent on cond1 (branch instruction), and the result of the branch
instruction will be available after execute stage (E stage), therefore the pipeline has
to be stalled for two cycles. By the end of two cycles the address of next instruction is available in the program counter (PC), and then the next instruction will
be fetched.
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2. Pipeline flow with no stall:
䡲 Forwarding/Bypass Process:
Forwarding is a simple hardware technique used to minimize data hazard stalls. It
is also called a bypass process. The result of an ‘ADD’ instruction is not needed
until decode stage, or in extreme cases until execution stage. When the D stage of
‘SUB’ instruction needs the operand, it is not available since the result of ‘ADD’
instruction is not yet written into register, so a stall is created. If the result can be
moved from the execution stage of ‘ADD’ instruction to the start of the execution
stage of the ‘SUB’ instruction, then the need for a stall can be avoided. To achieve
this, ‘ALU result’ from both the E stage and M stage is fed back to the ALU inputs. If the forwarding hardware detects that the previous ALU operation generated a result which is going to be one of the inputs of a current ALU operation,
then the control logic selects the forwarded result as the ALU input instead of
reading from the register file.
ADD R1, R2
IF
D
E
(mop) div
E
Bypass process
SUB R3, R2
IF
D
E
WB
(mop) sub
Figure 3.22 Forwarding done to reduce the number of stalls.
Source: Hardware Manual, Figure
2.24, page 2–33.
䡲
When WB stages of two instructions are overlapped:
In this example, the first instruction is a ‘MOV’ instruction and the other instruction is an ‘ADD’ instruction. In Figure 3.23, the ADD instruction is more likely to
create a structural hazard in the WB stage. But this does not happen; instead, both
cause a write operation in the same cycle. In the first half of the cycle ‘MOV’ instruction writes and in the second half of the cycle ‘ADD’ instruction writes into
the register.
Mov [R1], R2
ADD R5, R3
IF
D
E
M
WB
(mop) load
IF
D
E
WB
(mop) add
Executed at the same timing
even when the WB stages are
overlapped
Figure 3.23 When WB Stages of two instructions are overlapped. Source: Hardware Manual, Figure 2.25, page 2–33.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
䡲
71
When subsequent instructions write to the same register before the end of
memory load:
In the following example, even when the subsequent instruction writes to the
same register before the end of memory load the operation processing is
pipelined, because the WB stage for the memory load is canceled.
X
MOV [R1], R2
IF
D
E
M
...
IF
D
E
WB
IF
D
E
WB
IF
D
E
M
WB
(mop) load
(Canceled when the register
number matches either of them)
WB
Figure 3.24 When subsequent Instruction writes to the same register before the end of
Memory Load. Source: Hardware Manual, Figure 2.26, page 2–34.
䡲
When the load data is not used by the subsequent instruction: Out of order completion is allowed in pipelining if the correctness of the program is maintained. As
in the following situation, when the load data is not used by the subsequent instruction, the subsequent operations are not stalled and in fact are allowed to execute. So, subsequent instructions are executed earlier and instructions are
processed out-of-order.
MOV [R1], R2
ADD R4, R5
IF
D
E
M
M
IF
D
E
WB
IF
D
E
SUB R6, R7
......
M
WB
(mop) load
(mop) add
WB
(mop) sub
Figure 3.25 When Load Instruction data is not used by the subsequent Instruction.
Source:
Hardware Manual, Figure 2.27, page 2–34.
3.4.2
Operating Modes
Operating Mode Types and Selection: There are five types of operating modes in the
RX62N/RX621 Group of MCUs. To specify the type of operating mode, the system control register 0 (SYSCR0) has to be set first. The bits that are set in the system control register are MD1, MD0, ROME, and EXBE. The MDE pin specifies the endianness.
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
72
TABLE 3.5
Selection of Operating Modes by the Mode Pins.
MD1
MD0
ROME
EXBE
0
1
1
0
1
0
1
1
1
1
OPERATING MODE
ON-CHIP ROM
EXTERNAL BUS
Boot mode
Enabled
Disabled
0
USB Boot mode
Enabled
Disabled
0
Single chip mode
Enabled
Disabled
Source: Hardware Manual, Table 3.1, page 3–1.
TABLE 3.6
ROME
EXBE
0
0
1
Selection of Operating Modes by Register Setting.
OPERATING MODE
ON-CHIP ROM
EXTERNAL BUS
Single chip mode
Disabled
Disabled
0
Single chip mode
Enabled
Disabled
0
1
On-chip ROM enabled extended mode
Disabled
Enabled
1
1
On-chip ROM enabled extended mode
Enabled
Enabled
Source: Hardware Manual, Table 3.2, page 3–1.
TABLE 3.7 Selection of Endianness.
MDE
ENDIAN
0
Little endian
1
Big endian
Source: Hardware Manual, Table 3.3, page 3–1.
TABLE 3.8
Registers Related to Operating Modes.
REGISTER NAME
SYMBOL
ACCESS SIZE
Mode monitor register
MDMONR
16
Mode status register
MDSR
16
System control register 0
SYSCR0
16
System control register 1
SYSCR1
16
Source: Hardware Manual, Table 3.4, page 3–2.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
73
1. Description of operating modes:
䡲 Single-Chip Mode: In this mode, on-chip ROM can be either disabled or en-
abled, but external bus is always disabled and all I/O ports are accessible.
The on-chip ROM is enabled when the microcontroller is started. When
ROME bit is set to 1 in SYSCR0, then on-chip ROM is enabled and it is again
disabled when ROME bit is set to 0. The same is not true in reverse operation.
While the on-chip ROM is disabled (i.e., ROME bit is set to 0 in SYSCR0), it
cannot be enabled by setting the ROME bit in SYSCR0 to 1.
䡲 On-chip ROM Enabled Extended Mode: In this mode, on-chip ROM is enabled and the external bus is always enabled. The on-chip ROM is enabled
when the ROME bit is set to 1 in SYSCR0. The external bus is available as external extended mode when EXBE bit is set to 1 in SYSCR0. This mode allows some I/O ports to be used as data bus input/output, address bus output, or
bus control signal input/output. The transition from this mode to single-chip
mode (on-chip ROM enabled) is possible if 0 is written to EXBE, and a transition to on-chip ROM disabled extended mode is possible if 0 is written to
ROME bit.
䡲 On-chip ROM Disabled Extended Mode: In this mode, on-chip ROM is disabled and external bus is always enabled. The on-chip ROM is disabled when
ROME bit is set to 0 in SYSCR0. The external bus is available as external extended mode when EXBE bit is set to 1 in SYSCR0. This mode allows some
I/O ports to be used as data bus input/output, address bus output, or bus control
signal input/output. It allows transition from this mode to single-chip mode
(on-chip ROM enabled) which is possible if 0 is written to EXBE. The transition to on-chip ROM enabled extended mode is not possible.
䡲 Boot Mode: Boot mode is provided for the flash memory. This mode functions
in the same manner as single-chip mode except for data write/erase function to
the flash memory.
䡲 USB Boot Mode: USB boot mode is provided for the flash memory. This
mode functions in the same manner as single-chip mode except for data
write/erase function to the flash memory.
2. Transitions of Operating Modes:
䡲 Operating Mode transitions according to Mode Pin Setting: Figure 3.26 shows
operating mode transitions according to the setting of pins MD1 and MD0.
Operating modes can shift in the direction of arrows.
䡲 Operating Mode Transitions according to Register Setting: Figure 3.27 shows
operating mode transitions according to the setting of the ROME and
EXBE bits in SYSCR0. Operating modes can shift in the direction of arrows.
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Reset* state
RES# 5 0
Reset* generated
Reset* generated
Reset* released
MD1 5 1
MD0 5 0
Reset* released
MD1 5 0
MD0 5 1
Boot mode
Reset* generated
Reset* released
MD1 5 1
MD0 5 0
USB boot mode
Single-chip mode
Mode can shift
Figure 3.26 Operating mode transitions according to Mode Pin Setting. Source: Hardware Manual, Figure 3.1, page 3–8.
Single-chip mode
On-chip ROM: Enabled*
External bus: Disabled
On-chip ROM enabled
extended mode
EXBE 5 0
EXBE 5 1
ROME 5 1
EXBE 5 0
On-chip ROM: Enabled
External bus: Enabled
ROME 5 1
EXBE 5 1
ROMF 5 0
ROME 5 0
EXBE 5 0
On-chip ROM: Disabled
External bus: Disabled
ROME 5 0
EXBE 5 0
EXBE 5 0
EXBE 5 1
ROME 5 0
EXBE 5 1
ROME 5 0
On-chip ROM disabled
extended mode
On-chip ROM: Disabled
External bus: Enabled
ROME 5 0
EXBE 5 1
Mode can shift
Figure 3.27 Operating mode transitions according to Mode Pin Setting. Source: Hardware Manual, Figure 3.1, page 3–8.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
3.4.3
75
Memory Organization
This section discusses some of the basic concepts of memory organization. The basic memory unit is organized into an array of addressable units. In a byte-addressable memory, each
memory location contains one byte (8-bits) of data. Another way of addressing the memory
is by grouping the bytes into a larger block called words or longwords and addressing that
block. Consider a memory unit having k locations (bytes). If, for addressing every location
(byte) a unique n-bit identifier is used, then the number of locations that can be addressed
would be 2n. So, k is equal to 2n which is equal to the size of the memory. If each location
stores m-bit value then the memory is said to be organized into an array of k m stored bits.
The address of each memory location will be a unique n-bit identifier and the content at each
location will be an m-bit value. Figure 3.28 shows the basic arrangement of memory unit. In
this figure the memory unit is a byte-addressable memory and, as can be seen, each location
is addressed by 4-bits; therefore the size of memory is 24 or 16 bytes.
Byte Addressing vs. Word Addressing
By using N address lines we can address 2N distinct addresses, numbered 0 through 2N 1.
Most of the modern computers use byte addressing but there are other cases possible, such
as word addressing. Consider the computer having 16-bit address space; if the addressing
scheme is byte-addressing, then the addressable entities would be 216 bytes with byte addresses from 0, 1, 2 . . . .216 1. If the addressing scheme is word-addressing then the addressable entities would be 215 words with byte addresses from 0, 2, 4 . . . .216 2.
216 bytes with byte addresses from 0, 1, 2, to 216 1
215 words with byte addresses 0, 2, 4, to 216 2
0000
0001
0010
0011
00101101
0100
0101
0110
..
.
1101
10100010
1110
1111
Figure 3.28 Logical layout of a block of memory.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
0
8 bits of data
1
8 bits of data
2
8 bits of data
3
8 bits of data
4
8 bits of data
5
8 bits of data
6
8 bits of data
Figure 3.29 Byte addressing.
0
16 bits of data
2
16 bits of data
4
16 bits of data
6
16 bits of data
Figure 3.30 Word addressing.
3.4.4
Memory Map
The following figure shows a memory map in various operating modes. The accessible areas
will differ according to the operating mode and the states of control bits. This microcontroller
has a 4-Gbyte address space, which ranges from 0000 0000h to FFFF FFFFh. The reserved areas shown in all three operating modes are not accessible by users/programmers.
In Figure 3.32, External Address Space is shown. It consists of CS areas (CS0 to CS7)
and SDRAM area (SDCS). The CS area is further divided into eight areas (CS0 to CS7),
each corresponding to the CSi signal output from a CSi (i 0 to 7) pin.
3.4.5
I/O Registers
This section focuses on preventive measures that should be taken while using I/O registers.
In some cases, after writing into I/O registers, you must check whether the write operation
is completed. In some cases, a CPU behaves differently and could lead to unpredictable results. In such cases, the CPU starts executing subsequent instructions before the write operation is over. If the next instruction deals with the same I/O register, and it tries to read
from the same register, then the subsequent instruction reads the value of an I/O register
that is not yet updated. So, in such scenarios where the updated value of an I/O register is
required in the future, or where a subsequent instruction must execute after the value in the
I/O register is changed, special care must be taken. Examples of such situations could be
where the subsequent instruction must be executed while an interrupt request is disabled,
or where a WAIT instruction is executed immediately after the preprocessing for causing a
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
On-chip ROM enabled
extended mode
Single-chip mode*2
On-chip ROM disabled
extended mode
0000 0000h
On-chip RAM
0000 0000h
On-chip RAM
0000 0000h
On-chip RAM
0001 8000h
Reserved area*1
0001 8000h
Reserved area*1
0001 8000h
Reserved area*1
0008 0000h
0008 0000h
0008 0000h
Perpheral I/O registers
0010 0000h
Perpheral I/O registers
0010 0000h
On-chip ROM
(data flash)
0010 8000h
FCU-RAM3
007F 8000h
Reserved area*1
FCU-RAM3
007F 8000h
007F A000h
0010 0000h
On-chip ROM
(data flash)
0010 8000h
Reserved area*1
Perpheral I/O registers
007F A000h
Reserved area*1
Reserved area*1
Perpheral I/O registers
007F C000h
Perpheral I/O registers
007F C000h
007F C500h
Reserved area*1
007F C500h
Reserved area*1
007F FC00h
Reserved area*1
007F FC00h
Perpheral I/O registers
0080 0000h
Perpheral I/O registers
0080 0000h
Reserved area*1
Reserved area*1
00F8 0000h On-chip ROM (program ROM)
00F8 0000h On-chip ROM (program ROM)
(write only)
(write only)
0100 0000h
0100 0000h
0100 0000h
<
0800 0000h
External address space
(CS area)
<
0800 0000h
External address space
(SDRAM)
1000 0000h
<
Reserved area*1
FF00 0000h
FF00 C000h
FF80 0000h
On-chip ROM (FCU firmware)*3
(read only)
Reserved area*1
On-chip ROM (user boot)
(read only)
Reserved area*1
(read only)
<
External address space
(SDRAM)
<
FFF8 0000h On-chip ROM (program ROM)
FFFF FFFFh
External address space
(CS area)
1000 0000h
<
FEFF E000h
<
FEFF E000h
FF00 0000h
FF7F C000h
FF80 0000h
Reserved area*1
<
<
Reserved area*1
<
On-chip ROM (FCU firmware)*3
(read only)
Reserved area*1
FF00 0000h
On-chip ROM (user boot)
(read only)
Extend address space
Reserved area*1
FFF8 0000h On-chip ROM (program ROM)
FFFF FFFFh
(read only)
FFFF FFFFh
Note:
1. Reserved areas should not be accessed, since the correct operation of LSI is not guaranteed if they are accessed.
2. The address space in boot mode and user boot mode is the same as the address space in single-chip mode.
3. For details on the FCU, see section 37, ROM (Flash Memory for Code Storage) and section 38, Data Flash
(Flash Memory for Data Storage) in the Hardware Manual.
Figure 3.31 Memory map in each operating mode. Source: Hardware Manual, Figure 4.1, page 4–1.
77
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
0000 0000h
0100 0000h
On-chip RAM
0001 8000h
Reserved area
*1
CS7 (16 Mbytes)
0008 0000h
Peripheral I/O registers
01FF FFFFh
0200 0000h
0010 0000h
CS6 (16 Mbytes)
<
Reserved area*1
<
02FF FFFFh
0300 0000h
CS5 (16 Mbytes)
03FF FFFFh
0400 0000h
0100 000h
CS4 (16 Mbytes)
<
External address space
(CS area)
<
04FF FFFFh
0500 0000h
CS3 (16 Mbytes)
0080 0000h
05FF FFFFh
0600 0000h
External address space
(SDRAM area)
1000 0000h
CS2 (16 Mbytes)
06FF FFFFh
0700 0000h
CS1 (16 Mbytes)
07FF FFFFh
0800 0000h
<
Reserved area*1
<
SDCS (128 Mbytes)
0FFF FFFFh
FF00 0000h
FF00 0000h
External address space*2
(CS area)
FFFF FFFFh
CS0 (16 Mbytes)
FFFF FFFFh
Note:
1. Reserved areas should not be accessed, since the correct operation of LSI is not guaranteed if they are accessed.
2. The CSO are is disabled in on-chip ROM enabled extended mode.
In this node, the address spare for addresses above 1000 0000h is as shown in Figure 3.1.
Figure 3.32 Correspondence between External Address Spaces, CS Areas (CS0 to CS7), and SDRAM
area (SDCS) (In On-chip ROM Disabled Extended Mode). Source: Hardware Manual, Figure 4.2, page 4–2.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
79
transition to the low power consumption state. The correct way to handle such situations is
by waiting until the write operation is completed and following a debugging procedure.
Follow these steps:
1.
2.
3.
4.
Write to an I/O register.
Read the value from the I/O register to a general register.
Execute the operation using the value read.
Execute the subsequent instruction.
Consider a situation where multiple registers need to be written first before subsequent instruction can execute. In other words, subsequent instructions should be executed after the
write operations are completed. In such a case only read the I/O register that was last written to, and execute the operation using that value. Do not read or execute operation for all
the registers that were written to.
3.5
ADVANCED EXAMPLES
EXAMPLE 1
Show how the C arrays are laid out in memory for the Renesas board and compiler.
Remember to pay attention to endianness, indicating which byte is located where. Assume
the space for “a” starts in the first available space of user RAM (lowest address), and
“b” starts 100 bytes (decimal) after where a starts.
a) int a [5]
ADDRESS
ARRAY ELEMENT
WHICH BYTE?
400
401
402
403
404
405
406
407
408
409
a[0]
a[0]
a[1]
a[1]
a[2]
a[2]
a[3]
a[3]
a[4]
a[4]
Lower
Upper
Lower
Upper
Lower
Upper
Lower
Upper
Lower
Upper
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
b) unsigned char b [4] [2]
ADDRESS
ARRAY ELEMENT
464
465
466
467
468
469
46A
46B
b[0][0]
b[0][1]
b[1][0]
b[1][1]
b[2][0]
b[2][1]
b[3][0]
b[3][1]
WHICH BYTE?
EXAMPLE 2
What is the speedup gained by implementing pipeline stages on a normal process?
Consider a normal process with n number of tasks, taking k number of clock periods to
execute one task.
Then, the time taken by the process to complete n tasks n * k clock periods.
If k pipeline stages are implemented for the above scenario, then the time
taken (k (n 1)) clock periods.
Therefore,
speedup d
nk
.
1k 1n 1 2 2
EXAMPLE 3
What are the various technologies used to implement embedded systems? Compare them
on the basis of various parameters such as design cost, unit cost, upgrades and bug fixes,
size, weight, power consumption, and system speed.
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
81
DESIGN
COST
UNIT
COST
UPGRADES
AND BUG
FIXES
Discrete
logic
Low
Mid
Hard
Large
High
ASIC
High
($500K/
mask set)
Very
low
Hard
Tiny
Very low
Low
Obscenely
fast
Programmable
logic-FPGA,PLD
Low
Mid
Easy
Small
Low
Medium
to high
Very fast
Microprocessor memory peripherals
Low to
mid
Mid
Easy
Small to
medium
Low to
moderate
Medium
Moderate
Microcontrollers
(including memory
and peripherals)
Low
Mid
to
low
Easy
Small
Low
Medium
Slow to
moderate
Embedded PC
Low
High
Easy
Medium
Moderate
to high
Medium
to high
Moderate
IMPLEMENTATION
3.6
SIZE
WEIGHT
POWER
?
SYSTEM
SPEED
Very fast
REFERENCES
Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
Hennesy, J. L. and Patterson, D. A. Computer Architecture: A Quantitative Approach. San Francisco,
CA: Morgan Kaufmann Publishers, c2003. Print.
Parhami, B. Computer Architecture: From Microprocessors to Supercomputers. Oxford, New York: Oxford
University Press, 2005. Print.
Stallings, W. Computer Organization & Architecture: Designing for Performance. Upper Saddle River,
NJ: Pearson/Prentice Hall, c2006. Print.
Tomek, I. Introduction to Computer Architecture. Rockville, MD: Computer Science Press, c1981. Print.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
3.7
EXERCISES
1. What are the benefits of a microprocessor/microcontroller-based embedded sys-
tem over an ASIC-based embedded system?
2. Consider a college food court which involves five steps before you select and eat
your food. Look at the following figure for solving the problem.
Show ID
Get token
Place the order
Cashier
Take the meal
Suppose that in the food court pipeline the latency varies at each window. It
varies from one to two minutes. When a student is done at each window he or she
waits until the next window is available. Assume that there is no overhead involved while a student passes from one window to another window.
a. How should this pipeline be used to maximize its throughput?
b. Is the method of part ‘a’ applicable to a processor’s data path?
c. What would be the throughput of the scheme in part ‘a’ if the latency of each
window were uniformly distributed?
d. Discuss a method other than ‘c’ for improving throughput?
3. Which memory is the fastest?
a. Level 2 cache
b. Registers
c. RAM
d. Disk storage
e. Level 1 cache
4. Consider 4 Kbyte SRAM chips having a data width of 4 bits. How many chips
will be required to build a 32 MB memory unit with the word width of 8-bits?
5. The double word 0x AC35 FA34 is stored in memory addresses N through N 3.
Which of the following represents storage using little endianness?
a.
N
43
N1
b.
N
AC
AF
N1
35
N2
53
N2
FA
N3
CA
N3
34
CHAPTER 3 / ORGANIZATION AND ARCHITECTURE . . .
c.
N
34
N1
d.
N
FA
FA
N1
34
N2
35
N2
AC
N3
AC
N3
35
83
6. How many bits wide is the program counter register?
a. 32 bits
b. 16 bits
c. 8 bits
d. 10 bits
e. 12 bits
7. What will happen if you try to write to an array element larger than your array?
a. An error will be reported.
b. The program won’t compile.
c. Nothing.
d. You don’t know, but it will most likely be bad.
e. The array will redefine itself bigger.
8. What is the total address space for our RX62N microcontroller?
a. 31 Kbytes
b. 384 Mbytes
c. 4 Kbytes
d. 4 Gbytes
e. 1024 Kbytes
9. What are the benefits of a microprocessor/microcontroller-based embedded sys-
tem over an FPGA-based embedded system?
10. What is the number of address bits required to address any byte in a memory that
contains 4096 address spaces?
a. 2
b. 8
c. 12
d. 16
e. 32
11. MCU can run in three modes: single chip, memory expansion, microprocessor
modes. If used in single-chip mode, what areas in memory could be addressed?
a. Only internal areas (SFR, internal RAM, internal ROM)
b. Internal areas (SFR, internal RAM, internal ROM) and external memory areas
c. SFR, internal RAM, and external memory
d. SFR, external memory
e. Only external memory
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
12. What is the number of address bits required to address any byte in a memory that
contains 65536 address spaces?
a. 2
b. 8
c. 12
d. 16
e. 20
13. Which of the following buses is not a valid bus?
a. Instruction bus
b. Internal main bus 1
c. Internal peripheral bus 1
d. External bus
e. External operand bus
14. Out of the following which bus request has the highest priority?
a. DMACA
b. DTC
c. CPU
d. EDMAC
Chapter Four
Software Development Tools
4.1
LEARNING OBJECTIVES
In this chapter the reader will learn about:
䡲
䡲
䡲
䡲
䡲
Process of compilation
Features of the RX family compiler
Debugging tools
Features of the High-performance Embedded Workshop
Various header files associated with C/C Compiler and the RX family
4.2
BASIC CONCEPTS
4.2.1
Compilation Mechanism
There are several steps involved from the stage of writing a C program to the stage of execution. Figure 4.1 shows these different steps.
In this process, a program written in C language gets translated into an assembly level
program which the computer can understand. It can be seen from Figure 4.1 that the program passes through several processors before it is ready to be executed. The functions of
each of these processors are:
䡲
䡲
䡲
The preprocessor performs text replacement according to preprocessor directives.
There are two main preprocessor directives—macro expansion (e.g. #define
SIZE 30) and file inclusion (e.g. #include “config.h”).
The compiler transforms source code, written in a programming language such as
C, or C (source language) into another target language (object code) which is
of binary form.
The linker is a program that takes one or more objects generated by a compiler
and combines them into a single executable program.
85
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
C
Source and
Header Files
C Preprocessor
Compiler
Source Code
Analysis
Symbol
Table
Target Code
Synthesis
Library
Object Files
Linker
Executable
Image
Figure 4.1 Compilation process for a C program.
The input and output to each of these processing stages is shown in Table 4.1.
TABLE 4.1
PROCESSOR
Input and Output to each Processor.
INPUT
OUTPUT
Preprocessor
C source code file
Source code file with processed
preprocessor commands
Compiler
Source code file with processed
preprocessor commands
Re-locatable object code
Linker
Re-locatable object code and the
standard C library functions
Executable code in machine
language
CHAPTER 4 / SOFTWARE DEVELOPMENT TOOLS
4.2.2
87
Compilers for Embedded Systems
Compilers for embedded systems differ from compilers for general-purpose processors
(GPPs). Minimizing code and data size is often critical for embedded systems since memory
sizes are limited due by price pressures. This makes compiler code and data size optimizations extremely important. The tongue-in-cheek “Software Gas Law” states that a program
will eventually grow to fill all available resources. Embedded system software evolves as features are added and defects are fixed, while the hardware changes much more slowly. It is
much easier to reprogram an MCU than redesign the hardware. As a result there is great value
in compiler optimizations which can squeeze more code and data into the available resources.
Speed optimization is also often critical. However, it is done differently for embedded
systems and GPPs. First, GPP instruction sets have evolved over time to enable extremely
high clock rates ( 2 GHz) and deep instruction processing pipelines. Embedded processors with their lower clock rates do not need such deep pipelines, which leads to different
code optimization trade-offs. Second, a lower clock rate means that embedded systems
have a smaller performance penalty than GPPs for accessing memory instead of registers.
This has two interesting effects. First, the compiler makes different optimization trade-offs
with data allocation. Second, instruction sets for embedded systems can support memorymemory and bit-level operations rather than being forced into a load/store model.
4.2.3
RX Compiler Package
The RX compiler package includes the following embedded system development tools.
䡲
䡲
䡲
䡲
C/Cⴙⴙ Compiler
The compiler translates source code into assembly code, and typically also invokes
the assembler and linker to create an executable file. The Compiler is ANSI-compliant
and supports exception processing and template functions. It supports C or C and
generates compact and high-speed object code. It offers general optimization techniques such as deletion of common expression and register allocation. There are additional non-ANSI features which are helpful or necessary for embedded systems.
Assembler
The Assembler translates assembly code into object (machine) code. It also provides pre-processor functions such as the file inclusion, conditional assembly, and
macros, in order to simplify programming.
Optimizing Linkage Editor
The Linkage Editor processes object files generated by the compiler and assembler
to create load modules and library files.
Standard Library Generator
The Standard Library Generator creates customized versions of the standard library files based on the user-specified options.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
䡲
Simulator/Debugger
This Simulator/Debugger provides the capability for debugging in targetless system.
It is also a highly accurate simulator, supporting program performance evaluation .
Utilities
The RX package contains various utility tools. Call Walker shows stack use corresponding to the C/C function call tree. Moreover, function allocation editing
by drag & drop is available. Map Viewer provides a GUI display of the various
sections in a map file (output by the Optimizing Linkage Editor).
IDE (Integrated Development Environment): HEW (High-performance
Embedded Workshop)
High-Performance Embedded Workshop provides a GUI-based integrated development environment on Windows operating systems for the development and debugging of embedded applications for the Renesas microcontrollers. It supports
seamless integration and easy access to all tools for coding, compiling, linking,
and debugging. All the tools in the package together offer a variety of functions
and increase productivity greatly.
Features of RX Family C/Cⴙⴙ Compiler
1. Easy optimization setting and the optimization features
䡲 Compiler Optimization: It provides an easy selection of optimization as in the
selection of size, speed, priority, and also in the selection of the optimization
level (optimize level: 0, 1, 2, or max).
䡲 Supports wide-ranging optimization when compiling; function’s inlineexpansion between files and symbol access optimization which uses external
symbol allocation information from the optimization linker.
䡲 Has a detailed setting of optimization that is useful in loop expansions, instructions order, optimization range specification, register allocation, etc.
2. Linker optimization
䡲 Handles inter-module optimization such as the removal of an unreferenced
symbol, optimization for branch order, and provides a detailed setting of partially disabled optimization.
3. Optimization of standard library
䡲 Application of compiler optimization: A standard library is targeted on optimization and a compact code is generated with the entire program.
4. Easy translation environment from the existing product
䡲 Supports the option of controlling different language specifications.
䡲 Language specification of another compiler is checked by the RX compiler.
䡲 RX supports Bi-endian operation. The compiler can select between big endian
and little endian.
CHAPTER 4 / SOFTWARE DEVELOPMENT TOOLS
4.2.4
89
Debugging Tools
There are two primary tools for debugging embedded real-time systems:
a. Debugger: The debugger allows a developer to observe and control a program’s
execution and data. The execution can be started, paused and stopped, or advanced
by a single instruction or program statement. Breakpoints can typically be inserted. Data stored in variables as well as raw memory and register values can be
examined and modified.
b. Monitor: The monitor allows a developer to examine the program’s temporal behavior. The most common monitors are oscilloscopes and logic analyzers connected to the embedded system. For instance, , while implementing interrupts in
serial communication, one can measure useful information such as the duration of
the transmit ISR and the receive ISR, or the delay between sending a character and
receiving a reply. This information can be used to find maximum latency, and maximum frequency. Hence the monitor tool is helpful in giving you insights about the
timing of various operations happening inside the system.
4.2.5
Introduction to HEW
This section deals with the concepts and functionalities associated with the Highperformance Embedded Workshop V.4.08 (HEW).
Overview: HEW organizes your work with the concepts of workspaces and projects.
䡲
䡲
Workspace: This is the largest unit which contains programs written in the
HEW workshop. It can have several projects. A project is automatically created
when we create the workspace.
Project: The project is where you write your program. In fact, creating a new project is making a new program. You can also make hierarchical levels between several modules. It, along with other projects, will be included in the workspace.
A simple diagram below shows the relationship between a project and the workspace.
file
project
file
workspace
project
project
Figure 4.2 Relationship
between a project and the
workspace.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Creating or Opening a Project in HEW-IDE
To launch HEW, open the start menu, select program, select Renesas, select HEW, and
then select the shortcut of the High-performance Embedded Workshop.
Figure 4.3 Launching of HEW. Source: RX62N RDK Renesas toolchain quick start guide.
Look for the dialog box just like this:
Figure 4.4 Welcome dialog box in HEW. Source: HEW User Manual V.4.08, page 15.
To create a new workspace:
䡲
䡲
䡲
Select the Create a new project workspace option from the Welcome! dialog box,
and click the OK button or select [File V New Workspace]. The New Project
Workspace dialog box will be displayed.
Enter the name of the new workspace into the Workspace Name field. To select
the directory in which you would like to create the workspace, use the Browse button or type the directory into the Directory field manually.
Select the CPU family and Tool chain upon which you would like to base the
workspace.
CHAPTER 4 / SOFTWARE DEVELOPMENT TOOLS
䡲
䡲
91
When a new workspace is created, the HEW will also automatically create a project and place it inside the new workspace. From the project types list, select the
type of project that you want to create from this list. The project types are of
mainly three types: tool chain-only, debug-only, and a full project generator that
contains both the debugger and tool chain aspect of the HEW.
Click the OK button to create. This then launches the HEW window.
To open a new workspace:
䡲
䡲
Select Browse to another project workspace option from the dialog box
shown in Figure 4.4 and then click the OK button or select [File V Open Workspace]. The Open Workspace dialog box will be displayed. Select the workspace
file (“.HWS” file) that you want to open.
Click the Select button to open the Properties dialog box to open the workspace.
Click the Cancel button to stop opening the workspace.
To open a recently used workspace:
䡲
Select Open a recent project workspace in the dialog box: select the name of the
workspace from the dropdown list, and then click the OK button.
Figure 4.5 HEW workspace showing various windows. Source: HEW User Manual V.4.08, page 2.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Windows in HEW
There are three main windows in HEW:
Workspace Window: Shows the projects and files that are currently in the workspace. It
has four tabs: Projects, Templates, Navigation, and Test.
Figure 4.6 Workspace window in HEW. Source: HEW User Manual V.4.08, page 6.
Output Window: Shows the results of a various processes (e.g., build). By default, it
has seven tabs (Build, Debug, Find in Files 1, Find in Files 2, Macro, Test, and Version
Control) on display.
Figure 4.7 Output window in HEW. Source: HEW User Manual V.4.08, page 9.
CHAPTER 4 / SOFTWARE DEVELOPMENT TOOLS
93
Editor Window: Provides file viewing and editing facilities. It is in this window where
you will edit files of your project. It allows you to have many files open at one time, so you
can switch between them. You can edit them in whichever order you want. Each file has a
separate tab associated with it, and you can navigate easily to any tab you want.
Figure 4.8 Editor window in HEW. Source: HEW User Manual V.4.08, page 9.
Concept of Configuration and Session
Figure 4.9 Configuration and session selection in HEW. Source: HEW User Manual V.4.08, page 20.
By looking at the Standard toolbar you will know your current configuration and session.
You can also select your session and configuration by looking into the drop-down list box.
For instance, Figure 4.9 shows that the selected debugger is “SH-4 Simulator” which
works along with Renesas SuperH Standard toolchain.
Before going any further, let me clarify the concept of configuration and session.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Configuration
After selecting a toolchain, you will create a project. Once the project is created, the
HEW will automatically create configurations “Debug” and “Release.” As shown in
Figure 4.9, configurations “SimDebug_SH-4,” “Debug,” and “Release” are available.
At the time of the creation of the project, if you have selected a target debugger
HEW will automatically create a configuration best suited for that debugger. For instance, if you have selected “SH-4 Simulator” in the Target tab while creating a project, configuration “SimDebug_SH-4” is created. Configurations are the settings
that have to be set before the building process starts. It can also be referred to as “build
configuration.”
Session
Sessions are the units basically used to manage various settings. For instance, they may
refer to the settings associated with debugging options of a specific debugger and data
values on the memory and register windows. The term “session” is also referred as “debugger session.” If you look at the figure of the Standard toolbar (Figure 4.9), sessions
“SimSessionSH-4” and “Default Session” are available. Information on each session is
saved in an individual file in the HEW project. Just like a configuration is created as
you create a project after selection of the toolchain, a session called “Default Session”
is also created. Also, if you select a target debugger at the creation of project, a session
is created for connecting the debugger. For example, if you have selected “SH-4 Simulator” in “Target” at the creation of a project, session “SimSessionSH-4” is automatically created.
4.2.6
Concepts of Header Files
Most of the programming languages (for instance C and C) use header files. These
files hold certain elements (program’s source code) which are reusable. Header
files contain common repeatable elements such as forward declarations of classes, subroutines, structure, unions, variables, and other identifiers. Declaring the same standardized identifiers in more than one source file can be a cumbersome task for a
programmer.
The solution to this is declaring that identifier in a single header file and when there is
a need for that identifier in some other source file, a programmer can just include that
header file in order to include all declarations. The C standard library and C standard
library traditionally declare their standard functions in header files that implement standard
processing operations such as input/output and string handling. They can be used by including the standard include files which contain declarations for the corresponding libraries and definitions of the macro names necessary to use them.
CHAPTER 4 / SOFTWARE DEVELOPMENT TOOLS
95
Header Files Used in RX Family C/Cⴙⴙ Compiler
C and C are the most famous programming languages that implement the concept of
header files.
Table 4.2 lists the various library types, and their corresponding standard include files.
Some include files consist only of macros, as seen in Table 4.3, to improve the program
efficiency.
Header Files Associated with RX62N
Some of the header files used in the demo program can be seen in Table 4.4.
TABLE 4.2
LIBRARY
TYPES
Library Types and Their Corresponding Header Files.
DESCRIPTION
STANDARD
INCLUDE
FILES
Program diagnostics
Outputs program diagnostic information.
<assert.h>
Character handling
Handles and checks characters.
<ctype.h>
Mathematics
Performs numerical calculations such as
trignometric functions.
<math.h>
<mathf.h>
Non-local jumps
Supports transfer of control between functions.
<setjmp.h>
Variable arguments
Supports access to variable arguments for
functions with such arguments.
<stdarg.h>
Input/output
Performs input/output handling.
<stdio.h>
General utilities
Performs C program standard processing such as
storage area management.
<stdlib.h>
String handling
Performs string comparison, copying, etc.
<string.h>
Complex arithmetic
Performs complex numeric operations.
<complex.h>
Floating-point environment
Supports access to floating-point environment.
<fenv.h>
Integer type format
conversion
Manipulates greatest-width integers and converts
integer format.
<inttypes.h>
Multibyte and wide
characters
Manipulates multibyte characters.
<wchar.h>
<wctype.h>
Source: Compiler Package User Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics
America, Inc., 2010. Table 9.26, page 328.
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TABLE 4.3
Header Files that Contain Macros.
STANDARD
INCLUDE FILE
DESCRIPTION
<stddef.h>
Defines macro names used in common by the standard include files.
<limits.h>
Defines various limit values relating to the compiler internal processing.
<errno.h>
Defines the value to be set in errno when an error is generated in a library function.
<float.h>
Defines various limit values relating to the limits of floating-point numbers.
<iso646.h>
Defines alternative spellings of macro names.
<stdbool.h>
Defines macros relating to logical types and values.
<stdint.h>
Declares integer types with specified width and defines macros.
<tgmath.h>
Defines type-generic macros.
Source: Compiler Package User Manual, Table 9.27, pg. 329.
TABLE 4.4
Header Files Used in Demo Program of RX62N Microcontroller Board.
STANDARD
INCLUDE FILE
DESCRIPTION
<config.h>
Defines macros relating to the font size.
<glyph.h>
Defines external constants, typedef enumerations and structures,
prototype for minimum, and full access for glyph API library.
<preamble.h>
Defines basic definitions of all simple constants and types.
<st7579_lcd.h>
Defines prototypes that are required by the LCD driver in the glyph API.
<yrdkrx62n_rspio.h>
Defines prototypes for the glyph communication API.
<typedefine.h>
Defines aliases of Integer Type.
<sbrk.h>
Defines macro relating to size of area managed by sbrk.
<vect.h>
Defines vector table.
<stacksct.h>
Defines macros that refer to setting of stack area.
<iodefine.h>
Define various input and output registers.
4.3
BASIC EXAMPLES
(Source: High-performance Embedded Workshop V.4.08, User’s Manual. Renesas Electronics America, Inc., 2010.)
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EXAMPLE 1
This is an example demonstrating how to Build, Debug, and Run a Project on the HEW-IDE.
If you are testing your board for the first time, you will test it with the demo code that
comes with the package. After launching the main window, you probably want to download and run it on the board. Follow these steps to acquaint yourself with the whole
process:
Step 1: Ensure that ‘SessionRX600_E1_E20_SYSTEM’ session in the right-hand drop-
down list on the tool bar is selected.
Step 2: Click the <Connect> button on the ‘debug’ toolbar.
When you click on the connect button, an initial settings window will appear. Ensure that you
select the right MCU group and device. Select the debugging mode as shown in Figure 4.10.
Figure 4.10 Initial setting window while connecting the board.
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After clicking OK, a window will pop up which will show the status as connecting. This
window indicates whether an initial configuration has been done or not. See Figure 4.11 to
get an idea.
Figure 4.11 Window
showing the status as
connecting.
This window will show up for just a few seconds, and after that a configuration properties
window will appear. You can see various configuration properties associated with MCU,
system, Internal flash memory overwrite, and external flash memory. You can select
any of them and edit the properties as your application demands. If you go to the MCU tab
on the same window, you need to select one of three operating modes; i.e., on chip ROM
enabled extended mode, on chip ROM disabled extended mode, or single chip mode.
For the demo application, you can go on with the settings shown in the Figure 4.12.
Figure 4.12 Window
showing configuration
properties.
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Once connected, you can see the status in the output window (Figure 4.13) as ‘connected.’
Also, you can see the status of the platform tab of other component windows. Here is the
snapshot:
Figure 4.13 Window showing the status after the board has connected.
Step 3: The next step is building the program to check for any compiling error. Typically, in
build process, each phase of the build takes a set of project files and builds them. If every file
builds successfully, then the next phase is executed. Let me shed some light on the build
process. The building process takes place in three phases: the Compiler is the first phase, the
Assembler is the second phase, and the Linker is the third and final phase. During the Compiler phase, the C/C source files from the various projects are compiled in turns. During
the Assembler phase, the assembler source files are assembled. During the Linker phase, all
library files and output files from the Compiler and Assembler phases are linked together to
produce the load module. Depending on your requirement, you can choose from the various
build options available to you. If you want to build an individual file, first select it from project tab of the workspace window, and then you can select any one of these options:
䡲
䡲
䡲
䡲
Click the Build File toolbar button (Figure 4.14)
Select Build <file> from the pop-up menu
Select the [Build V Build File] menu option
Press CTRL F7
If you want to build a project, you can select any one of these:
䡲
䡲
䡲
䡲
Click the Build toolbar button (Figure 4.14)
Press F7
Select [Build V Build]
Right-click on a project in the Project tab of the Workspace window and select
[Build V Build] from the pop-up menu
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Typically, the build operation compiles or assembles those files that are changed since the
last build command. The Build all operation builds all files irrespective of whether the file
has been modified or not.
For performing a build all operation, you may select any of these options:
䡲
䡲
䡲
Click the Build All toolbar button (Figure 4.14)
Select [Build V Build All]
Right-click on a project in the Projects tab of the Workspace window and select
[Build V Build All] from the pop-up menu
In each of the cases discussed, you can see the status of the build process in the build tab
of the output window. An example that shows the status in the output window after the
build process is next.
EXAMPLE
Build Finished
‘x’ Errors, ‘x’ Warnings
Here ‘x’ could be 0 or a larger number depending on your coding skills.
Figure 4.14 Explanation of icons on the toolbar. Source: HEW User Manual V.4.08.
Step 4: After the build process, you should download the code onto your board. For that,
first go to the debug tab on the menu bar. Click on it and select ‘download modules’ in the
drop-down menu list. Click on ‘all modules’ and wait for the HEW to download all modules onto the board. When downloaded, a status will appear on the memory tab of the other
component window, indicating the memory area where the program has been downloaded.
A snapshot of the same is shown in Figure 4.15.
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Figure 4.15 Memory tab of other component window showing status of download.
Step 5: After downloading the program onto the board, you need to make it run to see the
response. Click on ‘reset go’ from various other go options as shown in Figure 4.16.
Figure 4.16 Explanation of icons on the toolbar. Source: HEW User Manual V.4.08.
You can easily see the response on the output window as well as on the MCU board. The
status on the output window will look like: Reset CPU.
Step 6: If you need to halt the program for debugging or editing the code, you can just
click on the red stop button, as seen in Figure 4.17.
Figure 4.17 Snapshot of toolbar before halting the program.
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EXAMPLE 2
This is an example demonstrating how to create and save a header file in the workspace.
This example also demonstrates how to add that header file to the current project, and how
to edit it.
A programmer can create a ‘Header file’ when there is a need for some subroutines,
structure, variables, unions, enumerations, and other definitions to be commonly repeated.
Declaring the same identifiers again and again can be a tedious task, so the solution is creating a header file that contains all the elements that are being repeated in more than one
source file. In a header file, a programmer just declares common declarations, and when
there is need for any identifier the programmer can just include that header file in the main
source file, and the purpose will be fulfilled in an easier way. Follow these steps to add a
header file to your current project.
Step 1: Creating a header file
To create a new header file, you need to create a new editing window first. For this, you can
apply one of the following:
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䡲
䡲
Click the file tab on the menu bar, and then click the new file option in the dropdown menu
Press CTRL N
Click the new file toolbar icon
By default, a new file will be given an arbitrary name which you can change when you save
the file. To make a header file you just need to save that file as “.h” extension file. It is always good to name the file according to its functionality because other programmers who
might want to edit the project later must also know the types of declarations the header file
contains. This is the reason the header file that defines input and output registers is named
<iodefines.h>. After you have created a file, the next step is to edit the file.
Step 2: Editing a header file
In the editor window, you can declare the basic definitions that are being repeated in more
than one source file. Before writing the definitions and declarations, do yourself a favor by
writing the description of the current header file, to give other programmers an idea as to
what this header file contains in general. Then, you can proceed with writing your content as
your application demands. After you have written those basic definitions, you can edit it by
using the basic tools available to you such as the menu, toolbar, and keyboard shortcuts. In
addition, HEW provides you the functionality of editing through a pop-up menu that is local to the editor window. That menu will appear when you right click in an editor window.
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Table 4.5 outlines the basic operations.
TABLE 4.5
OPERATION
Undo
Basic Operations for Editing a Header File.
EFFECT
ACTION
Reverses the last editing operation.
Select [Edit V Undo]
Press CTRL Z
Redo
Cut
Repeats the last undone editing
operation.
Select [Edit V Undo]
Removes highlighted text and places it on
the Windows clipboard.
Click the Cut toolbar button ( )
Press CTRL Z
Press CTRL X
Select [Edit V Cut]
Select Cut from the pop-up menu
Copy
Places a copy of the highlighted text into
the Windows clipboard.
Click the Copy toolbar button ( )
Press CTRL C
Select [Edit V Copy]
Select Copy from the pop-up menu
®
Paste
Copies the contents of the Windows
clipboard into the active window at the
position of the insertion cursor.
Click the Paste toolbar button ( )
Press CTRL V
Select [Edit V Paste]
Select Paste from the pop-up menu
Clear
Select All
Removes highlighted text (it is not copied
to the Windows clipboard).
Select [Edit V Clear]
Selects (i.e. highlights) the entire contents
of the active window.
Select [Edit V Select All]
Press Delete
Press CTRL A
Source: HEW User Manual V.4.08, page 120.
While you are editing your file, the title bar will show an asterisk (*). For instance
global.h*
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Step 3: Saving a header file
This step discusses how to save a file as a header file and how to save the contents of the
editor window in general. To save the contents of a newly created file as a header file, make
sure that it is an active window; i.e., open in an editor window, and then select one of the
following:
䡲
䡲
䡲
Click the file button on menu bar, then click the new save button in the drop-down
menu
Press CTRL S
Click the Save File toolbar icon ( )
Since the file has not been saved before, the save operation will provide a file save dialog box.
Enter a filename, and ensure that you put “.h” as the extension of the file. After making it a (.h)
header file, specify a directory and then click the OK button to create the file with the name
given in the directory specified. If you edit and make changes to an already saved file, then you
just need to click on the save icon. No dialog box will appear in this case. If you want to save
the contents of the file under a new name, you must click the file button on the menu bar, then
click the save as instead of the new save button in the drop-down menu. Again a file save dialog box will be displayed. Enter a filename, specify a directory, and then click the OK button
to create the file with the name given in the directory specified. In order to save the contents of
every open window, either click on the save all toolbar button ( ) or Click the file button on
the menu bar and then click the save all button in the drop-down menu.
NOTE:
Saving the file as a “.h” extension file is the key in making a newly created file a header file.
Step 4: Opening a header file
To open a file you can do one of the following operations:
䡲
䡲
䡲
Click the file open toolbar button ( )
Press CTRL O
Click the file button on menu bar, and then click the open button in the drop-down
menu
This operation will lead to the directory browser. You can then navigate to the desired directory to open the file. Once located, you can open that file.
NOTE:
You can use the Files of Type combo box to select the type of file you want to open. For instance, if you select ‘.h’ extension in the combo box then you will be able to see only files
that are of the ‘.h’ extension. Surely this will narrow down your search.
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Step 5: Adding a header file to the current project
For adding a header file to the current project click on the projects tab in the menu bar, and
in the drop-down menu click on the “add files” button. This operation will lead to the directory browser. You can then navigate to the desired directory to find the header file. Once
located, you can add that file by clicking the “add” button on the directory browser window. If you want to add that file to one of the folders in the workspace window, such as the
C header file or C source file, then just go to that folder and right click. Select add files
from the pop-up menu. Again the directory browser will pop-up and you can navigate to
your desired file. Once added, you do not need to open that file in a conventional way as
discussed in Step 4. Follow these steps to open that header file:
䡲
䡲
䡲
Spot your file in workspace window and double-click the file to open it
Select the file and click the right-hand mouse button; select Open <file name>
from the pop-up menu
If it is already selected, press enter
NOTE:
To remove a header file:
For removing a header file from the current project, click on the projects tab in the
menu bar and in a drop-down menu, click on the “remove files” button. A window, as seen
in Figure 4.18, will appear.
Figure 4.18 Removing a header file.
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Select the header file you want to remove from your project. If you want to remove a
header file from one of the folders in the workspace window, such as the C header file or C
source file, then just go to that folder and right click. Select remove files from the pop-up
menu. Again, the window shown in Figure 4.18 will appear and you can select the file you
want to remove.
4.4
ADVANCED CONCEPTS
4.4.1
Advanced Debugging Concepts
(Source: HEW User Manual V.4.08.)
This section describes in detail the various debugging tools and operations present in
high performance embedded workshop. As discussed in Section 4.2.4 there are two primary tools for debugging embedded real-time systems: the debugger and the monitor. This
section discusses the first tool, the debugger, in detail. Details regarding the functionality
and operations of the debugger and its related windows and dialog boxes are discussed.
The debugger used in the RX family is the J-Link Debugger.
䡲
䡲
Debugger options in HEW
The debugger can debug at assembly language level, as well as at the C/C
source level. It depends on which setting the user chooses. If users make the debug option enabled, the debugger debugs the code at C/C source language
level; and if that setting is not enabled then the debugger by default debugs the
code at assembly language level. More precisely, your C/C program must
be compiled and linked with the debug option enabled for debugging at
C/C source level. When the debug option is enabled, the compiler puts all
the information necessary for debugging the C/C code into the management
information file, which is usually called the ‘debug object files.’ Thus, the debug object files are those absolute files that contain only the specific information essential for debugging, instead of the whole C/C code. While creating
a new project, an initial debug session will be automatically configured. A user
has to ensure that the debug option is enabled on the compiler and linker while
generating an object file for debugging. When the debug option is not enabled,
then debugging information will not be present in your debug object file. You
can still load that file into the debugger, but it will only debug at the assembly
language level.
Debugger sessions in HEW
The High-performance Embedded Workshop offers you the functionality of storing all of your builder options into a configuration. This means you can put all of
your building information into one place and refer to it with a name. Similarly, you
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can store all the debugger options in a session. Later on, you can get back to the
same session when required, and all of the debugger options will be restored.
These sessions allow the user to specify target, download modules, and debug—
which basically means you can have different sessions each targeted at different
debugger options. For instance, you can easily have different sessions using the
same target but with minor variations in session options. As an advantage, you can
easily switch sessions as and when required. You can even modify certain things
such as register values, or target settings such as clock speed. Look at Figure 4.19.
The five sessions shown share the same target, but the sessions are slightly different with regard to the options defined.
Figure 4.19 Sessions in HEW. Source: HEW User Manual V.4.08, page 356.
䡲
In this particular case, there is no need to rebuild because the sessions share the
same download module and they are never directly related to the build configuration data. In addition, each session’s information is stored in a separate file in the
High-performance Embedded Workshop project so that you can later manipulate
the data according to your application.
Selecting a session:
Click on the debug tab on the menu bar. In the drop-down menu, click on the debug sessions and the debug sessions dialog box will open. After that, select the
session that you want to use from the current session drop-down list box, and then
click the ok button.
Figure 4.20 Selecting a session. Source: HEW User Manual V.4.08, page 356.
䡲
Adding a session:
HEW provides you the functionality of creating and naming a new session with an
attached target and setup. You can create a new session by clicking on the file tab
on the menu bar. In the drop-down menu, click on new session and the new session dialog box will open.
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Figure 4.21 Creating and naming a new session.
䡲
You need to fill out the required fields one by one. You can start with the name of
the new session, and then select the target you wish to use, followed by selecting
the core from the internal core list. This item is only available when you use the
synchronized debugging facility. Select the generator in the session generator to
use the list. It is possible that there may be multiple generators that support the
same target. The last step is to click the OK button to launch the generation
process. At this point, an additional dialog box may be displayed for target setup
options. When finished, a new session is added to the current project. It should be
available in the session’s drop-down list box on the main toolbar.
Removing a session:
Click on the debug tab on the menu bar. In the drop-down menu, click on the debug sessions option, and the debug sessions dialog box will open. After that, select
the session that you want to remove and then click the remove button. Click the
OK button to close the debug sessions dialog box.
NOTE:
It is not possible to remove the current session.
䡲
䡲
Saving session information:
You can save the new session by clicking on the file tab on the menu bar, and then
in the drop down menu click on the save session button. If you have checked the
“prompt before saving session” checkbox, a dialog box is displayed which asks
you whether you wish to save the information. To see whether it is checked or not,
click on the settings tab on the menu bar, then click on the options in the dropdown menu (a dialog box will appear), and then click on the workspace tab to
look for the checked boxes.
Operating memory
This section describes one of the ways to debug your code. A user must know how
to look at the memory in the CPU’s address space. It would be very useful if a user
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knows how to look at the memory area in different formats. This section also discusses ways to fill and move a memory block.
Opening the memory window:
A memory window is a window that shows the contents of contiguous memory areas. To open the window, click on the view tab on the menu bar. In the drop-down
menu, click on the CPU, then on the memory; or click the Memory toolbar icon
( ). A box, as shown in Figure 4.22, will pop up. It is known as the Display address box. In that box, you can specify the display address, scroll start address,
and scroll end address.
Figure 4.22 Display address box.
䡲
Click the OK button to launch the memory window. The display can be scrolled up
and down. The range can be selected by entering the values of the scroll start and
scroll end address fields in the display address box.
Window configuration:
Figure 4.23 Memory window. Source: HEW User Manual V.4.08, page 381.
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䡲
The label and register columns are hidden by default. You can make it visible by
customizing the toolbar. The label column shows the name of the label allocated
to the data on the first memory address displayed on the row. Similarly, the register column shows the name of the register allocated to data on the first memory
address, displayed on the row. The ‘ⴙn’ in the column header of the data column
defines the offset value from the first address of the row. The header of the code
column shows the code name. In order to change the first address being displayed,
double-click the address or label column. In order to change the memory data at
the selected address, double-click the data or code column. Changing the values
can be recorded in a macro (Macro Recording) to help you remember previous settings. In case the new setting does not go your way, you can then always get back
to your initial settings since you have the previous data saved somewhere. Moreover, values in the address, data, and code columns can be changed by in-place editing. You can always customize your toolbar by right-clicking, and when it displays a pop up window you can select from the various options available. For
instance, one of the options would be ‘move’ which moves a specified memory
block. In this feature, macro recording is also available to retain your previous
memory block.
Setting data at a desired memory address:
To set data at a memory address, you can do an in-place editing of the code as well
as the data column.
Figure 4.24 Data and Code column. Source: HEW User Manual V.4.08, page 383.
The first figure in Figure 4.24 shows the data column and second figure shows the
code column. To change the contents of the memory, open a set dialog box. This
is done as follows:
a. Double-click the Data column
b. Double-click the Code column
c. Select the data you want to change and choose set from the pop-up menu
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Figure 4.25 Set dialog box. Source: HEW User Manual V.4.08, page 384.
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Fill in the required fields, such as address and data type. Value can be either a numeric value or a character. If you are setting a numeric value, then set value as the
data type. If you are setting a character value, then select string as the data type.
Make sure to select the verify check box.
Filling an area of memory with constant data:
HEW provides you with the feature of setting the range of memory addresses with
the constant value. For this, you need to select an address range to fill in the memory window. Select fill from the pop-up menu of the memory window, and then
edit the fill dialog box.
Figure 4.26 Fill dialog box. Source: HEW User Manual V.4.08, page 385.
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䡲
You must enter the start address and end address. The end address can also be
prefixed by a plus (): the end address will become (start address) (the entered value).
Copying an area of memory:
To copy an area of memory into another area, you can use the memory copy feature
provided by HEW. First, select a copy-source address range in the memory window
using the mouse. Right click on the memory window and choose ‘move’ from the
pop-up menu. The move dialog box opens as shown in Figure 4.27. Click on the
move address field pop-up menu and choose the copy destination address. Check
the verify check box. If you choose not to drag the copy-source address range, you
have to enter the start and end address. The end address can also be prefixed by a
plus (): the end address will become the (start address) (the entered value).
Figure 4.27 Move dialog
box. Source: HEW User Manual
V.4.08, page 386.
䡲
Comparing the memory contents:
To compare the contents of two memory blocks, you can use the memory compare
feature provided by HEW. First, select a source address range in the memory window using the mouse. Right click on the memory window and choose ‘compare’
from the pop-up menu. The compare memory dialog box opens as shown in
Figure 4.28. Enter the start address of the destination memory area in the compare address field and the data length in the data length field. Check the verify
check box. If you miss dragging the copy-source address range by any chance, you
can enter the start and end address now. The end address can also be prefixed by
a plus (): the end address will become the (start address) (the entered value).
Figure 4.28 Compare
memory dialog box. Source:
HEW User Manual V.4.08,
page 386.
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There exists only two cases, either mismatch or match. In the former case, the address where the mismatch was found is displayed in a message box. In the latter
case, the message “comparison successful” appears.
Saving memory contents in a text file:
What if you want to edit the contents of some of the memory addresses, and before
doing that you want to save those readings? HEW provides you the functionality
of saving the memory contents in a text file using the save memory contents feature. First, select a source address range in the memory window by dragging the
mouse. Right click on the memory window and choose ‘save memory contents’
from the pop-up menu. The save memory contents dialog box opens as shown in
Figure 4.29. Select the output range in the memory save area field, length of the
data in the data length field, number of digits in the column field and the radix in
the radix field. You can also select displaying/hiding the Label column and Register column by checking the output the label column and the output the register column fields, respectively. If you did not drag the address range to be saved,
you must enter the output range.
Figure 4.29 Save memory contents dialog box.
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Looking at I/O memory:
A microcontroller contains various on-chip peripheral modules. The modules vary
according to devices, but some of the common modules are DMA controllers,
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䡲
serial communications interfaces, A/D converters, integrated timer units, a bus
state controller, and a watchdog timer. Accessing registers play a very important
role in programming on-chip peripherals. Since the setting up of such on-chip peripheral registers is usually very important in an embedded microcontroller application, it would be very useful if we can look into the values of the registers. As
discussed in the previous section, the memory view allows you to look at the data
in the memory only as a byte, word, longword, single-precision floating-point,
double-precision floating-point, or ASCII values. So the High-performance Embedded Workshop also provides an I/O window to analyze the values inside the
registers.
Opening the I/O window:
To open the I/O window, click on the view tab on the menu bar. Select CPU from
the drop down menu. Choose I/O to open the window or click the view I/O toolbar
button ( ). Modules that match the on-chip peripheral modules organize the
I/O register information. The I/O window has two tabs: All Register and Selected
Register. When the I/O window is first opened, only a list of module names are
shown on the All Register tabbed pane.
Window configuration:
Figure 4.30 Input-output window. Source: HEW User Manual V.4.08, page 411.
The All register tab displays all I/O registers and the selected register tab displays
selected I/O registers. By default, this page is blank. I/O registers can be used as
and when required. While running the code, if the value of an I/O register is
changed, the value is displayed in red. If you need to change the value of a register, then double click on the line of an I/O register. You can even record the value
in a macro. In addition, the value can be changed in the value column by in-place
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editing. HEW provides various options which can be expanded by right-clicking
on the I/O window. It will display a pop-up menu containing options such as refresh, load I/O file, print, toolbar display, customize toolbar, etc. For displaying
the names, addresses and values of the I/O registers you can either double-click on
the module name or select the module name. To select the module name, click on
it or use the cursor keys, and press the right cursor key. The module display will
expand to show the individual registers names, addresses, and their values. To
close the I/O register display, once again double-click on the module name (or
press the left cursor key).
Modifying the values of I/O registers:
To modify the value of an I/O register, select either of the following:
In-place edit in the value column.
Figure 4.31 Selected register tab of Input-output window.
Source: HEW User Manual
V.4.08, page 413.
Double-click on the line of the I/O register or bit to open a dialog box.
Figure 4.32 Edit dialog box. Source: HEW User Manual V.4.08, page 413.
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Selecting the I/O register(s) for viewing:
First, click on the select register tabbed pane of the I/O window. To view the value
of the registers, open a pop-up menu by right-clicking within the window. Then select I/O register, and a dialog box will open as shown in Figure 4.33.
Figure 4.33 Selecting I/O register. Source: HEW User Manual V.4.08, page 414.
As you can see, there is a checkbox in front of every item; clicking on it selects the
specific item. Clicking the ‘’ sign expands the collapsed item while clicking on
‘’ collapses the expanded item. If you select the checkbox for an item with ‘’
or ‘’ the checkboxes for all of its elements are also selected. Similarly, if you deselect the checkbox for an item, all of its elements are also deselected. You should
select the checkboxes for the I/O register(s) you wish to view. After checking the
item, click OK to close the dialog box. The selected I/O registers are shown on the
select I/O register tabbed pane of the I/O window.
Figure 4.34 Selected register tab of Input-output window.
V.4.08, page 415.
Source: HEW User Manual
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Finding an I/O register:
Many times you might want to know the value stored in a particular register. In
such a case, instead of selecting an I/O register to view, you can try a faster way of
directly accessing your desired register. In order to achieve this, right click within
the window to open up a pop-up menu. After that select find and a dialog box will
open as shown in Figure 4.35.
Figure 4.35 Find dialog box. Source: HEW User Manual V.4.08, page 416.
Fill in the fields one by one in any order you want. Select the column of an
I/O register: you can select either the address or name of an I/O register. Then
in the find field, select the string to be found in the selected column. The characters are case-insensitive. You can use the ‘match whole word’ feature to
completely match the string entered. If you type a more general word and
want to see all registers that partially match with the entered string, then do not
check the ‘match whole word’ box. Finally, click OK to start the search from
the first line.
4.4.2
The J-Link Debugger
(Source: http://www.segger.com/cms/jlink.html.J-Link Debugger)
The debugger used for the RX family is the J-Link Debugger. J-Link RX supports all
RX-CPUs with RX600 core and JTAG interface. The RX610 Group, RX62N Group, and
RX621 Group are compatible with this debugger. The J-Link RX is compatible to the
Renesas E1 emulator and works with the Renesas HEW and the IAR Embedded
Workbench for RX (EWRX).
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4.4.3
Flash breakpoints are much faster on J-Link than on E1 or E20. J-Link uses different techniques like: Instruction set simulation, use of hardware breakpoints where
possible, dynamic conversion of breakpoint types, flash caching, CRC, and others
to minimize the amount of times a flash breakpoint is set or removed.
It supports direct download into flash memory.
It also supports software breakpoints in flash memory (Flash breakpoints).
Seamless integration into the Renesas HEW & IAR Embedded Workbench IDE.
Virtual UART support (C2E support) provided.
All kinds of events are supported (execution break, data access, trace break,
combination/sequence of events).
USB 2.0 interface provided.
JTAG speed up to 12 MHz or 25 MHz (depending on the J-Link model).
No power supply required since it is powered through the USB.
All JTAG signals can be monitored and the target voltage can be measured.
Supports multiple devices.
Wide target voltage range: 1.2V—3.3V, 5V tolerant.
Target power supply: J-Link can supply up to 300 mA to target with overload
protection.
Description of the Header Files Used in the RX Family
1. <config.h>
This is a configuration file for the generic API for graphics LCD glyph; i.e.,
“glyph.c”. It defines macro names used in common in the “glyph.h” include file.
The macros defined here can be used to select the font size. It includes a header
file “preamble.h” which defines simple types and constants.
2. <glyph.h>
This is the main header file for glyph API library. The Generic API for Graphics
LCD (nicknamed “Glyph”) is a reusable software design to support multiple
projects where the LCD size and resolution may change, but the basic feature set
will stay consistent. Glyph is a standard library interface for use with any graphic
LCD. It uses macros already defined in the header file “config.h”. It defines external constants, typedef enumerations, typedef structures, prototype for minimum access, and prototype for full access.
a. Type: External constant
This declares constant values for various font sizes that will be available to
all users of glyph API.
Example:
extern const uint8_t * FontHelvr10_table [256 ];
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FontHelvr10_table is a macro defined in “config.h” that signifies the default
font size.
b. Type: Typedef definition
The typedef keyword defines new types or provides an alternative name to
the already existing types.
1) The typedef allows you to use t_glyphhandle as a type rather than using
void*. Now, t_glyphhandle can be used to declare a pointer to the type
void.
Example:
typedef void *T_glyphHandle.
2) The enum keyword is used to create an enumerated type that consists of
constants that represent error identifiers of the glyph API. Since each
subsequent value is incremented by one over the previous constant, the
value of GLYPH_ERROR_ILLEGAL_OPERATION is 1.
Example:
typedef enum {
GLYPH_ERROR_NONE = 0,
GLYPH_ERROR_ILLEGAL_OPERATION
} T_glyphError;
3) The enum keyword is used to create enumerated type that consists of
constants that represent status values of the glyph API. By default, the
first constant in an enumeration is assigned value zero, and each subsequent value is incremented by one over the previous constant. In this particular case, since each constant is given a specific value, each subsequent value is not incremented. Instead, it retains the value that is set in
the declaration.
Example:
typedef enum {
GLYPH_STATUS_READY = 0,
GLYPH_STATUS_BUSY = 2,
GLYPH_STATUS_FULL = 4
} T_glyphStatusBits;
4) The enum keyword is used to create enumerated type that consists of
constants that represent font values of the glyph API. By default, the first
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constant in an enumeration is assigned value zero, and each subsequent
value is incremented by one over the previous constant.
Example:
typedef enum {
GLYPH_FONT_8_BY_8,
GLYPH_FONT_8_BY_16,
GLYPH_FONT_5_BY_7,
. . . . . . . . . . . . . . . .
} T_glyphFont;
5) The enum keyword is used to create an enumerated type that consists of
constants which define drawing modes of the glyph API. Since each subsequent value is incremented by one over the previous constant, the
value of GLYPH_CMD_ERASE_BLOCK is 8.
Example:
typedef enum {
GLYPH_CMD_NOP = 0,
GLYPH_CMD_SCREEN_CLEAR,
GLYPH_CMD_SCREEN_INVERT,
GLYPH_CMD_SCREEN_REGULAR,
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
} T_glyphDrawMode;
6) Description: The enum keyword is used to create enumerated type that
consists of constants that represent the glyph API registers. These are
used by Glyph Read and Glyph Write to specify a function of the glyph
API to run.
Example:
typedef enum {
GLYPH_STATUS = 0,
GLYPH_CHAR_X,
GLYPH_CHAR_Y,
. . . . .
. . . . .
. . . . .
GLYPH_CONTRAST,
GLYPH_CONTRAST_BOOST
} T_glyphRegisters;
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7) A struct in C programming language is a collection of elements, in which
each element belongs to a different type. The total storage required for a
struct object is the sum of the storage requirements of all the elements. This
typedef allows you to use T_glyphVersionInfo as a type rather than using
a struct. Now, T_glyphVersionInfo can be used instead of struct
T_glyphVersionInfo whenever you want to declare a new instance of the
structure_glyph_version_info named T_glyphVersionInfo. The structure
below contains elements that depict various versions of glyph API structure.
Example:
typedef struct_glyph_version_info
{
uint8_t strVersionAPI [50 ];
uint8_t strVersionIMPL [50 ];
int32_t nVersionAPIMajor;
int32_t nVersionAPIMinor;
int32_t nVersionIMPLMajor;
int32_t nVersionIMPLMinor;
int32_t nImplementationID;
} T_glyphVersionInfo;
8) In future statements, you can use the specifier T_LCD_API (instead of
the expanded struct T_LCD_API) to refer to the structure and create an
instance. The structure below contains elements that are used in applications where LCD is required. This is a glyph API LCD structure which is
frequently used by the LCD drivers.
Example:
typedef struct {
/* Adding Font-Decal Section */
const uint8_t ** iFont;
/* Define Global Variables */
uint32_t iCharX_Position;
uint32_t iCharY_Position;
uint32_t iCharX2_Position;
uint32_t iCharY2_Position;
uint32_t iCharFont;
. . . . . .
. . . . . .
. . . . . .
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T_glyphError (*iWrite)(T_glyphHandle aHandle, uint32_t
aRegister, uint32_t Value);
} T_LCD_API;
9) In future statements, you can use the specifier T_Comm_API (instead of
the expanded struct T_Comm_API) to refer to the structure and create an
instance. The following structure contains elements that are used in applications where communication needs to be set up. This is a glyph
API communication structure which is frequently used by the Communication drivers.
Example:
typedef struct {
T_glyphError (*iOpen)(T_glyphHandle aHandle);
void (*iCommandSend)(int8_t cCommand);
void (*iDataSend)(int8_t cData);
} T_Comm_API;
10) In future statements, you can use the specifier T_glyphworkspace (in-
stead of the expanded struct T_glyphworkspace) to refer to the structure
and create an instance. The following structure contains elements that
are used in applications where LCD is required and communication
needs to be set up. This is a glyph API workspace structure which is frequently used by Communication and LCD drivers.
Example:
typedef struct {
T_LCD_API *iLCDAPI;
T_Comm_API *iCommAPI;
} T_glyphWorkspace;
c. Type: Function
Glyph API provides you the capability to interact with the graphical LCD.
The prototypes defined in the following example are used to access the glyph
API library definitions. Its implementation totally depends on the type of application. These prototypes define the functions for minimum and full access
of the members of the glyph libraray.
Examples:
Prototypes for minimum access:
T_glyphError GlyphOpen(T_glyphHandle *aHandle, int32_t
aAddress);
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T_glyphError GlyphClose(T_glyphHandle *aHandle);
T_glyphError GlyphWrite(T_glyphHandle aHandle,
uint32_t aRegister, uint32_t * aValue);
T_glyphError GlyphRead(T_glyphHandle aHandle,
uint32_t aRegister, uint32_t *aValue);
Prototypes for full access:
T_glyphError GlyphGetStatus(T_glyphHandle aHandle,
T_glyphStatusBits *aStatus);
T_glyphError GlyphSetX(T_glyphHandle aHandle, uint32_t aX);
T_glyphError GlyphSetY(T_glyphHandle aHandle, uint32_t aY);
. . . . . . . .
. . . . . . . .
T_glyphError GlyphSetContrastBoost(T_glyphHandle aHandle,
uint8_t cContrastBoost);
3. <preamble.h>
Description: This header file contains basic definitions of all simple constants
and types. The purpose of this file is to maintain compatibility between the compilers and hardware. It defines macros which can be used in other header files or
in source code of any application.
a. Type: Constant.
Example:
#define ON 1
#define OFF 0
#define ENABLE 1
#define DISABLE 0
b. Type: Typedef definitions.
In future statements, any variable can be used as a type instead of its preexisting type. For instance, Int8_t can be used as a type instead of a signed
char.
Example:
typedef signed char int8_t;
typedef unsigned char uint8_t;
typedef signed short int16_t;
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c. Type: Bit definitions.
A bit from b0 to b7 signifies some hexadecimal value as defined in the following example.
Example:
#define b0 0x01
#define b4 0x10
#define b7 0x80
4. <st7579_lcd.h>
Description: It defines prototypes that are required by the LCD driver in the
glyph API. It includes all the definitions of “glyph.h”.
Note: The name of the header file comes from st7579 which is a driver and
controller LSI for the graphic dot-matrix liquid crystal display systems. This
chip is connected directly to a microprocessor, accepts 3-line serial peripheral interface (SPI) with a four wire independent transmit only, displays data,
and can store an on-chip display data RAM of 68 102 bits.
a. Type: Macros
These macros signify function sets, which are used to define the function set
call for every command that is sent to the ST7579 Display controller. When
setting the display controller to the four different function sets of commands
to be sent to the controller, setting the function set also sets the following:
MX direction: normal or reverse i [0⬊1 ]
MY direction: normal or reverse [0⬊1 ]
PD controller active or power down [0⬊1 ]
If the preprocessor directive #if, is set to 1, then every Function Set call will
produce MY set to the reverse direction. This is required for Glyph to work.
Otherwise, MY will be set to the normal direction and Glyph will not work.
These function sets do not take any arguments and do not return any value.
Example:
#if 1
//MY reverse direction
#define LCD_FUNCTION_ZERO 0X28
#define LCD_FUNCTION_ONE 0X29
#define LCD_FUNCTION_TWO 0X2A
#define LCD_FUNCTION_THREE 0X2B
//command sets
#define LCD_DISPLAY_REVERSE 0x280D
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#define LCD_DISPLAY_NORMAL 0x280C
#else
//MY normal direction
#define LCD_FUNCTION_ZERO 0X20
#define LCD_FUNCTION_ONE 0X21
#define LCD_FUNCTION_TWO 0X22
#define LCD_FUNCTION_THREE 0X23
//command sets
#define LCD_DISPLAY_REVERSE 0x200D
#define LCD_DISPLAY_NORMAL 0x200C
#endif
b. Type: Functions
1) The prototypes defined in the following example are used to access
“glyph LCD API” library definitions.
Example:
T_glyphError ST7579_Open(T_glyphHandle aHandle,
uint32_t aAddress);
T_glyphError ST7579_Close(T_glyphHandle aHandle);
T_glyphError ST7579_Write(T_glyphHandle aHandle,
uint32_t aRegister, uint32_t aValue);
T_glyphError ST7579_Read(T_glyphHandle aHandle,
uint32_t aRegister, uint32_t *aValue);
2) The prototypes defined in following example are used to access
“LCD API” library definitions.
Example:
void ST7579_Config(T_glyphHandle aHandle);
void ST7579_SetSystemBiasBooster(T_glyphHandle aHandle,
int8_t c Value 0 To 17);
void ST7579_SetVO_Range(T_glyphHandle aHandle,
int32_t n Value 0 to 254);
5. <YRDKRX62N_RSPI0.h>
Description: This header file defines prototypes for the glyph communication API.
NOTE:
The name of the header file indicates the hardware it is associated with. It is
Y Renesas Development Kit (RDK) for Renesas RX62N Group CPU. The transmitter number is 0 and the operational channel is 3.
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The Chip Select for the flash device (LCD) is set to PC_2. This is the RSPI channel used to communicate with the ST7579 Graphics Display. The RSPI configuration has the baud rate generator set for maximum speed, which is PLCK/2 or
25 MHz. The communications protocol followed is SPI 3-Wire Transmit only
MASTER SPI. Its Slave Device is OKAYA LCD with a ST2579 microprocessor.
Example:
void YRDKRX62N_CommandSend(int8_t cCommand);
void YRDKRX62N_DataSend(int8_t cData);
T_glyphError YRDKRX62N_RSPIOpen(T_glyphHandle aHandle);
6. <typedefine.h>
Description: In further statements, any variable can be used as a type instead of
its pre-existing type. For instance, _SBYTE can be used as a type instead of
signed char. Here, an underscore before the variable name SBYTE signifies that
it is a global variable.
Example:
typedef signed char _SBYTE;
typedef unsigned char _UBYTE;
typedef signed short _SWORD;
7. <sbrk.h>
Description: This is a header file for sbrk.c. It defines a macro that signifies the
size of the area managed by sbrk.
Example:
#define HEAPSIZE 0x400
8. <vect.h>
Description: This header file defines various vectors. The vector list is basically a
list which indicates where the ISRs (interrupt subroutines) are located in memory. Each entry in the list is called a vector. Vector signifies the four bytes address
of each ISR. Some of the vectors are reserved—like vector 16 is reserved by an
interrupt Excep_BUSERR; i.e., the ISR to be called when exception happens
during a bus error; and the rest of them are free to be occupied. Vector table starts
with the vectors that refer to the fixed interrupts. These vectors cannot be
changed since they point to ISRs at hardware-defined addresses such as undefined instruction, supervisor instruction, floating point, NMI, Dummy, or BRK.
Then comes the variable vectors that point to ISRs at user-definable vectors.
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Example:
Fixed interrupts:
//Exception(Supervisor Instruction)
#pragma interrupt (Excep_SuperVisorInst)
void Excep_SuperVisorInst(void);
//Exception(Undefined Instruction)
#pragma interrupt (Excep_UndefinedInst)
Variable Interrupts:
#pragma interrupt (Excep_BUSERR(vect = 16))
void Excep_BUSERR(void);
//vector 17 reserved
//vector 18 reserved
//vector 19 reserved
//vector 20 reserved
//FCU_FCUERR
#pragma interrupt (Excep_FCU_FCUERR(vect = 21))
void Excep_FCU_FCUERR(void);
//vector 22 reserved
9. <stacksct.h>
Description: This header file defines macros that refer to the setting of the stack
area.
Example:
#pragma stacksize su = 0x300
#pragma stacksize si = 0x100
10. <iodefine_RX62N.h>
Description: This header file uses numerous macros, about sixty-eight structures,
one union, and four enumerations to define the various input and output registers.
Example:
a. Macros:
#pragma bit_order left
#pragma unpack
#define SYSTEM (*(volatile struct st_system
__evenaccess *)0x80000)
#define BSC (*(volatile struct st_bsc __evenaccess *)0x81300)
#define IEN__IRQ1 IEN1
#define IEN__IRQ2 IEN2
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b. Structure:
The structure below defines various input and output registers that are used in
analog to digital conversion. Within the structure, a union is being used to declare variables of different types. It is the same as structure, except that instead of struct you write union. Also, in union you can only store information
in one field at any one time. Technically, it can be seen as a chunk of memory
that is used to store variables of different types. Once a new value is assigned
to a field, the existing data is wiped over and rewritten with the new data.
Example:
struct st_da {
unsigned short DADR0;
unsigned short DADR1;
union {
unsigned char BYTE;
struct {
unsigned char DAOE1⬊1;
unsigned char DAOE0⬊1;
unsigned char DAE⬊1;
unsigned char:5;
} BIT;
} DACR;
union {
unsigned char BYTE;
struct {
unsigned char DPSEL:1;
unsigned char:7;
} BIT;
} DADPR;
};
In this example, the structure st_da contains four members; namely DADR0,
DADR1, union DACR, and a union DADPR. This is an example of nested
unions. Union DACR has two members. BYTE and structure BIT. The BIT
member is a structure with four bit-field members, DAOE1, DAOE0, DAE
and one nameless field member, all of them are of type unsigned char. Member BYTE is of type unsigned char. Union DADPR has two members, BYTE
and structure BIT. The BIT member is a structure with two bit-field members, DPSEL and one nameless field member, both of which are of type unsigned char. Member BYTE is of type unsigned char. At any given time, each
union element holds either the unsigned char represented by BYTE or the
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structure represented by BIT. The other two variables of st_da are of type unsigned char. Table 4.6 provides an explanation of the terms that were used in
the previous example.
TABLE 4.6
Register Description.
ADDRESS
NUMBER
OF BITS
MODULEABBREVIATION
REGISTER
NAME
REGISTER
ABBREVIATION
0008 80C0h
16
D/A
D/A data register 0
DADR0
0008 80C2h
16
D/A
D/A data register 1
DADR1
0008 80C4h
8
D/A
D/A control register
DACR
0008 80C5h
8
D/A
D/A data placement
register
DADPR
c. Enumerations:
These are used to define various ICU registers.
1) Usage of some specific registers such as IR (interrupt register), DTCER
(DTC activation enable register), IER (interrupt request enable register),
and IPR (Interrupt source priority register) follows. The bit access operation is “bit name (interrupt source, name)”. A part of the interrupt
source can be omitted.
Example:
IR(TPU0,TGI0A) = 0;
DTCER( ,IRQ0) = 1;
IEN(CMT0,CMI0) = 1;
IPR(MTU0,TGIA0) = 3;
IPR(MTU0,TGI ) = 3;
//TGIA0,TGIB0,TGIC0,TGID0 is same
level.
IPR(CMT0, CMI0) = 1;
IPR(CMT0, ) = 1;
//CMT0 interrupt is only one factor.
2) Usage of the interrupts listed in vector table:
#pragma interrupt Function_Identifier (vect **).The number of vector
is “(interrupt source, name)”.
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Example:
#pragma interrupt INT_MTU0_TGIA0(vect = VECT(MTU0,TGIA0))
#pragma interrupt INT_IRQ0 (vect = VECT( ,IRQ0))
#pragma interrupt INT_CMT0_CMI0 (vect = VECT(CMT0,CMI0))
3) Usage of some specific system registers such as MSTPCRA (Module
stop control register A), MSTPCRB (Module stop control register B),
MSTPCRC (Module stop control register C), and MSTPCRD (Module
stop control register D) is given as follows: The bit access operation is
“MSTP (name)”. The name that can be used is a macro name defined
with “iodefine.h”.
Example:
MSTP (TMR2)
MSTP (PPG1)
MSTP (MTU6)
MSTP (CMT3)
4.5
=
=
=
=
0;
0;
0;
0;
//TMR Unit 1 (TMR3/TMR2)
//PPG1
//MTU Unit 1 (TPU6 to TPU11)
//CMT Unit 1 (CMT2/CMT3)
ADVANCED EXAMPLES
(Source: HEW User Manual V.4.08.)
EXAMPLE 1
This example demonstrates how to look at the contents of the CPU’s general registers.
To view the contents, first open the register window. For this, click on the view tab on
the menu bar, and in the popup menu select CPU from the drop down menu. Choose register to open the window or click on the registers toolbar button ( ).The Register window
gives the status of current register and flag data. You can even modify the register/flag value
from the window.
Window Configuration
Double-clicking the register display line opens a dialog box, which allows you to change a
register value. Everything can be recorded by macro recording. This is helpful in a case
where you want to get back to older values. The easy way to change the register’s contents
is by using in-place editing. Also, you can change a flag value by clicking the button corresponding to the flag. If you right click on the window, you can change the display radix
point and the register bank.
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Figure 4.36 Register window.
Popup menu:
Changing the Register Display Radix
To change the display radix, right click the mouse on the register to be changed and select
display radix from the pop-up menu. You can select one of the four radix options shown in
Table 4.7.
Setting the Layout
To change the layout of the register window, choose layout from the pop-up menu. The
following settings are displayed:
Radix: It Switches display or non-display of the radix.
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TABLE 4.7
Display Radix Point and the Register Bank Options.
MENU OPTION
FUNCTION
Radix: Hex
Displays in hexadecimal
Dec
Displays in Decimal
Oct
Displays in Octal
Bin
Displays in Binary
Layout: Radix
Switches display or non-display of radix
FLAGs
Switches display or non-display of flags display area
Settings
Chooses a register to be displayed
Edit
Changes a register’s contents
Refresh
Refreshes the Register window
Lock Refresh
Disables refresh of the Register window
Split
Splits up the window display
Save To File
Saves register contents in a text file
Source: HEW User Manual V.4.08, page 418.
Flags: It Switches display or non-display of the flags display area.
Figure 4.37 Displays the radix and flags. Source: HEW User Manual V.4.08, page 420.
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Choosing a Register to be Displayed
Figure 4.38 shows the dialog box which is displayed when you choose the settings tab
from the register pop-up menu. In this way you can choose a register to be displayed in the
Register window.
Figure 4.38 Settings dialog box to select register to be displayed.
Source: HEW User Manual
V.4.08, page 420.
Modifying the Register Contents
To change the register contents, enter a value in the value field of the register as shown in
Figure 4.39.
Figure 4.39 In place modification of register value. Source: HEW User Manual V.4.08, page 421.
To change a register’s contents, open the Set Value dialog box as described in the following and select one of the operations:
1. Double-click the register to be changed.
2. Select the register and choose the Edit option from the pop-up menu.
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Figure 4.40 Set value dialog box. Source: HEW User Manual V.4.08, page 421.
Setting the Flag Value
When the flag itself is displayed, click the flag which you want to change. Every time a flag
is clicked, the flag status switches from either 1 to 0 or 0 to 1. If a flag is composed of multiple bits, then a dialog box will open, where you can enter a value.
Screenshot:
Figure 4.41 Flag status. Source: HEW User Manual V.4.08, page 422.
When the flag is displayed in the register, double-click the FLG line. A dialog box will
open and then you can enter the value to be changed.
Figure 4.42 Debugger (FLG line (FPSCR)). Source: HEW User Manual V.4.08, page 422.
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Saving Register Contents
To save the register contents in a text file, choose Save to file from the register pop-up
menu. The Save As dialog box will open, which allows you to specify the file name.
EXAMPLE 2
Displaying memory contents as waveforms.
NOTE:
Support for this function depends on the debugger.
To analyze the data that has just been saved into the memory, creating a waveform
could be a very good option. It gives insight into how your code is responding to the application that you are making. For creating a waveform, first you need to open the waveform
properties dialog box. Click on the view tab on the menu bar, select graphics, and then
waveform to get the waveform window. The other way is to just click on the waveform
toolbar button ( ).
Figure 4.43 Waveform properties dialog box. Source: HEW User Manual V.4.08, page 407.
You need to fill in the properties before going any further. For data address property, you
need to specify the start address of the data in memory. It should be displayed in hexadecimal. Data size property signifies the size of the data, which can be either 8 bit or 16 bit.
Two types of channels are supported: mono and stereo. Select buffer size to specify the
buffer size of the data in hexadecimals. Now click the OK button to open the waveform
window. You can change the display contents later by right clicking the window and choosing ‘properties’ from the pop-up menu. In the pop-up menu, some of the other fields are
zoom in, zoom out, zoom magnification, scaling, refresh now, etc.
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Figure 4.44 shows the display of the memory contents as a waveform. The Xcoordinate refers to the number of sampling data and the Y-coordinate refers to the sampling value.
Figure 4.44 Memory contents as waveform. Source: HEW User Manual V.4.08, page 407.
If you double-click the coordinate where you wish to view the sampling information, the
sample information dialog box appears. For refreshing the window, there is a function
called auto refresh, available in the pop-up menu. Selecting auto refresh and then non refresh will not refresh the window. Selecting auto refresh and then stop from the pop-up
menu will allow the window contents to be automatically refreshed. Selecting auto refresh
and then real time from the pop-up menu will allow the window contents to be refreshed
while the user program is running. To specify the refresh interval, select update interval
from the pop-up menu. This item can be selected only when it is supported by the debugger.
4.6
REFERENCES
RX Compiler Package, http://america.renesas.com/products/tools/coding_tools/c_compilers_assemblers/
rx_compiler/rx_c_tools_product_landing.jsp
Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
CHAPTER 4 / SOFTWARE DEVELOPMENT TOOLS
137
Compiler Package User Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America, Inc., 2010. Print.
High-performance Embedded Workshop V.4.08, User’s Manual. Renesas Electronics America, Inc., 2010.
Print.
4.7
EXERCISES
1. What is the difference between compilers used for embedded systems and com2.
3.
4.
5.
6.
7.
8.
pilers used for desktops PCs?
How does the linker differ from the compiler?
Other than macro definition, for what purpose can the “#define” identifier can be
used?
What are the various phases of the building process in HEW?
Where in HEW debugger options are saved and why?
Can all debuggers display the contents of the memory as a waveform?
For what purpose is synchronized debugging used?
We have an integer array called x. All the numbers from 1 to 100 appear exactly
once in x but the numbers are not sorted (e.g., the order can be x[100] {2; 10;
3; 8; 9; 4; 97; 94; . . . . . . . . . .37; 99}). Due to alpha particles destroying a particular entry in x, a number is missing and is read as 0 when accessed. Use less
than ten lines of C code (one statement per line) to find the missing number (not
the index) and put it in an integer variable called missing. Don’t forget to include
proper documentation suggested in coding guidelines (comments, header, etc.).
99
99
i0
i0
(Hint: consider the current a x 3i4 and what the uncorrupted value of a x 3i4
would be).
9. What is the one thing that all of our code should have?
a. Your name and file name in comments at the top of every file.
b. Twelve subroutines.
c. A while(1) loop in every subroutine.
d. A function call to the ST7579_LCD.c file.
e. None of the above.
10. Which header file defines prototypes for the glyph communication API?
a. yrdkrx62n_rspio.h
b. config.h
c. ST7579_lcd.h
d. glyph.h
e. sbrk.h
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11. Which header file is mandatory to include in source code if your code uses an In-
terrupt Subroutine?
a. <stacksct.h>
b. <vect.h>
c. ST7579_lcd.h
d. glyph.h
e. sbrk.h
12. Which of the following fully describes the outcome of the code below?
int i,sum;
sum = 0;
i = 0;
for(i = N; i < 100; i++)
{
if((i % 2))
sum += i;
}
Add all the numbers from 0 to 100 and put the result in sum.
Add all the odd numbers from 0 to 100 and put the result in sum.
Add all the even numbers from 0 to 100 and put the result in sum.
Add all the odd numbers from N to 100 and put the result in sum.
Add all the even numbers from N to 100 and put the result in sum.
13. Which of the following is not a part of the compiler?
a. Linker
b. Pre-processor
c. Code generator
d. Garbage collector
e. Parser
14. Consider the code below. The first printf statement below prints “1C3F”. What is
printed by the second printf?
a.
b.
c.
d.
e.
union {
int w;
char b [2 ];
}x;
x.w = 0x1C3F;
printf(“%X \ n”, x.w);
x.b [1 ] = 0xA6;
printf(“%X \ n”, x.w);
CHAPTER 4 / SOFTWARE DEVELOPMENT TOOLS
1C3F
A63F
1CA6
1A6F
None of the above.
In C, the term volatile is applied to a variable in order to:
a. Tell the compiler that a variable’s value may change due to forces other than
the program in which the variable appears.
b. Tell the compiler that a variable’s value is not constant.
c. Mark that a variable may be optimized out of the code when unused.
d. Tell the compiler to store the variable’s value in “volatile” ram instead of
“non-volatile” ram, such as an EEPROM.
e. None of the above.
For our processor and compiler, does the stack grow toward larger or smaller
addresses?
a. Larger
b. Neither
c. Smaller
d. Both
e. None of the above
For our processor and compiler,
a. How many bytes are required to represent the data type: char?
1) 1
2) 2
3) 3
4) 4
5) 8
b. How many bytes are required to represent the data type: int?
1) 1
2) 2
3) 3
4) 4
5) 8
c. How many bytes are required to represent the data type: short?
1) 1
2) 2
3) 3
4) 4
5) 8
d. How many bytes are required to represent the data type: long?
1) 1
2) 2
3) 3
4) 4
5) 8
e. How many bytes are required to represent the data type: float?
1) 1
2) 2
3) 3
4) 4
5) 8
A C source program is converted into an executable file with the help of:
a. An interpreter
b. A compiler
c. An operating system
d. None of the above
a.
b.
c.
d.
e.
15.
16.
17.
18.
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19. Which among the following best describes a header file?
a. A file that consists of functions
b. A file that consists of definitions and macros
c. A file that is a main source file
d. A file that consists of standard library functions
20. State the difference between the following two #include directives:
#include <“Config.h”>
#include <Config.h>
Chapter Five
Software Engineering for Embedded Systems
5.1
LEARNING OBJECTIVES
We have tremendous flexibility when creating software; we make many decisions going from
an idea to a final working system. There are technical decisions, such as which components
we use to build a system, their internal structure, and how we interconnect them. Some of the
technical decisions will lead to a product that works, but not all will. There are also process
decisions, such as how we plan to build the system and how to select those components. Similarly, some process decisions can lead to an easier or more predictable development effort,
while others will lead to project delays or cancellation, or can even bankrupt the company. A
good software process will evolve over time, incorporating lessons learned from each project’s successes and failures. Hence a good process will make it easier to do the technical
work. The goal of this chapter is to show how both process and technical issues need to be
considered to successfully create a product on time and on budget.
In this chapter we try to present just the most critical concepts to help the reader understand that “does the code work?” is one question, but not the only question to answer. There
are many excellent books and articles which go into great depth on software engineering for
embedded and general purpose software; a few are listed in the references section. For example, Jack Ganssle has a “top ten list” of why embedded systems projects get into trouble
(Ganssle, J.). In this chapter we discuss how a good software engineering process addresses
eight of them. Phil Koopman presents a detailed and practical book on embedded software
development processes and issues (Koopman, P.). We will refer the reader to specific chapters
in the latter text periodically in order to keep this chapter short and readable.
5.2
INTRODUCTION
5.2.1
Risk Reduction
Reducing risks is a driving force behind software engineering and project management. A
software development organization can benefit by constantly refining its processes as it
learns both what it does well, and how to improve what it does poorly.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Developing embedded software is usually unpredictable. For example:
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What if there is a bug in our code? What if the compiler sometimes seems to generate buggy code?
What if the code we need to write actually turns out to be a lot more complex than
we thought?
What if we don’t have enough memory for our program or its data? What if the
processor can’t run our code fast enough?
What if activating a motor resets the processor due to a weak power supply?
What if that external A/D converter peripheral doesn’t seem to work the way the
datasheet said it would?
What if the lead developer wins the lottery and quits a month before the product
deadline?
What if the new developer we hired turns out to be incompetent, lazy, or both?
What if half of our development team gets sick, is laid off, or is reassigned?
What if the customer adds new requirements every week, or wants the product
done two months early?
If any of these risks actually occur they will increase the amount of development work
needed. Whether it affects the product development deadlines depends on how much
overtime the development team is willing to put in, whether other developers can
help out, whether anything in the development process turns out to be faster than expected, and so forth. Missing deadlines will have negative financial impacts: project
costs will increase and income from product sales will be delayed. Some of these risks
also have other impacts: higher power consumption, fewer features, board redesign, and
so forth.
Ganssle identifies “Unrealistic Schedules” as the number one reason for embedded
system project problems. Successful software organizations create a development plan for
the project to show development tasks and output products, as well as risk management approaches. Koopman discusses development plans in detail in Chapters 2 through 4 of his
book Better Embedded System Software (Koopman).
5.3
SOFTWARE DEVELOPMENT STAGES
5.3.1
Development Lifecycle Overview
The embedded product lifecycle has multiple steps, as shown in Figure 5.1.
The software process consists of multiple steps within the embedded product lifecycle.
One example process model is the V model, shown in Figure 5.2. It consists of:
CHAPTER 5 / SOFTWARE ENGINEERING FOR EMBEDDED SYSTEMS
143
NEED/
OPPORTUNITY
CONCEPT
DEVELOPMENT
RETIREMENT/
DISPOSAL
PRODUCT
DESIGN
UPGRADES
SUPPORT/
MAINTENANCE
MANUFACTURING
PROCESS
DESIGN
PRODUCTION
DEPLOYMENT
Figure 5.1 The embedded product lifecycle. Courtesy P. Koopman.
Requirements
Analysis
Validation provided by testing
Requirements
Specification
Functional
Testing
Review
Integration
Testing
Architectural
Design
Review
Integration
Testing
Detailed
Design
Review
S/W Unit
Testing
Coding
Review
Code
Figure 5.2 The “V” model of software development emphasizes testing at each level of design detail.
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Defining system requirements.
Creating an architectural or high-level design, deciding on the general approach
to build the system, and then creating appropriate hardware and software
architectures.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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Creating detailed designs.
Implementing code and performing unit testing.
Integrating the code components and performing integration testing.
Changing the code after “completion” to fit custom deployment requirements, fix
bugs, add features, etc.
The process breaks a problem into smaller easier problems through the process of topdown design or decomposition. Each small problem is solved and the solutions are combined into a software solution. There are many approaches possible:
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Do we design everything up front, and then code it? This is called a big up-front
design.
Do we have a prototype or a previous version which we can build upon?
Do we design and build a little at a time?
What do we work on first, the easy or the hard parts?
Which model we should use depends on the types and severity of risks. Some industries
may be required to follow a specific development process in order for the product to receive certification. Ganssle identifies “Poorly Defined Process” as reason number six for
embedded system project troubles.
In this chapter we will use an example embedded system to illustrate the issues involved.
Our target system is an electronic chartplotter for boats. The chartplotter can display a depth
chart on a graphical LCD with an icon superimposed to show the boat’s current position and
direction, as shown in Figure 5.3. This helps the user steer the boat to avoid shallow water.
Alternatively, we may choose to have a numerical display and omit the chart, as shown
Figure 5.3 Chartplotter screen with boat icon overlaid on depth chart.
CHAPTER 5 / SOFTWARE ENGINEERING FOR EMBEDDED SYSTEMS
145
Figure 5.4 Chartplotter screen with numerical depth and speed information.
in Figure 5.4. The chartplotter receives position, direction, and speed information from a
GPS receiver, and depth and battery voltage information from a depth sounder.
Later in this chapter we discuss various development models. At this point, it is sufficient to understand that there are different ways to “slice and dice” the work to be done,
keeping in mind that we should develop each sub-system in the order: architect-designimplement. For example, don’t start writing code if you haven’t designed the algorithm
yet. This sequencing is quite important, so we discuss it further.
5.3.2
Requirements
A system design begins with functional requirements. Ganssle identifies “Vague Requirements” as reason number five for projects getting into trouble. Koopman presents an excellent discussion of software requirements (Chapters 5 through 9) so we will just present
a high-level view here.
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Requirements should be written down. This helps everyone have the same picture
of what needs to be accomplished, and makes omissions easier to spot.
There are three types of requirements. Functional requirements define what the
system needs to do. Nonfunctional requirements describe emergent system behaviors such as response time, reliability, and energy efficiency. Constraints define the limits on the system design, such as cost and implementation choices.
There are multiple ways to express requirements, both in text and graphically.
The most appropriate and convenient method should be used. Graphical methods
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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5.3.3
such as state charts, flow charts, and message sequence charts should be used
whenever possible because (1) they concisely convey the necessary information
and (2) they often can be used as design documents.
Requirements should be traceable to tests. How will the system be tested to ensure
that a requirement is met? Requirements should be quantified and measurable.
The requirements should be stable. Frequent changes to requirements (“churn”)
often have side effects and disrupt the ideal prioritization of work tasks. It is easy
for the latest changed requirement to be interpreted as the most important requirement, when in fact this is rarely the case.
Design Before Coding
One of the most effective ways to reduce risks in developing software is to design before
writing code1. Ganssle identifies “Starting Coding Too Soon” as reason number nine for
projects getting into trouble. We refer to high-level design as the architecture, and the lowlevel design as the detailed design.
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1
2
Writing code locks you in to specific implementations of an algorithm, data
structure, object, interface method, and so forth. If this happens before you understand the rest of the system, then you probably haven’t made the best possible
choice, and may end up having to make major changes to the code you’ve written,
or maybe even throw it away.
Designing the system before coding also gives you an early insight into what parts
are needed, and which ones are likely to be complex. This helps prevent the surprises which slow down development. One of the best ways of reducing schedule
risk is to understand the system in depth before creating a schedule, and then add
in extra time buffers for dealing with the risky parts. Estimation is the process of
predicting how long it will take to create the system.
Designs should include graphical documents such as flowcharts and state machines when possible. The goal is to have a small and concise set of documents
which define how the system should do its work. Graphical representations are
easier to understand than code because they abstract away many implementation
details, leaving just the relevant items2. This makes it easy for others to understand
your design and identify risks. It also helps bring new hires up to speed on the project and reduces the chances they’ll break something when they start maintaining
or enhancing the code.
There is related prior work in carpentry: Think thrice, measure twice, cut once.
Different businesses may have differing levels of formality (e.g., UML), but do not underestimate the benefit
of a simple diagram (whether hand-written or created in Visio).
CHAPTER 5 / SOFTWARE ENGINEERING FOR EMBEDDED SYSTEMS
5.3.4
147
Peer Reviews of Design Artifacts
It is very helpful to have other team members review artifacts before proceeding to the next
phase of development. First, having another perspective on an issue brings in greater experience and helps detect oversights. Ganssle identifies “Bad Science” as reason number
seven for projects getting into trouble. Second, if you know that someone else will be reviewing what you are creating, you are likely to be more careful and professional. Peer reviews should be applied to all development artifacts: requirements, test plans, architecture, detailed designs, and code. We refer the reader elsewhere for more details on peer
reviews (Koopman).
SONAR
UART
Rx ISR
GPS
UART
Rx ISR
UART
Tx ISR
RxQ1
RxQ2
Process
NMEA
data
CurTemp
CurVelG
Pri.
user
interf.
CurVelW
MemUsed
TxQ
Sec.
user
interf.
ISR
CurDepth
CurLat
CurLon
CurTime
CurDate
Format
and save
data
Task
Global Variable
Flash Data
Memory
Figure 5.5 System architecture for chartplotter.
5.3.5
System Architecture and Design Approach
The system architecture defines your approach to building the system. What pieces are there,
and how are they connected? What type of microcontroller and peripherals will be used? What
major pieces of software will there be? How do they communicate? What will make them run
at the right time? We present a summary of architectural concepts here, and encourage the
reader to dig deeper in the referenced text (see Chapter 10 and Chapter 11 in Koopman).
In Figure 5.5 we see the system architecture for the chartplotter. Sonar and GPS information is delivered through two serial ports to the system. We will use interrupt service
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
routines and queues to buffer the data between the serial ports and the main application
task code. There are four separate tasks in the system:
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The Process NMEA Data task will receive the data from the sonar and GPS, decode it, and update the relevant variables which indicate current depth, position,
and so forth.
The Primary User Interface task will update the display.
The Format and Save Data task will convert the depth and other variables into a
human-readable text format and write them to flash memory.
The Secondary User Interface task will provide a serial console interface so we can
read the logged data from flash memory, erase it, and perform other system maintenance functions.
We also see how information is shared between tasks in the system:
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Queues buffer the incoming and outgoing serial data.
A table of global variables is written by Process NMEA Data and read by two
other tasks.
How does this architecture meet the most critical aspects of the requirements? These may
be related to time, safety, robustness, or something else which is application-specific. In
any case it is important to convey these concepts.
Time-Critical Processing
It is quite helpful to have a section in the architecture document which describes which
processing is time-critical, and how the system is architected to ensure the timing requirements are met. For example, consider a light dimmer controller:
The system must switch power outputs within 50 microseconds of a zero-crossing of the
AC power line. Failure to switching within this time will lead to electrical noise and interference with other devices. The system is designed so that a hardware analog window comparator detects zero crossings and triggers a non-maskable interrupt. All power output
switching is performed by the ISR, which controls its outputs based on flags set by the main
code which indicates which outputs to enable. Hence interrupts must not be disabled for
longer than x microseconds.
The system must shut down within 10 ms of an overcurrent or overvoltage condition occurring. Failure to shut down within this time can lead to equipment damage and failure. We
plan to use a periodic interrupt running at 1 kHz in order to sample dedicated analog hardware comparators which detect these conditions. Because of the 1 kHz interrupt rate, interrupts must not be disabled for longer than 8 ms, in order to allow a 1 ms safety margin.
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149
Further information on real-time system design is available in Chapter 14 of the referenced text (Koopman).
Safety-Critical Processing
It is quite helpful to have a section in the architecture document which describes which
processing is safety-critical and how the system is architected, to ensure the safety requirements are met. For example:
The software tasks X, Y, and Z are safety-critical. They cannot be modified without triggering recertification. In order to ensure real-time performance, we use a preemptive
scheduler and assign X, Y, and Z priorities higher than all other tasks. In order to minimize
the chances of data corruption, all critical variables used by X, Y and Z are protected by
storing them with complements or with a block CRC.
Again, there is further detailed information in the referenced text (Chapters 26–30 in
Koopman cover critical system properties).
5.3.6
Detailed Design
After we have decided upon an architecture for the system, we can work on designing the
subsystems within it. Again, graphical representations can be quite useful; especially if the
corresponding requirements are graphical, as in this and similar cases they can be reused.
For example, state-based system behavior is best presented graphically. Figure 5.6 shows
a finite state machine design for a UART Receive data ISR (the two circles labeled “UART
Rx ISR” in Figure 5.5) which recognizes certain valid NMEA-0183 messages and enqueues
them for later decoding. Corrupted or unneeded messages are discarded, saving buffer space
in RAM and processor time. These messages have a specific format which includes the talker
type (GPS, depth sounder, etc.), the message type, multiple data fields (often with each followed by engineering units), and a checksum for error detection.
We use an FSM-plus-ISR combination for two reasons. First, we want to minimize the
amount of time spent in the ISR. Structuring the problem as an FSM allows us to write
code which doesn’t waste any time waiting for things to happen. The ISR is only executed
when the UART has received a byte of data. Second, parsing data such as text is a good
match for FSMs as it allows us to define rules to step through the different fields in a message and validate them.
Figure 5.7 shows a flowchart design for the task “Process NMEA Data” which decodes
these enqueued messages and acts on the data. This code is much less time-critical, so it is
implemented in a task which the scheduler runs after being notified that the RxQ holds at
least one valid message. The flowchart emphasizes the consecutive and conditional processing nature of the activity: decode the message, check to see if it is valid or not, update
variables, and so on.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Start
$
Append char to buf.
*, \r or \n, or
counter == 6
Any char. except *, \r or \n
Append char to buf.
Inc. counter
Talker 1
Sentence
Type
buf == $SDDBT, $VWVHW, or
$YXXDR
Enqueue all chars. from buf
\r or \n
Sentence
Body
Any char. except *
Enqueue char
*
Enqueue char
Checksum
1
Any char.
Save as checksum 1
Checksum
2
Any char.
Save as checksum2,
Increment # of msgs available
Figure 5.6 Finite state machine design for recognizing NMEA-0183 depth below transducer,
heading and speed through water, and battery voltage messages.
Start
RxQ
Data In
Decode NMEA
Sentence
Invalid?
Yes
No
CurPos
Update
Data Out
Skip?
No
Yes
Write to
Data Flash
Update
MemUsed
Data Out
End
Figure 5.7 Flowchart for decoding NMEA sentence and saving data to flash memory.
CHAPTER 5 / SOFTWARE ENGINEERING FOR EMBEDDED SYSTEMS
151
There are various other representations available beyond these two workhorses, so we
direct the reader other texts (see Chapter 12 and Chapter 13 of Koopman).
5.3.7
Implementation
Now that we have a detailed design it should be straightforward to proceed to the actual implementation of the code. C is the dominant programming language for embedded systems,
followed by C⫹⫹ and assembly language. C is good enough for the job, even though there
are some languages which are much safer. The risk with C is that it allows the creation of all
sorts of potentially unsafe code. Ganssle identifies “The Use of C” (or “The Misuse of C”)
as reason eight for projects getting into trouble. There are a few points to keep in mind as
you develop the code:
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Three fundamental principles should guide your decisions when implementing
code: simplicity, generality, and clarity (Kernighan and Pike).
▫ Simplicity is keeping the programs and functions short and manageable.
▫ Generality is designing functions that can work, in a broad sense, for a variety
of situations and that require minimum alterations to suit a task.
▫ Clarity is the concept of keeping the program easy to understand, while remaining technically precise.
Code should conform to your company’s coding standards to ensure that it is
easy to read and understand. See Koopman’s Chapter 17 for more information on
why coding style matters. There are many coding standards examples available
(Ganssle, J.). The rules we have seen broken most often, and which have the
biggest payoff, are these:
▫ Limit function length to what fits onto one screen or page.
▫ Use meaningful and consistent function and variable naming conventions.
▫ Avoid using global variables.
▫ If you find yourself writing the same code with minor variations, it may be
worth parameterizing the code so only one version is needed.
Data sharing in systems with preemption (including ISRs) must be done very carefully to avoid data race vulnerabilities. See Chapter 12 of this text and Koopman’s
Chapters 19 and 20 for more details.
Static analysis should be used to ensure that your code is not asking for trouble. Most
(if not all) compiler warnings should be turned on to identify potential bugs lurking in
your source code. Tools such as LINT are also helpful and worth considering.
Magic numbers are hard-coded numeric literals used as constants, array sizes,
character positions, conversion factors, and other numeric values that appear directly in programs. They complicate code maintenances because if a magic number is used in multiple places, and if a change is needed, then each location must
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5.3.8
be revised and it is easy to forget about one. Similarly, some magic numbers may
depend on others (e.g., a time delay may depend on the MCU’s clock rate). It is
much better to use a const variable or a preprocessor #define to give the value a
meaningful name which can be used where needed.
It is important to track available design margin as you build the system up. How
much RAM, ROM, and nonvolatile memory are used? How busy is the CPU on
average? How close is the system to missing deadlines? The Software Gas Law
states that software will expand to fill all available resources. Tracking the resource
use helps give an early warning. For more details, see Koopman’s discussion on
the cost of nearly full resources.
Software configuration management should be used as the code is developed
and maintained to support evolving code and different configurations as well.
Software Testing
Testing is an important part of software development. It is essentially impossible to develop
error-free non-trivial software in a single try. It is especially difficult to design up-front a system which will handle all possible input conditions (including failures) correctly. Ganssle identifies “Inadequate Testing” and “Writing Optimistic Code” as reasons number three and two
for projects getting in trouble. Koopman covers verification and validation of systems in detail.
Testing the developed software ensures that the product meets the requirements defined. That is, testing proves that the software does what it is supposed to do. A corollary is that testing identifies the software’s weaknesses. These defects are typically prioritized based on their criticality.
Although one can never completely test a program, some tests are more useful and important than others. Hence, it makes sense to think while planning the tests in order to get
the biggest return. Testing should be a logical, disciplined, and systematic process, rather
than a rote and mechanical process. As with other subjects covered here, there are many
excellent texts on software testing for further information (Phillips).
There are several independent dimensions of testing to consider:
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Software tests may or may not depend on the internal details of how the module is
built. Black box testing assumes no knowledge about the internal structure, and
focuses instead on functionality. White box (or clear box) testing takes advantage
of such knowledge, so it can be more efficient in finding faults.
Software testing should be done at various phases of the development process.
Unit tests are performed during coding on a per-module basis. Integration tests
are performed as the system is assembled (integrated) from modules.
Regression testing ensures that past bugs which were fixed have not been
re-introduced.
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153
Do We Know How the System is Built?
Black Box Testing tests the functionality of the software by treating it like a black box
with unknown contents. How the software performs a task is unknown and unimportant
to the test. The only needed thing to pass the test is for the software to do what it should.
There are many types of black box testing. Among them are tests for readiness, finite state
machine, cause-effect graphing, boundary value testing, and user profile:
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Readiness: This test checks if a function is present and functional, and ready for
testing. Black box testing should always begin with this form of testing.
Finite state machine: Much software can be considered as finite state machines
that transit between different states based on different events. This form of testing
tests the transitioning between states and for errors that may occur with them.
Cause effect graphing: This form of testing helps to organize the concepts in other
black box techniques. For this test, the tester organizes all possible inputs and outputs of a program. This results in a form of a complete software test and helps to
systematically organize test cases.
Boundary value testing: In this form of testing the inputs to the test system are divided into meaningful sets and then tested in groups. One value from each set is
then input to the system rather than the whole set. This helps save time.
User profile: This form of testing focuses on how the user intends to use the software and which errors are important to their proper functioning while using the
software. This minimizes the amount of time needed to be put into testing. However, learning what part of the program is used often is the difficult part of the test.
White Box Testing relies on knowledge of the structure of the software. It is also known as
clear box testing. How the software performs a task is known to the testers, enabling them
to identify probable errors. Important elements of white box testing are coverage and
branch and conditioning testing.
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Coverage: The aim of white box testing is to cover every statement, state, and path
in a program within the constraints of time and money. This can be a daunting task,
especially if the program has many conditional statements.
Branch and condition testing: The goal of branch testing is to traverse every path
through the program. One way to do this is to use a flow chart of the program. The
first test goes through one part of the program. The next one differs from the one before. In this manner, all paths are traversed, even those that share a common part.
How Many Modules Do We Test at a Time?
Individual unit testing of modules is typically done by the software developer as the code
is created. As the developer has intimate knowledge of the implementation of the module,
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
this testing is typically white-box testing to maximize the effectiveness. The developer
writes test harness code to run the unit under specific conditions and verify the correct responses. Unit testing is quite effective because if there is a bug, it is in that module’s code,
design, or requirements.
With integration testing each module is merged into the main program and is tested to
check if it works individually as well as with the rest of the program without causing any
errors. There are often scenarios where a subroutine works perfectly on its own, but fails
when integrated into the overall system due to unexpected dependencies, requirements, or
interactions.
There are various types of integration testing: Bottom up, top down, sandwich, and
build. Selecting the type of integration testing depends upon the people and product involved in development.
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Bottom up: This is one of the classic approaches for design and testing. Each problem is broken down into smaller parts and solutions are written for them, also
called modules. Each module is tested individually and combined into subsystems
which in turn are also tested and then combined into a larger system. This goes on
till the complete solution is acquired and tested.
Top down: The top down form of integration testing is similar to the bottom up
form, but starts with a fully tested main routine. Modules are added to the main
routine one after the other and tested as a combination. The process thus continues
until all the modules have been added to the main program and tested.
Sandwich: The sandwich testing form combines the bottom up and the top down
forms of testing. The top down part tests the main controlling subsystems whereas
the bottom up part integrates and tests the individual modules into subsystems.
Build: The build form of integration testing starts with a core system to which
functionally related module sets are added consecutively.
There is also a “worst-practice” integration testing method known as Big Bang testing.
With this form of testing, all modules are combined and tested as a whole. Big bang testing
is not advisable with untested modules as diagnosing the error can be very difficult—
which of the many modules is really causing the problem? Or is an interaction between two
or more modules the cause?
How Do We Keep from Breaking Old Bug Fixes?
The goal of regression testing is to ensure that bugs which were found in past testing were
fixed and are still fixed. Sometimes an effort to fix a bug introduces other bugs. Regression
testing uses a suite of tests which triggered bugs in the past. Automated regression testing
allows developers to verify quickly and easily that their bug fix really is a fix. Regression
testing may be applied to both unit and integration testing.
CHAPTER 5 / SOFTWARE ENGINEERING FOR EMBEDDED SYSTEMS
5.4
155
SOFTWARE DEVELOPMENT LIFECYCLE MODELS
We now discuss software development lifecycle models in more detail. We can divide them
into two categories: waterfall (big up front design) and everything else (build a piece at a
time). The advantage of the latter approaches is that they deliver portions of the implementation to the customer and other stakeholders earlier. This allows problems and misconceptions to be found earlier, and therefore fixed without disrupting the schedule as much. Projects with greater risks will benefit more from more iterative approaches, while less risky
projects may be implemented more efficiently with a less iterative approach.
This chapter only provides a general description of these software processes. Further
details can be found in the references of this chapter.
5.4.1
Waterfall Process
The waterfall model of software development is an idealized process which assumes that
we know everything up front. The process gets its name because the processes flows down
the steps like falling water. This process is most appropriate when the problem is very well
understood so there is little risk. The following are the steps for the waterfall process:
1.
2.
3.
4.
5.
6.
Determine user needs
Gather requirements
Design
Build
Test
Demonstrate user product
Figure 5.8 illustrates the waterfall process. In practice, there are often arrows jumping back
up the waterfall3 which makes this model an idealization.
User Needs
Requirements
Design
Waterfall Process
Build
Test
User Product
Figure 5.8 The waterfall process expressed as a V-chart.
3
Imagine salmon leaping upstream over the rapids.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
5.4.2
Iterative Process
The iterative process is used to deliver a product in increments. The customers define the
goals of the product at the beginning of development and are always anxious to have something quickly working. The iterative process provides the product to the customer in parts
and provides developers an opportunity to learn about the product and the customer while
building the product. This type of process is typically used when there is enough time for
developing a project in parts and the customer is eager to provide feedback on the how the
product functions while it is being developed. Figure 5.9 illustrates the iterative process.
First
Delivery
Second
Delivery
Third
Delivery
Figure 5.9 Example of an iterative process with one development team, expressed as a V-chart.
5.4.3
Spiral Process
The spiral process combines many fundamental contents of different process models into a
single process. This process works best for projects that have a high risk of failure, such as
research projects dealing with developing a new technology. Figure 5.10 illustrates the spiral process. Each cycle starts with the steps shown in the upper left quadrant, which are objectives (goals to achieve), constraints (limitations on resources), and alternatives (different
approaches to achieve the objectives). The second quadrant (clockwise direction) shows
the next steps in the process, which are risk analysis and prototyping. It begins with alternatives produced in the first quadrant. The developers then use the prototypes to analyze
each alternative’s risks and gain more insight. The third quadrant consists of the evaluation
and decision making processes, followed by building the solution. The final quadrant consists of understanding what to do for the next cycle, which is repeated in the first quadrant.
The developers revise the previous phases and create a plan for the next quadrant, review
the same, and then decide whether to go ahead with the plan or stop building the project.
CHAPTER 5 / SOFTWARE ENGINEERING FOR EMBEDDED SYSTEMS
Acquire Objectives
Acquire Constraints
157
Evalute the risk
using prototyping
Acquire Alternatives
Evalute product
Plan the next cycle
Continue or stop
Evalute the risk
aversion approach.
Build the product
of the cycle
Figure 5.10 The general spiral process.
5.4.4
Agile Development Methods
The most common agile development methods are scrum, extreme programming, and lean
development. These methods seek to deliver the product to the customer in satisfactory
condition as early as possible in a continuous manner.
Let’s examine scrum. With scrum, development activity is divided into a series of
sprints lasting two to four weeks. At the end of the sprint the team will have a working, deliverable software product. There are three main types of participants:
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The product owner speaks for the customer.
The team delivers the product.
The Scrum Master is responsible for eliminating obstacles from the team’s path.
Each sprint begins with the team members and product owner discussing features from a prioritized feature list (the product backlog). The product owner identifies the desired features,
and the team estimates which can be delivered within the sprint, adding them to a task list
called the sprint backlog. The sprint backlog is frozen for the sprint, so that the team members
have clear goals during that development period. Each day during the sprint there is a brief (fifteen minute) status meeting in which each team member answers three specific questions:
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What have you done since yesterday’s meeting?
What are you going to do today?
Are there any issues keeping you from meeting your goals?
The Scrum Master then seeks to address the issues. Finally, each sprint is time-boxed. If a
feature is not completed by the end of the sprint, it goes back into the product backlog. One
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
of scrum’s main strengths is the short development cycle, which improves the speed of
feedback. There are other aspects to scrum which we do not cover here, but further details
are available in numerous texts on the subject.
5.4.5
Prototyping
Prototyping is a popular and useful software process, especially when determining the look
and feel of the software has a higher priority than its basic functions. One of the drawbacks
of the prototyped process is that when the waterfall model of development is used the developer may create something completely different from what the customer expected, since
the requirements are gathered only at the beginning of the development process. Thus, prototyping is better when it is performed as either an iterative or evolutionary process.
Two basic types of prototypes used are the throw away and evolutionary prototype. In
the throw away prototype, developers use a demonstration tool or language. Once the customer is satisfied with the prototype, the developers throw away the prototype and build the
actual product with real programming languages. In the evolutionary prototype, the developers use code from the prototype in the actual system.
5.5
RECAP
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5.6
A major risk of software development is starting coding too early. Designing the
system and its components before coding reduces development risks significantly,
and also provides other benefits.
Industry follows many (and sometimes differing) processes when developing software. A process gives a directional path to developing software in an organized
manner, and allows the people developing the software and using the software to
maintain expectations from the development process at regular intervals.
Pseudo code and graphical methods to design solutions to a software programming
problem allows understanding, resolving, and maintaining logical flow of a program. They can also be directly included in the documentation for the program.
Testing is an integral part of software testing and software not subjected to testing
is bound to fail. There are different techniques available for testing which should
be applied as appropriate.
REFERENCES
Ganssle, Jack. “Breakpoints: Jack’s Top Ten.” Embedded Systems Design, December (2006): 61–63. Print.
Ganssle, Jack. The Art of Designing Embedded Systems. 2nd ed. Lawrence, KS: Newnes, 2008. Print.
CHAPTER 5 / SOFTWARE ENGINEERING FOR EMBEDDED SYSTEMS
159
Kernighan, Brian W., and Rob Pike. The Practice of Programming. Indianapolis: Addison-Wesley, 1999.
Print.
Koopman, Philip J. Better Embedded System Software. New Castle, PA., Drumnadrochit Education, 2010.
Print.
Phillips, Dwayne. The Software Project Manager’s Handbook: Principles That Work at Work. Los Alamitos,
CA: John Wiley & Sons, 2004. Print.
5.7
EXERCISES
1. Create a set of requirements for a vending machine which accepts coins and one-
dollar bills, and provides change. Assume that each type of item has its own
button.
2. Create a set of requirements for a controller for an elevator in a ten-story building.
3. Create a state machine for use in a cellphone to identify local phone numbers,
long-distance phone numbers, and invalid phone numbers.
4. Estimate how long it will take you to create a working program to flash the LEDs
on your favorite microcontroller board at a frequency proportional to the ambient
Celsius temperature. Then go ahead and create the program. Log the time spent for
each development activity. Analyze the time required for each activity, the accuracy of your estimations, and finally suggest improvements.
Chapter Six
Converting Between the Analog
and Digital Domains
6.1
LEARNING OBJECTIVES
Embedded systems often measure physical parameters such as light intensity and temperature. These parameters are analog but the embedded system’s microcontroller requires digital values to work on. An Analog to Digital Converter (ADC) is used to convert those parameters into a digital form.
In some cases, the microcontroller may need to provide analog signals to another system. For this, the digital output produced by the microcontroller has to be converted to analog an analog before being fed to the interfaced system. A Digital to Analog Converter
(DAC) is used for this purpose.
In this chapter we will learn about:
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6.2
Converting an analog value to digital, mathematically
ADCs in the RX62N
Setting up registers and using the 12-bit and 10-bit ADC
Using a DAC
BASIC CONCEPTS
A microcontroller represents information digitally: a voltage less than Vcc/2 represents a
logical 0, while a voltage above Vcc/2 represents a logical 1. An analog signal can represent
an infinite number of possible values. For example, consider an electronic thermometer
with an output voltage which is proportional to the temperature in Celsius: Vout ⫽ Temperature*0.05 V/°C. At 5° C, Vout ⫽ 0.25 V. At 40° C, Vout ⫽ 2.0 V. At 40.1° C, Vout ⫽ 2.005 V.
If we connect this thermometer directly to a microcontroller’s digital input we will not
be able to measure temperatures very accurately. In fact, we can only determine if the voltage is above or below Vcc/2. Assuming a supply voltage of 3.3 V, we can only determine if
the temperature is above or below (3.3 V/2)/(0.05 V/°C) ⫽ 33° C, throwing away all other
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
temperature information. In order to preserve this information we need a more sophisticated conversion approach.
Analog Input
Digital Output (bits)
Reference Voltage
Figure 6.1 Simple ADC.
An ADC measures an analog input voltage and determines a digital (binary) value
which represents it best. This measurement process is called quantization. The conversion
is based on reference voltages which define the high (V⫹Ref) and low (V⫺Ref) ends of the
input voltage range. Often microcontrollers have V⫺Ref connected to ground (0 V).An input
voltage of V⫹Ref will result in an output code which is all ones, while an input voltage of
V⫺Ref will result in an output code of all zeroes. An intermediate input voltage will result
in the proportional binary code value. This is discussed in more detail in Section 6.2.3.
A block diagram for a simple ADC is shown in Figure 6.1. The number of bits in the
digital output is called the resolution of the ADC. A 10-bit ADC produces an output with
10 bits, with 1024 (210) different binary outputs. Thus, in a 10-bit ADC, a range of input
voltages (analog) will map/translate to a unique binary output (0000000000 to
1111111111). A 12-bit ADC will have 4096 (212) unique binary outputs to represent 0 to
100% of an analog input.
Quantization usually introduces some error. A specific code (e.g. 0000101010) corresponds to a range of analog input voltages. The term quantization error describes how
large the error can be. An ADC with higher resolution has more binary codes possible,
which reduces the range of voltages corresponding to each code. This reduces the quantization error.
Quantization error ⫽
1
, where N ⫽ number of quantization levels.
(2 * 2N)
The rate at which new outputs are calculated in an ADC is called the conversion rate or
sampling frequency. Sampling theory states that an input signal with no frequency compo-
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
163
nents greater than or equal to one half of the sampling frequency (called the Nyquist frequency) will be completely and accurately represented by the samples. If the input signal
has any frequency components above the Nyquist frequency, these will be aliased by the
sampling and appear as noise in the signals (as lower frequency components).
Hence input signals may be bandwidth-limited with a low-pass filter before sampling
and quantization. In addition, the system is typically designed so that the Nyquist frequency is well above the filter’s corner frequency, allowing the use of less expensive,
lower-order filters.
Sampling Switch
Output Signal
Input Signal AC
Hold Capacitor
Figure 6.2 Sample and hold circuit.
Some types of ADC will generate incorrect results if the analog input signal changes
too much during the conversion time. To avoid this problem, a sample and hold circuit
(shown in Figure 6.2) can be used to sample the input voltage and save it in a capacitor. The
capacitor is then disconnected from the input voltage by opening the sampling switch. The
output signal can then be sampled by the ADC without interference from the changing
input.
6.2.1
Analog to Digital Conversion by Successive Approximation
Analog to Digital conversion can be performed using many methods, such as Flash Conversion, Dual Slope Integrating, and Successive Approximation. The ADC method used in
the RX62N board is Successive Approximation. Conversion using this method gives good
resolution and has a wide range.
In the Successive Approximation method, the input voltage is repeatedly compared with
the output of a DAC, until the best approximation is achieved. The DAC is fed by the current
value of the approximation. The binary value of the approximate is found in every step of this
method and is stored in the SAR. The SAR then compares the binary value and the reference
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
voltage. Successive Approximation requires the same number of clock cycles as the output
bits of the ADC; i.e., 12-bit ADC requires 12 clock cycles and 10-bit ADC requires 10 clock
cycles (ADC clock cycles, not CPU clock cycles) to perform A/D conversion.
This process can be better understood with an example. The reference voltage for the
RX62N board is 3.3 V. Let us assume that an input voltage of 2.5 has to be converted to
digital form and the ADC used is 10-bit.
In the first clock cycle, 2.5 V is compared with 1.65 V (voltage is generated by the
DAC and is half the reference voltage of 3.3 V). The 2.5 V is greater than 1.65 V and hence
a ‘1’ is set at the MSB of the binary value of the approximate, making the value
1xxxxxxxxx. This value is stored in the SAR.
In the second clock cycle, the input (2.5 V) is compared with 2.47 V (halfway between
1.65 V and 3.3 V). Since the input (2.5 V) is greater than the output from DAC (2.47 V), the
next bit of the binary value is set to ‘1.’ The binary value of the approximate is now
11xxxxxxxx.
In the third clock cycle, the input (2.5 V) is compared with 2.89 V, (halfway between
2.47 V and 3.3 V). The input (2.5 V) is less than the output from DAC (2.89 V), so the next
bit of the binary value is set to ‘0.’ The binary value of the approximate is now
110xxxxxxx.
In the next cycle, the input (2.5 V) is compared with 2.68 V, (halfway between 2.47 V
and 2.89 V). The input (2.5 V) is less than the output from DAC (2.68 V), so the next bit of
the binary value is set to ‘0.’ The binary value of the approximate is now 1100xxxxxx.
The same process takes place until all the bits of the binary value are found. The final
result of this conversion is 1100000111.
11XXXXXXXX
110XXXXXXX
1100XXXXXX
11000XXXXX
110000XXXX
1100000XXX
11000001XX
110000011X
1100000111
Voltage
1XXXXXXXXX
Analog
Input
XXXXXXXXX
164
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
Start of Conversion
Time
Figure 6.3 A/D conversion using successive approximation.
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
165
Gereration of A/D
converstion start condition
<<
Input sampling timing
ADI
tD
tSPL
tSAM
tCONV
[Legend]
tD:
A/D conversion start delay time
tSPL:
Input sampling time
tSAM: Successive conversion time
tCONV: A/D conversion time
Figure 6.4 ADC conversion timing. Source: Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/
RX600 Series. Renesas Electronics America, Inc., 2010, page 1748.
6.2.2
Conversion Speed
The analog input is sampled after A/D conversion start delay time (tD). Input sample time
(tSPL) is the time that the capacitor in the sample and hold circuit takes to charge. Successive conversion time (tSAM) is the time after which the next conversion can start. It is fixed
at 25 ADC clock cycles.
Conversion time (tCONV), or sampling time, is the inverse of conversion speed or
sampling frequency. Conversion time is the sum of tD, tSPL, and tSAM only during the
first conversion. The following conversions always have a conversion time of tSPL and
tSAM.
A/D Sampling State Register (ADSSTR) gives the flexibility of altering the sampling
time. One may want to alter this if the analog input signal has high impedance or if the analog input is a fast changing signal and the original sampling time is insufficient, or when
the Peripheral module clock (PCLK) is slow.
6.2.3
Transfer Function Calculation
The digital value for a particular analog value can be found mathematically. This can be
useful as a guide to see if the ADC output obtained is correct.
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SETTING
RANGE
EXAMPLE OF SETTING
SAMPLE TIME*
Standard (initial value)
19h
0.5 ms (When PCLK ⫽ ADCLK ⫽ 50 MHz)
Analog input signal impendance is
high and the sampling time may be
insufficient
1Ah to FFh
Example: FFh
5.1 ms (When PCLK ⫽ ADCLK ⫽ 50 MHz)
Input sampling time is less than the
initial value when ADCLK is below
50 MHz.
02h to 18h
Example: 14h
0.5 ms (When PCLK ⫽ ADCLK ⫽ 40 MHz)
Figure 6.5 ADSSR settings. Source: Hardware Manual, page 1748.
FORMULA
ITEM
SYMBOL
MIN
MAX
A/D conversion start delay time (1)
ID
3
PCLK (MHz)
1
4
⫹
ADCLK (MHz) PCLK (MHz)
Input sampling time (2)
ISPL
Successive conversion time (3)
ISAM
25
ADCLK (MHz)
A/D conversion time*1
ICONV
(1) ⫹ (2) ⫹ (3)
A/D conversion time*2
ICONV
(2) ⫹ (3)
Setting value of ADSSTR
ADCLK (MHz)
Notes: 1. A/D conversion time in single mode and scan mode (first round)
2. A/D conversion time in scan mode (after the second round)
Figure 6.6 ADC conversion time. Source: Hardware Manual, page 1749.
If Vin is the sampled input voltage, V⫹ref is the upper end of the input voltage range,
V⫺ref is the lower end of the input voltage range, and n is the number of bits of resolution
in ADC, then the digital output (n) can be found using the following formula:
n⫽ c
(Vin ⫺ V⫺ref)(2N ⫺ 1) 1
⫹ d int
V⫹ref ⫺ V⫺ref
2
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
n⫽ c
6.3
BASIC EXAMPLES
6.3.1
Conversion Speed
167
(Vin)(2N ⫺ 1) 1
⫹ d int (if V⫺ref ⫽ 0)
V⫹ref
2
Let us calculate the conversion time for the first conversion. Let PCLK ⫽ ADCLK ⫽ 50 Mhz,
and ADSSR is the standard value of 19h.
From Figure 6.6, it can be seen that for the first conversion:
tCONV ⫽ (tD ⫹ tSPL ⫹ tSAM)
tCONV ⫽ (3 / PCLK ⫹ ADSSR / ADCLK ⫹ 25 / ADCLK)
ADSSR value is 19h or 2510. Decimal value has to be used for calculation.
tCONV ⫽ (3 / 50 MHz ⫹ 25 / 50 MHz ⫹ 25 / 50 MHz)
tCONV ⫽ (0.06 ms ⫹ 0.5 ms ⫹ 0.5 ms)
tCONV ⫽ 1.06 ms
While calculating conversion time for the second and subsequent conversions,
tCONV ⫽ (tSPL ⫹ tSAM).
6.3.2
Digital Value for a Given Analog Value
Let us assume that the analog voltage to be calculated is 2.7 V and the 12-bit ADC has to
be used. The digital value will be:
(Vin)(2N ⫺ 1)
1
n⫽ c
⫹ d int (Since V⫺ref ⫽ 0)
V⫹ref
2
⫽c
(2.7)(212 ⫺ 1)
1
⫹ d
3.3
2
⫽c
(2.7)(4095)
1
⫹ d
3.3
2
n ⫽ 335210
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6.3.3
Step Size
While reference voltage is the maximum analog value that can be converted to digital
form, step size is the smallest change in voltage that can be converted. Step size is also
known as the resolution of the ADC.
Step Size ⫽
(Vref)
(Since V⫺ref ⫽ 0)
2N
(3.3)
⫽ 3.2 mV
210
(3.3)
The step size for 12-bit ADC ⫽ 12 ⫽ 0.8 mV
2
The step size for 10-bit ADC ⫽
The resolution (step size) of the 12-bit ADC is much better than that of the 10-bit ADC.
Hence, for applications, which need to detect very small changes in voltage, 12-bit ADC
should be used.
6.4
ADVANCED CONCEPTS
The RX62N has a 12-bit and a 10-bit A/D converter. Depending on the resolution the
application needs, either the 12-bit or 10-bit ADC should be selected. By default peripherals are in the stop state. They can be enabled by using the Module Stop Register A or B
(MSTPRA or MSTPRB). To use the 12-bit ADC, SYSTEM.MSTPCRA.BIT.MSTPA17
must be set to 0; and to use the 10-bit ADC, SYSTEM.MSTPCRA.BIT.MSTPA22 and
SYSTEM.MSTPCRA.BIT.MSTPA23 must be set to 0.
The ADC has eight channels (AN0 to AN7). They are at Port 4 pin 0 to 7. To use a particular channel, the respective port has to be set up as input. For example, to use AN0, port
4 pin 0 use PORT4.DDR.BIT.B0 = 0. For inputs, the Input Buffer Control Register (ICR)
also has to set up. This can be done using PORT4.ICR.BIT.B0 = 1.
Next, the ADC registers have to be set up. The 12-bit ADC and the 10-bit ADC have
different registers. In this section we shall see how to set the registers and use the use the
different operating modes of the ADCs.
6.4.1
12-Bit A/D Converter
The ADC usually consists of a sample and hold circuit and a comparator. The sample and
hold circuit gets a one-time snap shot of the analog input (voltage) and this is compared
against a reference voltage using the comparator.
.
..
..
.
Impedance
converting circuit
..
..
.
.
AN7
..
..
.
.
ADDR0 to
ADDR7
2
1
Comparator
ADCER
ADADC
ADANS
Bus interface
Control circuit
(including decoder)
ACSTRGR
ADADS
Succesive
approximation
register
Analog multiplexer
Figure 6.7 Block diagram of 12-bit ADC.
Sample &
hold circuit
ADREF
Impedance
converting circuit
Power
generator
(for self test)
12-bit D/A
ADCSR
AN0
VRERL
VREFH
AVLL
AVDF
AD0
External trigger
(ADTRG0#)
A/D conversion trigger
(MTU, TMR)
Interrupt signal
(A/D conversion end)
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Registers
The 12-bit ADC registers are presented as structures and unions for easy manipulation, just
like the ports, in the ‘iodefine_RX62N.h’ file. The registers can be accessed using the syntax
S12AD.REGISTER.WORD to set up an entire register or S12AD.REGISTER.BIT.BIT_
NAME to set up a particular bit of a register.
A/D Data Registers n (ADDRn) (n ⴝ A to H)
The 12-bit ADC has eight Data Registers each corresponding to the input channels of the
ADC. A/D data registers ADDRA to ADDRH are 16-bit read-only registers. They store the
A/D conversion results of channels AN0 to AN7. The width of the ADDRn (16-bit) is
greater than the width of the ADC output (12-bit). To avoid reading wrong data, the output
has to be aligned either to the right or left of ADDRn. This can be done using the A/D Control Extended Register (ADCER). This is explained a little later.
A/D Control Register (ADCSR)
The ADCSR is used to select different settings of the ADC.
Address: 0008 9000h
Value after reset:
b7
b6
b5
b4
ADST
ADCS
—
ADIE
0
0
0
0
b3
b2
CKS[1:0]
0
0
b1
b0
TRGE
EXTRG
0
0
Figure 6.8 A/D control register. Source: Hardware Manual, page 1717.
The b0 bit is used to specify if an external trigger, ADTRG0# (port 0 pin 7), should start
A/D conversion. If 1 is set, the microcontroller starts A/D conversion when a trigger is received. The value 0 is set when A/D conversion is to be started by other means.
To receive the external trigger (if b0 ⫽ 0), the external trigger has to be enabled. This
is done by setting b1 bit to 1. The value 0 disables external trigger.
The frequency of the ADC clock can be selected using the following table. PCLK is
the peripheral clock.
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
TABLE 6.1
171
Clock Selection.
b3
b2
FUNCTION
0
0
PCLK/8
0
1
PCLK/4
1
0
PCLK/2
1
1
PCLK
The A/D Scan Conversion End Interrupt Enable (ADIE) bit is used to enable or disable
A/D interrupt after A/D conversion has been performed. Setting this bit to 0 disables the interrupt, and setting it to 1 enables this interrupt.
The A/D Scan Conversion Mode Select (ADCS) is used to select mode of operation of
the ADC. Setting this bit to 0 selects Single Cycle Scan Mode, and setting it to 1 selects
continuous mode.
The A/D Conversion Start (ADST) is used to stop/start the A/D conversion. Setting this
bit to 1 starts the ADC and setting it to 0 stops the ADC. If ADC is to be started using software trigger, ADST must be set to 1 only after all the ADC registers have been set up.
Hence set ADST ⫽ 0 when setting up this register initially.
A/D Channel Select Register (ADANS)
This register is 16 bits wide and is used to select the channel(s) on which A/D conversion
should be performed. The top 8 bits (b15 to b8) are reserved and the bottom 8 bits (b7 to
b0) are used to select channels. To select a channel, set the corresponding bit to 1. For example, to select channel 0, set S12AD.ADANS.WORD ⫽ 0x0001; and to select all eight
channels set S12AD.ADANS.WORD ⫽ 0x00FF.
A/D-Converted Value Addition Mode Select Register (ADADS)
The 12-bit ADC has a special setting which is called the Converted Value Addition Mode.
This setting is used to successively convert and sum two to four times the channels that
have been selected using the ADANS register. To perform value addition on a particular
channel, set S12AD.ADADS.BIT.ADS [n] ⫽ 1 (n ⫽ 0 to 7).
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Address: 0008 9008h
Value after reset:
b14
b13
b12
b11
b10
b9
b8
—
—
—
—
—
—
—
0
0
0
0
0
0
0
b7
b6
b5
b4
b3
b2
b1
0
0
0
ADS[7:0]
0
0
0
0
Figure 6.9 A/D converted value addition mode select register. Source: Hardware Manual, page 1720.
To understand value addition better, let us consider an example in which all eight channels
have been selected (S12AD.ADANS.WORD ⫽ 0x00FF) and value addition is to be performed on channels 2 and 6.
Continuous
conversion count
3 times
4 times
AN2
AN6
AN2
3 times
AN2
AN6
AN2
2 times
AN2
AN6
AN2
1 time
AN0 AN1 AN2 AN3 AN4 AN5 AN6 AN7 AN0 AN1 AN2
....
Conversion in progress
Figure 6.10 A/D converted value addition mode. Source: Hardware Manual, page 1720.
According to our example, analog inputs at channels 0, 1, 3, 4, 5, and 7 are A/D converted
once, but inputs at channels 2 and 6 are successively converted four times (the number of
times can be changed) and added. This added value is stored in the A/D data register. Finding the average of this value can improve A/D conversion accuracy.
A/D-Converted Value Addition Count Select Register (ADADC)
The ADADC is the register that is used to select the number of times the value adding has to
be performed. This register is an 8-bit register. The top 6 bits are reserved and the lower
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
173
2 bits (b1, b0) are used to select the value addition count. Value addition can be performed
two to four times. The setting for the value addition count can be seen from the following
table.
TABLE 6.2
A/D Converted Value Addition Count Setting.
b1
b0
FUNCTION
0
0
1-time conversion (no addition)
0
1
2-time conversion (addition once)
1
0
3-time conversion (addition twice)
1
1
4-time conversion (addition three times)
A/D Control Extended Register (ADCER)
The ADCER is a 16-bit register. All bits except bit 5 and bit 15 of this register are reserved.
Bit 5 is for Automatic Clearing Enable (ACE). Thus, setting bit 5 to 1 enables automatic
clearing of the Data Register once the A/D value has been read by the microcontroller. This
setting makes sure that older A/D values are not read by mistake.
Bit 15 (ADRFMT) of the ADCER is used to select the format of the Data Register. Setting bit 15 to 0 sets the format of the Data Register to right alignment. Setting this bit to 1
selects left alignment of Data Register. However, if the A/D converted value addition mode
is selected, this formatting becomes void. Selection of the value addition mode automatically sets left alignment format for the Data Register. Note that the number of bits output
after value addition is fourteen and not twelve.
A/D Start Trigger Select Register (ADSTRGR)
The ADSTRGR is an 8-bit register. The top four bits (b7 to b4) of this register are reserved
and the lower four bits (b3 to b0) are used to select the type of trigger that will start the
Analog to Digital Conversion process.
Address: 0008 9010h
Value after reset:
b7
b6
b5
b4
—
—
—
—
0
0
0
0
b3
b2
b1
b0
ADSTRS[3:0]
0
0
0
0
Figure 6.11 A/D start trigger select register. Source: Hardware Manual, page 1723.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
A/D conversion can be started by one of three sources. They are a) Multi-function Timer
pulse Unit (MTU) and Timer (TMR), b) external trigger (ADTRG0#), and c) Software
Trigger. To choose a type of trigger, use the following table.
TABLE 6.3
MODULE
SOURCE
ADC
ADST
External
input
MTU
TMR
Trigger Selection.
REMARKS
Software trigger
ADSTRS[3] ADSTRS[2] ADSTRS[1] ADSTRS[0]
—
—
—
—
ADTRG0# A/D conversion startup
trigger pin
0
0
0
0
TRG1N
Input capture/compare
match A from MTU0
0
0
0
1
TRG2N
Input capture/compare
match B from MTU0
0
0
1
0
TRG3N
Input capture/compare
match from MTU0 to MTU4
0
0
1
1
TRG4N
Input capture/compare
match from MTU6 to MTU10
0
1
0
0
TRG5N
Compare match E from MTU0
0
1
0
1
TRG6N
Compare match F from MTU0
0
1
1
0
TRG7N
Compare match from MTU4
0
1
1
1
TRG8N
Compare match from MTU10
1
0
0
0
TRG9N
Compare match from TMR0
1
0
0
1
TRG10N
Compare match from TMR2
1
0
1
0
Source: Hardware Manual, page 1723.
When the MTU and TMR are to be used as the trigger, the TRGE bit in ADCSR has to
be set to 1 and the EXTRG bit in ADCSR has to be set to 0.
When an external input is to be used as the trigger (ADTRG0#), the TRGE bit in
ADCSR has to be set to 1 and the EXTRG bit in ADCSR has to be set to 1. ADTRG0# has
to be set up as an input pin and ICR has to be enabled.
Software trigger is enabled at all times irrespective of the values set using TRGE,
EXTRG, and ADSTRGR bits in ADCSR.
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175
Let us now look at an example of setting up the registers of the 12-bit ADC. It is always better to write register set up as a function.
1. void ADC_Init(){
2.
SYSTEM.MSTPCRA.BIT.MSTPA17 = 0;
3.
S12AD.ADCSR.BYTE = 0x0C;
4.
S12AD.ADANS.WORD = 0x01;
5.
S12AD.ADCER.BIT.ACE = 1;
6.
S12AD.ADCER.BIT.ADRFMT = 0;
7. }
The setting up of registers has been written as a function named ADC_Init() in line 1. In
line 2, the 12-bit ADC has been selected using the Module Stop Control Register A. In
line 3, the Control Register is set up—the Software trigger has been enabled (b1 ⫽ 0, b0 ⫽
0), the clock PCLK (b3 ⫽ 1, b2 ⫽ 1) has been selected, A/D Interrupt Enable has not been
enabled (b4 ⫽ 0) and Single-Cycle Scan mode has been selected (b6 ⫽ 0). In line 4, channel 0 (AN0) has been selected. Next, automatic clearing of ADDRn (line 5) and right alignment of ADDRn (line 6) is done.
Operation
The 12-bit ADC is capable of operating in two modes: single-cycle scan mode and continuous scan mode.
Single-Cycle Scan Mode
In this mode, one to eight channels (number of channels selected using ADANS register)
are scanned/converted to digital once in ascending order and then the ADC is stopped. This
can be better understood with the following figure in which conversion is performed on
three channels (AN4, AN5, and AN6).
The ADC in Single-Cycle Scan Mode is started (represented by (1) in Figure 6.12)
when the ADST bit (ADCSR) is set to 1. The channels are A/D converted in ascending order (AN4, AN5, AN6) and the converted value is stored in the respective Data Register
(represented by (2) in the figure). An ADI interrupt request is raised is ADIE bit (ADCSR)
is enabled (represented by (3) in the figure). Finally, the ADST bit gets cleared to 0 when
inputs of all the channels have been converted (represented by (4) in the figure).
The ADC operates similarly when ADC is started using MTU, TMR, or an external
trigger input.
Waiting for
conversion
ADI
ADDR6
ADDR5
ADDR4
A/D conversion 3
Interrupt generated
(3)
A/D conversion result 1
(2)
A/D conversion result 2
(2)
A/D conversion result 3
Storing
A/D converision 2
(4)
Figure 6.12 Single-cycle scan mode. Source: Hardware Manual, page 1724.
Channel 6 (AN6) Waiting for conversion
(2)
A/D conversion 1
(1)
A/D conversion time
Setting*
Channel 5 (AN5) Waiting for conversion
Channel 4 (AN4)
A/D conversion
ADST
started
A/D conversion is performed only once.
Waiting for conversion
Waiting for conversion
Waiting for conversion
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Waiting for
conversion
A/D conversion
started
A/D conversion 3
Waiting for conversion
A/D conversion 4
A/D conversion
time
A/D
conversion 5*2
Waiting for
conversion
(4)
Interrupt generated
(3)
Figure 6.13 Continuous scan mode. Source: Hardware Manual, page 1725.
A/D conversion 6
(5)
Setting*
Waiting for conversion
Waiting for conversion
Clear
A/D conversion result 1
A/D conversion result 4
(2)
A/D conversion result 2
(2)
A/D conversion result 3
Storing
A/D converision 2
Waiting for conversion
Notes: 1. indicates the point when the instruction is executed by software.
2. Converted data are ignored.
ADF
ADDR2
ADDR1
ADDR0
Channel 2 (AN2) Waiting for conversion
(2)
A/D conversion 1
(1)
Setting*
Channel 1 (AN1) Waiting for conversion
Channel 0 (AN0)
ADST
A/D conversion is performed sequentially.
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Continuous Scan Mode
In this mode, one to eight channels (number of channels selected using ADANS register)
are scanned/converted to digital continuously in ascending order until the ADC is stopped
manually. This can be better understood with the following figure in which conversion is
performed on three channels (AN0, AN1, and AN2).
The ADC in Continuous Scan Mode is started (represented by (1) in Figure 6.13) when
the ADST bit (ADCSR) is set to 1.
The channels are A/D converted in ascending order (AN0, AN1, AN2) and the converted
value is stored in the respective Data Register (represented by (2) in the figure). An ADI interrupt request is raised is ADIE bit (ADCSR) is enabled (represented by (3) in the figure).
Unlike Single-Cycle Scan Mode, the above two processes ((1) and (2)) are repeated
until the ADST is set to 0 manually. When ADST is set to 1, the ADC stops and enters a
wait state. When ADSR is set to 1 later, A/D conversion starts again.
The ADC operates similarly when ADC is started using MTU, TMR, or an external
trigger input.
6.4.2
10-Bit A/D Converter
The RX62N has two 10-bit A/D converters (Units 0 and 1). Each unit can convert up to
four analog input channels. Channels AN0 to AN3 are considered as unit 0 and channels
AN4 to AN7 are considered as unit 1.
Like the 12-bit ADC, 10-bit ADC registers are also presented as structures and unions
for easy manipulation, just like the ports, in the ‘iodefine_RX62N.h’file. The registers can
be accessed using the syntax AD.REGISTER.WORD to set up an entire register or
AD.REGISTER.BIT.BIT_NAME to set up a particular bit of a register.
Registers
A/D Data Register (ADDRn) (n ⴝ A to D)
The 10-bit ADC has four Data Registers, each corresponding to the input channels of the
ADC. A/D data registers ADDRA to ADDRD are 16-bit read-only registers. They store the
A/D conversion results of channels AN0 to AN3, or AN4 to AN7. The width of the ADDRn
(16-bit) is greater than the width of the ADC output (10-bit). To avoid reading wrong data,
the output has to be aligned either to the right or left of ADDRn. This can be done using the
DPSEL bit in the A/D Placement Register (ADDPR). This will be explained a little later.
A/D Control/Status Register (ADCSR)
The Control/Status Register is used to select the input channels, start or stop A/D conversion, and enable or disable ADI interrupt.
Bus interface
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
AD0.ADSSTR
AD0.ADDPR
AD0.ADCR
AD0.ADCSR
AD0.ADDRD
Internal data bus
AD0.ADDIAGR
AVSS
AD0.ADDRC
VREFL
10-bit
D/A
AD0.ADDRB
VREFH
AD0.ADDRA
AVCC
Sucessive approximation
register
Module data bus
179
AN0
AN2
Multiplexer
1
AN1
Control circuit
2
Comparator
Sample-andhold circuit
ADI0 interrupt signal
Compare-match/input-capture A
from MTU0
AN3
Compare-match/input-capture A
from MTU0 to MTU4, and MTU6 to MTU10
Compare-match from MTU4 and MTU10
Compare-match A from TMR0
Synchronous
circuit
ADTRG0#
Internal clock
PCLK
ADCLK
PCLK/2
Clock
selection
PCLK/4
PCLK/8
Figure 6.14 Block Diagram of 10-bit ADC (Unit 0).
Value after reset:
b7
b6
b5
b4
—
ADIE
ADST
—
x
0
0
0
b3
b2
b1
b0
CH[3:0]
0
0
0
0
Figure 6.15 A/D control/status register. Source: Hardware Manual, page 1737.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The CH [3⬊0] is used to select the analog channels which have to be A/D converted. The
channels can be selected using the following table.
TABLE 6.4
Channel Selection.
b3
b2
b1
b0
CHANNEL
0
0
0
0
AN0 or AN4
0
0
0
1
AN0 and AN1 or AN4 and AN51
0
0
1
0
AN0 to AN2 or AN4 to AN6
0
0
1
1
AN0 to AN3 or AN4 to AN7
The A/D Start bit (ADST) is used to start or stop the ADC. Setting this bit to 1 starts
the ADC, and setting it to 0 stops the ADC. The A/D Scan Conversion End Interrupt Enable
(ADIE) is used to enable or disable the A/D scan conversion end interrupt (ADI). When
A/D conversion is complete, an interrupt is generated. Setting the ADIE bit to 1 enables the
interrupt and setting it to 0 disables the interrupt.
A/D Control Register (ADCR)
The Control register is used to select the type of A/D conversion mode, clock, and trigger.
b7
b6
b5
—
TRGS[2:0]
Value after reset:
0
0
b4
0
0
b3
b2
CKS[1:0]
0
0
b1
b0
MODE[1:0]
0
0
Figure 6.16 A/D control register. Source: Hardware Manual, page 1739.
Like the 12-bit ADC, the 10-bit ADC also has different modes of operation. They are Single mode, Continuous Scan mode, and One-cycle scan mode. Setting MODE [1⬊0] to 00 is
used to select Single mode, 10 to select Continuous Scan mode, and 11 to select One-cycle
mode. Setting MODE [1⬊0] to 01 is prohibited. Details of these modes are explained later.
The ADC clock can be set using the CSK [1⬊0] bits. Setting CKS [1⬊0] to 00 is used
to select PCLK/8, 01 to select PCLK/4, 10 to select PCLK/2, and 11 to select PCLK.
PCLK is the peripheral clock.
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181
The TRGS bits are used to select the type of trigger that will start the A/D conversion
process.
TABLE 6.5
Trigger Select for 10-bit ADC Unit 0.
b7
b6
b5
TRIGGER
0
0
0
Software Trigger
0
0
1
Compare-match/input-capture A from MTU0 to MTU4
0
1
0
Compare-match from TMR0
0
1
1
Trigger from ADTRG0#
1
0
0
Compare-match/input-capture A from MTU0
1
0
1
Compare-match/input-capture A from MTU06 to MTU10
1
1
0
Compare-match/input-capture A from MTU04
1
1
1
Compare-match/input-capture A from MTU10
The trigger select for Unit 1 is similar to the above table but 011 selects trigger from
ADTRG1# and 100 selects compare-match/input-capture B from MTU0.
A/D Data Placement Register (ADDPR)
The A/D output registers (ADDRn) are 16-bits wide, but the output of the ADC is 10-bits
wide. Hence the data in the Data Register has to be aligned. The A/D Data Placement Register (ADDPR) is used to align data. This register is 8 bits wide. All bits except the eighth
bit are reserved. The DPSEL bit is the eighth bit. Setting this bit to 0 aligns data to the right
(LSB), and setting it to 1 aligns data to the left (MSB).
A/D Self-Diagnostic Register (ADDIAGR)
This register is used to check if the 10-bit ADC has any defects. This register is an 8-bit
register and the lower two bits (b1 and b0) are used to set up the test voltage for fault detection. To perform fault detection, do the following:
䡲
䡲
䡲
䡲
䡲
Set up the ADC in Single mode (AD.ADCR.BIT.MODE ⫽ 00)
Enable analog input AN0 (AD.ADCSR.BIT.CH ⫽ 0000)
Set up software trigger for the ADC (AD.ADCR.TRGS ⫽ 000)
Set the test voltage by setting (AD.ADDIAGR.DIAG) using Table 6.7
Start conversion (AD.ADCSR.BIT.ADST ⫽ 1)
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
TABLE 6.6
Test Voltage Setting.
b1
b0
FUNCTION
0
0
Self-diagnostic function is off
0
1
A/D conversion of Vref ⫻ 0 voltage value is enabled
1
0
A/D conversion of Vref ⫻ 1⁄ 2 voltage value is enabled
1
1
A/D conversion of Vref ⫻ 1 voltage value is enabled
The test voltage (0V or Vref/2 or 2Vref) is A/D converted and the result is stored in ADDRA.
The result should approximately be 010 if 0V was chosen as test voltage, 102310 if Vref was
chosen, and 204610 if 2Vref was chosen. If the result does not correspond to these values
then the ADC is at fault.
Self-diagnosis takes the same time as A/D conversion for one channel.
Let us now look at an example of setting up the registers of the 10-bit ADC. It is always better to write register set up as a function.
1. void ADC_Init(){
2.
SYSTEM.MSTPCRA.BIT.MSTPA23 = 0;
3.
SYSTEM.MSTPCRA.BIT.MSTPA22 = 0;
4.
AD.ADCSR.BYTE = 0x03;
5.
AD.ADCR.BYTE = 0x0F;
6.
AD.ADDPR.BYTE = 0x00;
7.
AD.ADDIAGR.BYTE = 0x0;
8. }
The setting up of registers has been written as a function named ADC_Init() in line 1. The
10-bit ADC has been selected using the Module Stop Control Register A (lines 2 and 3). In
line 4, the Control/Status Register is set up—four channels (AN0 to AN3) have been selected
and A/D Interrupt Enable has not been enabled (b6 ⫽ 0). Next, One-Cycle Scan mode,
PCLK, and software trigger have been selected using the A/D Control Register in line 5. The
format of the Data Register has been set to right alignment using line 6. In line 7 the
A/D Self-diagnostic function has been turned off as we are not trying to detect any faults.
Operation
The 10-bit A/D converter has two operating modes: Single Mode and Scan Mode. In the
Single Mode, A/D conversion is performed on the specified single channel only once. In
the Scan mode, A/D conversion is performed sequentially on the specified channel(s) (up
to four). The Scan Mode can be further classified as the One-Cycle Scan mode and the
Continuous Scan mode. The operation of the One-Cycle scan mode is the same as the
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
183
Single-Cycle Scan mode of the 12-bit ADC and the operation of the Continuous Scan
mode is the same as the continuous Scan mode of the 12-bit ADC.
D/A Converter
The Digital to Analog converter, as the name suggests, is used to convert Digital Signals to
Analog values. A DAC can convert bits to signals only if the Nyquist condition is met. The
output of the DAC is in the form of pulses and this could cause harmonics above the
Nyquist frequency. This could be avoided by using a low-pass filter. DACs face the issue of
high output impedance and slow settling time.
DACs are used in digital devices such as iPods to play back stored music. The RX62N
has a 10-bit Digital to Analog converter. This DAC has two channels.
Module data bus
Bus Interface
Internal data bus
AVCC
DADPR
10-bit D/A
AVSS
ADCR
VREFL
DADR1
VREFH
DADR0
6.4.3
DA1
DA0
Control circuit
Figure 6.17 Block diagram of DAC. Source: Hardware Manual, page 1762.
D/A Registers
The DAC has three registers that have to be set in order to perform D/A conversion. They
are D/A Data Register, D/A Control Register, and D/A Data Placement Register.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
D/A Data Register (DADRm) (m ⴝ 0, 1)
DADR0 and DADR1 are 16-bit registers which store the digital value that has to be converted to analog. The format of the 10-bit data register can be changed by setting the
DPSEL bit (D/A Data Placement Register).
D/A Control Register (DACR)
The D/A Control register is an 8-bit register used to enable or disable D/A conversion. It is
also used to select the channel for the D/A operation.
Address: 0008 80C4h
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
DAOE1
DAOE0
DAE
—
—
—
—
—
0
0
0
0
0
0
0
0
Figure 6.18 D/A control register. Source: Hardware Manual, page 1764.
The lower five bits (b0 to b4) are reserved. The b5, b6, and b7 bits can be set
Table 6.7.
D/A Data Placement Register (DADPR)
The format of the D/A Data Register can be set using this register. This is an 8-bit register.
All bits except the eighth bit are reserved. The eighth bit is the Data Placement Selection
bit (DPSEL). Setting DPSEL to 0 aligns the D/A Data Register to the right (LSB), and setting it to 1 aligns the D/A Data Register to the left (MSB).
Operation
The RX62N has two circuits for D/A conversion and they can operate independently. To
perform D/A conversion:
䡲
䡲
䡲
Port 0 pin 5 or Port 0 pin 3 has to be set up as the output port (PORT0.DDR.BIT.
B3 ⫽ 1) and disable ICR (PORT0.ICR.BIT.B3 ⫽ 0) for channel 0 (DA0) and
PORT0.DDR.BIT.B5 ⫽ 1 and PORT0.ICR.BIT.B5 ⫽ 0 for channel 1 (DA1).
The value to be converted has to written into the D/A Data Register.
DAOEn bit (n ⫽ 0 or 1) in DACR has to be set to 1.
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
TABLE 6.7
BIT
SYMBOL
b4 to b0
—
b5
DAE*1
185
Setting of DACR.
BIT NAME
DESCRIPTION
(Reserved)
These bits are read as 1. The write value should
always be 1.
D/A Enable
0: D/A conversion is independently controlled
on channels 0 and 1.
1: D/A conversion on channels 0 and 1 is
controlled as a single whole.
b6
DAOE0
D/A Output Enable 0
0: Analog output of channel 0 (DA0) is disabled.
1: D/A conversion of channel 0 is enabled.
Analog output of channel 0 (DA0) is enabled.*2
b7
DAOE1
D/A Output Enable 1
0: Analog output of channel 1 (DA1) is disabled.
1: D/A conversion of channel 1 is enabled.
Analog output of channel 1 (DA1) is enabled.*2
Source: Hardware Manual, page 1764.
If a new value is written to DADRn (n ⫽ 0 or 1), conversion takes place again. Conversion
takes place until DAOEn bit (n ⫽ 0 or 1) is cleared.
Analog value ⫽
Write to
DADR0
DADR0
Setting value of DADRn
⫻ Vrefh
1024
Write to
DACR
Write to
DADR0
Conversion data (1)
Write to
DACR
Conversion data (2)
DACR.DAOE0
High-impedance state
Conversion
result (2)
Conversion result
(1)
DA0
tDCONV
tDCONV
[Legend]
tDCONV: D/A conversion time
Figure 6.19 Operation of DAC. Source: Hardware Manual, page 1766.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
6.5
ADVANCED EXAMPLES
6.5.1
12-Bit ADC
Let us consider the example of a simple 12-bit ADC. A DC voltage supply of 3 V is converted to its corresponding digital code and displayed on the LCD. To perform this SingleCycle Scan mode an AN0 will be used. Software trigger will be used to start the ADC.
1.
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28.
29.
30.
31.
32.
33.
34.
#include “iodefine_RX62N.h”
#include <stdlib.h>
#include <stdio.h>
#include “src\Glyph\Glyph.h”
#define LCD_LINE1 0
#define LCD_LINE2 1
#define LCD_LINE3 2
#define LCD_LINE4 3
void ADC_Init(void);
void BSP_Display_String(int8_t, char *);
T_glyphHandle G_lcd;
void main(void){
unsigned short ADC_out;
int i = 0;
char ADC_OUT [13 ];
PORT4.DDR.BIT.B0 = 0;
PORT4.ICR.BIT.B0 = 1;
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
GlyphNormalScreen(G_lcd);
GlyphSetFont(G_lcd, GLYPH_FONT_6_BY_13);
GlyphClearScreen(G_lcd);
BSP_Display_String(LCD_LINE1,“12-bit ADC”);
ADC_Init();
while(1){
if(S12AD.ADCSR.BIT.ADST == 0 && i == 0){
ADC_out = S12AD.ADDRA & 0X0FFF;
sprintf (ADC_OUT,“%d”,ADC_out);
BSP_Display_String(LCD_LINE2,ADC_OUT);
i++;
}
}
}
GlyphClose(&G_lcd);
}
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
187
void ADC_Init(){
SYSTEM.MSTPCRA.BIT.MSTPA17 = 0;
S12AD.ADCSR.BYTE = 0x0C;
S12AD.ADANS.WORD = 0x01;
S12AD.ADCER.BIT.ACE = 1;
S12AD.ADCER.BIT.ADRFMT = 0;
S12AD.ADSTRGR.BIT.ADSTRS = 0x0;
S12AD.ADCSR.BIT.ADST = 1;
}
void BSP_Display_String(int8_t aLine, char * aText){
int8_t y = aLine * 16;
GlyphEraseBlock(G_lcd, 0, y, 95, y + 15);
GlyphSetXY(G_lcd, 0, y);
GlyphString(G_lcd, (uint8_t *)aText, strlen(aText));
}
The iodefine_RX62N.h in line 1 defines the ports and the ADC registers which need to be
set for the ADC operation. Hence it should be included in the program. Line 2 and line 3 are
used to include standard C libraries. The src\Glyph\Glyph.h header file in line 4 is included
to enable the LCD display. The start of the LCD lines has been set up as macros in lines 5 to
8. G_lcd is a variable of type T_glyphHandle (line 11) used to open the graphic LCD.
In lines 9 and 10, the functions ADC_Init and BSP_Display_String have been prototyped. The ADC_Init() function (lines 35 to 43) is used to set up the registers for the
Single-Cycle Scan mode on AN0 and use a software trigger to start the ADC. The Module
Stop Control Register A (MSTPCRA) is set such that the 12-bit ADC is selected (line 36).
The A/D Control register (ADCSR) is set for software trigger, PCLK, and Single-cycle
scan mode (line 37). Channel AN0 is selected and the A/D Channel Select register
(ADANS) is set accordingly (line 38). Automatic clearing of the data registers and rightalignment of the data register has been selected (lines 39 and 40). The A/D Start Trigger
Select register (ADSTRGR) is set for the software trigger (line 41). The 12-bit ADC is then
started (line 42). The BSP_Display_String() function is used to display strings on the specified line of the LCD.
In the main program, three variables have been used: ADC_out, ADC_OUT, and i.
ADC_out declared in line 13 is used to get the ADC value from the data register.
ADC_OUT declared in line 15, is a string which contains the ADC_out in string form so
that it can be displayed on the LCD. The variable i, declared in line 14, is used to print the
A/D value once on the LCD.
Next, the Port 4 pin 0 (AN0) is set up as an input pin (lines 16 and 17). The LCD is then
set up and the string ‘12-bit ADC’ is made to display on the LCD (lines 18 to 22). ADC_Init()
function is called to initialize the ADC registers and start the conversion (line 23).
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
After conversion is complete, the ADST bit of the ADCSR gets cleared to 0. This condition is checked (line 25) and the next few lines are executed only once using the variable
‘i.’ If conversion is complete, the A/D converted value is written to the variable ADC_out
(line 26). The Data Register was set to be right aligned. Hence to avoid reading wrong bits,
the value 0X0FFF is used to mask the upper four bits (using zeros) and read the lower
twelve bits (right bits). ADC_out is then converted into a string ADC_OUT (line 27) and
displayed on the LCD (line 28).
Output
When a 3 V input was given to channel AN0, the A/D conversion result displayed was
3728. Using the formula, the A/D value is 3723.
6.5.2
10-Bit ADC
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3.
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10.
11.
12.
13.
14.
15.
16.
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19.
20.
21.
22.
23.
#include “iodefine_RX62N.h”
#include <stdlib.h>
#include <stdio.h>
#include “src\Glyph\Glyph.h”
#define LCD_LINE1 0
#define LCD_LINE2 1
#define LCD_LINE3 2
#define LCD_LINE4 3
void ADC_Init(void);
void BSP_Display_String(int8_t, char * );
T_glyphHandle G_lcd;
void main(void){
unsigned short ADC_value;
int i = 0;
char ADC_OUT [13 ];
PORT4.DDR.BIT.B0 = 0;
PORT4.ICR.BIT.B0 = 1;
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
GlyphNormalScreen(G_lcd);
GlyphSetFont(G_lcd, GLYPH_FONT_6_BY_13);
GlyphClearScreen(G_lcd);
BSP_Display_String(LCD_LINE1,“12-bit ADC”);
ADC_Init();
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
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25.
26.
27.
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29.
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36.
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38.
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42.
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44.
45.
46.
47.
48.
189
while(1){
if(AD0.ADCSR.BIT.ADST == 0 && i == 0){
ADC_value = AD0.ADDRA & 0x0FFF;
sprintf (ADC_OUT,“%d”,ADC_value);
BSP_Display_String(LCD_LINE2,ADC_OUT);
i++;
}
}
}
GlyphClose(&G_lcd);
}
void ADC_Init(){
SYSTEM.MSTPCRA.BIT.MSTPA23 = 0;
AD0.ADCSR.BYTE = 0x00;
AD0.ADCR.BYTE = 0x0C;
AD0.ADDPR.BYTE = 0x00;
AD0.ADDIAGR.BYTE = 0x0;
AD0.ADCSR.BIT.ADST = 1;
}
void BSP_Display_String(int8_t aLine, char * aText){
int8_t y = aLine * 16;
GlyphEraseBlock(G_lcd, 0, y, 95, y + 15);
GlyphSetXY(G_lcd, 0, y);
GlyphString(G_lcd, (uint8_t *)aText, strlen(aText));
}
The iodefine_RX62N.h in line 1 defines the ports and the ADC registers which need to be set
for the ADC operation. Hence it should be included in the program. Line 2 and line 3 are used
to include standard C libraries. The src\Glyph\Glyph.h header file in (line 4) is included to
enable the LCD display. The start of the LCD lines has been set up as macros in lines 5 to 8.
G_lcd is variable of type T_glyphHandle (line 11) used to open the graphic LCD).
In lines 9 and 10, the functions ADC_Init and BSP_Display_String have been prototyped. The ADC_Init() function (lines 35 to 42) is used to set up the registers for Single
mode on AN0 (unit 0) and use a software trigger to start the ADC. The Module Stop Control Register A (MSTPCRA) is set such that Unit 0 of 10-bit ADC is selected (line 36). The
A/D Control register (ADCSR) is used to select Channel 0 (AN0) and disable A/D end interrupt (line 37).The A/D Control Register (ADCR) is used to select Single mode, PCLK
and software trigger (line 38). The Data Placement register (ADDPR) is used to select right
alignment (line 39).The Self-Diagnostic function is set to off by default and it need not be
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
set explicitly if the Self-Diagnostic function is not going to be used. The ADC is then
started (line 42). The BSP_Display_String() function is used to display strings on the specified line of the LCD.
In the main program three variables have been used: ADC_value, ADC_OUT, and i.
ADC_value declared in line 13 is used to get the ADC value from the data register.
ADC_OUT declared in line 15, is a string which contains the ADC_value in string form so
that it can be displayed on the LCD. The variable i, declared in line 14, is used to print the
A/D value once on the LCD.
Next, the Port 4 pin 0 (AN0) is set up as an input pin (lines 16 and 17). The LCD is then
set up and the string ‘10-bit ADC’ is made to display on the LCD (lines 18 to 22). ADC_Init()
function is called to initialize the ADC registers and start the conversion (line 23).
After conversion is complete, the ADST bit of the ADCSR gets cleared to 0. This condition is checked (line 25) and the next few lines are executed only once using the variable
‘i.’ If conversion is complete, the A/D converted value is written to the variable ADC_value
(line 26). The Data Register was set to be right aligned. Hence, to avoid reading wrong bits,
the value 0X0FFF is used to mask the upper four bits (using zeros) and read the lower
twelve bits (right bits). ADC_value is then converted into a string ADC_OUT (line 27) and
displayed on the LCD (line 28).
Output
When a 3 V input was given to channel AN0, the A/D conversion result displayed was
1007. Using the formula, the A/D value is 930.
6.5.3
DAC
To understand how to program DACs let us look at an example in which DAC unit1 has
been used.
1.
2.
3.
4.
5.
6.
7.
8.
9.
#include “iodefine_RX62N.h”
#include <stdlib.h>
#include <stdio.h>
#include “src\Glyph\Glyph.h”
void DAC_Init(void);
T_glyphHandle G_lcd;
void main(void){
PORT0.DDR.BIT.B5 = 1;
PORT0.ICR.BIT.B5 = 0;
CHAPTER 6 / CONVERTING BETWEEN THE ANALOG AND DIGITAL DOMAINS
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191
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
GlyphNormalScreen(G_lcd);
GlyphSetFont(G_lcd, GLYPH_FONT_6_BY_13);
GlyphClearScreen(G_lcd);
BSP_Display_String(LCD_LINE1,“DAC”);
DAC_Init();
while(1){}
}
GlyphClose(&G_lcd);
}
void DAC_Init(){
SYSTEM.MSTPCRA.BIT.MSTPA19 = 0;
DA.DADR1 = 102;
DA.DACR.BYTE = 0x9F;
}
void BSP_Display_String(int8_t aLine, char * aText){
int8_t y = aLine * 16;
GlyphEraseBlock(G_lcd, 0, y, 95, y + 15);
GlyphSetXY(G_lcd, 0, y);
GlyphString(G_lcd, (uint8_t *)aText, strlen(aText));
}
Programming the DAC also requires the same header files as the ADC example. The output of DAC1 can be observed on DA1, which is port 0 pin 5. This pin is set up as an output
pin to observe the result (lines 8 and 9). The DAC has been set up using the DAC_Init()
function (line 15). In the DAC_Init() function, the DAC unit is started up by setting
SYSTEM.MSTPCRA.BIT.MSTPA19 to 0 (line 21). The digital value that has to be converted to
analog value is set using DA.DADR1 (line 22), and DAC unit 1 has been selected by setting
DA.DACR.BYTE = 0x9F.
Thus the DAC can be programmed and the analog value can be observed from
port 0 pin 5 using a multimeter.
6.6
RECAP
Thus we have seen how the ADC and DAC of the RX62N board can be programmed. The
methods discussed above have been using polling. Polling is not very efficient. An efficient
method of using these features would be using interrupts. Interrupts are discussed in detail
in Chapter 9.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
6.7
REFERENCES
Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
RX62N Quick Start Guide. Renesas Electronics America, Inc., 2010. Computer Disc.
RX Family C/C⫹⫹ Compiler, Assembler, Optimizing Linkage Editor; Compiler Package User’s manual.
Renesas Electronics America, Inc., 2010. Print.
6.8
EXERCISES
1. What is the output code (in decimal) of a 12-bit ADC with Vin ⫽ 2.7 V? V⫹ref ⫽ 5 V?
V⫺ref ⫽ ⫺5 V?
2. What is the output code (in decimal) of a 10-bit ADC with Vin ⫽ 3 V? V⫹ref ⫽ 5 V?
V⫺ref ⫽ 0 V?
3. Given the following information of a particular analog to digital converter, deter-
4.
5.
6.
7.
8.
mine the value of the digitally represented voltage and the step size of the converter:
䡲 The device is 10-bit ADC with a V⫹ref —reference voltage of 3.3 volts and a
V⫺ref reference voltage of 0 volts.
䡲 The digital representation is: 0100110010.
What is the maximum quantization error for a 10-bit ADC with V⫹ref ⫽ 3.3 V,
V⫺ref ⫽ 0 V?
Write a simple subroutine to set up the ADC registers for a 12-bit ADC operation
of the following specifications: continuous scan mode, software triggered,
PCLK/4, and Channel AN3.
Identify the modifications to be made if the above problem works on the value addition mode (3—time conversion).
Write a subroutine to set up the registers for a 10-bit ADC operation of the following specifications: continuous scan mode on channels AN1 and AN2, software
triggered, PCLK/2, and data aligned to the LSB end.
Write a program to display the percentage of light intensity given a light sensor
circuit. Record the ‘darkness’ (cover the sensor to make it dark) and ‘brightness’
(shine a bright LED or other light on the sensor) values. Identify the correct calibration such that the average room light lies between these values.
Chapter Seven
Serial Communications
7.1
LEARNING OBJECTIVES
Microcontrollers often need to communicate with other devices. Sending information serially (rather than in parallel) reduces the number of signal connections needed, saving space
and cost. This chapter introduces how microcontrollers can exchange information serially
using the UART, SPI, and I2C communication controllers.
7.2
BASIC CONCEPTS OF SERIAL COMMUNICATIONS
Communication is the exchange of information between entities. In computers, information can be of any form which can be represented in a digital form. The medium of communication is electrical signals that vary continuously between high and low. The patterns
in which they vary follow a set of rules that dictate the information the two entities want to
exchange. Also these signals can be communicated one at a time, or as we are familiar with
by now, bit by bit; or all at the same time on a single set of wires. The former is called serial communication wherein the information/data is sent one bit at a time, and the latter is
called parallel communication where more than a single bit of data is shifted out at the
same time from one side of the communication channel. Also there can be information
channels where both ends can send as well as receive information at the same time. Such
channels are called full duplex channels.
Parallel communication is primarily used when there is a need to transfer data at a very
high speed over short distances, such as inside a computer from one peripheral to another.
In such cases, the data and its delivery is of utmost importance. Parallel forms of communication are usually implemented using a bus. You may already be familiar with commonly
used terms when talking about computer peripherals such as the IDE bus or the PCI bus.
A fact to note is that these are low capacitance wires bundled together to form the bus and
are usually not extremely long. Among other factors which affect the choice of parallel or
serial communication are: the PCB board space, number of I/O pins, density, capacitance,
signal integrity, and optical/electrical.
Serial communication, on the other hand, is a preferred medium when data is to be
transferred over long distances. This may include a range of a couple hundred feet, from
193
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
one building to another, or one computer to another. Serial communication is usually much
slower than parallel. However, with the advent of time and technology, serial busses are becoming more and more high speed and are now also being used for short distances; i.e., internal communication mechanisms of computers.
In this chapter, we will primarily deal with serial communication only to establish data
transfer between the Renesas microcontroller and a PC or other microcontroller boards or
devices using various protocols such as USART, SPI, and I2C. It should be noted that there
are other protocols beyond these that are also available with the RX62N; however, they require implementation using complex techniques. As you go through this chapter you will
learn:
䡲
䡲
䡲
The basics of each technique for serial communication, through polling; since
polling is the best way to understand the exact details of the working of the peripheral device.
The practical working of each technique through guided and intricately explained
examples.
How to distinguish between the implementation of each technique and the overheads of communication along with necessary precautions.
Before we jump into understanding the working of each serial communication interfacing
technique, it is necessary to understanding the terminologies that are used while talking
about serial communication, and also understand the need for communication. So why
would we need communication between different peripherals? A few examples are mentioned below:
䡲
䡲
䡲
䡲
Parallel Computation: In these cases, a complex problem is broken down into
smaller, less complex parts and is distributed to other computers on a network,
solved and then returned back to the source. The result is a reduction in the time
taken to solve the problem, full use of available resources, etc.
Data acquisition from remote locations: This is prominent in industrial applications where there are sensors deployed in the field or inside a factory. The sensors
continuously gather data and send it to a central controller which monitors them
and controls the overall system.
Control of remote devices such as smart transducers.
Developing fault tolerant systems.
Terminologies
Serial Port: A communication junction that provides for connecting a cable responsible
for conducting electrical signals between the communicating entities, usually a 9 pin DBI
male/female header.
CHAPTER 7 / SERIAL COMMUNICATIONS
195
Bus: One or more wires shared between devices in order to communicate electrical
signals.
Baud Rate: Number of symbols transferred per second. A symbol may represent one or
more bits of data through its encoding.
Bit Rate: Number of bits of information transferred per second.
Start Bit: Initial bit sent on the communication channel before communication begins.
Stop Bit: Final bit sent on the communication channel before communication terminates.
Parity Bit: A bit included in the communicated data whose status determines the parity
(even/odd) of the information/data byte transferred.
Simplex Communication: A communication channel that can perform communication in
only one direction, for example, family radios and walkie-talkies.
Full Duplex Communication: A communication channel is considered to be full duplex
if both entities at the end of the channel can communicate in both directions simultaneously; i.e., transmit and receive data.
Half Duplex Communication: A communication channel/port is said to be half duplex if
it can either transmit or receive data at an instant of time, but not simultaneously.
Synchronous: A clock signal accompanies the data being transmitted on a separate line
thereby synchronizing the two end processors. Examples of such buses are HDMI and DVI
for video signals.
Asynchronous: A clock signal does not accompany the data being transmitted. Instead an
internal clock is maintained on both ends of the communicating modules to assist in synchronizing the data transfer. Typical PC serial port communications devices are an example of such transfers.
Now that we are familiar with some of the terms and needs of serial communication, we
are ready to learn a few of the different interfaces available with the RX62N in detail.
Section 7.2 will introduce basic concepts applicable to each serial communication interface.
Section 7.3 will demonstrate the concepts of Section 7.2 by providing an example for each
interface. Section 7.4 will describe advanced concepts of serial communication and Section
7.5 will demonstrate them with more complex examples.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
7.2.1
Introduction to the RX62N Serial Communication Interfacing
In order to fulfill the previously mentioned needs for communication between the processor and its desired peripherals or other devices, the RX62N has been provided with various
mechanisms. These include the serial communication interface (SCI), Renesas serial peripheral interface (RSPI), and the Renesas Inter Integrated Chip (RIIC) bus interface. All
three interfaces perform the same task of communicating data between various entities serially; i.e., one bit every cycle, however, the manner in which they do so is different for
each interface. Depending upon the different requirements of communication, such as
speed, number of devices needed to connect to, or topography of the communication, you
may choose between the three different interfaces as desired. The three interfaces along
with their features are described in the following:
Serial Communication Interface (SCI): This interface provides for one of the oldest
and most fundamental methods in serial communication, the Universal Synchronous/
Asynchronous Receiver/Transmitter (USART). The RX62N microcontroller has a total of
six of these interfaces available which support USART communication as well as provide
an interface to smart cards. The SCI has a variable transfer speed due to the availability of
an on chip bit-rate generator and can transfer data with either the MSB or LSB leading the
communication. It also provides for multi-processor communication functions. Other
available functions include data length selection (i.e., 7 or 8 bits), number of stop bits, parity selection, clock source selection, receive error detection, and break detection. Details of
the SCI are further discussed in Section 7.2.2.
Serial Peripheral Interface (RSPI): The Renesas SPI is a means for high-speed synchronous data transfer between the microcontroller and other connected serial peripherals, such as an SD card or other Renesas microcontrollers. The RSPI provides two channels for serial transfer. Each channel has either 3 or 4 pins; i.e., MISO, MOSI, SPCK,
and SSL depending upon the mode of operation. The RSPI also has interchangeable
data formats with which one can transmit either the LSB or MSB at the start of communication. The RSPI is also capable of handling data as either a master or slave. These
shall be further discussed in Section 7.2.3. The number of bits transferred by the RSPI
can be varied between eight to thirty-two bits. The RSPI operates through the means of
a double buffer for both transmission and reception; each of which is 128-bits long,
thereby permitting storage of four 32-bit long frames.
I2C Bus Interface (RIIC): The RIIC is a simple, powerful, and flexible serial transmission method that generally operates using only two wires with a well-defined protocol. The
RIIC provides for two channels with variable communication formats and transfer rates up
CHAPTER 7 / SERIAL COMMUNICATIONS
197
to 1 Mbps. Also a total of 128 devices may be connected on a single RIIC bus may be connected at a time with only the requirement of a pull up resistor. Details of the RIIC bus are
discussed in Section 7.2.4.
Table 7.1 provides for a comparison between the mentioned interfaces:
TABLE 7.1
Comparison Between Different Interfaces.
SERIAL
COMMUNICATION
INTERFACE
RENESAS SERIAL
PERIPHERAL
INTERFACE
RENESAS INTER
INTEGRATED
CHIP BUS
Modes
USART/Smart
Card interface
Four wire/Three
wire mode
I2C mode or SM
bus mode
Max transfer speed
1.92 Mbps with
PCLK @ 50 Mhz
Up to 25 Mbps
Up to 1Mbps
Max. number of
devices/slaves
connected per bus
Number of wires
required for
communication (not
including ground)
Max. length of wires1
Number of bits per
unit transfer
(excluding start and
stop)
Slave selection
method
1
1
2 to 3
500 ft @ 9600 bps
7 or 8
Addressed during
communication when
in multiprocessor
communication
mode, or else not
available.
8 SPI integrated
channels for slave
selection
3 to 4
10 feet with clock
speed of few kHz
Up to 32 bits
Using slave select line
127
2
10 meters @ 100 kbps
8
Through addressing
Becke et al., Comparing Bus Solutions; High-Performance Linear/Interface: An Application Report, Texas
Instruments, revised 2004. http://www.lammertbies.nl/download/ti-appl-slla067a.pdf
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
198
Now that we have an idea of some of the different available techniques of serial communication available on the Renesas board and the differences between each of them, we can
proceed to the details of operation for each interface available.
7.2.2
Universal Asynchronous Receiver and Transmitter
The UART/USART is one of the oldest mechanisms available for the serial transmission of
data. The idea of a UART was developed in order to convert parallel data into serial data to
be transmitted over large distances. This is usually done by means of a shift register which
shifts out a one bit per clock cycle. Given the premise that the shift register clocks out a one
bit per clock cycle, it requires one clock cycle to fill the shift register in parallel; and where
the clock provided to both the CPU and the shift register is the same, one can easily determine that serial transmission is at least N times slower than parallel transmission, where
N is the number of bits available in the serial register; i.e., if the size of the shift register is
eight bits, serial communication is at least eight times slower than parallel communication.
Before we jump into detailed concepts of the Renesas UART, let us look at the mechanism
of a shift register.
CLR
CLK
R
D
SERIAL
IN
R
R
Q
D
D-FLIP
FLOP
Q
D
D
D-FLIP
FLOP
D-FLIP
FLOP
Q1
R
Q
Q2
Q
D-FLIP
FLOP
Q3
SERIAL
OUT
Q4
Figure 7.1 Serial Input Parallel Output (SIPO) shift register.
If one is familiar with digital circuits, one may easily note from Figure 7.1 that a shift register is nothing but a series of cascaded flip-flops that share the same clock. The most commonly used flip-flop for shift registers is the D flip-flop where the D stands for Delayed.
More detailed information on the D flip-flop can be found in Digital Logic and Microprocessor Design with VHDL (Hwang), but in essence it is enough to know that the flipflop outputs the state of the input (D), or data, for every rising edge of the clock, and main-
CHAPTER 7 / SERIAL COMMUNICATIONS
199
tains it until the next rising edge. Depending on the configuration, there can be two types
of shift registers, Parallel In Serial Out (PISO) and Serial In Parallel Out (SIPO). A PISO
type shift register usually shifts out data serially, that is, the data is input to the shift register through a parallel bus and gets shifted out onto the serial bus in parallel, and is therefore
used on the transmitter side of the interface; whereas the SIPO type shift register takes data
in serially and converts it to parallel form, and is thus used at the receiver side of the interface. The two types of shift registers are shown in Figure 7.1 and Figure 7.2 respectively.
This is the basis of operation for the UART. More reading on the electronics part of
the flip-flops can be found at http://faculty.lasierra.edu/⬃ehwang/digitaldesign (Hwang,
Digital Logic and Microprocessor Design with VHDL).
D0
D2
D1
D3
WRITE/
SHIFT
D
Q
D
Q
D
Q
D
Q
Q
CLK
or Q
or Q
or Q
or Q
CLEAR
Figure 7.2 Parallel Input Serial Output (PISO) shift register.
Now that we are aware of the basic mechanism of UART serial communication, it is
worthwhile to notice that there are various other overheads to communication that are
required, such as ensuring that the data has been communicated properly and identified.
These are usually done by addition of extra bits in the communication process. Additional bits are padded to the eight bits of data, and then the data is transmitted. The additional bits padded are the START and STOP bits. When not communicating, both the
TX(transmit) and RX(receive) lines are held in the Hi-Z (high impedance) state. When
transmission/reception of data is about to occur, the line is first pulled low. This period
is called the START bit and is maintained for one clock cycle. After eight bits of data
transmission, the line is pulled high again and maintained high. This is the STOP bit
and is maintained for at least one clock cycle before the next byte of data can be communicated. In this manner data is recognized over the channel for reception. But this
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
does not yet resolve the problem of incorrect data transmission. Over distances, electrical signals have a tendency to weaken, reduce in amplitude, and also pick up noise. This
may result in data corruption. This is checked by the addition of an extra bit to the data,
also called the parity. The parity bit is set to 1 or 0 in order to make the total number of
1 bits even (for even parity) or odd (for odd parity). One more note is that all the above
mentioned transactions are performed at logic levels; i.e., voltages range from 0 to 3 V
at most 5 V. These voltages are very much susceptible to noise and signal corruption
over long distances. To prevent this, an amplifier circuit boosts and inverts the voltages
so that they vary from 15 V (logic high) to 15 V (logic low). These are the voltage
levels for the telecommunications Recommended Standard 232(RS-232). A level-shifting
inverter circuit converts the RS232 voltages back to logic levels at each receiver. More
information regarding the RS-232 standard can be found in “EIA Standard RS-232-C
Interface between Data Terminal Equipment and Data Communication Equipment Employing Serial Data Interchange” (Electronic Industries Association). This concludes
the basic working mechanism of the UART. Now we come to the control part of the
UART, which is essentially done by means of a few special function registers (SFRs)
that are linked to the serial communications interface available with the Renesas Microcontroller.
Registers Related to the SCI in UART Mode
The Serial Communications Interface provides for a Universal Synchronous Transmitter/
Receiver, a Universal Asynchronous Transmitter/Receiver, and a Smart Card interface. The
Renesas Microcontroller has six serial communication interfaces, which can provide for
the previously mentioned three communication methods. However, before one can use the
SCI it needs to be properly configured to work in one of the three modes. We shall be configuring the SCI to work as a UART, and therefore we would be talking about the special
function registers and the values to be injected into them to make the UART work successfully. Finally, we will discuss how to test the configured UART and the physical variations
possible to the communication signals.
The special function registers related to the UART are:
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Serial Mode Register (SMR)
Bit Rate Register (BRR)
Serial Control Register (SCR)
Transmit Data Register (TDR)
Serial Status Register (SSR)
Receive Data Register (RDR)
Smart Card Mode Register (SCMR)
Serial Extended Mode Register (SEMR)
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201
Smart Card Mode Register (SCIx.SCMR): This is the register that selects whether the
SCI is going to be in either the Smart Card Interface mode or act as a UART or USART. It
has four bits that need to be assigned values. However, since we are only concerned with
setting up the SCI as a UART, the only bit we need to be concerned with is the SMIF bit.
Setting this bit to 1 causes the particular SCI to enter smart card interface mode else the
SCI can behave as either a Synchronous or Asynchronous transmitter/receiver. Hence we
always set it to 0.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
BCP2
—
—
—
SDIR
SINV
—
SMIF
1
1
1
1
0
0
1
0
Figure 7.3 The SCI Smart card mode register.
Source: Hardware Manual, Renesas 32-Bit Microcom-
puter, RX Family/RX600 Series, Renesas Electronics America, Inc., 2010, page 1418.
Serial Mode Register (SCIX.SMR)
This special function register is concerned with operational variations of the UART. The
register details are as follows:
Value after reset:
b7
b6
b5
b4
b3
b2
CM
CHR
PE
PM
STOP
MP
0
0
0
0
0
0
b1
b0
CKS[1:0]
0
0
Figure 7.4 The SCI Serial mode register. Source: Hardware Manual, page 1405.
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Clock speed applied to the shift register: The clock applied to the Shift Register
which is related to the TDR is the PCLK. The frequency of this clock can be reduced by means of a frequency divider. This is selectable by the CKS1 and
CKS0 bits which give combinations to divide the PCLK frequency by 1, 4, 16, or
64. Refer to Table 7.2 for details. These bits usually depend upon the acceptable
baud rate error and the value of the BRR register.
Whether the communication line is concerned with multiprocessor communication: Setting the Multiprocessor mode bit MP in the SMR causes the UART to become aware of multiprocessor communication taking place on the channel. If one
is not using multiprocessor communication, this bit is set to 0.
Multiprocessor mode (or 9 bit wake-up mode, or multidrop mode) was a very
common way of placing more than one slave on an UART bus or giving it multidrop capability. In these systems when the ninth bit was set as a high this indicated
that the remaining eight bits were the address of the device that the Master wanted
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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to communicate with. All devices processed the address field. Only the device with
the corresponding address continued to communicate, all other devices went back
to “sleep” waiting for the next address command. In most devices that support MP
the UART peripheral will create an interrupt when the ninth bit is high. This allows
the devices that are not actively communicating with the Master to ignore all other
traffic on the bus, reducing the overhead on those MCUs.
Stop bit length: STOP determines the length of the Stop bit, whether it is either one
or two bits wide. Setting this bit to 0 selects length of stop bit as 1 whereas setting
it to 1 causes the length of stop bit to be 2 bits wide.
Parity mode: Setting this bit to 1 causes the parity bit to be high when the parity of
the data is odd; whereas, setting this bit to 0 causes the parity bit to be high if the
parity of the data is even.
Parity enable: Setting the PE bit to 1 enables the transmission of the parity bit and
disables otherwise.
Length of data being transmitted: Setting the CHR bit to 1 truncates the size of the
data being transmitted to seven bits, or else 8-bit long data is transmitted.
Communications mode: The CM bit determines the operation of the SCI, whether
it is operating in synchronous or asynchronous mode. If this bit is set to 1, the interfaces act in the Clock synchronous mode, or else it enters the Clock asynchronous mode. If operating in the Clock synchronous mode, a clock signal can be
generated on the SCLK line by the transmitter which also acts as the clock input to
the shift register on the receiver end of the module. Selection whether the clock is
input or output is dependent on the state of the CKE bit in register SCIx.SCR.
Serial Control Register (SCIx.SCR)
This register is responsible for controlling the Serial Communications Interface; whether it
is turned on or off, the choice of input clock to the shift register, and function of the SCK
pin. The register details are as follows:
Value after reset:
b7
b6
b5
b4
b3
b2
TIE
RIE
TE
RE
MPIE
TEIE
0
0
0
0
0
0
b1
b0
CKE[1:0]
0
0
Figure 7.5 The SCI serial control register. Source: Hardware Manual, page 1409.
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Clock Enable bits (CKE 0, CKE 1): These bits determine which clock is to be used
when transferring data, internal or external, and the function of the SCKn pin corresponding to the SCIn module. The Table 7.2 determines the functions depending on
each of the four combinations of the 2 bits when the SCI is in Asynchronous mode.
Transmit end interrupt enable: Setting this bit to 1 and 0 enables and disables the transmit end interrupt that is generated every time a byte is transmitted from the SCI.
CHAPTER 7 / SERIAL COMMUNICATIONS
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203
Multiprocessor Interrupt Enable: This bit is related to Multiprocessor communication and is usually set to 0 when there is no multiprocessor communication occurring on the bus.
Receive Enable: Setting this bit to 0 and 1 disables and enables reception of data
on the Rxn pin, respectively.
Transmit Enable: Setting this bit to 0 and 1 disables and enables transmission of
data on the Txn pin, respectively.
Receive Interrupt Enable: Setting this bit to 1 and 0 enables and disables the generation of a receive interrupt, respectively.
Transmit Interrupt Enable: Setting this bit to 1 and 0 enables and disables the generation of a transmit interrupt, respectively.
Serial Status Register (SCIx.SSR)
This is a read only type of register (except for bit 0) which determines the condition of the
currently received byte over the corresponding SCI by means of various flag bits.
b7
TDRE
Value after reset:
1
b6
b5
RDRF ORER
1
1
b4
b3
b2
b1
b0
FER
PER
TEND
MPB
MPBT
1
1
1
1
1
Figure 7.6 The SCI serial status register. Source: Hardware Manual, page 1411.
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Multiprocessor bit transfer: This bit sets the value of the multiprocessor bit for
adding to the transmission frame
Multiprocessor bit (received): This bit holds the value of the multiprocessor bit in
the received frame. Note that the value of this bit does not change when RE bit in
SCR is kept as 0. This is a read only type bit.
Transmit End Flag: This flag is set at the end of transmission of a byte from the
TDR or in case the serial transmission is disabled. Resetting this flag requires one
to write data to the TDR.
Parity Error Flag: This bit indicates a parity error has occurred during reception in
asynchronous mode and reception ends abnormally. When a parity error occurs,
data is maintained in the RDR and the parity error flag is set but subsequent reception in terminated until PER is reset
Error signal status flag: This flag is set when a low error signal and reset after
clearing to 0 manually
Overrun Error Flag: This flag is set if data is received in RDR before the previous
data has been read. The flag is cleared when 0 is written to it.
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
204
Bit Rate Register (SCIx.BRR)
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
1
1
1
1
1
1
1
1
Figure 7.7 The SCI bit rate register. Source: Hardware Manual, page 1419.
This is the register that controls the generation of the clock signal to be provided to the
shift registers. Table 7.2 shows the relation between the value N input into the BRR and the
bit rate B for normal asynchronous mode. In asynchronous mode, one should note that
there is always a minor difference in timings between the two processors involved in communication, due to the minor differences in parts (oscillator circuits). The actual bit rate
may not exactly meet the desired rate because only rates which can be generated by dividing PCLK by multiples of 16 are possible. Therefore, an error in communication, such as
loss of reception of a bit, may occur if the bit rate mismatch (error) between the transmitter and receiver is too large. Table 7.2 defines a few standard values of BRR along with the
generated bit rate’s percentage error for each case.
TABLE 7.2 Bit Rates and Percent Errors
(N BRR value, n Clock source setting with CKS bits in SMR).
OPERATING FREQUENCY PCLK (MHZ)
25
BIT
RATE
(bit/s)
n
110
30
N
ERROR
(%)
n
N
3
110
0.02
3
150
3
80
0.47
300
2
162
600
2
1200
33
ERROR
(%)
n
N
132
0.13
3
3
97
0.35
0.15
2
194
80
0.47
2
1
162
0.15
2400
1
80
4800
0
9600
50
ERROR
(%)
n
N
ERROR
(%)
145
0.33
3
221
0.02
3
106
0.39
3
162
0.15
0.16
2
214
0.07
3
80
0.47
97
0.35
2
106
0.39
2
162
0.15
1
194
0.16
1
214
0.07
2
80
0.47
0.47
1
97
0.35
1
106
0.39
1
162
0.15
162
0.15
0
194
0.16
0
214
0.07
1
80
0.47
0
80
0.47
0
97
0.35
0
106
0.39
1
40
0.77
19200
0
40
0.76
0
48
0.35
0
53
0.54
0
80
0.47
31250
0
24
0.00
0
29
0.00
0
32
0
0
49
0.00
38400
0
19
1.73
0
23
1.73
0
26
0.54
0
40
0.77
CHAPTER 7 / SERIAL COMMUNICATIONS
205
Transmit Data Register (SCIx.TDR)
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
1
1
1
1
1
1
1
1
Figure 7.8 The SCI transmit data register. Source: Hardware Manual, page 1404.
This register contains the data to be transmitted over the communication channel. The data
is usually eight bits long and is padded with the start, stop, and parity bits. The TDR acts as
a buffer to the transmit shift register which is the actual register responsible for shifting out
the data serially on to the transmit pin.
Receive Data Register (SCIx.RDR)
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
1
1
1
1
1
1
1
1
Figure 7.9 The SCI receive data register. Source: Hardware Manual, page 1404.
This register contains the data received over the communication channel. The data is usually eight bits long and is stripped off the start, stop, and parity bits.
Variations to the UART
Before we move on to other techniques of serial communication, it is worthwhile to mention that there are other UART-based communication standards which use different types
of voltage signaling, such as the RS-422, RS-423, RS-449, and RS-485. More readings on
these can be found at http://focus.ti.com/lit/an/slla070d/slla070d.pdf (Soltero et al.).
7.2.3
Renesas Serial Peripheral Interface
Serial Peripheral Interface (SPI) uses synchronous communication, so a dedicated clock signal must be transmitted in addition to the serial data. Providing this clock signal lets us simplify the hardware down to just the shift registers and some minor supporting logic. This is
much simpler than the USART, as there is no need for a bit rate generator, start and stop bits,
206
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
and other modules. The dedicated clock signal determines the bit rate. This interface is similar to the USART. SPI is a full duplex mode of communication in which data can be transmitted and received simultaneously. The SPI was designed by Motorola to achieve high
speed data transfer between peripherals of a microcontroller, and generally requires three
wires for communication. In case multiple slave devices (devices to communicate with) are
attached on the SPI bus, additional lines for selecting the device are required. However if not
more than one slave device is connected on the bus, communication may be performed with
only three wires. A typical SPI set up between a microcontroller and a peripheral is shown in
Figure 7.10. As seen in the figure, the devices connected on the SPI bus usually have one
master and one or more slave peripherals. However a multi-master mode may also be used.
Master devices are usually microcontrollers or processors that control the flow of data to and
from the slave peripheral device. The four required lines for communication are Serial Clock
(SCLK), Master In Slave Out (MISO), Master Out Slave In (MOSI), and Slave Select (SSL).
This LSI (master)
RSPCK
MOSI
MISO
SSL0
SSL1
SSL2
SSL3
RSPI slave 0
RSPCK
MOSI
MISO
SSL
RSPI slave 1
RSPCK
MOSI
MISO
SSL
RSPI slave 2
RSPCK
MOSI
MISO
SSL
RSPI slave 3
RSPCK
MOSI
MISO
SSL
Figure 7.10 Serial Peripheral Interface bus; Single master with multiple slaves connected.
Source: Hardware Manual, page 1664.
CHAPTER 7 / SERIAL COMMUNICATIONS
207
Serial Clock: Accompanying each data transfer is a clock signal that synchronizes the
Master and Slave device. The length of the clock signal also determines the amount of data
transferred on the MISO and MOSI pins. The serial clock is always generated by the master device and the slave synchronizes itself and the data transfer using the same clock.
Master Out Slave In: This line is similar to the transmit line of the USART, provided the
Master device remains the same.
Master In Slave Out: This line is similar to the receive line of the USART, provided the
Master device remains the same.
Slave Select: This pin, when acting as an output pin, provides for an active low signal that
activates or de-activates the slave. The slave is usually in sleep mode until this line is toggled to the desired state (low or high) for activating the device. When in multi master
mode, this pin acts as an input, and when pulled low indicates that another master is trying
to communicate on the SPI bus.
Now that we have an introduction to the physical part of the SPI interface, it is time to
understand the working. But before we move on, it is worthwhile to note some of the features of the Renesas SPI that are different from most other microcontrollers. The Renesas
Microcontroller has two independent SPI modules with multiple (four) slave select lines
for each channel. The important features of the Renesas Serial Peripheral Interface are:
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Transmit only operation available.
Switching of phase and polarity of the serial clock.
LSB/MSB first option.
128-bit transmit/receive buffers.
Transfer bit length is selectable as 8, 9, 10, 11, 12, 13, 14, 15, 16, 20, 24, or 32 bits.
Up to four frames can be transferred in one round of transmission/reception (each
frame consisting of up to 32 bits).
Mode fault error, overrun error, and parity error detection.
A transfer of up to eight commands can be executed sequentially in looped execution with SSL signal value, bit rate, RSPCK polarity/phase, transfer data length,
LSB/MSB-first, burst, RSPCK delay, SSL negation delay, and next-access delay
which can be changed for each command.
A transfer can be initiated by simply writing to the transmit buffer.
General Working of SPI Modules
During every SPI transfer, there always exists a Master device and a slave device. The master device is the one responsible for performing the transfer of data and generating the
clock signal for performing the synchronous transfer of data. The slave device, while receiving data also sends out data of its own to the master over the MISO line. Thus full
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
duplex communication occurs. The slave is active only when the master pulls the corresponding Slave Select Line low. This results in a “chip select” and activates the slave
device.
Events take place in this sequence:
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Master selects slave by pulling SSL low, thereby activating the slave device for
communicating data.
Master starts synchronous transfer of data by sending out a clock signal over the
SCLK pin and the data over the MOSI line. The master waits until the data transfer completes.
On reception of the serial clock signal from the master, the slave device starts outputting data that it might want to transfer to the master.
Data transfer halts as soon as the clock signal stops.
Master deselects the slave by pulling the SSL line high.
Configurations of the Renesas SPI
The Renesas microcontroller SPI bus can be configured to have:
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Single Master Single Slave
Single Master Multiple Slaves
Multiple Masters Multiple Slaves
For the sake of simplicity, and understanding the basics of SPI, we shall consider only the Single Master Single Slave configuration. These configurations are shown in Figures 7.11 to 7.13.
Registers Related to the Renesas Serial Peripheral Interface
The following describes the registers that are responsible for control of the RSPI with a
short explanation, and the values to be assigned to each bit for setting up the SPI in the single master single slave configuration with the RX62N functioning as the master device.
Serial Peripheral Control Register (SPCR): This register controls the operating mode
of the RSPI. The functions of the bits are as follows:
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SPMS: This is the RSPI mode select bit which determines whether the SPI will act
as a three wire (SCLK, MOSI, MISO) or a four wire interface (SCLK, MOSI,
MISO, and SSLn). Setting this bit to 0 makes the RSPI operate in four wire mode
whereas setting it to 1 makes the RSPI function in three wire clock synchronous
mode. When operating in four wire mode, the pins SSL0 to SSL3 become
available for chip selection; the default chip (slave) select pin being SSL0. When
CHAPTER 7 / SERIAL COMMUNICATIONS
This LSI (master X)
RSPCK
MOSI
MISO
SSL0
SSL1
SSL2
SSL3
Port Y
This LSI (master Y)
RSPCK
MOSI
MISO
SSL0
SSL1
SSL2
SSL3
Port X
RSPI slave 1
RSPCK
MOSI
MISO
SSL
RSPI slave 2
RSPCK
MOSI
MISO
SSL
Figure 7.11 Multiple Masters Multiple Slaves. Source: Hardware Manual, page 1666.
This LSI (master)
RSPCK
MOSI
MISO
SSL0
SSL1
SSL2
SSL3
RSPI slave 0
RSPCK
MOSI
MISO
SSL
RSPI slave 1
RSPCK
MOSI
MISO
SSL
RSPI slave 2
RSPCK
MOSI
MISO
SSL
RSPI slave 3
RSPCK
MOSI
MISO
SSL
Figure 7.12 Single Master Multiple Slaves. Source: Hardware Manual, page 1664.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
RSPI slave 0
This LSI (master)
RSPCK
MOSI
MISO
SSL0
SSL1
SSL2
SSL3
RSPCK
MOSI
MISO
SSL
Figure 7.13 Single Master Single Slave (also shows clock synchronous configuration). Source:
Hardware Manual, page 1663.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
SPRIE
SPE
SPTIE
SPEIE
MSTR
MODFEN
TXMD
SPMS
0
0
0
0
0
0
0
0
Figure 7.14 The SPI serial peripheral control register. Source: Hardware Manual, page 1635.
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operating in three wire mode, it is assumed that either the desired chip is selected
manually or there is only one active SPI slave on the device.
TXMD: This is the Communications Operating Mode Select bit that determines
whether the SPI will be acting in full duplex mode or perform transmit operations
only.
MODFEN: This bit enables or disables mode fault error detection. Mode fault error occurs when the SPI is in master mode and an external device drives a slave select pin low.
MSTR: This bit determines whether the microcontroller acts as a master or a slave.
SPEIE: Setting this bit to 1 enables the generation SPI error interrupt. This interrupt occurs when the RSPI module detects a mode fault or an overrun error, and
sets the corresponding bits in the status register SPSR to 1.
SPTIE: Setting this bit to 1 enables SPI transmit interrupt to indicate that the transmit buffer is empty.
SPE: Setting this bit to 1 enables the SPI module.
SPRIE: Setting this bit to 1 enables SPI receive interrupt. The interrupt occurs
whenever the receive buffer is successfully written without errors.
Serial Peripheral Control Register (SPCR2): This register adds to the controllability of
the operating mode of the Renesas SPI. The functions of the bits are as follows:
CHAPTER 7 / SERIAL COMMUNICATIONS
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
PTE
SPIIE
SPOE
SPPE
0
0
0
0
0
0
0
0
211
Figure 7.15 The SPI serial peripheral control register 2. Source: Hardware Manual, page 1653.
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SPPE: The SPPE bit enables or disables the parity function. The parity bit is added
to transmit data, and parity checking is performed for receive data when the communications operating mode select bit (TXMD) in the RSPI control register
(SPCR) is 0 and the SPPE bit in SPCR2 is 1. The parity bit is added to transmit
data but parity checking is not performed for receive data when the SPCR.TXMD
bit is 1 and the SPPE bit in SPCR2 is 1.
SPOE: When even parity is set, parity bit addition is performed so that the total
number of 1-bits in the transmit/receive character plus the parity bit is even. Similarly, when odd parity is set, parity bit addition is performed so that the total number of 1-bits in the transmit/receive character plus the parity bit is odd. The SPOE
bit is valid only when the SPPE bit is 1.
SPIIE: The SPIIE bit enables or disables the generation of RSPI idle interrupt requests when the RSPI being in the idle state is detected and the IDLNF flag in the
RSPI status register (SPSR) is cleared to 0.
PTE: The PTE bit enables the self-diagnosis function of the parity circuit in order
to check whether the parity function is operating correctly.
Slave Select Polarity (SSLP): This register sets the polarity of the slave select lines SSL0
to SSL3 of the Renesas SPI module. SSLP has four usable bits that select the polarity (active low/active high) for the corresponding slave select lines.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
SSL3P
SSL2P
SSL1P
SSL0P
0
0
0
0
0
0
0
0
Figure 7.16 The SPI slave select polarity register. Source: Hardware Manual, page 1637.
Setting the SSLxP bits to 0 sets the SSLx pin to active low, while setting SSLxP bit to
1 sets the SSLx pin to active high (x 0 or 1 or 2 or 3).
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Serial Peripheral Pin Control Register (SPPCR): This register sets the modes of the
RSPI pins.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
MOIFE
MOIFV
—
SPOM
SPLP2
SPLP
0
0
0
0
0
0
0
0
Figure 7.17 The SPI pin control register. Source: Hardware Manual, page 1638.
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SPLP: When the SPLP (SPI Loopback) bit is set to 1, the RSPI shuts off the path
between the MISOn pin and the shift register, and between the MOSIn pin and the
shift register, and connects (reverses) the input path and output path for the shift
register (loopback mode).
SPLP2: The function of this bit is the same as the SPLP. When the SPLP2 bit is set
to 1, the RSPI shuts off the path between the MISOn pin and the shift register, and
between the MOSIn pin and the shift register, and connects (reverses) the input
path and output path for the shift register (loopback mode).
SPOM: The SPI Output Mode bit when set to 0 sets the RSPI output pins to function as CMOS output pins, or open drain output pins when set to 0.
MOVIFV: If the MOSI Idle Fixed Value bit is 1 in master mode, the MOIFV bit
determines the MOSIn pin output value during the SSL negation period (including
the SSL retention period during a burst transfer).
MOVIFE: The MOSI Idle Value Fixing Enable bit fixes the MOSI output value
when the RSPI in master mode is in an SSL negation period (including the SSL retention period during a burst transfer). When the MOIFE bit is 0, the RSPI outputs
the last data from the previous serial transfer during the SSL negation period.
When the MOIFE bit is 1, the RSPI outputs the fixed value set in the MOIFV bit to
the MOSI bit.
Serial Peripheral Status (SPSR): This register is an indicator of the current operating
status of the RSPI.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
PERF
MODF
IDLNF
OVRF
x
0
x
0
0
0
0
0
Figure 7.18 The SPI serial peripheral status register. Source: Hardware Manual, page 1640.
CHAPTER 7 / SERIAL COMMUNICATIONS
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OVRF: This Overrun error flag is set when a serial transfer ends while the
SPCR.TXMD bit is 0 and the receive buffer holds data that has not yet been read
out, thereby indicating an overrun error. It is cleared when the CPU writes the
value 0 to the OVRF bit.
IDLNF: The RSPI Idle Flag indicates the transfer status of the RSPI. The IDLNF,
when in master mode, is cleared when all of the following conditions are satisfied:
▫ The SPCR.SPE bit is 0 (RSPI is initialized).
▫ The transmit buffer (SPTX) is empty (data for the next transfer is not set).
▫ The SPSSR.SPCP[2⬊0] bits are 000 (beginning of sequence control).
▫ The RSPI internal sequencer has entered the idle state (status in which operations up to the next-access delay have finished).
The IDLNF bit, when in master mode, is set when any of the above conditions are
not satisfied, thereby indicating a non-idle state.
When acting as a slave, this bit is set when the SPCR.SPE bit is 1 (RSPI function is enabled) and cleared when SPCR.SPE bit is 0 (RSPI is initialized).
MODF: A SPI Mode Fault is detected in a multi master mode when the input level of
the SSLn pin changes to the active level while the SPCR.MSTR bit is 1 (master mode)
and the SPCR.MODFEN bit is 1 (mode fault error detection is enabled). When in
slave mode, a mode fault is detected when the SSLn pin is negated before the RSPCK
cycle necessary for data transfer ends while the SPCR.MSTR bit is 0 (slave mode) and
the SPCR.MODFEN bit is 1 (mode fault error detection is enabled), the RSPI detects
a mode fault error. The MODF flag is cleared by writing 0 to the MODF bit.
PERF: The Parity Error Flag is set when a serial transfer ends while the
SPCR.TXMD bit is 0 and the SPCR2.SPPE bit is 1. This bit is cleared when CPU
reads SPSR when the PERF bit is 1, and then writes the value 0 to the PERF bit.
Serial Peripheral Data Register (SPDR): This register contains data to be transmitted
and data received over the SPI channel. Data written to this register is transmitted over the
SPI channel. When this register is read from it returns the data received over the transmission channel.
b31
b30
b29
b28
b27
b26
b25
b24
b23
b22
b21
b20
b19
b18
b17
b16
SPD31 SPD30 SPD29 SPD28 SPD27 SPD26 SPD25 SPD24 SPD23 SPD22 SPD21 SPD20 SPD19 SPD18 SPD17 SPD16
Value after reset:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
b15
b14
b13
b12
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
SPD8
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
0
0
0
0
0
0
0
0
0
SPD15 SPD14 SPD13 SPD12 SPD11 SPD10 SPD9
Value after reset:
0
0
0
0
0
0
0
Figure 7.19 The SPI serial peripheral data register. Source: Hardware Manual, page 1643.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The frame length and the number of bits transferred from this register depends upon the
setting of the SPFC[1⬊0] and SPB[3⬊0] bits.
Serial Peripheral Sequence Control (SPSCR): This register sets the sequence method
when the RSPI operates in master mode.
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
b2
b1
b0
SPSLN[2:0]
0
Figure 7.20 The SPI serial peripheral sequence control register.
0
0
Source: Hardware Manual,
page 1644.
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SPSLN[2⬊0]: The SPI Sequence Length Specification bits specify a sequence
length when the RSPI performs sequential operations in master mode. When in
slave mode, the RSPI always refers to SPCMD0.
Serial Peripheral Sequence Status (SPSSR): This register indicates the sequence control status when the RSPI operates in master mode.
b7
b6
—
Value after reset:
0
b5
b4
0
b2
—
SPECM[2:0]
0
b3
0
0
b1
b0
SPCP[2:0]
0
Figure 7.21 The SPI serial peripheral sequence status register.
0
0
Source: Hardware Manual,
page 1645.
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SPCP[2⬊0]: The RSPI command pointer bits point to the SPCMDn currently being
executed.
SPEM[2⬊0]: The RSPI Error command in conjunction with the SPSR register
points to the command SPCMDn which caused an error.
Serial Peripheral Bit Rate Register (SPBR): The value of this register determines the
rate of data transfer.
CHAPTER 7 / SERIAL COMMUNICATIONS
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
SPR7
SPR6
SPR5
SPR4
SPR3
SPR2
SPR1
SPR0
1
1
1
1
1
1
1
1
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Figure 7.22 The SPI bit rate register. Source: Hardware Manual, page 1646.
The SPBR register can have any value from 0 to 255. The following table shows a few example bit rate settings.
TABLE 7.3
Example Bit Rate Settings (n SPDR value, N BRDV[1⬊0]); value in SPCMDx.
BIT RATE
SPBR BRDV[1⬊0] DIVISION
(n)
Bits (N)
RATIO
PCLK ⴝ 32 MHz
PCLK ⴝ 36 MHz
PCLK ⴝ 40 MHz
PCLK ⴝ 50 MHz
16.0 Mbps*
18.0 Mbps*
20.0 Mbps*
25.0 Mbps*
0
0
2
1
0
4
8.00 Mbps
9.00 Mbps
10.0 Mbps
12.5 Mbps
2
0
6
5.33 Mbps
6.00 Mbps
6.67 Mbps
8.33 Mbps
3
0
8
4.00 Mbps
4.50 Mbps
5.00 Mbps
6.25 Mbps
4
0
10
3.20 Mbps
3.60 Mbps
4.00 Mbps
5.00 Mbps
5
0
12
2.67 Mbps
3.00 Mbps
3.33 Mbps
4.16 Mbps
5
1
24
1.33 Mbps
1.50 Mbps
1.67 Mbps
2.08 Mbps
5
2
48
667 kbps
750 kbps
833 kbps
1.04 Mbps
5
3
96
333 kbps
375 kbps
417 kbps
521 kbps
255
3
4096
7.81 kbps
8.80 kbps
9.78 kbps
12.2 kbps
Serial Peripheral Data Control Register (SPDCR): This register determines the number of frames that can be stored in SPDR, controls the SSLn pin output reading from
SPDR, and selects width access to SPDR.
Value after reset:
b7
b6
b5
b4
—
—
SPLW
SPRDTD
0
0
0
0
b3
b2
b1
SLSEL[1:0]
0
0
b0
SPLF[1:0]
0
0
Figure 7.23 The SPI serial peripheral data control register. Source: Hardware Manual, page 1647.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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SPFC[1⬊0]: These bits specify the number of frames that can be stored in SPDR.
Up to four frames can be transmitted or received in one round of transmission or reception, and the amount of data is determined by the combination of the RSPI data
length specification bits (SPB[3⬊0]) in the RSPI command register (SPCMD), the
RSPI sequence length specification bits (SPSLN[2⬊0]) in the RSPI sequence control register (SPSCR), and the number of frames specification bits (SPFC[1⬊0]) in
the RSPI data control register (SPDCR). Also, the SPFC[1⬊0] bits specify the number of received data at which the RSPI receive buffer full interrupt is requested. The
following table shows the frame configurations that can be stored in SPDR and examples of combinations of settings for transmission and reception.
TABLE 7.4
SETTING
Setting the Number of Frames Transmitted from SPDR.
SPB[3⬊0]
SPSLN[2⬊0]
SPFC[1⬊0]
NUMBER OF
FRAMES FOR
TRANSFER
NUMBER OF FRAMES
AT WHICH RECEIVE
BUFFER FULL INTERRUPT
OCCURS OR TRANSMIT
BUFFER HOLDING DATA
IS RECOGNIZED
1–1
N
000
00
1
1
1–2
N
000
01
2
2
1–3
N
000
10
3
3
1–4
N
000
11
4
4
2–1
N, M
001
01
2
2
2–2
N, M
001
11
4
4
3
N, M, O
010
10
3
3
4
N, M, O, P
011
11
4
4
5
N, M, O, P, Q
100
00
5
1
6
N, M, O, P, Q, R
101
00
6
1
7
N, M, O, P, Q, R, S
110
00
7
1
8
N, M, O, P, Q, R, S, T
111
00
8
1
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SLSEL[1⬊0]: SSL Pin Output Selection bits control the SSLn pin output in master
mode for the corresponding RSPI.
CHAPTER 7 / SERIAL COMMUNICATIONS
TABLE 7.5
217
SSL Pin Output Selection Configuration/Function.
SLSEL
[1⬊0] ⴝ 00
SLSEL
[1⬊0] ⴝ 01
SLSEL
[1⬊0] ⴝ 10
SSL3
Output
I/O
I/O
SSL2
Output
I/O
I/O
SSL1
Output
I/O
Output
SSL0
Output
Output
Output
SLSEL
[1⬊0] ⴝ 11
Setting
prohibited
Serial Peripheral Clock Delay Register (SPCKD): The value of this register sets a period from the beginning of SSL signal assertion to the clock oscillations on the RSPK line.
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
b2
b1
b0
SCKDL[2:0]
0
0
0
Figure 7.24 The SPI serial peripheral clock delay register. Source: Hardware Manual, page 1650.
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SCKDL [2⬊0]: The RSPCK Delay Setting bits set an RSPCK delay value when the
SPCMD.SCKDEN bit is 1. When using the RSPI in slave mode, set the
SCKDL[2⬊0] bits to 000.
Slave Select Line Negation Delay (SSLND): This register sets a period/delay from the
transmission of final RSPCK edge to the negation of the SSL signal during a serial transfer
by the RSPI in master mode.
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
b2
b1
b0
SLNDL[2:0]
0
0
0
Figure 7.25 The SPI serial peripheral slave select negation delay register. Source: Hardware Manual, page 1651.
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SLNDL [2⬊0]: The SSL Negation Delay Setting bits set an SSL negation delay
value when the RSPI is in master mode. When using the RSPI in slave mode, set
the SLNDL [2⬊0] bits to 000.
Serial Peripheral Next Access Delay Register (SPND): This register sets a non-active
period after termination of a serial transfer.
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
b2
b1
b0
SPNDL[2:0]
0
0
Figure 7.26 The SPI serial peripheral next access delay register.
0
Source: Hardware Manual,
page 1652.
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SPNDL [2⬊0]: The RSPI Next-Access Delay Setting bits set a next-access delay
when the SPCMD.SPNDEN bit is 1. When using the RSPI in slave mode, set the
SPNDL[2⬊0] bits to 000.
Serial Peripheral Command Register (SPCMDx): SPCMD0 to SPCMD7 are used to
set a transfer format/method for the RSPI in master mode. The SPCMDx register has various fields that can be set to control the corresponding feature of the RSPI.
b15
b14
b13
SCKDEN SLNDEN SPNDEN
Value after reset:
b11
b10
b9
b8
SPB[3:0]
LSBF
0
0
0
0
0
1
1
1
b7
b6
b5
b4
b3
b2
b1
b0
CPOL
CPHA
0
1
SSLA[2:0]
SSLKP
Value after reset:
b12
0
0
0
BRDV[1:0]
0
1
1
Figure 7.27 The SPI serial peripheral command register. Source: Hardware Manual, page 1655.
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CPHA: The RSPCK Phase Setting bit sets an RSPCK phase of the RSPI in master
mode or slave mode. Data communications between RSPI modules require the
same RSPCK phase setting between the modules.
CHAPTER 7 / SERIAL COMMUNICATIONS
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BRDV[1⬊0]: Bit Rate Division Setting bits are used to determine the bit rate. A bit
rate is determined by combinations of the settings in the BRDV[1⬊0] bits and
SPBR (See Section 32.2.8, RSPI Bit Rate Register (SPBR) in the hardware manual). The settings in SPBR determine the base bit rate. The settings in the
BRDV[1⬊0] bits are used to select a bit rate, which is obtained by dividing the base
bit rate by 1, 2, 4, or 8. In SPCMD0 to SPCMD7, different BRDV[1⬊0] bit settings
can be specified. This permits the execution of serial transfers at a different bit rate
for each command.
SSLA[2⬊0]: The SSL Signal Assertion Setting bits control the SSL signal assertion
when the RSPI performs serial transfers in master mode. Setting the SSLA[2⬊0]
bits controls the assertion for the SSL0 to SSL3 signals. When an SSL signal is asserted, its polarity is determined by the set value in the corresponding SSLP. When
the SSLA[2⬊0] bits are set to 000 in multi-master mode, serial transfers are performed with all the SSL signals in the negated state (as the SSLn0 pin acts as input).
When using the RSPI in slave mode, set the SSLA[2⬊0] bits to 000.
SSLKP: SSL Signal Level Keeping bit RSPI in master mode performs a serial
transfer, the SSLKP bit specifies whether the SSL signal level for the current command is to be kept or negated between the SSL negation timing associated with the
current command and the SSL assertion timing associated with the next command.
When using the RSPI in slave mode, the SSLKP bit should be set to 0.
SPB[3⬊0]: RSPI Data Length Setting bits set a transfer data length for the RSPI in
master mode or slave mode.
LSBF: RSPI LSB First bit sets the data format of the RSPI in master mode or slave
mode to MSB first or LSB first.
SPNDEN: RSPI Next-Access Delay Enable
The SPNDEN bit sets the period from the time the RSPI in master mode terminates a serial transfer and sets the SSL signal inactive until the RSPI enables the
SSL signal assertion for the next access (next-access delay). If the SPNDEN bit
is 0, the RSPI sets the next-access delay to 1 RSPCK 2 PCLK. If the SPNDEN
bit is 1, the RSPI inserts a next-access delay in compliance with the SPND setting.
When using the RSPI in slave mode, the SPNDEN bit should be set to 0.
Port Function Control Register G (PFGSPI): The PFGSPI special function register is
used to select I/O pins for RSPI channel 0.
Value after reset:
b7
b6
b5
b4
b3
SSL3E
SSL2E
SSL1E
SSL0E
MISOE
0
0
0
0
0
b2
b1
MOSIE RSPCKE
0
0
b0
RSPIS
0
Figure 7.28 The port function control register. Source: Hardware Manual, page 1665.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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RSPIS Bit (RSPI Pin Select): This bit selects a pin for an RSPI input/output. As an
enable bit is provided for each RISPI input/output pin, the input/output pin is
selectable while the corresponding enable bit is 1. Otherwise, the pin cannot be
selected.
RSPCKE Bit (RSPCK Enable): This bit enables or disables the output of the
RSPCK pin. Set this bit to 1 to use the RSPCK pin.
MOSIE Bit (MOSI Enable): This bit enables or disables the output of the
MOSI pin. Set this bit to 1 to use the MOSI pin.
MISOE Bit (MISO Enable): This bit enables or disables the output of the
MISO pin. Set this bit to 1 to use the MISO pin.
SSL0E Bit (SSL0 Enable): This bit enables or disables the output of the SSL0 pin.
Set this bit to 1 to use the SSL0 pin.
SSL1E Bit (SSL1 Enable): This bit enables or disables the output of the SSL1 pin.
Set this bit to 1 to use the SSL1 pin.
SSL2E Bit (SSL2 Enable): This bit enables or disables the output of the SSL2 pin.
Set this bit to 1 to use the SSL2 pin.
SSL3E Bit (SSL3 Enable): This bit enables or disables the output of the SSL3 pin.
Set this bit to 1 to use the SSL3 pin.
Configuring the RSPI to Function in Single Master Single Slave Mode
This is the simplest configuration possible in which we have 1 slave device connected to
the Renesas Serial Peripheral Interface. Section 7.3.2 describes the setup of the aforementioned RSPI registers for the Single Master Single Slave configuration as shown in
Figure 7.29.
This LSI (master)
RSPCK
MOSI
MISO
SSL0
SSL1
SSL2
SSL3
RSPI slave
RSPCK
MOSI
MISO
SSL
Figure 7.29 Single Master Single Slave Configuration. Source: Hardware Manual, page 1662.
CHAPTER 7 / SERIAL COMMUNICATIONS
7.2.4
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Renesas Inter Integrated Circuit Bus
The Inter Integrated Circuit (I2C) bus was invented by Philips Electronics for serial communications between low speed peripherals in an embedded system. The bus allows multiple peripheral devices to be connected on the same set of wires to communicate with each
other with only two devices, one master device and one slave device, communicating with
each other at a given time. The bus mainly consists of two wires Serial Clock (SCL) and
Serial Data (SDA) that are responsible for transferring the data from one end to the other.
These lines are constantly held high by pull up resistors when the bus is inactive. All devices connected on these lines need to communicate with the I2C protocol. Figure 7.30 illustrates devices connected on an I2C bus.
Vcc
Device 1
Device 2
Device 3
Device 4
Address
(0x80)
Address
(0xC0)
Address
(0xE1)
Address
(0x70)
SCL
SDA
Figure 7.30 Four Devices Connected on the I2C Bus with pull up resistors. 128 such devices can be
connected on a single bus.
I2C Bus Protocol
Each device connected on the bus is assigned a 7-bit address. Data is usually transferred as
a byte plus an additional bit and is accompanied by a clock signal that synchronizes the
data transfer between the communicating devices. The device that takes control of the bus
at the beginning of communication is usually the master device, and is responsible for addressing the slave device and generating a clock signal during data transmission.
Before any form of data transfer takes place, a device wanting to transfer data must
take control of the bus. This is done by monitoring the bus. If the bus is currently held high
(both SDA and SCL are at a high voltage), it implies that the bus is currently free. Otherwise the bus is assumed to be busy and the device must wait for the bus to be free in order
to transmit data. When the bus becomes free, the master acquires the control of the bus by
sending a START condition in which the device pulls the SDA line low while keeping the
SCL line high and thus becomes the current master of the bus. Figure 7.31 (A) illustrates a
START condition. The generation of the START condition also informs the other devices
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
that the bus is currently busy, and the other devices start listening to the next byte to be
transferred on the bus.
When the current master of the bus is ready to release the bus from its control, it transmits a STOP condition in which the SDA line gets pulled high while the SCL line is high.
During the entire period in which the master is in control of the bus, the SDA line is constantly held low, except that when there is data being transmitted there is toggling of both
lines. Figure 7.31 (B) shows a STOP condition.
SCL
SCL
SDA
SDA
(A)
(B)
Figure 7.31 (A) START condition; (B) STOP condition.
Once control of the bus is obtained, the next priority for the master is to address the slave device by transmitting one byte which consists of a seven bit address and one bit that specifies if
the master device wants to read from or write to the slave device. This bit is called the
Read/Write bit (R/W). If this bit is low, it indicates that the master wants to write to the slave
device; if high, the master device wishes to read from the slave. The status of the R/W bit determines whether the next transactions are going to be read from or written to the slave devices.
After transfer of these eight bits, the master clocks out an additional pulse while keeping the
SDA high. If a device with the transmitted seven bit address is presently listening on the bus, it
responds immediately on the ninth clock pulse by pulling the SDA line low. This is an ACK bit
signaling an acknowledgement, and the slave device becomes an active listener on the bus
while other devices stop listening to the bus. Thus the master is now ready to transfer more data
to the slave. If the SDA line remains low during the ninth clock pulse, the master gets a “no acknowledgement” (NACK) indication and stops transfer of data by sending a STOP bit.
I2C Communication Modes
Depending upon the initial transactions mentioned above, a device can be set up in any of
the four following modes:
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Master Transmitter: In this mode, the device functions as a master and transmits
data to a slave after acquiring the control of the bus. This device usually transmits
the seven bit address with the R/W bit set to write. It may also transmit additional
bytes if an ACK is received for every byte it transfers.
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Master Receiver: In this mode, the device functions as a master and clocks out data
from the slave. In this case, the master generates the clock pulses to which the
slave toggles data on the SDA pin. Before any reception can take place, the master
must output the slave device address with the R/W bit set to R and then output the
desired number of clock cycles with pseudo data (usually 0xFF). On every ninth
clock pulse, the master receiver is required to send an ACK pulse to the slave device acknowledging the reception of data. Slave device stops transmitting the data
to the master receiver as soon as the master clocks a NACK as the ninth bit on the
most recent 8 byte data.
Slave Transmitter: A device enters this mode when another device gains control of
the bus and addresses the device with the address assigned to it with the R/W bit
set to R. Such a device works in conjunction with a master receiver and responds
to commands sent to it by the master receiver. The slave device stops transmitting
the data to the master receiver as soon as the master clocks a NACK as the ninth bit
on the most recent 8 byte data.
Slave Receiver: A device enters this mode as soon as it is successfully addressed
by a master transmitter with the R/W bit transmitted as W. The slave device is required to clock out an ACK bit for every relevant byte it successfully received.
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Now that we understand some of the basics of the I2C protocol, we can move on to understand the detailed working of the I2C interface provided by Renesas; i.e., the Renesas Inter
Integrated Circuit bus interface and the registers related to it. Figure 7.32 shows the typical
transfers supported by the RIIC interface.
[7-bit address format]
S
SLA (7 bit)
RW#
A
DATA (8 bits)
A
A/A#
P
1
7
1
1
8
1
1
1
n (n 5 1 or more)
[10-bit address format]
S
11110b+SLA(2 bits) W#
1
7
1
A
SLA (8 bits)
A
DATA (8 bits)
A
A/A#
P
1
8
1
8
1
1
1
n (n 5 1 or more)
S
11110b+SLA(2 bits) W#
1
7
1
A
SLA (8 bits)
A
Sr
11110b+SLA(2 bits)
R
A
DATA (8 bits)
A
A/A#
P
1
8
1
1
7
1
1
8
1
1
1
n (n 5 1 or more)
Figure 7.32 Typical data transfers supported by the Renesas I2C Interface.
page 1662.
Source: Hardware Manual,
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Registers related to the RIIC interface:
I2C Bus Control Register 1 (ICCR1): ICCR1 enables or disables the RIIC, resets the internal state of the RIIC, outputs an extra SCL clock cycle, and manipulates and monitors
the SCLn pin and SDAn pin.
Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
ICE
IICRST
CLO
SOWP
SCLO
SDAO
SCLI
SDAI
0
0
0
1
1
1
1
1
Figure 7.33 The ICCR1 register. Source: Hardware Manual, page 1483.
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I2C Bus Interface Enable (ICE): Setting this pin to 1 enables the RIIC transfer
function (the SCLn pin and SDAn pin drive the bus) and vice versa.
I2C Interface Internal Reset (IICRST): Setting this bit to 1 initiates the RIIC reset
resulting in all control, mode, and status registers resetting to default values. This
bit needs to be manually cleared to finish the reset. The bit should usually be set
when the ICE bit is set to 0. If this bit is set when ICE is 1, it resets the BC[2⬊0]
bits in ICMR1; the ICSR1, ICSR2, ICDRS registers; and the internal states of the
RIIC.
(CLO): Setting this bit to 1 causes the RIIC interface to output an extra SCL clock
cycle (the CLO bit is cleared automatically after one clock cycle is output).
(SOWP): This bit controls the modification of the SCLO and SDAO bits. Setting
this bit to 0 allows the SCLO and SDAO bits to be rewritten. This bit is always
written as 1.
(SCLO): This bit controls the output level of the SCLn pin. This bit also monitors
the output state of the SCLn pin. Setting this bit to 0 sets the SCLn pin to low level,
and vice versa.
(SDAO): This bit controls the output level of the SDAn pin. This bit also monitors
the output state of the SDAn pin. Setting this bit to 0 sets the SDAn pin to low
level, and vice versa.
(SCLI): This bit monitors the input level of the SCLn pin. If this bit is high, it implies that the SCL pin is acting as input and is high. If this bit is low, it implies that
the SCL pin is acting as input and is low.
(SDAI): This bit monitors the input level of the SDAn pin. If this bit is high, it implies that the SDA pin is acting as input and is high. If this bit is low, it implies that
the SDA pin is acting as input and is low.
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225
I2C Bus Control Register 2 (ICCR2): ICCR2 has a flag function that indicates
whether or not the I2C bus is occupied and whether the RIIC is in transmit/receive or
master/slave mode, as well as a function to issue a start or stop condition. Bits in this
register are:
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
BBSY
MST
TRS
—
SP
RS
ST
—
0
0
0
0
0
0
0
0
Figure 7.34 The ICCR2 register. Source: Hardware Manual, page 1486.
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(BBSY): The BBSY flag indicates whether the I2C bus is occupied (bus busy)
or released (bus free). This bit is set to 1 when the SDAn line changes from high
to low under the condition of SCLn high, assuming that a start condition has
been issued. When the SDAn line changes from low to high under the condition
of SCLn high, this bit is cleared to 0 after the bus free time (specified in
ICBRL) start condition is not detected, assuming that a stop condition has been
issued or if an Internal Interface Reset occurs.
(MST): This bit indicates whether the RIIC interface is acting as a master or slave
mode. This bit is set when:
▫ A start condition is issued normally according to the start condition issuance
request (when a start condition is detected with the ST bit set to 1).
▫ A 1 is written to the MST bit with the MTWP bit in ICMR1 set to 1.
It is reset when:
▫ A stop condition is detected.
▫ The AL (arbitration lost) flag in ICSR2 is set to 1.
▫ A 0 is written to the MST bit with the MTWP bit in ICMR1 set to 1.
▫ A 1 is written to the IICRST bit in ICCR1 to apply an RIIC reset or an internal
reset.
Manual setting of this is permitted only when MTWP in ICMR1 is 1.
(TRS): This bit indicates transmit or receive mode. This bit is set when:
▫ A start condition is issued normally according to the start condition issuance
request (when a start condition is detected with the ST bit set to 1).
▫ The R/W# bit added to the slave address is set to 0 in master mode.
▫ The address received in slave mode matches the address enabled in ICSER,
with the R/W# bit set to 1.
▫ A 1 is written to the TRS bit with the MTWP bit in ICMR1 set to 1.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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This bit is cleared when:
▫ A stop condition is detected.
▫ The AL (arbitration lost) flag in ICSR2 being set to 1.
▫ In master mode, reception of a slave address to which an R/W# bit with the
value 1 is appended.
▫ In slave mode, a match between the received address and the address enabled
in ICSER, when the value of the received R/W# bit is 0 (including cases where
the received address is the general call address).
▫ In slave mode, a restart condition is detected (a start condition is detected with
ICCR2.BBSY 1 and ICCR2.MST 0).
▫ When 0 is written to the TRS bit with the MTWP bit in ICMR1 set to 1.
▫ When 1 is written to the IICRST bit in ICCR1 to apply an RIIC reset or an internal reset.
A combination of this bit and the MST bit indicates the operating mode of the
RIIC. Also, writing to this bit is not necessary during normal usage.
(SP): This bit is used to request that a stop condition be issued in master mode.
This bit is manually set to 1 to request to issue a stop condition, a stop condition
is issued only when the BBSY flag is set to 1 (bus busy) and the MST bit is set
to 1 (master mode). This bit is set when a 1 is written to it and cleared when any
of the following conditions occur:
▫ A 0 is written to the SP bit after reading SP 1.
▫ A stop condition has been issued or a stop condition is detected.
▫ The AL (arbitration lost) flag in ICSR2 is set to 1.
▫ A start condition and a restart condition are detected.
▫ A 1 is written to the IICRST bit in ICCR1 to apply an RIIC reset or an internal
reset.
(RS): This bit is used to request that a restart condition be issued in master mode.
When this bit is set to 1 to request to issue a restart condition, a restart condition is
issued when the BBSY flag is set to 1 (bus busy) and the MST bit is set to 1 (master mode). This bit is set when a 1 is written to it and cleared when any of the following conditions occur:
▫ A 0 is written to the RS bit.
▫ A restart condition has been issued or a start condition is detected.
▫ The AL (arbitration lost) flag in ICSR2 is set to 1.
▫ A 1 is written to the IICRST bit in ICCR1 to apply an RIIC reset or an internal
reset.
(ST): This bit is used to request transition to master mode and issuance of a start condition. When this bit is set to 1 to request to issue a start condition, a start condition
is issued when the BBSY flag is set to 0 indicating that the bus is free. This bit is set
when a 1 is written to it and cleared when any of the following conditions occur:
▫ A 0 is written to the ST bit.
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A start condition has been issued.
The AL (arbitration lost) flag in ICSR2 is set to 1.
A 1 is written to the IICRST bit in ICCR1 to apply an RIIC reset or an internal
reset.
I2C Mode Register 1 (ICMR1): ICMR1 specifies the internal reference clock source
within the RIIC, indicates the number of bits to be transferred, and protects the MST and
TRS bits in ICCR2 from being written. Bits in this register are:
b7
b6
b5
MTWP
Value after reset:
0
b4
0
b2
BCWP
CKS[2:0]
0
b3
0
1
b1
b0
BC[2:0]
0
0
0
Figure 7.35 The ICMR1 register. Source: Hardware Manual, page 1490.
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(MTWP): This bit controls the modification of the MST and TRS bits in ICCR2.
Setting this bit enables writing to the MST and TRS bits in ICCR2.
(CKS[2⬊0]): These bits select a reference clock source (IIC) inside the RIIC.
Table 7.6 shows the selections possible:
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TABLE 7.6
Clock Source Selection for the RIIC Interface.
CKS2
CKS1
CKS0
CLOCK SOURCE TO RIIC
0
0
0
PCLK/1 clock
0
0
1
PCLK/2 clock
0
1
0
PCLK/4 clock
0
1
1
PCLK/8 clock
1
0
0
PCLK/16 clock
1
0
1
PCLK/32 clock
1
1
0
PCLK/64 clock
1
1
1
PCLK/128 clock
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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(BCWP): Clearing this bit to 0 enables a value to be written in the BC[2⬊0] bits.
(BC[2⬊0]): These bits function as a counter that indicates the number of bits remaining to be transferred at the detection of a rising edge on the SCLn line. Although these bits are writable and readable, it is not necessary to access these bits
under normal conditions. To write to these bits, specify the number of bits to be
transferred plus one (data is transferred with an additional acknowledge bit) between transferred frames when the SCLn line is at a low level. Table 7.7 shows
how the Bit counter indicates the number of bits remaining:
TABLE 7.7
Bit Counter Indications.
BC2
BC1
BC0
NUMBER OF BITS REMAINING
0
0
0
9
0
0
1
2
0
1
0
3
0
1
1
4
1
0
0
5
1
0
1
6
1
1
0
7
1
1
1
8
I2C Mode Register 2 (ICMR2): ICMR2 has a timeout function and an SDA output delay function. Bits in this register are:
b7
b6
DLCS
Value after reset:
0
b5
b4
SDDL[2:0]
0
0
0
b3
b2
b1
b0
—
TMOH
TMOL
TMOS
0
1
1
0
Figure 7.36 The ICMR2 register. Source: Hardware Manual, page 1492.
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(DCLS): This bit is used to select the internal reference clock (IIC) if set to 0, or
the internal reference clock divided by 2 (IIC/2) if set to 1, as the clock source of
the SDA output delay time.
(SDDL[2⬊0]): The SDA output can be delayed by the SDDL[2⬊0] setting. This
counter works with the clock source selected by the DLCS bit. The setting of this
function can be used for all types of SDA output, including the transmission of the
acknowledge bit.
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229
TABLE 7.8
DELAY TIME WHEN
DCLS ⴝ 0
DELAY TIME WHEN
DCLS ⴝ 1
SDDL2
SDDL1
SDDL0
0
0
0
No Delay in output
No Delay in output
0
0
1
1 IIC cycle
1 or 2 IIC cycles
0
1
0
2 IIC cycle
3 or 2 IIC cycles
0
1
1
3IIC cycle
5 or 2 IIC cycles
1
0
0
4 IIC cycle
7 or 2 IIC cycles
1
0
1
5 IIC cycle
9 or 2 IIC cycles
1
1
0
6 IIC cycle
11 or 2 IIC cycles
1
1
1
7 IIC cycle
13 or 2 IIC cycles
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(TMOH): This bit is used to enable (when set to 1) or disable (when set to 0) the
internal counter of the timeout function to count up while the SCLn line is held
high when the timeout function is enabled (TMOE bit 1 in ICFER).
(TMOL): This bit is used to enable (when set to 1) or disable (when set to 0) the internal counter of the timeout function to count up while the SCLn line is held low
when the timeout function is enabled (TMOE bit 1 in ICFER).
(TMOS): This bit is used to select long mode or short mode for the timeout detection time when the timeout function is enabled (TMOE bit 1 in ICFER). When
this bit is set to 0, long mode is selected. When this bit is set to 1, short mode is selected. In long mode, the timeout detection internal counter functions as a 16 bitcounter. In short mode, the counter functions as a 14 bit-counter. While the SCLn
line is in the state that enables this counter as specified by bits TMOH and TMOL,
the counter counts up in synchronization with the internal reference clock (IIC)
as a count source.
I2C Mode Register 3 (ICMR3): ICMR3 has functions to send/receive acknowledge and
to select the RDRF set timing in RIIC receive operation, WAIT operation, and the SCLn
pin and SDAn pin input level of the RIIC. Bits in this register are:
Value after reset:
b7
b6
SMBS
WAIT
0
0
b5
b4
b3
b2
b1
RDRFS ACKWP ACKBT ACKBR
0
0
0
0
b0
NF[1:0]
0
Figure 7.37 The ICMR3 register. Source: Hardware Manual, page 1494.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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(SMBS): Setting this bit to 1 selects the SMBus and enables the HOAE bit in
ICSER. Otherwise the interface acts as the standard I2C interface.
(WAIT): This bit is valid only in receive mode and is used to control whether to
hold the period between the ninth SCL clock cycle and the first SCL clock cycle
low until the receive data buffer (ICDRR) is completely read each time single-byte
data is received in receive mode.
(RDRFS): This bit is used to select the RDRF flag set timing in receive mode and
also to select whether to hold the SCLn line low at the falling edge of the eighth
SCL clock cycle. When the RDRFS bit is 0, the SCLn line is not held low at the
falling edge of the eighth SCL clock cycle, and the RDRF flag is set to 1 at the rising edge of the ninth SCL clock cycle. When the RDRFS bit is 1, the RDRF flag is
set to 1 at the rising edge of the eighth SCL clock cycle and the SCLn line is held
low at the falling edge of the eighth SCL clock cycle. The low-hold of the SCLn
line is released by writing a value to the ACKBT bit. After data is received with this
setting, the SCLn line is automatically held low before the acknowledge bit is sent.
This enables processing to send ACK (ACKBT 0) or NACK (ACKBT 1) according to receive data.
(ACKWP): This bit is used to control the modification of the ACKBT bit.
(ACKBT): This bit holds the acknowledgement to be sent in receive mode. When
set to 0, ACK is transmitted as 0, and vice versa.
(ACKBR): This bit is used to store the acknowledge bit information received from
the receive device in transmit mode. This bit is set to 1 when a 1 is received as the
acknowledge bit with the TRS bit in ICCR2 set to 1. This bit is set to 0 when a 0 is
received as the acknowledge bit with the TRS bit in ICCR2 set to 1, or an interface
internal reset occurs.
(NF [1⬊0]): These bits are used to select the number of stages (1, 2, 3, or 4) of the
digital noise filter.
I2C Bus Function Enable Register (ICFER): ICFER enables or disables the timeout
function, the arbitration lost detection function, and the receive operation suspension function during NACK reception, and selects the use of a digital noise filter circuit and
SCL synchronous circuit. Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
FMPE
SCLE
NFE
NACKE
SALE
NALE
MALE
TMOE
0
1
1
1
0
0
1
0
Figure 7.38 The ICFER register. Source: Hardware Manual, page 1497.
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(FMPE): This bit is used to specify whether to use a slope control circuit for Fastmode Plus[fm].
CHAPTER 7 / SERIAL COMMUNICATIONS
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231
(SCLE): This bit is used to specify whether to synchronize the SCL clock with the
SCL input clock. Normally, set this bit to 1.
(NFE): This bit is used to specify whether to use a digital noise filter circuit.
(NACKE): This bit is used to specify whether to continue or discontinue the transfer operation when NACK is received from the slave device in transmit mode. Normally, set this bit to 1.
(SALE): This bit is used to specify whether to cause arbitration to be lost when a
value different from the value being transmitted is detected on the bus in slave
transmit mode (such as when slaves with the same address exist on the bus, or
when a mismatch with the transmit data occurs due to noise).
(NALE): This bit is used to specify whether to cause arbitration to be lost when
ACK is detected during transmission of NACK in receive mode (such as when
slaves with the same address exist on the bus, or when two or more masters select
the same slave device simultaneously with a different number of receive bytes).
(MALE): This bit is used to specify whether to use the arbitration lost detection
function in master mode. Normally, set this bit to 1.
(TMOE): This bit is used to enable or disable the timeout function.
I2C Bus Status Enable Register (ICSER): ICSER enables or disables comparison of
slave addresses, general call address detection, device-ID command detection, and host address detection. Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
HOAE
—
DIDE
—
GCAE
0
0
0
0
1
b2
b1
b0
SAR2E SAR1E SAR0E
0
0
1
Figure 7.39 The ICSER register. Source: Hardware Manual, page 1499.
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(HOAE): This bit is used to specify whether to ignore a received host address
(0001 000b) when the SMBS bit in ICMR3 is 1.
(DIDE): This bit is used to specify whether to recognize and execute the Device-ID
address when a device ID (1111 100b) is received in the first frame after a start condition or restart condition is detected. Setting this bit to 1 enables Device ID detection.
(GCAE): This bit is used to specify whether to ignore the general call address
(0000 000b 0 [W]: All 0) when it is received. When this bit is set to 1, if the received slave address matches the general call address as the first frame received after the START condition, the GCA bit is set in the I2C status register 1.
(SAR2E): This bit is used to enable or disable the received slave address and the
slave address set in SARL2 and SARU2.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
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(SAR1E): This bit is used to enable or disable the received slave address and the
slave address set in SARL1 and SARU1.
(SAR0E): This bit is used to enable or disable the received slave address and the
slave address set in SARL0 and SARU0.
I2C Bus Interrupt Enable Register (ICIER): ICIER enables or disables various interrupt sources. Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
TIE
TEIE
RIE
NAKIE
SPIE
STIE
ALIE
TMOIE
0
0
0
0
0
0
0
0
Figure 7.40 The ICIER register. Source: Hardware Manual, page 1501.
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(TIE): This bit is used to enable or disable transmit data empty interrupts (ICTXI)
when the TDRE flag in ICSR2 is set to 1.
(TEIE): This bit is used to enable or disable transmit end interrupts (ICTEI) when
the TDRE flag in ICSR2 is set to 1. An ICTEI interrupt request is canceled by
clearing the TEND flag or the TEIE bit to 0.
(RIE): This bit is used to enable or disable receive data full interrupt requests
(ICRXI) when the RDRF flag in ICSR2 is set to 1.
(NAKIE): This bit is used to enable or disable NACK reception interrupt requests
(NAKI) when the NACKF flag in ICSR2 is set to 1. A NAKI interrupt request is
canceled by clearing the NACKF flag or the NAKIE bit to 0.
(SPIE): This bit is used to enable or disable stop condition detection interrupt requests (SPI) when the STOP flag in ICSR2 is set to 1. An SPI interrupt request is
canceled by clearing the STOP flag or the SPIE bit to 0.
(STIE): This bit is used to enable or disable start condition detection interrupt requests (STI) when the START flag in ICSR2 is set to 1. An STI interrupt request is
canceled by clearing the START flag or the STIE bit to 0.
(ALIE): This bit is used to enable or disable arbitration lost interrupt requests
(ALI) when the AL flag in ICSR2 is set to 1. An ALI interrupt request is canceled
by clearing the AL flag or the ALIE bit to 0.
(TMOIE): This bit is used to enable or disable timeout interrupt requests (TMOI)
when the TMOF flag in ICSR2 is set to 1. TMOI interrupt request is canceled by
clearing the TMOF flag or the TMOIE bit to 0.
I2C Bus Status Register 1 (ICSR1): ICSR1 indicates various address detection status.
Bits in this register are:
CHAPTER 7 / SERIAL COMMUNICATIONS
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
HOA
—
DID
—
GCA
AAS2
AAS1
AAS0
0
0
0
0
0
0
0
0
233
Figure 7.41 The ICSR1 register. Source: Hardware Manual, page 1503.
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(HOA): When the received slave address matches the host address (0001 000b)
with the HOAE bit in ICSER set to 1 (host address detection enabled).
(DID): This bit is set when the first frame received immediately after a start condition or restart condition is detected matches a value of (device ID (1111 100b) 0
[W]) with the DIDE bit in ICSER set to 1 (Device-ID address detection enabled),
and is cleared when 0 is written to the DID bit after reading DID 1, when a stop
condition is detected, or when the first frame received immediately after a start
condition or restart condition is detected does not match a value of the device IDs
assigned to the device.
(GCA): When the received slave address matches the general call address with the
GCAE bit in ICSER set to 1 (general call address detection enabled). This flag is set
to 1 at the rising edge of the ninth SCL clock cycle in the frame. This bit is cleared
when a stop condition is detected, an internal interface reset occurs, the address does
not match the general call address (0b0000000 [0]), or if 0 is written to the GCA
bit after reading GCA 1.
(AAS2): This bit is set if either the 7-bit or 10-bit slave address is received/addressed by the master transmitter. This bit is cleared when a stop condition is detected, an internal interface reset occurs, an address mismatch has occurred, or if
0 is written to the AAS0 bit after reading it.
(AAS1): This bit is set if either the 7-bit or 10-bit slave address is received/addressed by the master transmitter. This bit is cleared when a stop condition is detected, an internal interface reset occurs, an address mismatch has occurred, or if
0 is written to the AAS0 bit after reading it.
(AAS0): This bit is set if either the 7-bit or 10-bit slave address is received/addressed by the master transmitter. This bit is cleared when a stop condition is detected, an internal interface reset occurs, an address mismatch has occurred, or if
0 is written to the AAS0 bit after reading it.
I2C Bus Status Register 2 (ICSR2): ICSR2 indicates various interrupt request flags and
statuses. Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
TDRE
TEND
RDRF
NACKF
STOP
START
AL
TMOF
0
0
0
0
0
0
0
0
Figure 7.42 The ICSR2 register. Source: Hardware Manual, page 1501.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
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(TDRE): This flag when set to 1 indicates that ICDRT contains no transmit data.
(TEND): This flag when set to 1 indicates that data has been transmitted.
(RDRF): This flag when set to 1 indicates that ICDRR contains receive data.
(NACKF): This flag when set to 1 indicates that NACK is detected.
(STOP): This flag when set to 1 indicates that stop condition is detected.
(START): This flag when set to 1 indicates that start condition is detected.
(AL): This flag when set to 1 indicates that arbitration is lost.
(TMOF): This flag when set to 1 indicates that timeout is detected.
Slave Address Register Upper (SARUm): SARUm selects 7-bit address format or 10-bit
address format and sets the upper bits of a 10-bit slave address. Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
b2
b1
SVA[9:8]
0
0
b0
FS
0
Figure 7.43 The SARUm register. Source: Hardware Manual, page 1512.
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(SVA[9⬊8]): These two bits are the upper bits 10-bit address.
(FS): This bit, when set to 0 selects the seven bit address format and when set to
1 selects the ten bit addressing format for the device.
Slave Address Register Lower (SARLm): SARLm sets slave address m (7-bit address
or lower eight bits of 10-bit address). Bits in this register are:
b7
b6
b5
b4
b3
b2
b1
SVA0
SVA[7:1]
Value after reset:
0
0
0
0
b0
0
0
0
0
Figure 7.44 The SARLm register. Source: Hardware Manual, page 1511.
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SVA[7⬊1]: When the 7-bit address format is selected (SARUm.FS 0) these
bits function as a 7-bit address. When the 10-bit address format is selected
(SARUm.FS 1) these bits function as the lower eight bits of a 10-bit address in
combination with the SVA0 bit. While the SARmE bit in ICSER is 0, the setting of
these bits is ignored.
SVA0: This bit forms the LSB of the 10-bit or 7-bit address assigned to the device.
CHAPTER 7 / SERIAL COMMUNICATIONS
235
I2C Bus Bit Rate Low Level Register (ICBRL): ICBRL is a 5-bit (BRL[4⬊0]) register
used to set the low-level period of the SCL clock. It also works to generate the data setup
time for automatic SCL low-hold operation. ICBRL counts the low-level period with the
internal reference clock source (IIC) specified by the CKS[2⬊0] bits in ICMR1. When the
RIIC is used only in slave mode, this register needs to be set to a value longer than the data
setup time. Bits in this register are:
Value after reset:
b7
b6
b5
—
—
—
1
1
1
b4
b3
b2
b1
b0
1
1
BRL[4:0]
1
1
1
Figure 7.45 The ICBRL register. Source: Hardware Manual, page 1513.
I2C Bus Bit Rate High Level Register (ICBRH): ICBRH is a 5-bit (BRH[4⬊0]) register
used to set the high-level period of SCL clock. ICBRH is valid in master mode. If the RIIC
is used only in slave mode, this register need not be set. ICBRH counts the high-level period with the internal reference clock source (IIC) specified by the CKS[2⬊0] bits in
ICMR1. Bits in this register are:
Value after reset:
b7
b6
b5
—
—
—
1
1
1
b4
b3
b2
b1
b0
1
1
BRH[4:0]
1
1
1
Figure 7.46 The ICBRH register. Source: Hardware Manual, page 1514.
I2C Bus Transmit Data Register (ICDRT): ICDRT is an 8-bit readable/writable register
that stores transmit data. When ICDRT detects a space in the I2C bus shift register
(ICDRS), it transfers the transmit data that has been written to ICDRT to ICDRS and starts
transmitting data in transmit mode. ICDRT can always be read and written. Write transmit
data to ICDRT once when a transmit data empty interrupt (ICTXI) request is generated.
Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
1
1
1
1
1
1
1
1
Figure 7.47 The ICDRT. Source: Hardware Manual, page 1516.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
I2C Bus Receive Data Register (ICDRR): ICDRR is an 8-bit read-only register that
stores received data. When one byte of data has been received, the received data is transferred from the I2C bus shift register (ICDRS) to ICDRR to enable the next data to be received. ICDRR cannot be written. Read data from ICDRR once when a receive data full interrupt (ICRXI) request is generated. Bits in this register are:
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
0
0
0
0
0
0
0
0
Figure 7.48 The ICDRR register. Source: Hardware Manual, page 1516.
I2C Bus Shift Register (ICDRS): ICDRS is an 8-bit shift register used to transmit and
receive data as shown below. ICDRS cannot be accessed directly.
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
—
—
—
—
Figure 7.49 The ICDRS register. Source: Hardware Manual, page 1516.
7.3
BASIC EXAMPLES
In this section we shall put into implementation the theoretical concepts learned in
Section 7.1 and Section 7.2, the process of setting up the interfaces, and understand the
practical working of each of the communication interfaces. Interfaces studied so far include the USART using the SCI, SPI using the RSPI, and the two wire serial interface using the RIIC interface. Sections 7.3.1 to 7.3.3 demonstrate the procedures to setup communication using each of the aforementioned interfaces by means of simple examples.
7.3.1
Basic Transmission/Receiving of Serial Data via UART
Aim: Demonstration of only transmission and only reception using the UART interface
of SCI.
CHAPTER 7 / SERIAL COMMUNICATIONS
237
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0,
RX62N Development kit, PC with RS-232 communication port.
Details: In this example, we will setup the RX62N processor to transmit a single byte
of information and receive a single byte of information at 9600 baud, no parity, and 1 stop
bit via polling.
Procedure: The process of transmitting and receiving a data byte from the SCI ports
can be divided into three parts: Initialization, Transmitting/Receiving the actual data, Getting ready to transmit the next byte/saving the received data into the desired location.
As seen in Figure 7.50 the registers required to control the USART SCI are: Baud Rate
Register (BRR), Serial Control Mode Register (SCMR), Serial Status Register (SSR), Serial Control Register (SCR), Serial Mode Register (SMR), and Serial Extended Mode Register (SEMR). Upon proper configuration of the values of each of these registers, the SCI
can be set up in the desired USART mode with a given baud rate. The step of Initialization
consists of setting up the initial values of these registers.
In the next step, for transmission, Transmit Data Register (TDR) is filled with the desired value of the data and on the few next clock cycles the data is output on the corresponding SCI port. This concludes the process of transmitting data. In the case of receiving
data, a flag is raised whenever a data byte is received in the Receive Data Register (RDR).
This may cause an interrupt to occur. When the receive flag is raised, we need to copy the
contents of the RDR into the desired location and conclude the process of reception.
The following code snippets show the process for setting up the SCI 2 of RX62N for
initialization, transmission, and reception:
1. void init_SCI2(void){
2.
MSTP(SCI2) = 0;
3.
IOPORT.PFFSCI.BIT.SCI2S = 1;
4.
PORT1.DDR.BIT.B2 = 0;
5.
PORT1.ICR.BIT.B2 = 1;
6.
PORT1.DDR.BIT.B3 = 1;
7.
SCI2.SCR.BYTE = 0;
8.
SCI2.SMR.BYTE = 0x00;
9.
SCI2.SCR.BIT.RIE = 1;
10.
SCI2.SCR.BIT.TIE = 1;
11.
IR(SCI2, RXI2) = 0;
12.
IR(SCI2, TXI2) = 0;
13.
IEN(SCI2, RXI2) = 0;
14.
IEN(SCI2, TXI2) = 0;
15.
SCI2.BRR = 12;
16.
SCI2.SCR.BYTE |= 0x30;
17. }
SCKn
TxDn
[Legend]
RSR:
RDR:
TSR:
TDR:
SMR:
SCR:
SSR:
SCMR:
BRR:
SEMR:
Parity check
SMR
Transmission
and reception
control
SEMR
BRR
Baud rate
generator
External clock
Clock
Serial control register
Serial status register
Smart card mode register
Bit rate register
Serail extended mode register
Parity error occurrence
TSR
SCR
SSR
SCMR
ERI
RXI
TXI
TEI
Figure 7.50 Serial Communications Architecture. Source: Hardware Manual, page 1339.
Receive shift register
Receive data register
Transmit shift register
Transmit data register
Serial mode register
RSR
TDR
PCLK/64
PCLK/16
PCLK/4
PCLK
Bus interface
RxDn
RDR
Module data bus
238
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Internal data bus
CHAPTER 7 / SERIAL COMMUNICATIONS
239
Explanation of Initialization Code
Line 2:
MSTP(SCI2) = 0;
This line of code enables the SCI2 module on the Renesas
Microcontroller.
Line 3:
IOPORT.PFFSCI.BIT.SCI2S = 1;
This line enables the use of TxD2-B and RxD2-B. This line of code is
applicable to ports that support differential mode of communication.
Line 4:
PORT1.DDR.BIT.B2 = 0;
Here, the SCI 0 interface is setup such that the on-chip baud rate
generation circuit is used and the SCK pin operates as a normal Digital I/O
pin. The transmission end interrupt is disabled with normal reception,
Serial transmission is enabled, reception is disabled, transmit interrupt and
reception interrupt are disabled.
Line 5:
PORT1.ICR.BIT.B2 = 1;
Here the input buffer to RxD2-B is enabled.
Line 6:
PORT1.DDR.BIT.B3 = 1;
This line of code enables TxD2-B on port 1 pin 3 as output.
Line 7:
SCI2.SCR.BYTE = 0;
This line of code disables the transmission and reception.
Line 8:
SCI2.SMR.BYTE = 0x00;
This line of code sets the SCI in Asynchronous mode with 8 bits of data
being transmitted with no parity, 1 stop bit, and no frequency division for
PCLK.
Line 9:
SCI2.SCR.BIT.RIE = 1;
This line of code enables the receive interrupts of the SCI2. These need to
be enabled in order to generate flags which we will poll to acquire data.
Line 10:
SCI2.SCR.BIT.TIE = 1;
This line of code enables the transmit interrupts of the SCI2. These need to
be enabled in order to generate flags which we will poll to acquire data.
Line 11:
IR(SCI2, RXI2) = 0;
Clear the interrupt request bits for the receive.
Line 12:
IR(SCI2, TXI2) = 0;
Clear the interrupt request bits for the transmit.
Line 13:
IEN(SCI2, RXI2) = 0;
Disable interrupt request for receive from RXI 2.
Line 14:
IEN(SCI2, TXI2) = 0;
Disable interrupt request for receive from TXI 2.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Line 15:
SCI2.BRR = 12;
Set the Baud rate register for communication to occur at 115200 baud.
Line 16:
SCI2.SCR.BYTE |= 0x30;
Enable Transmission and reception. We are now ready to transmit and
receive data.
The following code snippet shows the process for transmitting data from the SCI2 of
RX62N:
1. int transmit_data(unsigned char data){
2.
while(IR(SCI2, TXI2) == 0)
3.
;
4.
IR(SCI2, TXI2) = 0;
5.
SCI2.TDR = data;
6. }
Explanation of Transmission Code
Line 2: while(IR(SCI2, TXI2) == 0);
This line of code makes the microcontroller enter a wait state until the
transmit buffer becomes empty and generates an interrupt request.
Line 3: ;
Line 4: IR(SCI2, TXI2) = 0;
This line of code clears the interrupt request generated when the transmit
buffer becomes empty.
Line 5: SCI2.TDR = data;
This line of code copies the one byte data passed as an argument to the
function in to the transmit data register.
The following code snippet shows the process for receiving data from the SCI2 of RX62N:
1. unsigned char receive_data(void){
2.
unsigned char rcvd_data = 0;
3.
while(IR(SCI2, RXI2) != 1)
4.
;
5.
rcvd_data = SCI2.RDR;
6.
IR(SCI2, RXI2) = 0;
7.
return(rcvd_data);
8. }
CHAPTER 7 / SERIAL COMMUNICATIONS
241
Explanation of Reception Code
Line 2: unsigned char rcvd_data = 0;
Here we initialize an unsigned character variable “rcvd_data” to hold the
data received from the SCI2 RxD2-B pin.
Line 3: while(IR(SCI2, RXI2) != 1)
This line of code makes the microcontroller enter a wait state until an
interrupt request is generated after data is successfully received in the RDR.
Line 4: ;
Line 5: rcvd_data = SCI2.RDR;
Here we copy the contents of the data received in the receive data register
RDR into the variable rcvd_data.
Line 6: IR(SCI2, RXI2) = 0;
We now clear the interrupt request flag generated due to reception of data,
and make the SCI2 interface ready to receive data again.
Line 7: return(rcvd_data);
Here we return the received data back to the main program/function.
Putting it together:
1. void main(void){
2.
init_sci2();
3.
transmit_data(‘A’);
4.
unsigned char data = 0;
5.
data = receive_data();
6.
printf(“\ndata = %c”,data);
7.
return 0;
8. }
Explanation of Main Program
Line 2: init_sci2;
We call and execute the initialization function so that the SCI 2 gets set up
as a UART functioning at 115200 baud, no parity, 1 stop bit, and clocking
with no frequency division of PCLK.
Line 3: transmit_data(‘A’);
We call and execute the transmit_data function to transmit a character “A”
over the transmission line.
Line 4: unsigned char data = 0;
Here a unsigned character variable “data” is declared and initialized to 0.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Line 5: data = receive_data();
Here we call the function receive_data to receive data from the SCI2. The
function returns a character when data is received from SCI2 and is stored
in the variable “data.”
Line 6: printf(“\ndata = %c”,data);
Here we print the value of the variable data as a character over the standard
output of the microcontroller.
Line 7: return 0;
This line of code terminates the program and the microcontroller comes to a
halt.
7.3.2
Basic Transmission of Data Using Serial Peripheral Interface Bus
Aim: Demonstration of transmitting data with the serial peripheral interface bus.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0,
RX62N Development kit, Digital Oscilloscope, Oscilloscope probes.
Details: In this example, we will set up the RX62N processor to transmit a single byte
of information using the clock synchronous serial peripheral interface bus.
Procedure: The process of transmitting and receiving a data byte from the RSPI ports
can be divided in to three parts; namely: initialization, selection of a slave device, and
transmitting/receiving the actual data.
As seen in Figure 7.51 the registers required to control the RSPI are: SPCR, SPCR2,
SSLP, SPPCR, SPSR, SPDR, SPSSR, SPDCR, SSLND, SPCKD, SPND, SPCMD, and
SPBR. Upon proper configuration of the values of each of these registers, the RSPI can be
set up in the desired clock synchronous mode with a given bit rate. The step of Initialization consists of setting up the initial values of these registers.
In the next step for slave selection, a chip select/active low signal is output from one of
the SSL pins, or any other digital I/O pins, bringing the device out of the sleep state.
Next, the SPDR and SPCMDn registers are loaded with the proper values and the data
is transmitted as soon as the RSPI becomes idle.
In order to view the transmission of data, it is recommended to connect an oscilloscope
probe to the SCK, MOSI, MISO, and SSL-0 pins. If configuration of the RSPI is done as
shown in initialization code, an output similar to that of Figure 7.52 would be observed on
the oscilloscope. For our configuration D1 was connected to serial clock, D2 connected to
Master Out Slave In, D3 connected to Master In Slave Out and D4 was connected Slave
Select/Chip Select pins.
Bus interface
CHAPTER 7 / SERIAL COMMUNICATIONS
Module data bus
SPRX
SPTX
SPPCR
SPSR
Peripheral
bus
SPBR
SPCR
SSLP
243
Baud rate
generator
PCLK
SPDR
SPSCR
Parity circuit
SPSSR
SPDCR
SPCKD
SSLND
Shift register
SPND
SPCR2
SPCMD
Selector
Normal
Transmission/
reception controller
Clock
Loopback
MOSI
Normal
Loopback
Loopback 2
Normal
Loopback
Loopback 2
Master
Loopback 2
Slave
Master
SPTI
SPRI
SPII
SPEI
Slave
SSLn0
SSLn1 to SSLn3
RSPCKn
(n 5 A, B)
[Legend]
SPCR:
SPCR2:
SSLP:
SPPCR:
SPSR:
SPDR:
SPSCR:
SPSSR:
SPDCR:
SPCKD:
RSPI control register
RSPI control register 2
RSPI slave select polarity register
RSPI pin control register
RSPI status register
RSPI data register
RSPI sequence control register
RSPI sequence status register
RSPI data control register
RSPI clock delay register
SSLND:
SPND:
SPCMD:
SPBR:
SPTX:
SPRX:
SPTI:
SPRI:
SPII:
SPEI:
RSPI slave select negate delay register
RSPI next-access delay register
RSPI command registers 0 to 7 (eight registers)
RSPI bit rate register
RSPI transmit buffer
RSPI receive buffer
RSPI transmit interrupt
RSPI receive interrupt
SPI idle interrupt
RSPI error interrupt
Figure 7.51 Block Diagram of the Renesas Serial Peripheral Interface. Source: Hardware Manual, page 1631.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The following are the codes for initialization, transmission, and the main program.
1. void Init_RSPI(void){
2.
MSTP(RSPI0) = 0;
3.
IOPORT.PFGSPI.BIT.RSPIS = 0;
4.
PORT.PFGSPI.BIT.RSPCKE = 1;
5.
IOPORT.PFGSPI.BIT.SSL3E = 0;
6.
IOPORT.PFGSPI.BIT.MOSIE = 1;
7.
PORTC.DDR.BIT.B4 = 1;
8.
PORTC.DR.BIT.B4 = 1;
9.
PORTC.DDR.BIT.B7 = 1;
10.
PORTC.DR.BIT.B7 = 1;
11.
PORTC.DDR.BIT.B6 = 1;
12.
PORTC.DR.BIT.B6 = 1;
13.
PORTC.DDR.BIT.B5 = 1;
14.
PORTC.DR.BIT.B5 = 1;
15.
RSPI0.SPPCR.BYTE = 0x00;
16.
RSPI0.SPBR.BYTE = 0x00;
17.
RSPI0.SPDCR.BYTE = 0x00;
18.
RSPI0.SPCKD.BYTE = 0x00;
19.
RSPI0.SSLND.BYTE = 0x00;
20.
RSPI0.SPND.BYTE = 0x00;
21.
RSPI0.SPCR2.BYTE = 0x00;
22.
RSPI0.SPCMD0.WORD = 0x0700;
23.
RSPI0.SPCR.BYTE = 0x6B;
24.
RSPI0.SSLP.BYTE = 0x08;
25.
RSPI0.SPSCR.BYTE = 0x00;
26. }
Explanation of Initialization Code
Line 2:
MSTP(RSPI0) = 0;
This line of code enables the RSPI0(RSPI-A) module on the Renesas
Microcontroller, since the SPI2 is the interface connected to the RS-232
convertor on board the development kit.
Line 3:
IOPORT.PFGSPI.BIT.RSPIS = 0;
This line of code Selects the proper bank of pins for SPI0.
CHAPTER 7 / SERIAL COMMUNICATIONS
Line 4:
IOPORT.PFGSPI.BIT.RSPCKE = 1;
SCK (PC.5) is active and acts as a serial clock output.
Line 5:
IOPORT.PFGSPI.BIT.SSL3E = 0;
SSL3 (PC.2) is inactive (toggled as GPIO instead).
Line 6:
IOPORT.PFGSPI.BIT.MOSIE = 1;
MOSI (PC.6) is active.
Line 7:
PORTC.DDR.BIT.B4 = 1;
Select Port C bit 4 as Chip select pin, set up chip select pin, make it an
output.
Line 8:
PORTC.DR.BIT.B4 = 1;
Set level to high so as to not perform a chip select.
Line 9:
PORTC.DDR.BIT.B7 = 0;
Set MISO as an input.
Line 10:
PORTC.DR.BIT.B7 = 1;
Enable input buffer for peripheral.
Line 11:
PORTC.DDR.BIT.B6 = 1;
Set MOSI as an output.
Line 12:
PORTC.DR.BIT.B6 = 1;
Enable input buffer for peripheral.
Line 13:
PORTC.DDR.BIT.B5 = 1;
Set SCK as an output.
Line 14:
PORTC.DR.BIT.B5 = 1;
Set level to inactive.
Line 15:
RSPI0.SPPCR.BYTE = 0x00;
Initialize SPI (per flowchart in hardware manual), no loopback, CMOS
Output.
Line 16:
RSPI0.SPBR.BYTE = 0x00;
Run the RSPI at Full Speed with PCLK frequency of 48 MHz.
Line 17:
RSPI0.SPDCR.BYTE = 0x00;
16-bit data 1 frame 1 chip select.
Line 18:
RSPI0.SPCKD.BYTE = 0x00;
This line of code sets up the RSPI to have two clock delays before next
access to SPI device.
Line 19:
RSPI0.SSLND.BYTE = 0x00;
This line of code sets up the RSPI to have two clock delays after
de-asserting SSL.
245
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Line 20:
RSPI0.SPND.BYTE = 0x00;
This line of code sets up the RSPI to have two clock delays before next
access to SPI device.
Line 21:
RSPI0.SPCR2.BYTE = 0x00;
Initialize the RSPI with no parity, no idle interrupts.
Line 22:
RSPI0.SPCMD0.WORD = 0x0700;
MSB first 8-bit data, keep SSL low.
Line 23:
RSPI0.SPCR.BYTE = 0x6B;
Enable RSPI 3-wire in master mode with RSPI Enable Transmit only and
Interrupts.
Line 24:
RSPI0.SSLP.BYTE = 0x08;
SSL3A Polarity is active high.
Line 25:
RSPI0.SPSCR.BYTE = 0x00;
Transmit One frame of data.
Transmission Code
1. void RSPI_Transmit_LWord(int16_t sLowWord, int16_t sHighWord){
2.
PORTC.DR.BIT.B4 = 0;
3.
while(RSPI0.SPSR.BIT.IDLNF)
4.
;
5.
RSPI0.SPDR.WORD.L = sLowWord;
6.
RSPI0.SPDR.WORD.H = sHighWord;
7.
while(RSPI0.SPSR.BIT.IDLNF)
8.
;
9.
(void)RSPI0.SPDR.WORD.L;
10.
(void)RSPI0.SPDR.WORD.H;
11.
PORTC.DR.BIT.B4 = 1;
//CS OFF
12. }
Explanation of Transmission Code
Line 2: PORTC.DR.BIT.B4 = 0;
Here we set the bit to be pulled low so as to perform a chip select manually
to begin transmission.
Line 3: while(RSPI0.SPSR.BIT.IDLNF)
Wait for the RSPI to become idle. Program proceeds as soon as the IDLNF
flag becomes 0.
CHAPTER 7 / SERIAL COMMUNICATIONS
247
Line 4: ;
Line 5: RSPI0.SPDR.WORD.L = sLowWord;
Set the lower word of the SPDR to the value passed through the argument.
Line 6: RSPI0.SPDR.WORD.H = sHighWord;
Set the higher word of the SPDR to the value passed through the argument.
Line 7: while(RSPI0.SPSR.BIT.IDLNF);
Wait for the RSPI to finish transmission.
Line 8: ;
Line 9: (void)RSPI0.SPDR.WORD.L;
Read the lower word of the SPDR;
Line 10: (void)RSPI0.SPDR.WORD.H;
and read the higher word of the SPDR to clear interrupt flag.
Line 11: PORTC.DR.BIT.B4 = 1 ;
Set the Chip select pin to high to terminate transmission.
Main Code
1. void main(void) {
2.
Init_RSPI();
3.
while(1)
4.
RSPI_Send_LWord(0x0000, 0x0055);
5. }
Explanation of Main Code
Line 2: Init_RSPI();
We initialize the Renesas SPI by calling the Init_RSPI function.
Line 3: while(1)
Perform the next step forever.
Line 4: RSPI_Send_LWord(0x0000, 0x0055);
Transmit 0x00000055.
248
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
THU AUG 05 03:41:02 2010
Agilent Technologies
1
2
184.0 ns
200.0 ns /
Stop
D10
TTL
D4
D3
D2
D1
Cursors Menu
Mode
<None>
X1
-12.00ns
X2
30.00ns
X1 X2
Figure 7.52 Oscilloscope capture of a functional RSPI.
7.3.3
Basic Transmission and Reception of Data Using the Renesas I2C Bus
Aim: To demonstrate the setting up of the RIIC module to transmit and receive data from
a peripheral.
Details: In this example we will set up the RIIC peripheral module to transmit and receive 1 byte of data from an on board peripheral device.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0,
RX62N Development kit, Digital Oscilloscope, Oscilloscope probes.
Procedure: The YRDKRX62N development kit has an on board accelerometer
ADXL345. This is a three axis accelerometer capable of measuring accelerations in the X,
Y, and Z axis directions. The ADXL345 can communicate the measured values through the
SPI and I2C buses. Depending on the mode of communication selected using the CS pin,
one can use either of the two communication methods to obtain details and data from the
ADXL345. The ADXL345 is composed of several registers that it constantly updates when
not in the SLEEP or STAND BY mode. One particular register of interest is the 0x00 register that contains the value 0xE5 that symbolically represents “345.” Therefore when the
0x00 address location is read using the I2C mechanism, the value 0xe5 is acquired/read. The
address that we are going to write to is the pointer address for the ADXL 345 which is the
default register location select for the first byte of data transferred to the device after transmitting the device address 0x3A. The procedure for writing data to a peripheral device is:
CHAPTER 7 / SERIAL COMMUNICATIONS
249
1. Generate START condition.
2. Transmit address of device to communicate with and wait for the acknowledge bit
to arrive.
3. Transmit the data to be communicated with the device and wait for the acknowl-
edge bit to arrive for each byte transmitted.
4. If all bytes to be communicated have been transmitted, generate a STOP condition.
The procedure to read data from a peripheral device is in two parts that consist of writing
to the register pointer and then reading the desired bytes from the peripherals. In the first
half of the read cycle, the RX62N:
1. Generate a START condition.
2. Transmit address of device to communicate with and wait for acknowledge bit to
arrive.
3. Transmit the value of the register pointer and wait for an acknowledge.
4. Generate a STOP condition.
Next comes the read cycle which begins with:
1. Generating a START condition.
2. Transmitting the address of the device to communicate with ⴙ1 (note that this
address is always odd) and wait for an acknowledge.
3. Generate clock cycles or generate pseudo transactions of 0xFF to which the slave
device or peripheral clocks out the desired data. To each byte successfully received
the RIIC has to output an ACK bit which is a 0 on the ninth bit. If the Master receiver RX62N wishes to terminate a transaction, it needs to generate a NACK,
which is a 1 on the ninth bit of the last desired byte.
4. Generate a STOP condition.
To be able to do all of these activities, the microcontroller needs to be configured/initialized properly. The following code shows the procedure for initialization of the RIIC channel 0 aboard the RX62N. If RIIC channel 1 is available, then similar steps should be
followed:
1. void RiicIni(unsigned char in_SelfAddr){
2.
SYSTEM.MSTPCRB.BIT.MSTPB21 = 0;
3.
RIIC0.ICCR1.BIT.ICE = 0;
4.
RIIC0.ICCR1.BIT.IICRST = 1;
5.
RIIC0.ICCR1.BIT.IICRST = 0;
6.
RIIC0.SARU0.BIT.FS = 0;
7.
RIIC0.SARL0.BYTE = in_SelfAddr;
250
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23. }
RIIC0.ICMR1.BIT.CKS = 7;
RIIC0.ICBRH.BIT.BRH = 28;
RIIC0.ICBRL.BIT.BRL = 29;
RIIC0.ICMR3.BIT.ACKWP = 1;
RIIC0.ICIER.BIT.RIE = 1;
RIIC0.ICIER.BIT.TIE = 1;
RIIC0.ICIER.BIT.TEIE = 0;
RIIC0.ICIER.BIT.NAKIE = 1;
RIIC0.ICIER.BIT.SPIE = 1;
RIIC0.ICIER.BIT.STIE = 0;
RIIC0.ICIER.BIT.ALIE = 0;
RIIC0.ICIER.BIT.TMOIE = 0;
PORT1.ICR.BIT.B3 = 1;
PORT1.ICR.BIT.B2 = 1;
RIIC0.ICCR1.BIT.ICE = 1;
The following is the explanation of the above code line by line:
Line 1:
void RiicIni(unsigned char in_SelfAddr)
Declaring the function and the arguments.
Line 2:
SYSTEM.MSTPCRB.BIT.MSTPB21 = 0;
Enable the RIIC channel zero.
Line 3:
RIIC0.ICCR1.BIT.ICE = 0;
Disable the RIIC channel 0 manually just to make sure.
Line 4:
RIIC0.ICCR1.BIT.IICRST = 1;
Reset the RIIC0 module.
Line 5:
RIIC0.ICCR1.BIT.IICRST = 0;
Release the reset.
Line 6:
RIIC0.SARU0.BIT.FS = 0;
Set the device address as a 7 bit address.
Line 7:
RIIC0.SARL0.BYTE = in_SelfAddr;
Set the device address from the argument of the function.
Line 8:
RIIC0.ICMR1.BIT.CKS = 7;
Select clock input to the RIIC0 module as PCLK/128.
Line 9:
RIIC0.ICBRH.BIT.BRH = 28;
Set the bit counter for the high level of the serial clock cycle.
Line 10:
RIIC0.ICBRL.BIT.BRL = 29;
Set the bit counter for the low level of the serial clock cycle.
CHAPTER 7 / SERIAL COMMUNICATIONS
Line 11:
RIIC0.ICMR3.BIT.ACKWP = 1;
Disable write protect for the ACK bit.
Line 12:
RIIC0.ICIER.BIT.RIE = 1;
Enable the Receive data full interrupt.
Line 13:
RIIC0.ICIER.BIT.TIE = 1;
Enable the Transmit data full interrupt.
Line 14:
RIIC0.ICIER.BIT.TEIE = 0;
Enable the Transmit End interrupt.
Line 15:
RIIC0.ICIER.BIT.NAKIE = 1;
Enable the NACK received interrupt.
Line 16:
RIIC0.ICIER.BIT.SPIE = 1;
Enable the Stop condition received interrupt.
Line 17:
RIIC0.ICIER.BIT.STIE = 0;
Disable the Start condition received interrupt.
Line 18:
RIIC0.ICIER.BIT.ALIE = 0;
Disable the Arbitration lost interrupt.
Line 19:
RIIC0.ICIER.BIT.TMOIE = 0;
Timeout interrupt request is disabled.
Line 20:
PORT1.ICR.BIT.B3 = 1;
Enable input buffer on PORT1 pin 3.
Line 21:
PORT1.ICR.BIT.B2 = 1;
Enable input buffer on PORT1 pin 2.
Line 22:
RIIC0.ICCR1.BIT.ICE = 1;
Enable the RIIC0 module.
Line 23:
}
End of function definition.
The process to uninitialized the RIIC0 is
1. void RiicUnIni(void){
2.
SYSTEM.MSTPCRB.BIT.MSTPB21 = 1;
3. }
The following is the explanation of the above code line by line:
Line 1:
void RiicUnIni(void){
Declare the function name to uninitialization
251
252
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Line 2:
SYSTEM.MSTPCRB.BIT.MSTPB21 = 1;
Disable the RIIC0 module
Line 3:
}
End function definition
The following snippet of code demonstrates how data transfer takes place, using polling:
There are three essential parts to data transfer when using the I2C protocol:
1. Generating the START condition.
2. Performing the transfer.
3. Sending the STOP condition.
The following is the code for generating the START condition:
1. unsigned char RiicSendStart(void){
2.
if(RIIC0.ICCR1.BIT.ICE){
3.
while(RIIC0.ICCR2.BIT.BBSY)
4.
;
5.
RIIC0.ICCR2.BIT.ST = 1;
6.
while(!(RIIC0.ICCR2.BIT.BBSY && RIIC0.ICSR2.BIT.START))
7.
;
8.
RIIC0.ICSR2.BIT.START = 0;
9.
return 1;
10.
}
11.
else return 0;
12. }
The following is the explanation for the above code:
Line 1:
unsigned char RiicSendStart(void){
Declare the function name and arguments.
Line 2:
if(RIIC0.ICCR1.BIT.ICE){
Check if the RIIC0 module is enabled.
Line 3:
while(RIIC0.ICCR2.BIT.BBSY)
Wait here until the bus becomes free.
Line 4:
Line 5:
;
RIIC0.ICCR2.BIT.ST = 1;
When bus becomes free, request for transmitting a START condition.
Line 6:
while(!(RIIC0.ICCR2.BIT.BBSY && RIIC0.ICSR2.BIT.START))
Wait here until START condition is detected by the RIIC0 module.
CHAPTER 7 / SERIAL COMMUNICATIONS
Line 7:
Line 8:
253
;
RIIC0.ICSR2.BIT.START = 0;
After detecting the module, disable the interrupt bit in the status register.
Line 9:
return 1;
Report success.
Line 10:
Line 11:
}
else return 0;
Report failure if RIIC0 module is not enabled.
Line 12:
}
The following is the code for generating the STOP condition:
1. unsigned char RiicSendStop(void){
2.
if(RIIC0.ICCR1.BIT.ICE){
3.
while(RIIC0.ICCR2.BIT.BBSY){
4.
RIIC0.ICCR2.BIT.SP = 1;
5.
}
6.
return 1;
7.
}
8.
else return 0;
9. }
The following is the explanation for the code given above:
Line 1: unsigned char RiicSendStop(void){
Declare the function name and arguments.
Line 2: if(RIIC0.ICCR1.BIT.ICE){
If the RIIC0 module is enabled perform the following steps.
Line 3: while(RIIC0.ICCR2.BIT.BBSY){
Line 4: RIIC0.ICCR2.BIT.SP = 1;
While the bus is busy, request to generate a stop condition.
Line 5: }
Line 6: return 1;
Report Success.
Line 7: }
Line 8: else return 0;
If the RIIC0 module is disabled report failure.
Line 9: }
254
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The following is the code for writing a data byte to a peripheral device on the I2C bus:
1. unsigned char RiicWriteByte(unsigned char slave_addr, unsigned
char slave_register_num, unsigned char data_byte){
2.
RIIC0.ICDRT = slave_addr & (0xFE);
3.
while(!RIIC0.ICSR2.BIT.TDRE)
4.
;
5.
RIIC0.ICDRT = slave_register_num;
6.
while(!RIIC0.ICSR2.BIT.TEND){
7.
if(RIIC0.ICSR2.BIT.NACKF){
8.
RIIC0.ICSR2.BIT.NACKF = 0;
9.
return 0;
10.
}
11.
}
12.
while(!RIIC0.ICSR2.BIT.TDRE)
13.
;
14.
RIIC0.ICDRT = data_byte;
15.
while(!RIIC0.ICSR2.BIT.TEND){
16.
if(RIIC0.ICSR2.BIT.NACKF){
17.
RIIC0.ICSR2.BIT.NACKF = 0;
18.
return 0;
19.
}
20.
}
21.
while(!RIIC0.ICSR2.BIT.TDRE)
22.
;
23.
while(!RIIC0.ICSR2.BIT.TEND){
24.
if(RIIC0.ICSR2.BIT.NACKF){
25.
RIIC0.ICSR2.BIT.NACKF = 0;
26.
return 0;
27.
}
28.
}
29.
return 1;
30. }
The following is the explanation for the above codes:
Line 1:
unsigned char RiicWriteByte2(unsigned char slave_addr,
unsigned char slave_register_num, unsigned char data_byte){
Declare and define the function and its arguments.
CHAPTER 7 / SERIAL COMMUNICATIONS
Line 2:
255
RIIC0.ICDRT = slave_addr & (0xFE);
Fill the transmit buffer with the slave address input as an argument to the
function.
Line 3:
while(!RIIC0.ICSR2.BIT.TDRE)
Wait until the Transmit data empty flag becomes high.
Line 4:
Line 5:
;
RIIC0.ICDRT = slave_register_num;
Fill the transmit data buffer with the slave register number to be written to.
Line 6:
while(!RIIC0.ICSR2.BIT.TEND){
Since the RIIC has a double buffer for transmission and reception, we
need to wait until the previous transmission is finished.
Line 7:
if(RIIC0.ICSR2.BIT.NACKF){
Check if a NACK is received in response to the transmit operation.
Line 8:
RIIC0.ICSR2.BIT.NACKF = 0;
If a NACK is received, then Reset the NACKF flag.
Line 9:
return 0;
And report failure.
Line 10:
Line 11:
Line 12:
}
}
while(!RIIC0.ICSR2.BIT.TDRE)
Wait here until the transmit data register becomes empty again.
Line 13:
Line 14:
;
RIIC0.ICDRT = data_byte;
Fill the transmit data register with the actual data byte that needs to be
transmitted.
Line 15:
while(!RIIC0.ICSR2.BIT.TEND){
Since the RIIC has a double buffer for transmission and reception, we
need to wait until the previous transmission is finished.
Line 16:
if(RIIC0.ICSR2.BIT.NACKF){
Check if a NACK is received in response to the transmit operation.
Line 17:
RIIC0.ICSR2.BIT.NACKF = 0;
If a NACK is received, then Reset the NACKF flag.
Line 18:
return 0;
And report failure.
Line 19:
Line 20:
}
}
256
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Line 21:
while(!RIIC0.ICSR2.BIT.TDRE)
Wait here until the transmit data register becomes empty again.
Line 22:
Line 23:
;
while(!RIIC0.ICSR2.BIT.TEND){
Since the RIIC has a double buffer for transmission and reception, we
need to wait until the previous transmission is finished.
Line 24:
if(RIIC0.ICSR2.BIT.NACKF){
Check if a NACK is received in response to the transmit operation.
Line 25:
RIIC0.ICSR2.BIT.NACKF = 0;
If a NACK is received, then Reset the NACKF flag.
Line 26:
return 0;
And report failure.
Line 27:
Line 28:
Line 29:
}
}
return 1;
If all goes well, report success.
Line 30:
}
The following is a piece of code similar to the above code, however it writes only the slave
address and the register number to the I2C peripheral device. This is useful when reading
data from the peripheral device in which one needs to write to the slave device the register
from which the data is to be transferred and then data is read consecutively from the
registers.
1. unsigned char RiicWriteByte(unsigned char slave_addr, unsigned
char data_byte){
2.
RIIC0.ICDRT = slave_addr & (0xFE);
3.
while(!RIIC0.ICSR2.BIT.TDRE)
4.
;
5.
RIIC0.ICDRT = data_byte;
6.
while(!RIIC0.ICSR2.BIT.TEND){
7.
if(RIIC0.ICSR2.BIT.NACKF){
8.
RIIC0.ICSR2.BIT.NACKF = 0;
9.
return 0;
10.
}
11.
}
12.
while(!RIIC0.ICSR2.BIT.TDRE)
13.
;
CHAPTER 7 / SERIAL COMMUNICATIONS
14.
15.
16.
17.
18.
19.
20.
21. }
257
while(!RIIC0.ICSR2.BIT.TEND){
if(RIIC0.ICSR2.BIT.NACKF){
RIIC0.ICSR2.BIT.NACKF = 0;
return 0;
}
}
return 1;
The following is the code for reading a data byte from a peripheral device on the I2C bus:
1. unsigned char RiicReadByte(unsigned char slave_addr, unsigned char
slave_register_num){
2.
RiicWriteByte(slave_addr,slave_register_num);
3.
RiicSendStop();
4.
RIIC0.ICSR2.BIT.STOP = 0;
5.
RiicSendStart();
6.
while(!RIIC0.ICSR2.BIT.TDRE)
7.
;
8.
RIIC0.ICDRT = slave_addr | (0x01);
9.
while(!RIIC0.ICSR2.BIT.RDRF)
10.
;
11.
if(RIIC0.ICSR2.BIT.NACKF == 0){
12.
RIIC0.ICMR3.BIT.WAIT = 1;
13.
RIIC0.ICMR3.BIT.ACKBT = 1;
14.
read_byte = RIIC0.ICDRR;
15.
while(!RIIC0.ICSR2.BIT.RDRF)
16.
;
17.
RIIC0.ICSR2.BIT.STOP = 0;
18.
RIIC0.ICCR2.BIT.SP = 1;
19.
read_byte = RIIC0.ICDRR;
20.
while(!RIIC0.ICSR2.BIT.STOP)
21.
;
22.
return read_byte;
23.
}
24.
else return 0xFF;
25. }
258
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The following explains the above given code :
Line 1:
Line 2:
unsigned char RiicReadByte(unsigned char slave_addr, unsigned
char slave_register_num){
RiicWriteByte(slave_addr,slave_register_num);
Write the data register from which the data is to be read.
Line 3:
RiicSendStop();
Send a STOP condition.
Line 4:
RIIC0.ICSR2.BIT.STOP = 0;
Reset the STOP condition flag.
Line 5:
RiicSendStart();
Send a START condition over the I2C Bus.
Line 6:
while(!RIIC0.ICSR2.BIT.TDRE)
Wait here until transmit buffer gets empty.
Line 7:
Line 8:
;
RIIC0.ICDRT = slave_addr | (0x01);
Request a read from the peripheral device by transmitting the read address
as Slave device (write) address 1.
Line 9:
while(!RIIC0.ICSR2.BIT.RDRF)
Wait until the read buffer becomes full.
Line 10:
Line 11:
;
if(RIIC0.ICSR2.BIT.NACKF == 0){
If a ACK is received; i.e., the device is ready, do the following actions.
Line 12:
RIIC0.ICMR3.BIT.WAIT = 1;
Set the WAIT bit to 1, due to which the period between ninth clock cycle
and first clock cycle is held low.
Line 13:
RIIC0.ICMR3.BIT.ACKBT = 1;
Set the ACK bit transmitted as 1, which corresponds to a NACK for the
peripheral device.
Line 14:
read_byte = RIIC0.ICDRR;
Read dummy data from the I2C receive data register.
Line 15:
while(!RIIC0.ICSR2.BIT.RDRF);
Wait here until the ICDRR becomes full again when the shift register
transfers data from itself to the ICDRR. This is due to double buffering of
data.
Line 16:
;
CHAPTER 7 / SERIAL COMMUNICATIONS
Line 17:
259
RIIC0.ICSR2.BIT.STOP = 0;
Reset the status of the STOP bit in the ICSR2.
Line 18:
RIIC0.ICCR2.BIT.SP = 1;
Request for generation of STOP signal.
Line 19:
read_byte = RIIC0.ICDRR;
Read data from the ICDRR.
Line 20:
while(!RIIC0.ICSR2.BIT.STOP)
Wait here until the STOP condition is generated.
Line 21:
Line 22:
;
return read_byte;
Return the Data received as the return value of the function.
Line 23:
Line 24:
}
else return 0xFF;
If a NACK was received return 0xFF (or any desired value) as a Failure
value.
Line 25:
}
The following code shows the entire process of reading one byte from a peripheral connected on the I2C bus:
1. void main(void){
2.
RiicIni(0x10);
3.
RiicSendStart();
4.
RiicWriteByte2(0x3A, 0x2D, 0x00);
5.
RiicSendStop();
6.
RiicSendStart();
7.
i = RiicReadByte(0x3A, 0x00);
8.
RiicSendStop();
9.
RiicUnIni();
10.
while(1)
11.
;
12. }
The following is the explanation of the above code:
Line 1:
void main(void){
Define the main function.
260
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Line 2:
RiicIni(0x10);
Initialize the I2C module RIIC0 with self address as 0x10.
Line 3:
RiicSendStart();
Send a START condition.
Line 4:
RiicWriteByte2(0x3A, 0x2D, 0x00);
Write a byte 0x00 to the register 0x2D of the peripheral device with
address 0x3A.
Line 5:
RiicSendStop();
Send a STOP condition.
Line 6:
RiicSendStart();
Send a START condition again.
Line 7:
i = RiicReadByte(0x3A, 0x00);
Read a byte from the register 0x00 of the peripheral with address 0x3A.
Line 8:
RiicSendStop();
Send a STOP condition.
Line 9:
RiicUnIni();
Disable the RIIC0 interface.
Line 10:
while(1)
Wait here forever.
Line 11:
Line 12:
;
}
Agilent Technologies
1
1.00V/
FRI OCT 08 05:48:01 2010
11.40 ms 5.000ms /
2
Stop
TTL
D8
D8 D8
D9 D9
1 1
Digital Channel Menu
D15
D9
Turn on
D15 - D8
Turn on
D7 - D0
____ __ __ ____ ____ D
0
Thresholds
1.56MSa/s
Bus
Figure 7.53 Oscilloscope Capture of the complete I2C communication for Basic Example 7.3.3.
CHAPTER 7 / SERIAL COMMUNICATIONS
Agilent Technologies
1
1.00V/
261
FRI OCT 08 05:46:54 2010
5.260 ms 2 .000ms /
2
Stop
TTL
D8
D8 D8
D9 D9
1 1
Digital Channel Menu
D15
D9
Turn on
D15 - D8
Turn on
D7 - D0
____ __ __ ____ ____ D
0
1.56MSa/s
Thresholds
Bus
Figure 7.54 Oscilloscope Capture of the beginning of I2C communication for Basic Example 01
(scaled along x-axis). There are three data bytes transferred for the write cycle (first twenty-seven
clock pulses).
Agilent Technologies
1
1.00V/
FRI OCT 08 05:47:23 2010
16.22 ms 2 .000ms /
2
Stop
TTL
D8
D8 D8
D9 D9
1 1
Digital Channel Menu
D15
D9
Turn on
D15 - D8
Turn on
D7 - D0
____ __ __ ____ ____ D
0
Thresholds
1.56MSa/s
Bus
Figure 7.55 Oscilloscope Capture of the end of I2C communication for Basic Example 7.3.3
(scaled along the x-axis). There are two cycles here, each consisting of two data bytes. First is
the 2 byte write cycle and the other is the 2 byte read cycle.
262
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
7.4
ADVANCED CONCEPTS
Now that we have learned the details of the working behind various communication techniques with polling; i.e., the UART, SPI, and I2C interfaces, in this section we will study some
of the advanced features and implementations of the same. Concepts learned in these chapters
will be implemented in Section 7.5 by means of examples. Concepts learned in this section
will require basic knowledge of interrupts and interrupt service routines, and additional hardware to be present. It is advisable for the reader to be aware of the additional peripherals being
used while illustrating the advanced features of the communication techniques in this section.
7.4.1
Applying FIFO Data Structures for Transmission and Reception Using the UART
Serial Communications Interface
As mentioned in Section 7.2.1 the UART in essence contains a single byte buffer each for
transmitting and receiving data from other peripherals connected via the UART interface.
These buffers are occasionally filled with data and then the data is transmitted or received.
But what if an application is required to transmit data continuously? Usually the peripherals of a Microcontroller operate slower than the actual processing unit. In short, the data
output by the processing unit to be transmitted is more quickly generated than transmitted.
In such a case, there are two options available: wait for the peripheral to finish transmitting
the current data and then load the peripheral with new data, or maintain a First In First Out
type of mechanism in which bulk data is stored in a given data structure and then transmitted as and when the peripheral becomes available. The advantage of the latter technique is
that the processing unit is free to perform other tasks as data transmission is going on. Before we move on to understanding the design of a UART FIFO, let us take a quick look at
a FIFO data structure.
A FIFO type data structure can be visualized as a queue of units standing in line for
service. The unit that gets in line first gets service earlier than the unit that enters the queue
at a later point of time. This is quite contrary to a LIFO type of data structure in which the
last unit to enter the queue gets service prior to the one which entered the queue earlier.
FIFOs are generally used wherever operations are to be done on all data in a sequential/
consecutive manner. An example of a FIFO is shown in Figure 7.56.
older
data
head
newer
data
tail
Figure 7.56 Example of a
FIFO (queue).
CHAPTER 7 / SERIAL COMMUNICATIONS
263
As seen in Figure 7.56 the FIFO consists of a head and a tail where the head contains data
that was added to the queue earlier, whereas the tail end contains relatively new data. The
size of the queue is also maintained by monitoring variables. Essentials for regulating
queues for the UART SCI are as follows:
䡲
䡲
䡲
䡲
䡲
䡲
䡲
Need to maintain one queue for transmission and one queue for reception.
The transmit ISR unloads data from the transmission queue.
The receive ISR loads data to the reception queue.
Pointers are used to maintain the head and tail of the queue.
A variable “size” keeps track of the current size of the queue.
Pointers are wrapped around the queue when queue is not empty but the queue
reaches the end of the allotted area.
The main program is responsible for loading the transmit queue and unloading the
receive queue.
Queues are implemented with interrupt service routines and not polling, since polling requires the microcontroller to wait and do nothing until current operation is performed. Interrupt Service Routines, on the other hand, are performed intermittently when required
and do not disturb the working of the main program. As we shall see in the Advanced
Example 7.5.1, the queues will be loaded at a single occasion and then the main program
proceeds without waiting for the transmission to complete. The ISRs continue to occur intermittently and finish the transfer of data. The following is the algorithm followed for the
complex example in Section 7.5.1.
䡲
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Initialize the UART.
Set up switches and define the size of the queue.
Define a FIFO queue structure consisting of a data array, a pointer to the head of
the array, a pointer to the tail of the array, and a variable for holding the current
size of the queue.
Allot memory for two queues, one for transmission and other for reception.
Define function for checking if a queue is empty and another function to check if a
queue is full.
Initialize the queues by setting the data in the queue, head and tail to zero.
Define a function for queuing data in a given queue. In order for the data to be
queued, perform a check if the queue is full. If queue is not full, then queue data by
adding to the tail of the array, update the tail and size values, and report success.
Otherwise abort queuing and report failure.
Define a function for dequeuing data. In order to dequeue data, check if the queue
is empty. If the queue is not empty, copy a byte of data from the head of the queue,
update the head and size of the queue, and return the copied variable. If the queue
is empty, exit the function.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
Define the interrupt service routines that do the following:
▫ Transmit routines: Check if the queue is empty. If the queue is not empty, dequeue a byte of data from the transmission queue and give it to the transmit
buffer of the microcontroller.
▫ Receive routine: Try to enqueue the data to the receive queue. If the queue is
full, provide with an indication.
Setting up the interrupts: The following is the procedure for setting up the serial communication interface interrupts:
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7.4.2
In the vect.h file define the vector table locations of the interrupts and declare them
as follows:
▫ #pragma interrupt (Excep_SCI2_RXI2(vect 223)) void Excep_SCI2_RXI2
(void);
▫ #pragma interrupt (Excep_SCI2_TXI2(vect 224)) void Excep_SCI2_TXI2
(void);
In the file intprg.c write the detailed interrupt service routines for transmit and receive under the function names void Excep_SCI2_RXI2 (void) and void Excep_
SCI2_TXI2 (void).
Multiprocessor Communication Using the Renesas Serial Peripheral Interface
One of the advantages of the serial peripheral interface is the high rate of data transfer.
Data is usually transferred at a rate more than 1 MHz’s. These speeds are much higher than
most other communication protocols and makes SPI well suited for setting up communication amongst processors. As an example, we shall set up two microcontrollers, one as a
master and the other as a slave, and demonstrate high speed data transfer between the two.
This setup can be used for various applications such as rapid data accumulation or distributed problem solving; in which a problem is split up into various smaller sections and sent
to different processors, solved simultaneously in parts, and then transferred back to the
main processor. The following section will demonstrate how to set up two microcontrollers, one in master mode and the other in slave mode, such that data can be rapidly
transferred between two or more processors. In essence the setup here is the Single Master
Multiple Slave configuration, as shown in Figure 7.57.
Data transfer in the above mentioned configuration is done by means of interrupts and
interrupt service routines. The two important interrupts for SPI transfer are the SPTIx and
SPRIx interrupts, where x 0, 1 and “x” is the module number of the RSPI,
RSPI0/RSPIA, and RSPI1/RSPIB. Timing details of the interrupts and data transfer are described as follows.
CHAPTER 7 / SERIAL COMMUNICATIONS
265
RSPI slave 0
This LSI (master)
RSPCK
MOSI
MISO
SSL
RSPCK
MOSI
MISO
SSL0
SSL1
SSL2
SSL3
RSPI slave 1
RSPCK
MOSI
MISO
SSL
RSPI slave 2
RSPCK
MOSI
MISO
SSL
RSPI slave 3
RSPCK
MOSI
MISO
SSL
Figure 7.57 Single Master Multiple Slaves. Source: Hardware Manual, page 1664.
W
SPTI
1
2
3
4
5
I
W
(4)
(3)
6
7
8
<
RSPCKn
(CPHA 5 1,
CPOL 5 0)
(2)
< <
SPRI
W
I
(5)
<
(1)
I
<<<
I
<<<
SPDR access
1
2
3
4
5
6
7
8
(n 5 A, D)
Figure 7.58 Operation and timing diagram of SPI interrupts. Source: Hardware Manual, page 1681.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Interrupts occur at times (1) to (5) and are as follows:
1. If the interrupts are enabled and currently no data is present in the transmit buffer,
2.
3.
4.
5.
an interrupt, SPTI, is generated, which writes to SPDR. Since the transmit buffer is
empty, data is copied into the transmit buffer.
When the shift register is/becomes empty, the RSPI copies the data from the transmit buffer to the shift register, starts shifting out the data, and generates a transmit
buffer empty request (SPTI).
When transmit data is written to SPDR by the transmit buffer empty interrupt routine, the data is transferred to the transmit buffer. Because the data being transferred serially is stored in the shift register, the RSPI does not copy the data in the
transmit buffer to the shift register.
The serial transfer ends. Since the receive buffer is empty, the RSPI copies the received data from the shift register into the receive buffer and generates a receive
buffer full interrupt SPRI. As the transmit buffer is filled from step 3, the RSPI
copies the data from the transmit buffer into the shift register and resumes transmission of data.
When SPDR is read by the receive buffer full interrupt routine, the RSPI sends the
data in the receive buffer to the bus inside the chip.
In this manner, the data transfer keeps occurring continuously when the RSPI is enabled.
Next we will proceed to the setting up of the microcontrollers in required modes and
then proceed to use FIFO queues as explained and demonstrated in Section 7.4.1. Using
FIFO queues for communication simplifies the transfer of data and enables fast and continuous communication. Rules for operating the queues remain the same as in Section
7.4.1 however one must notice that now data transfer is taking place in both directions at
the same time, with much higher speeds as compared to the SCI interface. For setting up
multiprocessor communication, at least two microcontrollers are needed. One microcontroller will be set up in Master mode while the other will be set up in the Slave mode. The
complex example in Section 7.5.2 follows the algorithms for the two microcontrollers as
mentioned in the following:
Master Algorithm
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Initialize one Renesas Microcontroller as the master device by assigning the correct values for the registers.
Define a FIFO queue structure consisting of a data array, a pointer to the head of
the array, a pointer to the tail of the array, and a variable for holding the current
size of the queue.
Allot memory for two queues, one for transmission and the other for reception.
CHAPTER 7 / SERIAL COMMUNICATIONS
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267
Define function for checking if the queue is empty, and another function to check
if the queue is full.
Initialize the queues by setting the data in the queue, head and tail to zero.
Define a function for queuing data in a given queue. In order for the data to be
queued, perform a check if the queue is full. If the queue is not full, then queue
data by adding to the tail of the array, update the tail and size values, and report
success. Otherwise, abort queuing and report failure.
Define a function for dequeuing data. In order to dequeue data, check if the queue
is empty. If the queue is not empty, copy a byte of data from the head of the queue,
update the head and size of the queue, and return the copied variable. If the queue
is empty, exit the function.
Define the interrupt service routines that do the following:
▫ Transmit routines: Check if the queue is empty. If the queue is not empty, dequeue a byte of data from the transmission queue and give it to the transmit
buffer of the microcontroller.
▫ Receive routine: Try to enqueue the data to the receive queue. If the queue is
full, provide with an indication.
Setting up the interrupts: The following is the procedure for setting up the serial communication interface interrupts:
䡲
䡲
In the vect.h file define the vector table locations of the interrupts and declare them
as follows:
▫ #pragma interrupt (Excep_RSPI0_SPRIO(vect 45)) void
Excep_RSPI0_SPRIO (void);
▫ #pragma interrupt (Excep_RSPI0_SPTIO(vect 46)) void
Excep_RSPI0_SPTIO (void);
In the file intprg.c write the detailed interrupt service routines for transmit and receive under the function names void Excep_RSPI0_SPRIO (void) and void Excep
Excep_RSPI0_SPTIO (void).
Slave Algorithm
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Initialize another Renesas Microcontroller as the slave device by assigning the correct values for the registers.
Define a FIFO queue structure consisting of a data array, a pointer to the head of
the array, a pointer to the tail of the array, and a variable for holding the current
size of the queue.
Allot memory for two queues, one for transmission and the other for reception.
Define function for checking if the queue is empty, and another function to check
if the queue is full.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
䡲
䡲
Initialize the queues by setting the data in the queue, head and tail to zero.
Define a function for queuing data in a given queue. In order for the data to be
queued, perform a check if the queue is full. If the queue is not full, then queue
data by adding to the tail of the array, update the tail and size values, and report
success. Otherwise, abort queuing and report failure.
Define a function for dequeuing data. In order to dequeue data, check if the queue
is empty. If the queue is not empty, copy a byte of data from the head of the queue,
update the head and size of the queue, and return the copied variable. If the queue
is empty, exit the function.
Define the interrupt service routines that do the following:
▫ Transmit routines: Check if the queue is empty. If the queue is not empty, dequeue a byte of data from the transmission queue and give it to the transmit
buffer of the microcontroller.
▫ Receive routine: Try to enqueue the data to the receive queue. If the queue is
full, provide with an indication.
Setting up the interrupts: The following is the procedure for setting up the serial communication interface interrupts:
䡲
䡲
7.4.3
In the vect.h file define the vector table locations of the interrupts and declare them
as follows:
▫ #pragma interrupt (Excep_RSPI0_SPRIO(vect 45)) void
Excep_RSPI0_SPRIO (void);
▫ #pragma interrupt (Excep_RSPI0_SPTIO(vect 46)) void
Excep_RSPI0_SPTIO (void);
In the file intprg.c write the detailed interrupt service routines for transmit and receive under the function names void Excep_RSPI0_SPRIO (void) and void
Excep_RSPI0_SPTIO (void).
Transfer of Data Between Peripherals Connected on the I2C Bus Using FIFOs
In section 7.2.3 we explained the details of the Renesas I2C interface module and the procedure for setting it up. In section 7.3.3 we demonstrated how to transfer a single byte of
data to and from a peripheral. As observed, there is a lot of overhead to transfer a single
byte to a peripheral. It thus makes sense to transfer more than one byte at a single time to
the device.
Most devices that operate using the I2C interface store and read out data bytes from
registers; i.e., we read and write data from registers of the device. The devices usually have
a register address pointer which points to the register to write to or read from. This register
is usually auto incremented when the data is transferred. This allows us to transfer multiple
CHAPTER 7 / SERIAL COMMUNICATIONS
269
bytes to and from the device. Thus we can use FIFOs to implement the transfer of data. The
easiest method to operate the FIFOs is by using interrupts.
The following are the algorithms to read and write data to the device. Data provided to
the transmit buffer is from the transmit FIFO and data received from the receive buffer is
input into the receive FIFO:
Writing data to a peripheral device/Master transmitter operation using interrupts:
1. Set the IICRST bit in ICCR1 to 1 (internal reset) and then clear the IICRST bit
to 0 (canceling reset) with the ICE bit in ICCR1 cleared to 0 (disabling the interface). This initializes the internal state and the various flags of ICSR1. After that,
set registers SARLn, SARUn, ICSER, ICMR1, ICBRH, and ICBRL (n 0 to 2),
and set the other registers as necessary (for initial settings of the RIIC, see Figure
30.5 in the hardware manual). When the necessary register settings have been
completed, set the ICE bit to 1 (to enable transfer). This step is not necessary if initialization of the RIIC has already been completed.
2. Read the BBSY flag in ICCR2 to check that the bus is open, and then set the ST
bit in ICCR2 to 1 (start condition issuance request). Upon receiving the request,
the RIIC issues a start condition. At the same time, the BBSY flag and the
START flag in ICSR2 are automatically set to 1 and the ST bit is automatically
cleared to 0. At this time, if the start condition is detected, and the internal levels
for the SDA output state and the levels on the SDAn line have matched while the
ST bit is 1, the RIIC recognizes that issuing of the start condition as requested by
the ST bit has been successfully completed, and the MST and TRS bits in ICCR2
are automatically set to 1, placing the RIIC in master transmitter mode. The
TDRE flag in ICSR2 is also automatically set to 1 in response to the setting of
the TRS bit to 1.
3. Check that the TDRE flag in ICSR2 is 1, and then write the value for transmission (the slave address and the R/W# bit) to ICDRT. Once the data for transmission are written to ICDRT, the TDRE flag is automatically cleared to 0, the data
are transferred from ICDRT to ICDRS, and the TDRE flag is again set to 1. After the byte containing the slave address and R/W# bit has been transmitted, the
value of the TRS bit is automatically updated to select master transmitter or master receiver mode in accord with the value of the transmitted R/W# bit. If the
value of the R/W# bit was 0, the RIIC continues in master transmitter mode.
Since the ICSR2.NACKF flag being 1 at this time indicates that no slave device
recognized the address or that there was an error in communications, write 1 to
the ICCR2.SP bit to issue a stop condition. For data transmission with an address
in the 10-bit format, start by writing 1111 0b, the two higher-order bits of the
slave address, and W to ICDRT as the first address transmission. Then, as the
second address transmission, write the eight lower-order bits of the slave address
to ICDRT.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
4. After confirming that the TDRE flag in ICSR2 is 1, write the data for transmission
to the ICDRT register. The RIIC automatically holds the SCLn line low until the
data for transmission are ready, or a stop condition is issued.
5. After all bytes of data for transmission have been written to the ICDRT register,
wait until the value of the TEND flag in ICSR2 returns to 1, and then set the SP bit
in ICCR2 to 1 (stop condition issuance request). Upon receiving a stop condition
issuance request, the RIIC issues the stop condition.
6. Upon detecting the stop condition, the RIIC automatically clears the MST and
TRS bits in ICCR2 to 00b and enters slave receiver mode. Furthermore, it automatically clears the TDRE and TEND flags to 0, and sets the STOP flag in
ICSR2 to 1.
7. After checking that the ICSR2.STOP flag is 1, clear the ICSR2.NACKF and STOP
flags to 0 for the next transfer operation.
The following two figures show the timings of the operations:
Reading data from a peripheral device/Master receiver operation:
1. Set the IICRST bit in ICCR1 to 1 (internal reset) and then clear the IICRST bit to 0
(canceling reset) with the ICE bit in ICCR1 cleared to 0 (disabling the interface). This
initializes the internal state and the various flags of ICSR1. After that, set registers
SARLn, SARUn, ICSER, ICMR1, ICBRH, and ICBRL (n 0 to 2), and set the other
registers as necessary (for initial settings of the RIIC, see Figure 30.5 in the hardware
manual). When the necessary register settings have been completed, set the ICE bit to
1 (to enable transfer). This step is not necessary if initialization of the RIIC has already been completed.
2. Read the BBSY flag in ICCR2 to check that the bus is open, and then set the ST bit
in ICCR2 to 1 (start condition issuance request). Upon receiving the request, the
RIIC issues a start condition. When the RIIC detects the start condition, the BBSY
flag and the START flag in ICSR2 are automatically set to 1 and the ST bit is automatically cleared to 0. At this time, if the start condition is detected and the levels
for the SDA output and the levels on the SDAn line have matched while the ST bit
is 1, the RIIC recognizes that issuing of the start condition as requested by the ST
bit has been successfully completed. As a result the MST and TRS bits in ICCR2 are
automatically set to 1, placing the RIIC in master transmitter mode. The TDRE flag
in ICSR2 is also automatically set to 1 in response to setting of the TRS bit to 1.
3. Check that the TDRE flag in ICSR2 is 1, and then write the value for transmission
(the first byte indicates the slave address and value of the R/W# bit) to ICDRT.
Once the data for transmission are written to ICDRT, the TDRE flag is automatically cleared to 0, the data are transferred from ICDRT to ICDRS, and the TDRE
flag is again set to 1. Once the byte containing the slave address and R/W# bit has
been transmitted, the value of the ICCR2.TRS bit is automatically updated to
S
[2]
b6
2
b4
4
[4]
W
ACK
9
b7
1
b6
2
b5
3
DATA 1
b2
6
DATA 2
b3
5
DATA 1
b4
4
b1
7
b7
1
2
b6
Write
ICDRT
(DATA 3)
[4]
[4]
b4
4
DATA 2
b5
3
DATA 3
“0” (ACK)
DATA 2
Write
ICDRT
(DATA 2)
“0” (ACK)
“0” (ACK)
ACK
9
Transmit data (DATA 2)
b0
8
XXXX (Initial value/last data for reception)
Transmit data (DATA 1)
b0
8
Figure 7.59 Operation of the RIIC module in master transmitter mode. Source: Hardware Manual, page 1522.
[3]
b1
7
DATA 1
b2
6
7-bit address 1 W
“X” (ACK/NACK)
Write
ICDRT
(DATA 1)
7-bit address 1 W
b3
5
7-bit slave address
b5
3
Transmit data (7-bit address 1 W)
b7
1
Write 1 Write ICDRT
to ST (7-bit address
1 W)
ST
START
ACKBR
ACKBT
ICDRR
ICDRS
ICDRT
RDRF
TEND
TDRE
TRS
MST
BBSY
SDAn
SCLn
Automatic low-hold (to prevent wrong transmission)
CHAPTER 7 / SERIAL COMMUNICATIONS
271
DATA n-1
DATA n-2
ICDRS
SP
STOP
ACKBR
ACKBT
ICDRR
ACK
9
b7
1
b6
2
3
b3
5
DATA n-1
DATA n-1
b4
4
ACK
9
b7
1
b6
2
DATA n
b5
3
b3
5
DATA n
b4
4
b1
“0” (ACK)
b0
8
Figure 7.60 RIIC module in master transmitter mode. Source: Hardware Manual, page 1522.
P
[7]
Clear
STOP 5 0
“X” (ACK/NACK)
A/NA
9
[5]
“0” (ACK)
7
DATA n
b2
6
XXXX (Initial value/final receive data)
Transmit data (DATA n)
b0
8
[4]
b1
7
Write
SP 5 1
b2
6
Write ICDRT
(Final transmit data [DATA n])
“0” (ACK)
b5
Transmit data (DATA n-1)
b0
8
DATA n-2
b1
7
ICDRT
RDRF
TEND
TDRE
TRS
MST
BBSY
SDAn
SCLn
272
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
CHAPTER 7 / SERIAL COMMUNICATIONS
4.
5.
6.
7.
8.
9.
273
select master transmitter or master receiver mode in accord with the value of the
transmitted R/W# bit. If the value of the R/W# bit was 1, the TRS bit is cleared to
0 on the rising edge of the ninth cycle of SCLn (the clock signal), placing the RIIC
in master receiver mode. At this time, the TDRE flag is automatically cleared to 0
and the ICSR2.RDRF flag is automatically set to 1.
Since the ICSR2.NACKF flag being 1 at this time indicates that no slave device
recognized the address or there was an error in communications, write 1 to the
ICCR2.SP bit to issue a stop condition. For master reception from a device with a
10-bit address, start by using the master transmission to issue the 10-bit address, and
then issue a restart condition. After that, transmitting 1111 0b, the two higher-order
bits of the slave address, and the R bit places the RIIC in master receiver mode.
Dummy read ICDRR after confirming that the RDRF flag in ICSR2 is 1. This
makes the RIIC start output of the SCL (clock) signal and start data reception.
After one byte of data has been received, the RDRF flag in ICSR2 is set to 1 on the
rising edge of the eighth or ninth cycle of SCL clock (the clock signal) as selected
by the RDRFS bit in ICMR3. Reading out ICDRR at this time will produce the received data, and the RDRF flag is automatically cleared to 0 at the same time. Furthermore, the value of the acknowledgement field received during the ninth cycle
of SCL clock is returned as the value set in the ACKBT bit of ICMR3. Save the received data into the FIFO and increment the pointer to the FIFO.
When the next value to be received will be the final byte, set the WAIT bit in
ICMR3 to 1 (so that waiting is applied) before reading ICDRR. This causes the
SCLn line to be held low from the falling edge of the ninth clock cycle after reception of the next data (i.e., the final byte), enabling issuance of a stop condition.
However, when the ICMR3.RDRFS bit is 0 and the slave device must be notified
that it is to end transfer for data reception after transfer of the next (final) byte, set
the ACKBT bit in ICMR3 to 1 (NACK).
After reading out the byte before last from the ICDRR register, if the value of the
ICSR2.RDRF flag is confirmed to be 1, write 1 to the SP bit in ICCR2 (stop condition issuance request) and then read the last byte from ICDRR. Save the received
data bytes into the FIFO and increment the pointer to the FIFO. When ICDRR is
read, the RIIC is released from the wait state and issues the stop condition after
low-level output in the ninth clock cycle is completed or the SCL line is released
from the low-hold state.
Upon detecting the stop condition, the RIIC automatically clears the MST and
TRS bits in ICCR2 to “00b” and enters slave receiver mode. Furthermore, detection of the stop condition leads to setting of the STOP flag in ICSR2 to 1.
After checking that the ICSR2.STOP flag is 1, clear the ICSR2.NACKF and STOP
flags to 0 for the next transfer operation.
The following two figures show the timings of the operations.
[2]
b6
2
b4
4
“X” (ACK/NACK)
7
R
b0
8
ACK
9
b7
1
b6
2
b5
3
[4]
Read ICDRR
(Dummy read
[7-bit address 1 R])
“0” (ACK)
b3
5
“0” (ACK)
6
b1
7
b0
8
ACK
9
Receive data (DATA 1)
b2
DATA 1
DATA 1
b4
4
7-bit address 1 R
7-bit address 1 R
Receive data (7-bit address 1 R)
b1
XXXX (Initial value/last data for reception)
7-bit address 1 R
b2
6
Master receive mode
[5]
3
b4
4
DATA 2
DATA 2
b5
“0” (ACK)
DATA 1
b6
2
Read
ICDRR
(DATA 1)
b7
1
Figure 7.61 Operation of the RIIC module in master receiver mode. Source: Hardware Manual, page 1526.
[3]
b3
5
Master transmit mode
7-bit slave address
b5
3
Transmit data (7-bit address 1 R)
b7
1
Write 1 Read ICDRT
to ST (7-bit address
1 R)
ST
START
ACKBR
ACKBT
ICDRR
ICDRS
ICDRT
RDRF
TEND
TDRE
TRS
MST
BBSY
SDAn
SCLn
S
Automatic low-hold
(error transmission protected)
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
b0
WAIT
SP
STOP
“0” (ACK)
DATA n-2
DATA n-3
ACKBT
b7
1
b6
2
b5
3
b3
5
DATA n-1
b4
4
b2
6
b0
8
b7
1
Write 1
to WAIT
[6]
Write 1
to ACKBT
b5
3
b3
5
“0” (ACK)
b1
7
b0
8
NACK
9
DATA n
Receive data (DATA n)
b2
6
“1” (NACK)
“0”
DATA n
P
[7]
[9]
Write 1
Read ICDRR
Clear WAIT Clear STOP
to SP (last data for reception)[DATA n]
to 0
to 0
“1” (NACK)
DATA n-1
DATA n
b4
4
Automatic low hold (error transmission protected)
Read ICDRR
(Data n-1)
b6
2
Figure 7.62 RIIC module in master receiver mode. Source: Hardware Manual, page 1527.
[5]
Read ICDRR
(Data n-2)
“0” (ACK)
“0” (ACK)
DATA n-2
DATA n-1
ACK
9
Receive data (DATA n-1)
b1
7
XXXX (last data for transmission [7-bt address 1 R/Upper 10 bits 1 R])
ICDRS
ACKBR
ACK
9
Receive data (DATA n-2)
DATA n-2
b1
8
ICDRR
ICDRT
RDRF
TEND
TDRE
TRS
MST
BBSY
SDAn
SCLn
7
CHAPTER 7 / SERIAL COMMUNICATIONS
275
276
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Advanced Section 7.5.3 helps demonstrate these concepts.
7.5
ADVANCED EXAMPLES
7.5.1
FIFO Data Structures for Transmission and Reception Using the UART Serial
Communications Interface
Aim: Demonstration of the use of FIFOs towards transmission and reception.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0, Renesas
Development Kit; PC with RS-232 serial port.
Details: In this example we demonstrate the use of FIFO data structures for transmission and reception to show how the communication interface operates using interrupts, and
how the microcontroller manages to work on other tasks while communication proceeds
normally. This example is based on the initialization codes of the Basic Example 7.3.1 and
is similar to the one detailed in Section 7.4.1.
Procedure: For this example, create a new workspace in HEW and fill the given lines
of code in the corresponding files mentioned before the following code. Compile; build all
files and Download to board as mentioned in Chapter 4. When downloaded, connect the
RX62N development board to a standard PC with an RS-232 port configured at
115200 baud, no parity, and 1 stop bit to view the results on a HyperTerminal program or
on a Serial Port Terminal.
Code: The following is the code related to the demonstration:
Setting up Interrupt Service Routines
Filename: vect.h
1.
2.
3.
4.
pragma interrupt (Excep_SCI2_RXI2(vect = 223))
void Excep_SCI2_RXI2(void);
#pragma interrupt (Excep_SCI2_TXI2(vect = 224))
void Excep_SCI2_TXI2(void);
Filename: intprg.c
1.
2.
3.
4.
5.
#include “RX62N_SCI_UART.h”
#include <machine.h>
#include “vect.h”
#pragma Section IntPRG
void Excep_SCI2_RXI2(void){
CHAPTER 7 / SERIAL COMMUNICATIONS
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6.
if(!Q_Enqueue(&rx_q, SCI2.RDR)){
7.
}
8. }
9. void Excep_SCI2_TXI2(void){
10.
if(!Q_Empty(&tx_q))
11.
SCI2.TDR = Q_Dequeue(&tx_q);
12. }
Setting up function definitions for operating on the queues:
Filename: RX62N_SCI_UART.h
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#include “iodefine_RX62N.h”
#define Q_SIZE (32)
typedef struct {
unsigned char Data [Q_SIZE ];
unsigned int Head;
//points to oldest data element
unsigned int Tail;
//points to next free space
unsigned int Size;
//quantity of elements in queue
} Q_T;
int Q_Empty(Q_T * q);
int Q_Full(Q_T * q);
int Q_Enqueue(Q_T * q, unsigned char d);
unsigned char Q_Dequeue(Q_T * q);
void Q_Init(Q_T * q);
void delay(long unsigned int n);
void init_switches();
void init_LEDs();
void init_UART0();
void d3_send_string(far char * s);
void demo3(void);
extern Q_T tx_q, rx_q;
Setting up all the function details related to the functioning of the UART and FIFO queues:
Filename: RX62N_SCI_UART.c
1. #include “RX62N_SCI_UART.h”
2. Q_T tx_q, rx_q;
3. int Q_Empty(Q_T * q){
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return (q->Size == 0);
}
int Q_Full(Q_T * q){
return (q->Size == Q_SIZE);
}
int Q_Enqueue(Q_T * q, unsigned char d){
if(!Q_Full(q)){
q->Data [q->Tail++ ] = d;
q->Tail %= Q_SIZE;
q->Size++;
return 1;
}
else return 0;
}
unsigned char Q_Dequeue(Q_T * q){
unsigned char t = 0;
if(!Q_Empty(q){
t = q->Data [q->Head ];
q->Data [q->Head++ ] = 0;
q->Head %= Q_SIZE;
q->Size––;
}
return t;
}
void Q_Init(Q_T * q){
unsigned int i;
for(i = 0; i < Q_SIZE; i++)
q->Data [i ] = 0;
q->Head = 0;
q->Tail = 0;
q->Size = 0;
}
void init_UART0(){
MSTP(SCI2) = 0;
IOPORT.PFFSCI.BIT.SCI2S = 1;
PORT1.DDR.BIT.B2 = 0;
PORT1.ICR.BIT.B2 = 1;
PORT1.DDR.BIT.B3 = 1;
SCI2.SCR.BYTE = 0;
SCI2.SMR.BYTE = 0x00;
SCI2.SCR.BIT.RIE = 1;
SCI2.SCR.BIT.TIE = 1;
CHAPTER 7 / SERIAL COMMUNICATIONS
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IPR(SCI2,RXI2) = 1;
IPR(SCI2,TXI2) = 1;
IEN(SCI2, RXI2) = 1;
IEN(SCI2, TXI2) = 1;
SCI2.BRR = 12;
SCI2.SCR.BYTE |= 0x30;
}
void d3_send_string(far char * s){
while(*s){
if(Q_Enqueue(&tx_q, *s))
s++;
else { }
}
if(IR(SCI2, TXI2) == 0){
SCI2.TDR = Q_Dequeue(&tx_q);
}
}
void demo3(void){
char c;
d3_send_string(“Hello, interruptible world!\n\r”);
while(1){
if(!Q_Empty(&rx_q)){
c = Q_Dequeue(&rx_q);
d3_send_string(“Ouch!\n\r”);
}
}
}
Main Program
Filename: Workspace_name.c
1. void main(){
2.
init_switches();
3.
init_LEDs();
4.
init_UART0();
5.
Q_Init(&tx_q);
6.
Q_Init(&rx_q);
7.
demo3();
8.
while(1)
9.
;
10. }
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7.5.2
Multiprocessor Communication Using Queues and the Renesas
Serial Peripheral Interface
Aim: Demonstration of Multiprocessor Communication using queues and the RSPI for
rapid communication between microcontrollers.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0, Two
Renesas Development Kits.
Details: In the previous example, we demonstrated how communication takes place at
a continuous pace using queues. In this example we demonstrate how to perform Multiprocessor communication at much higher speeds than those available with the SCI interface.
Baud rates can reach maximum speeds of PCLK, which is the peripheral clock generated by
the RX62N processor. Since the RSPI operates much faster than the SCI, it is an ideal serial
bus for Multiprocessor communication as compared to the SCI and I2C interface.
Procedure: For this example, create a new workspace in HEW and fill the given lines
of code in the corresponding files mentioned before the following code. You now need to
download two separate pieces of codes on to each board; one for the master device and one
for the slave device. At the beginning of the main file for the master device, make sure
that the “#define RSPI_Master_Device” is not commented out while the “#define
RSPI_Slave_Device” is commented out. This will build the main example code for the
master device. Once this example code has been built, download the module on to one
board. For the slave device, make sure that the “#define RSPI_Slave_Device” is not commented where as the “#define RSPI_Master_Device” is commented out. This will build the
main example code for the slave device. Once this example code has been built, download
the module on to the other board. Make sure that you are not building both modules at the
same time; i.e., “#define RSPI_Master_Device” and “#define RSPI_Slave_Device” are not
defined at the same time, or else the code/device will not function.
Code: The following is the code related to the demonstration:
Setting Up Interrupt Service Routines
Filename: vect.h
1.
2.
3.
4.
#pragma interrupt (Excep_RSPI0_SPRI0(vect = 45))
void Excep_RSPI0_SPRI0(void);
#pragma interrupt (Excep_RSPI0_SPTI0(vect = 46))
void Excep_RSPI0_SPTI0(void);
Filename: intprg.c
1. void Excep_RSPI0_SPRI0(void){
2.
LED_Y = LED_ON;
CHAPTER 7 / SERIAL COMMUNICATIONS
3.
if(!SPI_Q_Enqueue(&rx_q, (0x00FF & RSPI0.SPDR.WORD.L))){
4.
LED_R = LED_ON;
5.
}
6.
LED_Y = LED_OFF;
7. }
8. void Excep_RSPI0_SPTI0(void){
9.
LED_G = LED_ON;
10.
if(!SPI_Q_Empty(&tx_q))
11.
RSPI0.SPDR.WORD.H = (0x00FF & SPI_Q_Dequeue(&tx_q));
12.
LED_G = LED_OFF;
13. }
Setting Up Function Definitions for Operating on the Queues
Filename: RX62N_RSPI.h
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25.
#include “iodefine_RX62N.h”
#define NULL (0)
#define SW1 (PORT4.PORT.BIT.B0)
#define SW2 (PORT4.PORT.BIT.B1)
#define SW3 (PORT4.PORT.BIT.B2)
#define SW1_EN (PORT4.DDR.BIT.B0)
#define SW2_EN (PORT4.DDR.BIT.B1)
#define SW3_EN (PORT4.DDR.BIT.B2)
#define Q_SIZE (32)
typedef struct {
unsigned char Data [Q_SIZE ];
unsigned int Head;
unsigned int Tail;
unsigned int Size;
} Q_T;
int SPI_Q_Empty(Q_T * q);
int SPI_Q_Full(Q_T * q);
int SPI_Q_Enqueue(Q_T * q, unsigned char d);
unsigned char Q_Dequeue(Q_T * q);
void SPI_Q_Init(Q_T * q);
void SPI_delay(long unsigned int n);
void SPI_init_switches();
void SPI_init_LEDs();
void SPI_init_RSPI_Master();
void SPI_init_RSPI_Slave();
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26. void SPI_d3_send_string(far char * s);
27. void SPI_demo3(void);
28. extern Q_T tx_q, rx_q;
Setting Up All the Function Details Related to the Functioning of the UART and FIFO
Queues
Filename: RX62N_SCI_UART.c
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#include “iodefine_RX62N.h”
#include “RX62N_RSPI.h”
#include “RX62N_LED_Defs.h”
Q_T tx_q, rx_q;
void SPI_init_RSPI_Master(void){
MSTP(RSPI0) = 0;
IOPORT.PFGSPI.BIT.RSPIS = 0;
IOPORT.PFGSPI.BIT.RSPCKE = 1;
IOPORT.PFGSPI.BIT.SSL0E = 1;
IOPORT.PFGSPI.BIT.MOSIE = 1;
IOPORT.PFGSPI.BIT.MISOE = 1;
PORTC.DDR.BIT.B7 = 0;
PORTC.DDR.BIT.B6 = 1;
PORTC.DDR.BIT.B5 = 1;
PORTC.DDR.BIT.B4 = 1;
PORTC.DR.BIT.B4 = 1;
PORTC.DR.BIT.B7 = 1;
PORTC.DR.BIT.B6 = 1;
PORTC.DR.BIT.B5 = 1;
RSPI0.SPPCR.BYTE = 0x00;
RSPI0.SPBR.BYTE = 0x00;
RSPI0.SPDCR.BYTE = 0x00;
RSPI0.SPCKD.BYTE = 0x00;
RSPI0.SSLND.BYTE = 0x00;
RSPI0.SPND.BYTE = 0x00;
RSPI0.SPCR2.BYTE = 0x00;
IPR(RSPI0, SPTI0) = 1;
//Clear Transmit interrupt bit
IEN(RSPI0, SPTI0) = 1;
//Enable Transmit interrupt bit
IPR(RSPI0, SPRI0) = 1;
//Clear Transmit interrupt bit
IEN(RSPI0, SPRI0) = 1;
//Enable Transmit interrupt bit
RSPI0.SPCMD0.WORD = 0x0701;
RSPI0.SPCR.BYTE = 0xE8;
CHAPTER 7 / SERIAL COMMUNICATIONS
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RSPI0.SSLP.BYTE = 0x00;
RSPI0.SPSCR.BYTE = 0x00;
}
void SPI_init_RSPI_Slave(void){
MSTP(RSPI0) = 0;
IOPORT.PFGSPI.BIT.RSPIS = 0;
IOPORT.PFGSPI.BIT.RSPCKE = 1;
IOPORT.PFGSPI.BIT.SSL0E = 1;
IOPORT.PFGSPI.BIT.MOSIE = 1;
IOPORT.PFGSPI.BIT.MISOE = 1;
PORTC.DDR.BIT.B7 = 1;
PORTC.DDR.BIT.B6 = 0;
PORTC.DDR.BIT.B5 = 0;
PORTC.DDR.BIT.B4 = 0;
PORTC.DR.BIT.B4 = 0;
PORTC.DR.BIT.B7 = 1;
PORTC.DR.BIT.B6 = 0;
PORTC.DR.BIT.B5 = 0;
RSPI0.SPPCR.BYTE = 0x04;
RSPI0.SPBR.BYTE = 0x00;
RSPI0.SPDCR.BYTE = 0x00;
RSPI0.SPCKD.BYTE = 0x00;
RSPI0.SSLND.BYTE = 0x00;
RSPI0.SPND.BYTE = 0x00;
RSPI0.SPCR2.BYTE = 0x00;
RSPI0.SPCMD0.WORD = 0x0701;
RSPI0.SPDR.WORD.L = 0xAA55;
RSPI0.SPDR.WORD.H = 0x55AA;
IEN(RSPI0, SPRI0) = 1;
//Enable Receive interrupt
IEN(RSPI0, SPTI0) = 1;
//Enable Transmit interrupt
IPR(RSPI0, SPRI0) = 1;
IPR(RSPI0, SPTI0) = 1;
RSPI0.SSLP.BYTE = 0x00;
RSPI0.SPCR.BYTE = 0xA0;
RSPI0.SPSCR.BYTE = 0x00;
RSPI0.SPCR.BIT.SPE = 1;
}
int SPI_Q_Empty(Q_T * q){
return (q->Size == 0);
}
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int SPI_Q_Full(Q_T * q){
return (q->Size == Q_SIZE);
}
int SPI_Q_Enqueue(Q_T * q, unsigned char d){
if(!SPI_Q_Full(q)){
q->Data [q->Tail++ ] = d;
q->Tail %= Q_SIZE;
q->Size++;
return 1;
}
else return 0;
}
unsigned char SPI_Q_Dequeue(Q_T * q){
unsigned char t = 0;
if(!SPI_Q_Empty(q)){
t = q->Data [q->Head ];
q->Data [q->Head++ ] = 0;
q->Head %= Q_SIZE;
q->Size—;
}
return t;
}
void SPI_Q_Init(Q_T * q){
unsigned int i;
for(i = 0; i < Q_SIZE; i++)
q->Data [i ] = 0;
q->Head = 0;
q->Tail = 0;
q->Size = 0;
}
void SPI_delay(long unsigned int n){
while(n—)
;
}
void SPI_init_switches(){
SW1_EN = SW2_EN = SW3_EN = 0;
//inputs
}
void SPI_init_LEDs(){
ENABLE_LEDS;
ALL_LEDS_ON;
}
CHAPTER 7 / SERIAL COMMUNICATIONS
114. void SPI_d3_send_string(far char * s){
115.
while(*s){
116.
if(SPI_Q_Enqueue(&tx_q, *s))
117.
s++;
118.
if(IR(RSPI0, SPTI0) == 0){
119.
SCI2.TDR = SPI_Q_Dequeue(&tx_q);
120.
}
121.
}
122. void SPI_demo3(void){
123.
char c;
124.
SPI_d3_send_string(“Hello, interruptible world!\n\r”);
125.
while(1){
126.
if(!SPI_Q_Empty(&rx_q)){
127.
c = SPI_Q_Dequeue(&rx_q);
128.
(void)c;
129.
SPI_d3_send_string(“Ouch!\n\r”);
130.
}
131.
}
132. }
Main Program
Filename: Workspace_name.c
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#include “iodefine_RX62N.h”
#include “RX62N_LED_Defs.h”
#include “RX62N_RSPI.h”
#define RSPI_SLAVE
#define RSPI_MASTER
void main(){
SPI_init_switches();
SPI_init_LEDs();
#ifdef RSPI_MASTER
SPI_init_RSPI_Master();
#endif
#ifdef RSPI_MASTER
SPI_init_RSPI_Slave();
#endif
SPI_Q_Init(&tx_q);
SPI_Q_Init(&rx_q);
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17.
18.
19.
20. }
7.5.3
SPI_demo3();
while(1)
;
Transfer of data between peripherals connected on the I2C bus using FIFOs
Aim: To demonstrate mass transfer of data between peripherals connected on the I2C bus.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0,
Renesas Development Kits (YRDKRX62N) with on board I2C peripherals.
Details: In this example we will demonstrate how to use the I2C bus to transfer large
amounts of data to the desired peripheral with minimum overhead. The device we will use
is the ADXL345 and will be writing the default values to the ADXL345, specified in the
device datasheet and reading the acceleration values for the X, Y, and Z values. The code
also provides for a standard framework that can be used to access other devices using the
RX62N microcontroller.
Procedure: For this example, create a new workspace in HEW and fill the given lines
of code in the corresponding files mentioned before the code below. To use the following
code for other peripherals make sure to specify the correct address and number of data
bytes to read and write. The given following code is for the Analog Devices Accelerometer
ADXL345 whose device sheet is found at http://www.analog.com/static/imported-files/
data_sheets/ADXL345.pdf (Analog Devices, Inc.; ADXL345 datasheet: 3-Axis, 2 g/4
g/8 g/16 g Digital Accelerometer, ADXL345). A point to note is for the user to use the
iodefine_RX62N.h header file instead of the standard iodefine.h file. Additional changes
may be required if the two header files are switched.
Filename: riic.h
This file contains the most declarations and #define variables used by the RIIC module.
1.
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3.
4.
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7.
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9.
10.
#ifndef _RIIC_SETTING_DEF
#define _RIIC_SETTING_DEF
#define RIIC_CH0
//When use channel0, define “RIIC_CH0”
#define RIIC_CH1
//When use channel1, define “RIIC_CH1”
#ifdef RIIC_CH0
#define RIIC RIIC0
//Replace I/O define
#else
#define RIIC RIIC1
//Replace I/O define
#endif
#define RIIC_OK 0
//Return value for function “RiicMst”
CHAPTER 7 / SERIAL COMMUNICATIONS
287
11.
12.
13.
14.
#define RIIC_NG 1
//Return value for function “RiicMst”
#define RIIC_BUS_BUSY 2
//Return value for function “RiicMst”
void RiicIni(unsigned char, unsigned char);
unsigned char RiicStart(unsigned char, unsigned char*, unsigned
long);
15. #endif
//_RIIC_SETTING_DEF
Filename: riic.c
This file contains definitions of functions that perform actions in response to calls from either the user or the interrupts.
1. void RiicIni(unsigned char in_SelfAddr, unsigned char in_Enable)
2. {
3.
#ifdef RIIC_CH0
4.
SYSTEM.MSTPCRB.BIT.MSTPB21 = 0;
//RIIC0(MSTPB21)
5.
#else
6.
SYSTEM.MSTPCRB.BIT.MSTPB20 = 0;
//RIIC1(MSTPB20)
7.
#endif
8.
RIIC.ICCR1.BIT.ICE = 0;
//RIIC disable
9.
RIIC.ICCR1.BIT.IICRST = 1;
//RIIC all reset
10.
RIIC.ICCR1.BIT.IICRST = 0;
11.
RiicMstCnt = 0;
12.
RiicMstNum = 0;
13.
if(in_Enable != 0){
//Initialise RIIC
14.
/* Self address setting */
15.
RIIC.SARU0.BIT.FS = 0;
//7bit address format
16.
RIIC.SARL0.BYTE = in_SelfAddr;
//Set self address
17.
RIIC.ICMR1.BIT.CKS = 7;
//IIC phi = PCLK/128 clock
18.
RIIC.ICBRH.BIT.BRH = 28;
//100kbps (PCLK = 50 MHz)
19.
RIIC.ICBRL.BIT.BRL = 29;
20.
RIIC.ICMR3.BIT.ACKWP = 1;
//Disable ACKBT protect
21.
RIIC.ICIER.BIT.RIE = 1;
//Edge interrupt
22.
RIIC.ICIER.BIT.TIE = 1;
//Edge interrupt
23.
RIIC.ICIER.BIT.TEIE = 0;
//Level interrupt
24.
RIIC.ICIER.BIT.NAKIE = 1;
//Level interrupt
25.
RIIC.ICIER.BIT.SPIE = 1;
//Level interrupt
26.
RIIC.ICIER.BIT.STIE = 0;
//Level interrupt
27.
RIIC.ICIER.BIT.ALIE = 0;
//Level interrupt
28.
RIIC.ICIER.BIT.TMOIE = 0;
//Level interrupt
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69. }
#ifdef RIIC_CH0
//RIIC channel0
ICU.IPR [0x88 ].BYTE = 0x04;
//EEI0 interrupt level
ICU.IPR [0x89 ].BYTE = 0x04;
//RXI0 interrupt level
ICU.IPR [0x8A ].BYTE = 0x04;
//TXI0 interrupt level
ICU.IPR [0x8B ].BYTE = 0x04;
//TEI0 interrupt level
ICU.IER [0x1E ].BIT.IEN6 = 1;
//EEI0 interrupt enable
ICU.IER [0x1E ].BIT.IEN7 = 1;
//RXI0 interrupt enable
ICU.IER [0x1F ].BIT.IEN0 = 1;
//TXI0 interrupt enable
ICU.IER [0x1F ].BIT.IEN1 = 1;
//TEI0 interrupt enable
ICU.IR [246 ].BIT.IR = 0;
//EEI0 clear interrupt flag
ICU.IR [247 ].BIT.IR = 0;
//RXI0 clear interrupt flag
ICU.IR [248 ].BIT.IR = 0;
//TXI0 clear interrupt flag
ICU.IR [249 ].BIT.IR = 0;
//TEI0 clear interrupt flag
PORT1.ICR.BIT.B3 = 1;
//SDA0 setting
PORT1.ICR.BIT.B2 = 1;
//SCL0 setting
#else
//RIIC channel1
ICU.IPR [0x8C ].BYTE = 0x04;
//EEI1 interrupt level
ICU.IPR [0x8D ].BYTE = 0x04;
//RXI1 interrupt level
ICU.IPR [0x8E ].BYTE = 0x04;
//TXI1 interrupt level
ICU.IPR [0x8F ].BYTE = 0x04;
//TEI1 interrupt level
ICU.IER [0x1F ].BIT.IEN2 = 1;
//EEI1 interrupt enable
ICU.IER [0x1F ].BIT.IEN3 = 1;
//RXI1 interrupt enable
ICU.IER [0x1F ].BIT.IEN4 = 1;
//TXI1 interrupt enable
ICU.IER [0x1F ].BIT.IEN5 = 1;
//TEI1 interrupt enable
ICU.IR [250 ].BIT.IR = 0;
//EEI1 clear interrupt flag
ICU.IR [251 ].BIT.IR = 0;
//RXI1 clear interrupt flag
ICU.IR [252 ].BIT.IR = 0;
//TXI1 clear interrupt flag
ICU.IR [253 ].BIT.IR = 0;
//TEI1 clear interrupt flag
PORT1.ICR.BIT.B3 = 1;
//SDA1 setting
PORT1.ICR.BIT.B2 = 1;
//SCL1 setting
#endif
//RIIC_CH0
RIIC.ICCR1.BIT.ICE = 1;
//RIIC enable
}
else {
//Stop RIIC
#ifdef RIIC_CH0
SYSTEM.MSTPCRB.BIT.MSTPB21 = 1;
#else
SYSTEM.MSTPCRB.BIT.MSTPB20 = 1;
#endif
}
//RIIC0(MSTPB21)
//RIIC1(MSTPB20)
CHAPTER 7 / SERIAL COMMUNICATIONS
289
70. unsigned char RiicStart(unsigned char in_addr, unsigned char
*in_buff, unsigned long in_num)
71. {
72.
if(in_num < 2){
//Check data number (include first byte
(address))
73.
return RIIC_NG;
74.
}
75.
if((RIIC.ICCR2.BYTE & 0xE0) != 0x00){
76.
return RIIC_BUS_BUSY;
//Bus busy
77.
}
78.
RIIC.ICCR2.BIT.ST = 1;
//Generate start condition
79.
RiicTrmAddr = in_addr;
//Set transmission address
80.
RiicMstBuff = in_buff;
//Set transmission buffer
81.
RiicMstCnt = 0;
82.
RiicMstNum = in_num;
83.
return RIIC_OK;
84. }
85. void RiicRDRF(void){
87.
volatile unsigned long cnt;
89.
if(RIIC.ICSR2.BIT.NACKF != 0){
//When receive NACK
90.
if(RIIC.ICCR1.BIT.SCLI == 0){
91.
for(cnt = RIIC_WAIT_VALUE; cnt! = 0; cnt— —);
92.
}
93.
RIIC.ICCR2.BIT.SP = 1;
//Generate stop condition
94.
*RiicMstBuff = RIIC.ICDRR;
//Dummy read
95.
return;
96.
}
98.
if(RiicMstCnt >= RiicMstNum){
//After receive all data
99.
if(RIIC.ICCR1.BIT.SCLI == 0){
100.
for(cnt = RIIC_WAIT_VALUE; cnt != 0; cnt— —);
101.
}
102.
RIIC.ICCR2.BIT.SP = 1;
//Generate stop condition
103.
RIIC.ICMR3.BIT.ACKBT = 0;
//Set ACK
104.
*RiicMstBuff = RIIC.ICDRR;
//Read data
105.
RiicMstBuff++;
//Add pointer
106.
}
107.
else if(RiicMstCnt == RiicMstNum -1){
//Next is last data
108.
RIIC.ICMR3.BIT.WAIT = 1;
109.
RIIC.ICMR3.BIT.ACKBT = 1;
//Set NACK
110.
*RiicMstBuff = RIIC.ICDRR;
//Read data
111.
RiicMstBuff++;
//Add pointer
290
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
112.
}
113.
else {
//Transfer next data
114.
*RiicMstBuff = RIIC.ICDRR;
//Read data
115.
RiicMstBuff++;
//Add pointer
116.
}
118.
RiicMstCnt++;
//Add internal counter
119. }
120. void RiicTDRE(void)
121. {
122.
volatile unsigned long cnt;
123.
if(RiicMstCnt >= RiicMstNum){
//After transfer all data
124.
#ifdef RIIC_CH0
125.
ICU.IER [0x1F ].BIT.IEN0 = 0;
//TXI0
126.
#else
127.
ICU.IER [0x1F ].BIT.IEN4 = 0;
//TXI1
128.
#endif
129.
RIIC.ICIER.BIT.TEIE = 1;
//TEND
130.
}
131.
else if(RiicMstCnt == 0){
//First byte
132.
#ifdef RIIC_CH0
133.
ICU.IER [0x1F ].BIT.IEN0 = 0;
//TXI0
134.
#else
135.
ICU.IER [0x1F ].BIT.IEN4 = 0;
//TXI1
136.
#endif
137.
RIIC.ICIER.BIT.TEIE = 1;
//TEND
139.
RIIC.ICDRT = RiicTrmAddr;
//Write slave address
140.
}
141.
else {
//Transfer next data
142.
if((RIIC.ICSR2.BIT.TEND == 1) &&
(RIIC.ICCR1.BIT.SCLI == 0)){
143.
for(cnt = RIIC_WAIT_VALUE; cnt != 0; cnt— —);
144.
}
145.
RIIC.ICDRT = *RiicMstBuff;
//Write next data
146.
RiicMstBuff++;
//Add pointer
147.
}
149.
RiicMstCnt++;
//Add internal counter
150. }
151. void RiicTEND(void)
152. {
153.
volatile unsigned long cnt;
154.
if(RiicMstCnt >= RiicMstNum){
//After transfer all data
CHAPTER 7 / SERIAL COMMUNICATIONS
155.
156.
157.
158.
159.
160.
161.
162.
163.
164.
165.
166.
168.
169.
170.
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172.
173.
174.
175.
176.
177.
179.
180.
181.
182.
183.
184.
185.
186.
187.
188.
189.
190.
191.
192.
193.
194.
196.
197.
198.
if(RIIC.ICCR1.BIT.SCLI == 0){
//
for(cnt = RIIC_WAIT_VALUE; cnt != 0; cnt— —);
}
RIIC.ICCR2.BIT.SP = 1;
//Generate stop condition
return;
}
#ifdef RIIC_CH0
ICU.IER [0x1F ].BIT.IEN0 = 1;
//TXI0
#else
ICU.IER [0x1F ].BIT.IEN4 = 1;
//TXI1
#endif
RIIC.ICIER.BIT.TEIE = 0;
//TEND
if(RIIC.ICCR1.BIT.SCLI == 0){
for(cnt = RIIC_WAIT_VALUE; cnt != 0; cnt— —);
}
RIIC.ICDRT = *RiicMstBuff;
//Write first data
RiicMstBuff++;
//Add pointer
RiicMstCnt++;
//Add internal counter
}
void RiicSTOP(void){
RIIC.ICSR2.BIT.STOP = 0;
RIIC.ICSR2.BIT.NACKF = 0;
#ifdef RIIC_CH0
ICU.IER [0x1F ].BIT.IEN0 = 1;
//TXI0
#else
ICU.IER [0x1F ].BIT.IEN4 = 1;
//TXI1
#endif
RIIC.ICIER.BIT.TEIE = 0;
//TEND
}
void RiicNACK(void)
{
volatile unsigned long cnt;
#ifdef RIIC_CH0
ICU.IER [0x1F ].BIT.IEN0 = 0;
//TXI0
#else
ICU.IER [0x1F ].BIT.IEN4 = 0;
//TXI1
#endif
RIIC.ICIER.BIT.TEIE = 0;
//TEND
if(RIIC.ICCR1.BIT.SCLI == 0){
for(cnt = RIIC_WAIT_VALUE; cnt != 0; cnt— —);
}
291
292
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
199.
200.
201.
202.
203.
RIIC.ICCR2.BIT.SP = 1;
}
void RiicSTART(void){}
void RiicAL(void){}
void RiicTMO(void){}
//Generate stop condition
Filename: vect.h
Add the following definition to vect.h to enable the working of the EEI0, RXI0, and TXI0
interrupts.
1.
2.
3.
4.
5.
6.
#pragma interrupt (Excep_RIIC0_EEI0(vect = 246))
void Excep_RIIC0_EEI0(void);
#pragma interrupt (Excep_RIIC0_RXI0(vect = 247))
void Excep_RIIC0_RXI0(void);
#pragma interrupt (Excep_RIIC0_TXI0(vect = 248))
void Excep_RIIC0_TXI0(void);
Filename: riic_int.c:
This file contains the definitions of the interrupts and what they should do whenever they
occur.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
#include “..\iodefine_RX62N.h”
#include “..\vect.h”
#include “riic.h”
void RiicSTART(void);
void RiicAL(void);
void RiicNACK(void);
void RiicTMO(void);
void RiicSTOP(void);
void RiicRDRF(void);
void RiicTDRE(void);
void RiicTEND(void);
void Excep_RIIC0_EEI0(void){
if((RIIC.ICIER.BIT.STIE != 0) && (RIIC.ICSR2.BIT.START != 0)){
RiicSTART();
}
if((RIIC.ICIER.BIT.NAKIE != 0) &&
(RIIC.ICSR2.BIT.NACKF != 0)){
RiicNACK();
CHAPTER 7 / SERIAL COMMUNICATIONS
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
293
}
if((RIIC.ICIER.BIT.ALIE != 0) && (RIIC.ICSR2.BIT.AL != 0)){
RiicAL();
}
if((RIIC.ICIER.BIT.TMOIE != 0) && (RIIC.ICSR2.BIT.TMOF != 0)){
RiicTMO();
}
if((RIIC.ICIER.BIT.SPIE != 0) && (RIIC.ICSR2.BIT.STOP != 0)){
RiicSTOP();
}
}
void Excep_RIIC0_RXI0(void){
RiicRDRF();
}
void Excep_RIIC0_TXI0(void){
RiicTDRE();
}
void Excep_RIIC0_TEI0(void){
RiicTEND();
}
void Excep_RIIC1_EEI1(void){
if((RIIC.ICIER.BIT.STIE != 0) && (RIIC.ICSR2.BIT.START != 0)){
RiicSTART();
}
if((RIIC.ICIER.BIT.NAKIE != 0) && (RIIC.ICSR2.BIT.NACKF != 0)){
RiicNACK();
}
if((RIIC.ICIER.BIT.ALIE != 0) && (RIIC.ICSR2.BIT.AL != 0)){
RiicAL();
}
if((RIIC.ICIER.BIT.TMOIE != 0) && (RIIC.ICSR2.BIT.TMOF != 0)){
RiicTMO();
}
if((RIIC.ICIER.BIT.SPIE != 0) && (RIIC.ICSR2.BIT.STOP != 0)){
RiicSTOP();
}
}
void Excep_RIIC1_RXI1(void){
RiicRDRF();
}
294
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
59.
60.
61.
62.
63.
64.
void Excep_RIIC1_TXI1(void){
RiicTDRE();
}
void Excep_RIIC1_TEI1(void){
RiicTEND();
}
Filename: main.c
This is the main file responsible for setting up the RIIC module correctly.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
#include “iodefine_RX62N.h”
#include “iic\riic.h”
#define SELF_ADDRESS 0x10
//Self address (bit0 = 0. (R/W bit))
#define SLV_ADDRESS 0x3A
//Slave address (bit0 = 0. (R/W bit))
#define DATA_NUM (1 + 1)
//Date number (“+1” means first
byte(slave address))
#define T_BUFF_SIZE (2)
#define R_BUFF_SIZE (7)
#define POWER_CTL_ADDR (0x2D)
#define POWER_CTL_VAL0 (0)
#define POWER_CTL_VAL1 (16)
#define POWER_CTL_VAL2 (8)
#define DATA_ADDRESS (0x32)
#define MST_WRITE 0x00
//Write bit (Don’t change)
#define MST_READ 0x01
//Read bit (Don’t change)
unsigned char MstTrmBuff [T_BUFF_SIZE ];
//Buffer for
transmission data
unsigned char MstRcvBuff [R_BUFF_SIZE ] = {255};
//Buffer for
reception data
void main(void)
{
unsigned long cnt,i;
unsigned char rtn;
SYSTEM.SCKCR.LONG = 0x00020100;
//ICLK = 100 MHz, BCLK =
25 MHz, PCLK = 50 MHz
(EXTAL = 12.5 MHz)
for(cnt = 0; cnt < T_BUFF_SIZE; cnt++){
MstTrmBuff [cnt ] = 0xFF;
MstRcvBuff [cnt ] = 0xFF;
}
CHAPTER 7 / SERIAL COMMUNICATIONS
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
MstTrmBuff [0 ] = POWER_CTL_ADDR;
MstTrmBuff [1 ] = POWER_CTL_VAL0;
RiicIni(SELF_ADDRESS, 1);
//Initialise RIIC (Enable)
rtn = RiicStart(SLV_ADDRESS | MST_WRITE, MstTrmBuff,
DATA_NUM + 1);
switch (rtn){
//Return value check
case RIIC_OK:
//OK
break;
case RIIC_BUS_BUSY:
//Bus busy
break;
case RIIC_NG:
//Data number error
break;
default:
//Internal error
while(1)
;
}
while(RIIC.ICCR2.BIT.BBSY != 1)
//Check Bus busy
;
while(RIIC.ICCR2.BIT.BBSY != 0)
//Check Bus free
;
MstTrmBuff [1 ] = POWER_CTL_VAL1;
rtn = RiicStart(SLV_ADDRESS | MST_WRITE, MstTrmBuff,
DATA_NUM+1);
switch (rtn){
//Return value check
case RIIC_OK:
//OK
break;
case RIIC_BUS_BUSY:
//Bus busy
break;
case RIIC_NG:
//Data number error
break;
default:
//Internal error
while(1)
;
}
MstTrmBuff [1 ] = POWER_CTL_VAL2;
while(RIIC.ICCR2.BIT.BBSY != 1)
//Check Bus busy
;
while(RIIC.ICCR2.BIT.BBSY != 0)
//Check Bus free
;
MstTrmBuff [0 ] = DATA_ADDRESS;
295
296
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
rtn = RiicStart(SLV_ADDRESS | MST_WRITE, MstTrmBuff,
DATA_NUM);
switch (rtn){
//Return value check
case RIIC_OK:
//OK
break;
case RIIC_BUS_BUSY:
//Bus busy
break;
case RIIC_NG:
//Data number error
break;
default:
//Internal error
while(1)
;
}
while(RIIC.ICCR2.BIT.BBSY != 1)
//Check Bus busy
;
while(RIIC.ICCR2.BIT.BBSY != 0)
//Check Bus free
;
rtn = RiicStart(SLV_ADDRESS | MST_WRITE, MstTrmBuff,
DATA_NUM);
switch (rtn){
//Return value check
case RIIC_OK:
//OK
break;
case RIIC_BUS_BUSY:
//Bus busy
break;
case RIIC_NG:
//Data number error
break;
default:
//Internal error
while(1)
;
}
while(RIIC.ICCR2.BIT.BBSY != 1)
//Check Bus busy
;
while(RIIC.ICCR2.BIT.BBSY != 0)
//Check Bus free
;
rtn = RiicStart(SLV_ADDRESS | MST_READ, MstRcvBuff,
DATA_NUM+6);
switch (rtn){
//Return value check
case RIIC_OK:
//OK
break;
case RIIC_BUS_BUSY:
//Bus busy
CHAPTER 7 / SERIAL COMMUNICATIONS
101.
102.
103.
104.
105.
106.
107.
108.
109.
110.
111.
112.
113.
114.
115. }
7.6
297
break;
case RIIC_NG:
//Data number error
break;
default:
//Internal error
while(1)
;
}
while(RIIC.ICCR2.BIT.BBSY != 1)
;
while(RIIC.ICCR2.BIT.BBSY != 0)
;
RiicIni(0, 0);
//Stop RIIC
while(1)
;
//Check Bus busy
//Check Bus free
RECAP
䡲
䡲
䡲
䡲
䡲
䡲
䡲
䡲
䡲
The Serial Communications Interface can act as a Smart Card Interface and as a
Universal Synchronous/Asynchronous Receiver and Transmitter.
The UART is one of the oldest, simplest, and most frequently used techniques
for half duplex serial communication that uses three wires at the most for data
transfer.
The SCI2 interface is available on the YRDKRX62N development board via an
RS-232 level shifter.
The Serial Peripheral Interface bus is a full duplex bus similar to the Universal
Synchronous Receiver/Transmitter and is capable of data transfer at very high
speeds.
Each SPI device can act as either a master or a slave device. The master device is
responsible for generating the clock cycles for synchronizing the data transfer.
Slave Selection is always required prior to transfer of data on the SPI bus, otherwise data on the bus is void.
Slave devices available aboard the YRDKRX62N on the SPI bus are the Graphical
LCD module, Micro SD card interface, and the Micron/Numonyx Omneo P5Q
Serial Flash Chip.
I2C is a two wire interface capable of talking to up to 128 devices connected on the
same bus.
The I2C cycle consists of generation of a start condition, selecting a slave device,
performing a data transfer, and sending a stop condition.
298
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
Devices available with the YRDKRX62N board that are connected on the I2C bus
are accelerometer: ADXL345 (slave address: 0x3A) and the temperature sensor
ADT7240 (slave address: 0x90).
The following table is a recap of Table 7.1 which summarizes the differences between the three protocols.
SERIAL
COMMUNICATION
INTERFACE
RENESAS SERIAL
PERIPHERAL
INTERFACE
RENESAS INTER
INTEGRATED
CHIP BUS
Modes
USART/Smart Card
interface
Four wire/Three wire
mode
I2C mode or SM bus
mode
Max Transfer Speed
1.92 Mbps with
PCLK @ 50 Mhz
Up to 25 Mbps
Up to 1 Mbps
Max. number of
devices/slaves
connected per bus
1
8 SPI integrated
channels for slave
selection
127
Number of wires
required for
communication
(not including ground)
2 to 3
3 to 4
2
Max. Length of wires
500 ft @ 9600 bps
10 feet with clock
speed of few kHz
10 meters @
100 kbps
Number of bits per
unit transfer
(excluding start
and stop)
7 or 8
Up to 32 bits
8
Slave Selection
method
Adressed during
communication when
in multiprocessor
communication
mode, else not
available.
Using slave select line
Through addressing
CHAPTER 7 / SERIAL COMMUNICATIONS
7.7
299
REFERENCES
Analog Devices, Inc. 0.25°C Accurate, 16-Bit Digital I2C Temperature Sensor, ADT7420 information and
datasheet. Norwood, MA: Analog Devices, Inc. 2011. Electronic publication. Accessed at
http://www.analog.com/en/mems-sensors/digital-temperature-sensors/adt7420/products/product.html
Analog Devices, Inc. ADXL345 datasheet: 3-Axis, 2 g/4 g/8 g/16 g Digital Accelerometer, ADXL345.
Norwood, MA: Analog Devices, Inc. 2009–2011. Electronic publication. Accessed at
http://www.analog.com/static/imported-files/data_sheets/ADXL345.pdf
Becke, G., Borgert, C., Corrigan, S., Dehmelt, F., Feulner, M., Gonzalez, C., Groenebaum, M., Kabir, F.,
Kacprzak, A., Kinnaird, C., and Zipperer, J. Comparing Bus Solutions; High-Performance Linear/Interface: An Application Report. Texas Instruments. Revised February 2004. Electronic publication. Accessed
at http://www.lammertbies.nl/download/ti-appl-slla067a.pdf
Electronic Industries Association, “EIA Standard RS-232-C Interface Between Data Terminal Equipment and
Data Communication Equipment Employing Serial Data Interchange,” August 1969. Reprinted in Telebyte
Technology Data Communication Library, Greenlawn, NY, 1985. Print.
Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
Hwang, Enoch. Digital Logic and Microprocessor Design with VHDL. Thomson. ISBN 0–534–46593–5.
2006. Electronic Publication. Accessed at http://faculty.lasierra.edu/⬃ehwang/digitaldesign
Soltero, M., Zhang, J. and Cockril, C. Revised by Kevin Zhang, Clark Kinnaird, and Thomas Kugelstadt,
2010. RS-422 and RS-485 Standards Overview and System Configurations, Application Report,
SLLA070D. Texas Instruments, Revised May 2010. Electronic publication. Accessed at
http://focus.ti.com/lit/an/slla070d/slla070d.pdf
7.8
EXERCISES
1. Write a program to setup the Renesas serial communication interface to operate
in the UART mode functioning at 9600 baud, odd parity, 2 Stop bits to transmit 8
bits of data with the LSB first.
2. Write a program to set up the Renesas Serial Peripheral Interface to transfer and
receive 32 bit and 16 bit long data alternately as a single unit at 5 Mbps, with parity enabled in clock synchronous mode. The RSPI should function only as a
master.
3. Write a program to maintain queues for multiprocessor communication using the
Renesas Serial Peripheral Interface so as to perform data transfer between one
master device and two slave devices. Mention algorithms for both. (Hint: Maintain six queues; two for each microcontroller).
4. Write a program to communicate with and to continuously obtain the values of
the X, Y, and Z axis of the onboard ADXL345 accelerometer at 100 kbps.
300
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
5. Write a program to interface two microcontrollers that are monitoring tempera-
tures and exchanging the observed temperature as strings with each other. Each
board should display the observed temperature of itself and the other board on
the graphical/character LCD. (Hint: Use FIFO type data structures).
Chapter Eight
Event Counters, Timers, and the Real Time Clock
8.1
LEARNING OBJECTIVES
In this chapter we show how timers work as event counters, as well as go into more advanced features. It is possible to cascade timers together when one timer does not provide
the range needed. Using timers it is also possible to output a square wave with a controllable frequency and duty cycle. Additionally, the RX62N includes a Real Time Clock peripheral that can keep track of the current date and time. In this chapter we will cover the
concepts behind these features and how to use them.
8.2
BASIC CONCEPTS
8.2.1
Timer and Event Counter
Timer
A timer in a microcontroller is a counter whose value can be read and written as a specialfunction register. When the timer is started, the value in the register increases or decreases
each time it is clocked, and the rate at which the value changes is based upon the clock
source provided to it. If the clock source for the timer is 10 MHz, then one count (increment or decrement) of the register would be equal to 0.1 ms. The timers may have a bit
length of 8-bit (0–255), 16-bit (0–65535) and 32-bit (0–4294967295). For an 8-bit timer
with a clock source of 10 MHz, the maximum time a timer can count depends on the maximum value a timer count register can hold; i.e., the maximum value in an 8-bit register is
255 (FFh). Therefore the maximum time for an 8-bit timer count is:
255
⫽ 255 * 0.1 msec ⫽ 25.5 msec
10 MHz
Therefore, with an 8-bit timer you can measure a maximum of 25.5 ms, but what if you
want to measure 100 ms with an 8-bit register? Should we count four times through an
8-bit timer? The answer is no. For this purpose the microcontroller has a prescaler, which
301
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is used to divide the external or internal clock source by a fixed integer. This increases the
amount of time a timer can count without adding much hardware. The general division
factor for the prescaler would be multiples of two. For example, if we have a division factor of thirty-two, then the maximum amount of time a timer can count with a 10 MHz
clock source is:
255
32
⫽ a255 * b msec ⫽ 816 msec
10 MHz
10
32
As a result, the maximum amount of time a timer can count increases as the prescaler division factor increases.
A timer can also be used as an event counter. The function of the event counter
is the same as the counter, but the event counter counts external events (indicated by
signal transitions on an input pin or on overflows of another timer). For example, an
event counter can be set up in a place where you need to automatically keep track of the
number of people entering a building using a particular entrance. A person passing the
entrance is tracked using an infrared sensor. The sensor is set up such that a person entering the building breaks an infrared light beam directed at the sensor, which changes
its output from high to low as long as the beam is broken. The event counter can be set
up to increment on the high to low transition of the sensor output, and in the end the
count would give us the amount of people who entered the building using a selected entrance. We can also use the event counter to calculate the time intervals between two
events.
Event Counter
The RX62N/RX621 group has two units (Unit 0, Unit 1) of 8-bit timers/counters. The 8-bit
timer can be used in different operating modes: timer mode, event counter mode, and pulse
output mode. The timer mode can also be used to generate interrupts at particular intervals,
and two timers can be cascaded to use a 16-bit timer. In this chapter we cover the basic
concepts of an event counter mode. The timer units can also generate a baud rate clock,
which can be used for serial communication. Table 8.1 shows the functionality available
from the timers.
The event counter of RX62N microcontroller is used detect the overflow of the timer.
After detecting the overflow, another timer can be made to start counting. For example, the
TMR0 (TMR2) can be made to start counting once the TMR1 overflows (TMR3). This feature is mainly used to cascade two timers. The overflow function can be used by setting the
CSS [1⬊0] bits in TCCR to a value of three. (The description of timer registers can be
found in Chapter 10.)
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
TABLE 8.1
ITEM
303
Specification of Timers.
DESCRIPTION
Count clock
䡲 Internal clock: PCLK, PCLK/2, PCLK/8, PCLK/32, PCLK/64,
PCLK/1024, PCLK/8192
䡲 External clock
Number of channels
8 bits ⫻ 4 channels (16 bits ⫻ 2 channels)
Compare match
䡲 8-bit mode (compare match A, compare match B)
䡲 16-bit mode (compare match A, compare match B)
Counter clear
Selected by compare match A or B, or an external reset signal.
Timer output
Output pulses with a desired duty cycle or PWM output
Cascading of two channels
䡲 16-bit count mode
16-bit timer using TMR0 for the upper 8 bits and
TMR1 for the lower 8 bits (TMR2 for the upper 8 bits and
TMR3 for the lower 8 bits)
䡲 Compare match count mode
TMR1 can be used to count TMR0 compare matches
(TMR3 can be used to count TMR2 compare matches).
Interrupt sources
Compare match A, compare match B, and overflow
DTC activation
DTC can be activated by compare match A interrupts or
compare match B interrupts.
Generation of trigger to start
A/D converted conversion
Compare match A of TMR0 and TMR2*1
Capable of generating baud rate
clock for SCI
Generates baud rate clock for SCI5 and SCI6.*2
Low power consumption facilities
Each unit can be placed in a module stop state.
Source: Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America, Inc.,
2010, page 20–1.
The RX62N has a TMR timer peripheral which provides two 8-bit timer units
(Units 1 and 0), each comprising two counter channels. Each timer can be used as an independent timer, to count an external event, or as a pulse output device. The timer works by
incrementing a register each time there is a ‘count’ within the device. The count is either
triggered by a pulse from the internal peripheral clock, a scaled version of the clock, or an
external count source. When this count overflows from its maximum value to zero and/or
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Internal clock
PCLK
PCLK/2
PCLK/8
PCLK/32
PCLK/64
PCLK/1024
PCLK/8192
TMCI1
Counter clock 1
Counter clock 0
Clock select
Compare match A1
Compare match A0
TO SCI5
Overflow 1
Overflow 0
Counter clear 0
Counter clear 1
Compare match B1
Compare match B0
TMO0
TMO1
TCORA
TCORA
Comparator A0
Comparator A1
TCNT
TCNT
Comparator B0
Comparator B1
TCORB
TCORB
TCSR
TCSR
TCR
TCR
TCCR
TCCR
Channel 0
(TMR0)
Channel 1
(TMR1)
Control logic
TMRI0
TMRI1
A/D conversion
strat request signal*
CMIA0
CMIA1
CMIB0
CMIB1
OVI0
OVI1
Interrupt signal
[Legend]
TCORA: Time constant register A
TCNT:
Timer counter
TCORB: Time constant register B
TCSR:
TCR:
TCCR:
Timer control/status register
Timer control register
Timer counter control register
Note: * Fore the corresponding A/D converter channels, see section 33, 12-Bit A/D Converter (S12AD), and
section 34, 10-Bit A/SD Converter (ADa).
Figure 8.1 Block diagram of timer unit 0. Source: Hardware Manual, page 1110.
Internal bus
TMCI0
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
305
there is a compare match with one of the timer constant registers; an action is performed,
such as toggling an output signal, or an interrupt is triggered. Before covering how the
timer works more specifically we will briefly describe the 8-bit timer device’s registers and
how they work.
Figure 8.1 is a block diagram of timer unit 0; Unit 1 is identical except for naming differences (e.g., Timer2 in place of Timer0, and Timer3 in place of Timer1). Do not feel like
you need to understand this entire diagram right away, we will cover the individual parts as
we go along and by the end of this chapter it should all seem very simple. We will start by
first covering the registers that are used when setting up a timer channel.
The legend in the bottom left of Figure 8.1 lists the registers you need to consider when
setting up the 8-bit timer unit. For some registers we have an illustration included of the
registers contents taken from the RX62N Hardware Manual. Make note of the register
parts, as we will use these later when setting them up for specific features. Further details
are available in the hardware manual if needed.
The TCNT (Timer Count) register holds the current timer value at any time after the
timer has been configured. Whenever you want to know the value of the timer or counter
you will read the value in this register. Also, when not currently operating the timer, you
can load a value into this register and the timer will begin counting from that value when
restarted. Note in Figure 8.2 that in the 16-bit mode TMR0.TCNT and TMR1.TCNT
(TMR2.TCNT and TMR3.TCNT as well) cascade into one 16-bit register. This holds true
for the timer constant registers as well.
Address: TMR0.TCNT 0008 8208h, TMR1.TCNT 0008 8209h
TMR2.TCNT 0008 8218h, TMR3.TCNT 0008 8219h
TMR0.TCNT (TMR2.TCNT)
Value after reset:
TMR1.TCNT (TMR3.TCNT)
b7
b6
b5
b4
b3
b2
b1
b0
b7
b6
b5
b4
b3
b2
b1
b0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 8.2 TCNT (Timer Count) register. Source: Hardware Manual.
The TCNT register is where the count is held. After the timer is started this register will increment every time a count is detected. If you want to know the current count, you can read
this register. If the timer is stopped you can write a value to this register and it will begin
counting from the written value when re-started.
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Timer Control Register (TCR)
Address: TMR0.TCR 0008 8200h, TMR1.TRC 0008 8201h
TMR2.TCR 0008 8210h, TMR3.TCR 0008 8211h
Value after reset:
BIT
SYMBOL
b2 to b0
—
b4, b3
CCLR[1:0]
b7
b6
b5
CMIEB
CMIEA
OVIE
0
0
0
b4
b3
b2
b1
b0
CCLR[1:0]
—
—
—
0
0
0
0
0
BIT NAME
DESCRIPTION
R/W
(Reserved)
This bit is read as 0. The write value
should always be 0.
R/W
Counter Clear*
b4 b3
R/W
0 0: Clearing is disabled
0 1: Cleared by compare match A
1 0: Cleared by compare match B
1 1: Cleared by the external reset
input
(Select edge or level by the TMRIS bit
in TCCR.)
b5
b6
b7
OVIE
CMIEA
CMIEB
Timer Overflow Interupt
0: Overflow interrupt requests
(OVIn) are disabled
Enable
1: Overflow interrupt requests
(OVIn) are ensabled
Compare Match Interrupt
0: Compare match A interrupt
requests (CMIAn) are disabled
Enable A
1: Compare match A interrupt
requests (CMIAn) are enabled
Compare Match Interrupt
0: Compare match B interrupt
requests (CMIBn) are disabled
Enable B
1: Compare match B interrupt
requests (CMIBn) are enabled
Note: * To use an external reset, set the Pn.DDR.Bi bit for the corresponding pin “0” and the Pn.ICR.Bi bit to “1”.
Figure 8.3 TCR (Timer Control Register) description. Source: Hardware Manual, Section 20.2.4.
R/W
R/W
R/W
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
307
The TCCR controls where the timers count source comes from. Depending what value is set
here will determine if the count comes from the internal peripheral clock, a pre-scaled peripheral clock, an external count source, or from another timer overflowing. This register also
enables the timer’s interrupts on the peripheral level. Keep in mind you must also enable to
interrupts in the ICU (Interrupt Controls Unit) in order for an interrupt routine to be called.
Timer Counter Control Register (TCCR)
Address: TMR0.TCCR 0008 820Ah, TMR1.TCCR 0008 820Bh
TMR2.TCCR 0008 821Ah, TMR3.TCCR 0008 821Bh
Value after reset:
b7
b6
b5
TMRIS
—
—
0
0
0
b4
b3
b2
CSS[1:0]
0
0
b0
CKS[2:0]
0
0
0
BIT
SYMBOL
b2 to b0
CKS[2⬊0]
Clock Select*
See table 20.5.
R/W
b4, b3
CSS[1⬊0]
Clock Source Select
See table 20.5.
R/W
b6, b5
—
(Reserved)
These bits are always read as 0. The write
value should always be 0.
R/W
Timer Reset Input
Select
0: Cleared at rising edge of the external reset
R/W
b7
TMRIS
BIT NAME
b1
DESCRIPTION
R/W
1: Cleared when the external reset is high
Note: * To use an external clock, set the Pn.DDR.Bi bit for the corresponding pin to “0” and the PnICR.Bi bit
to “1”. For details, see section 16, I/O Ports.
Figure 8.4 TCCR (Timer Counter Control Register) description. Source: Hardware Manual, Section 20.2.5.
The TCORA (Timer Constant Register A) and TCORB (Timer Constant Register B) are
used to store constants to compare against the TCNT register. Every time the TCNT increments it is constantly being compared against either of these registers. When TCNT
matches either of these registers, a compare match event occurs. Compare match events
have many uses depending on what mode we are using the timer in.
The TCSR (Timer Control Status) register controls compare match output. Each timer
has an output port assigned to it which is controlled via compare match events. This is one of
many uses of the compare match events. When a compare match event occurs this register
can set the output of the timer’s port to 1 or 0, or toggle it. This register is used when we want
the timer to control a pulse output.
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308
TCCR REGISTER
CSS[1⬊0]
CHANNEL
TMR0
(TMR2)
CKS[2⬊0]
b4
b3
b2
b1
b0
0
0
—
0
0
Clock input prohibited
1
Uses external clock. Counts at rising edge*1.
0
Uses external clock. Counts at falling edge*1.
1
Uses external clock. Counts at both rising and falling edges*1.
0
Uses internal clock. Counts at PCLK.
1
Uses internal clock. Counts at PCLK/2.
0
Uses internal clock. Counts at PCLK/8.
1
Uses internal clock. Counts at PCLK/32.
0
Uses internal clock. Counts at PCLK/64.
1
Uses internal clock. Counts at PCLK/1024.
1
0
Uses internal clock. Counts at PCLK/8192.
1
0
1
0
0
1
1
TMR1
(TMR3)
0
DESCRIPTION
1
Clock input prohibited
1
0
—
—
—
Setting prohibited
1
1
—
—
—
Counts at TMR1.TCNT (TMR3.TCNT) overflow signal*2
0
0
—
0
0
Clock input prohibited
1
Uses external clock. Counts at rising edge*1.
0
Uses external clock. Counts at falling edge*1.
1
Uses external clock. Counts at both rising and falling edges*1.
0
Uses internal clock. Counts at PCLK.
1
Uses internal clock. Counts at PCLK/2.
0
Uses internal clock. Counts at PCLK/8.
1
Uses internal clock. Counts at PCLK/32.
0
Uses internal clock. Counts at PCLK/64.
1
Uses internal clock. Counts at PCLK/1024.
0
Uses internal clock. Counts at PCLK/8192.
1
Clock input prohibited
1
0
1
0
0
1
1
0
1
1
0
—
—
—
Setting prohibited
1
1
—
—
—
Counts at TMR0.TCNT (TMR2.TCNT) overflow signal*2
Notes: 1. To use an external clock, set the Pn.DDR.BI bit for the corresponding pin to “0” and the Pn.ICR.BI bit to “1”.
For details, see section 16, I/O Ports.
2. If the clock input of TMR0 (TMR2) is the overflow signal of the TMR1.TCNT (TMR3.TCNT) counter and that of
TMR1 (TMR3) is the compare match signal of the TMR0.TCNT (TMR2.TCNT) counter, no incrementing clock is
generated. Do not use this setting.
Figure 8.5 Clock input to TCNT and count condition. Source: Hardware Manual, Table 20.5.
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
309
Timer Counter/Status Register (TCSR)
Address: TMR0.TCSR 0008 8202h, TMR2.TCSR 0008 8212h
Value after reset:
b7
b6
b5
b4
—
—
—
ADTE
x
x
x
0
b3
b2
b1
OSB[1:0]
b0
OSA[1:0]
0
0
0
0
b3
b2
b1
b0
Address: TMR1.TCSR 0008 8203h, TMR3.TCSR 0008 8213h
Value after reset:
TMR0, TCSR, TMR2
[Legend] x: Undefined
BIT
b1, b0
b7
b6
b5
b4
—
—
—
—
x
x
x
1
SYMBOL
BIT NAME
OSA[1⬊0]
Output
Select A*1
OSB[1:0]
0
0
OSA[1:0]
0
0
DESCRIPTION
b1 b0
R/W
R/W
0 0: No change when compare match A occurs
0 1: 0 is output when compare match A occurs
1 0: 1 is output when compare match A occurs
1 1: Output is inverted when compare
match A occurs (toggle output)
b3, b2
OSB[1⬊0]
Output
Select B*1
b3 b2
R/W
0 0: No change when compare match B occurs
0 1: 0 is output when compare match B occurs
1 0: 1 is output when compare match B occurs
1 1: Output is inverted when compare
match B occurs (toggle output)
b4
ADTE
A/D Trigger
Enable*2
0: A/D converter start requests by compare
match A are disabled
R/W
1: A/D converter start requests by compare
match A are enabled
b7 to b5
—
(Reserved)
These bits are always read as an indefinite
value. The write value should always be 1.
R/W
Notes: 1. Timer output is disabled when the OSB[1⬊0] and OSA[1⬊0] bits are all 0. Timer output is 0 until
the first compare match occurs after a reset.
2. For the corresponding A/D converter channels, see section 34, A/D Converter.
Figure 8.6 TCSR (Timer Control/Status Register) description. Source: Hardware Manual, Section 20.2.6.
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310
That is a basic overview of the registers and what they do. Now that we know a bit about
how the timer works we can start going into how we modify these registers to get the timer
to go into its different modes of operation.
8.2.2
Cascading Timers
Sometimes when using a timer for an application you need a delay longer than is allowed
when only using 8-bits. The RX62N allows both timer channels in either time unit to be
cascaded into one 16-bit channel. Essentially every time the first timer overflows, the next
timer will count. This multiplies the total time able to be counted by a factor of 28 (256).
Originally we could only count from 0 to 255, now we can count to 65535.
So how do we calculate how long it will take for the timer to count to 0xFFFF (our max
value)? First we consider the RX62N’s main clock which is 24 MHz. This means every
clock tick takes approximately 41.57 nanoseconds. We multiply by what division of the peripheral clock we are using, say 64, because the period for that clock is 64 times as long.
Then we multiply by the number of ticks which is 0xFFFF or 65535. So when using
PCLK/64 and a 16-bit counter, there will be approximately 174.76 ms between each overflow interrupt.
64 (clock division) 65535 (counts per interrupt)
1
⫽ 174.76 ms.
*
*
24 MHz (peripheral clock)
1
1
Table 8.2 lists the approximate time between interrupts for each clock division.
TABLE 8.2
CLOCK DIVISION
Clock Division and Interrupt Times.
TIMER PER COUNT
TIME BETWEEN OVERFLOW INTERRUPTS
IN 16-BIT MODE
PLCK
41.67 ns
2.73 ms
PLCK/2
83.33 ns
5.41 ms
PCLK/8
333.33 ns
21.84 ms
PCLK/32
1.33 ms
87.38 ms
PCLK/64
2.67 ms
174.76 ms
PCLK/1024
42.67 ms
2.79 s
PCLK/8192
341.333 ms
22.37 s
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
311
NOTE:
It is possible in hardware setup to alter the speed of the PCLK, make sure to take note of
this and alter your calculations accordingly. A basic HEW setup with no alterations will
still have a PCLK of 24 MHz.
To set up a timer unit in 16-bit cascaded timer mode, set the bits in TMR0.TCCR.CSS[1⬊0]
to 11b. This effectively sets the count source for Timer0 as Timer1. Whenever TCNT in
Timer1 overflows, Timer0 will count once. In effect, this makes TMR0.TCNT and
TMR1.TCNT combine into a single 16-bit register. The speed at which Timer1 can count
is still determined in TMR1.TCCR.CSS and TMR1.TCCR.CKS. The settings for clearing
the counter and interrupts are now controlled by the TMR0.TCR register; any settings in
TMR1.TCR are ignored.
We have just covered how to cascade two 8-bit timer units to make one 16-bit timer. In
the examples section we will give an example of how to set up a cascaded timer and an example of its usage.
8.2.3
Pulse Output Operation
Before covering how the RX62N 8-bit timer peripheral handles pulse outputs, we’ll do a
brief overview of pulse-width modulation concepts. There are three aspects of a wave we
will concern ourselves with when dealing with pulse output operation: the period, frequency, and duty cycle. Any wave is basically a repeating pattern in output over time, such
as a sine wave, square wave, or sawtooth wave. The period of the wave is defined as the
time between repeats in the simplest form of the wave’s pattern. In the case of a square
wave, the period is the time between the rising edges of the positive output portion.
The frequency is determined by how many periods there are of a wave in a second. We
Number of Periods
can determine frequency by the formula f ⫽
, yielding a value in Herz
Length of Time
(Hz, periods/second). If we want to determine the period using the frequency we use the
1
. Duty cycle is defined as the percentage of the period during
f(Hz)
Time High
which the waveform is high. Duty cycle can be determined by the formula
⫻ 100%.
T (period)
Using the 8-bit timer peripheral we can output a square wave where the frequency and duty
cycle are controlled by changing values in the registers we have already covered.
formula T (period) ⫽
312
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
1.5
Voltage
Period
2 ms
1
Duty
Cycle
1.75 ms
87.5%
0.5
0
20.5
0
2
4
6
8
Time 10
Figure 8.7 Pulse-width modulation signal attributes.
Pulse output mode is handy in applications such as interfacing the microcontroller to several types of motors. A servo motor usually uses a square wave input to determine the position or speed of the motor. Varying the duty cycle will vary the speed or position. When
interfacing to a DC motor, the microcontroller almost always lacks the power output to
drive the motor. A power amplifier must be used, most often an H-bridge. The H-bridge
will take a square wave signal from the microcontroller and amplify it to whatever voltage
and current levels are needed for the application. By varying the duty cycle of the wave we
vary the average power that is delivered to the motor, making an efficient means of digitally controlling an analog device.
Now we will go over how to set up the RX62N in pulse output mode. First in pulse output mode, TCR.CCLR[1⬊0] is set to 01b. This will make TCNT clear to 0x00 every time a
compare match A occurs. Now we set TCSR.OSA[1⬊0] to 10b and TCSR.OSB[0⬊1] to
01b. This will make the output from the timer channel change to 1 at the occurrence of
compare match A and change back to 0 at the occurrence of compare match B.
Here is a brief overview of what happens on a single timer channel when set up in
pulse output mode. TCNT begins to count up. Once it reaches the value of timer constant
register A the first time, the pulse output becomes 1 and TCNT resets to 00h. TCNT
restarts counting and upon reaching the value of timer constant register B, the output goes
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
313
to 0. TCNT continues to count until it reaches the value of timer constant register A again.
TCNT now resets to 00h again and the output goes back to 0. This process repeats, producing a square wave on the TCOn port (n being the number of the timer used). This is illustrated in Figure 8.8, TMOn being the waveform of the output pulse.
TCNT
FFh
Counter clear
TCORA
TCORB
00h
TMOn
(n 5 0 to 3)
Figure 8.8 An example of pulse output. Source: Hardware Manual, Figure 20.3.
By altering the value of TCORA we change the frequency of the pulse output, and by altering TCORB without altering TCORA we alter the duty cycle of the wave. Take note that
by altering TCORA without altering TCORB the duty cycle does not remain the same because the output is going low at the same amount of time after TCNT resets, but the time
between when the pulse goes low and a compare match A occurrence has become longer.
We have just covered a basic overview of concepts to do with pulse output and how to
control it on the RX62N. In the examples section we will show and explain a basic example of how to set up pulse output from one of the timer units.
8.3
REAL TIME CLOCK
The Real Time Clock is a separate unit unto itself. Without an independent Real Time Clock
unit it would be necessary to cascade timers, set up variables, and use interrupt routines to
track the time. Another advantage to a separate unit is that it takes less energy to keep running in low power modes. This unit makes keeping track of time much easier by keeping a
separate binary coded decimal register for the years, months, date, day of the week, hours,
minutes, and seconds. The unit also automatically tracks leap years. Using the Real Time
Clock is as simple as setting the values for the date then setting it to start counting. The
clock keeps count via a dedicated 32.768 KHz count source and outputs a 1 Hz clock.
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8.3.1
RTC Registers
We will now cover all of the registers in the RTC and their functions.
64-Hz Counter (R64CNT)
Address: 0008 C400h
b7
b6
b5
b4
b3
b2
b1
b0
—
F1HZ
F2HZ
F4HZ
F8HZ
F16HZ
F32HZ
F64HZ
0
x
x
x
x
x
x
x
Value after reset:
[Legend] x: Undefined
BIT
SYMBOL
BIT NAME
b0
F64HZ
64 Hz
b1
F32HZ
32 Hz
R
b2
F16HZ
16 Hz
R
b3
F8HZ
8 Hz
R
b4
F4HZ
4 Hz
R
b5
F2HZ
2 Hz
R
b6
F1HZ
1 Hz
R
b7
—
(Reserved)
DESCRIPTION
Indicate the state between 64 Hz and 1 Hz.
This bit is always read as 0 and cannot be modified.
R/W
R
R
Figure 8.9 R64CNT (64 Hz Counter). Source: Hardware Manual, Section 22.2.1.
The second counter uses the 64 Hz counter (R64CNT) as its count source. This register can
be read to determine time in the sub-seconds range.
RSECCNT is where the current count in seconds is read/written. Once the value is
above fifty-nine it will reset to zero and the minute counter will increment.
The RMINCNT register is where the current value of the minutes is read/written. This
counter behaves just like the second counter in that the hour counter will increment once it
counts past fifty-nine and the minute counter will reset.
The RHRCNT register is where the current value in hours is read/written. The register
counts from zero to twenty-three, then resets. When it resets, the day counter and day of the
week counter are incremented.
RWKCNT holds the value of the current day of the week. It counts from zero to six,
then resets.
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
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Second Counter (RSECCNT)
Address: 0008 C402h
b7
b6
b5
BIT
0
SYMBOL
b3
b2
SEC10[2:0]
—
Value after reset:
b4
x
x
x
b1
b0
SEC1[3:0]
x
x
x
x
BIT NAME
DESCRIPTION
R/W
b3 to b0
SEC1[3⬊0]
Ones Place of Seconds
Counts from 0 to 9 once per second.
When a carry is generated, 1 is added
to the tens place.
R/W
b6 to b4
SEC10[2⬊0]
Tens Place of Seconds
Counts from 0 to 5 for 60-second
counting.
R/W
(Reserved)
This bit is always read as 0. The write
value should always be 0.
R/W
b7
—
Figure 8.10 RSECCNT (Second Counter). Source: Hardware Manual, Section 22.2.2.
Minute Counter (RMINCNT)
Address: 0008 C404h
b7
b6
b4
b3
MIN10[2:0]
—
Value after reset:
b5
0
x
x
b2
b1
b0
MIN1[3:0]
x
x
x
x
x
[Legend] x: Undefined
BIT
SYMBOL
BIT NAME
DESCRIPTION
R/W
b3 to b0
MIN1[3⬊0]
Tens Place of Minutes
Counts from 0 to 9 once per minute.
When a carry is generated, 1 is added
to the tens place.
R/W
b6 to b4
MIN10[2⬊0]
Ones Place of Minutes
Counts from 0 to 5 for 60-minute
counting.
R/W
(Reserved)
This bit is always read as 0. The write
value should always be 0.
R/W
b7
—
Figure 8.11 RMINCNT (Minute Counter). Source: Hardware Manual, Section 22.2.3.
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Hour Counter (RHRCNT)
Address: 0008 C406h
Value after reset:
b7
b6
—
—
0
0
b5
b4
b3
b2
HOUR10[1:0]
x
x
b1
b0
HOUR1[3:0]
x
x
x
x
[Legend] x: Undefined
BIT
SYMBOL
BIT NAME
DESCRIPTION
R/W
b3 to b0
HOUR1[3⬊0]
Ones Place of Hours
Counts from 0 to 9 once per hour.
When a carry is generated, 1 is added
to the tens place.
R/W
b5, b4
HOUR10[1⬊0]
Tens Place of Hours
Counts from 0 to 2 once per carry from
the ones place.
R/W
b7, b6
—
(Reserved)
These bits are always read as 0. The
write value should always be 0.
R/W
Figure 8.12 RHRCNT (Hour Counter). Source: Hardware Manual, Section 22.2.4.
Day-of-Week Counter (RWKCNT)
Address: 0008 C408h
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
b2
b1
b0
DAY[2:0]
x
x
x
[Legend] x: Undefined
BIT
SYMBOL
BIT NAME
b2 to b0
DAY[2⬊0]
Day-of-Week
Counting
DESCRIPTION
000: Sunday
R/W
R/W
001: Monday
010: Tuesday
011: Wednesday
100: Thursday
101: Friday
110: Saturday
111: (Setting Prohibited)
b7 to b3
—
(Reserved)
These bits are always read as 0. The write value
should always be 0.
Figure 8.13 RWKCNT (Day-of-Week Counter). Source: Hardware Manual, Section 22.2.5.
R/W
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
317
Date Counter (RDAYCNT)
Address: 0008 C40Ah
Value after reset:
b7
b6
b5
b4
—
—
DAY10[1:0]
0
0
x
x
b3
b2
b1
b0
DAY1[3:0]
x
x
x
x
[Legend] x: Undefined
BIT
SYMBOL
BIT NAME
DESCRIPTION
R/W
b3 to b0
DAY1[3⬊0]
Ones Place of Days
Counts from 0 to 9 once per day. When a
carry is generated, 1 is added to the tens
place.
R/W
b5, b4
DAY10[1⬊0]
Tens Place of Days
Counts from 0 to 3 once per carry from
the ones place.
R/W
b7, b6
—
(Reserved)
These bits are always read as 0. The write
value should always be 0.
R/W
Figure 8.14 RDAYCNT (Date Counter). Source: Hardware Manual, Section 22.2.6.
RDAYCNT holds the current value of the day of the month. The counter automatically
accounts for the number of specifiable days in a month and leap years. When the count goes
above the days of the current month it resets to zero and the month counter is incremented.
RMONCNT holds the value for the current month. It counts from one to twelve, and
then resets. When it resets to zero, the year counter is incremented.
The RYRCNT register holds the current count of the years from zero to 9999.
For each counter register besides the 64 Hz Counter (R64CNT), there is a corresponding alarm register. Each of these is written to the same as the corresponding count register, other than the unused bit 7 which is now an enable bit; except in the case of the year
alarm register which uses an entire word (it has a separate enable register named
RYAREN). Whenever the values in each of the counters match the alarm registers with the
enable bits set, the Real Time Clock alarm interrupt is triggered.
Take note that writing the decimal value of the number you want to input to these registers will not be input as the value you want. This is because the registers are not read as
an 8-bit decimal value, but are instead split so that each 4-bit span is a binary encoded decimal digit. As a review of basic concepts of base 2 (binary) and base 16 (hexadecimal)
numbers you will remember that a hexadecimal number can be used as shorthand for 4 bits
of a binary number. As an example the hexadecimal 0x45 is equivalent to the binary
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
318
Month Counter (RMONCNT)
Address: 0008 C40Ch
b7
b6
b5
b4
—
—
—
MON10
0
0
0
x
Value after reset:
b3
b2
b1
b0
MON1[3:0]
x
x
x
x
[Legend] x: Undefined
BIT
SYMBOL
BIT NAME
DESCRIPTION
R/W
b3 to b0
MON1[3⬊0]
Ones Place
of Months
Counts from 0 to 9 once per month. When a carry
is generated, 1 is added to the tens place.
R/W
b4
MON10
Tens Place
of Months
Counts from 0 to 1 once per carry from the ones
place.
R/W
b7 to b5
—
(Reserved)
These bits are always read as 0. The write value
should always be 0.
R/W
Figure 8.15 RMONCNT (Month Counter). Source: Hardware Manual, Section 22.2.7.
Year Counter (RYRCNT)
Address: 0008 C40Eh
b15
b14
b13
b12
b11
YEAR1000[3:0]
Value after reset:
x
x
x
b10
b9
b8
b7
YEAR100[3:0]
x
x
x
x
b6
b5
b4
b3
YEAR10[3:0]
x
x
x
x
b2
b1
b0
YEAR1[3:0]
x
x
x
x
x
[Legend] x: Undefined
BIT
SYMBOL
BIT NAME
DESCRIPTION
R/W
b3 to b0
YEAR1[3⬊0]
Ones Place
of Years
Counts from 0 to 9 once per year.
When a carry is generated, 1 is added
to the tens place.
R/W
b7 to b4
YEAR10[3⬊0]
Tens Place
of Years
Counts from 0 to 9 once per carry
from ones place. When a carry is
generated in the tens place, 1 is added
to the hundreds place.
R/W
b11 to b8
YEAR100[3⬊0]
Hundreds Place
of Years
Counts from 0 to 9 once per carry
from tens place. When a carry is
generated in the hundreds place, 1 is
added to the thousands place.
R/W
b15 to b12
YEAR1000[3⬊0]
Thousands Place
of Years
Counts from 0 to 9 once per carry
from hundreds place.
R/W
Figure 8.16 RYRCNT (Year Counter). Source: Hardware Manual, Section 22.2.8.
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319
RTC Counter Register 1 (RCR1)
Address: 0008 C422h
b7
b6
BIT
b0
b1
0
b4
PES[2:0]
—
Value after reset:
b5
0
0
0
b3
b2
b1
b0
—
PIE
CIE
AIE
0
0
0
0
SYMBOL
BIT NAME
AIE
Alarm
Interrupt
Enable
0: An alarm interrupt is not requested
Carry
Interrupt
Enable
0: A carry interrupt is not requested when a carry to the
second counter occurred or a carry to the 64-Hz
counter occurred during react access to the 64-Hz
counter.
CIE
DESCRIPTION
R/W
R/W
1: An alarm interrupt is requested
R/W
1: A carry interrupt is requested when a carry to the
second counter occurred or a carry to the 64-Hz
counter occurred during read access to the 64-Hz
counter.
b2
PIE
Periodic
Interrupt
Enable
0: A periodic interrupt is not requested.
R/W
1: A periodic interrupt is requested.
b3
—
(Reserved)
This bit is always read as 0. The write value should
always be 0.
R/W
b6 to b4
PES[2⬊0]
Periodic
Interrupt
Select
000: No periodic interrupts generated
R/W
001: A periodic interrupt generated every 1⁄ 256 second
010: A periodic interrupt generated every 1⁄ 64 second
011: A periodic interrupt generated every 1⁄ 16 second
100: A periodic interrupt generated every 1⁄ 4 second
101: A periodic interrupt generated every 1⁄ 2 second
110: A periodic interrupt generated every 1 second
111: A periodic interrupt generated every 2 seconds
b7
—
(Reserved)
This bit is always read as 0. The write value should
always be 0.
Figure 8.17 RCR1 (RTC Control Register). Source: Hardware Manual, Section 22.2.17.
R/W
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
320
RTC Counter Register 2 (RCR2)
Address: 0008 C424h
Value after reset:
BIT
SYMBOL
b0
START
b1
RESET
b7
b6
b5
b4
b3
b2
—
—
—
—
RTOOE
ADJ
0
0
0
0
0
0
BIT NAME
Start
Reset
b1
b0
RESET START
0
1
DESCRIPTION
R/W
0: Year, month, day-of-week, date, hour,
minute, second, and 64-Hz counters, and
prescaler are stopped.
R/W
1: Year, month, day-of-week, date, hour,
minute, second, and 64-Hz counters, and
prescaler operate normally.
R/W
0: Normal count operation or the initialization is
completed
R/W
1: Prescaler, 64-Hz counter, and alarm registers
are initialized.
b2
ADJ
30-Second
Adjustment
0: Normal count operation or completion of
30-second adjustment
R/W
1: During 30-second adjustment
b3
RTOOE
RTOOUT Output
Control
0: Clock signals are not output from the
RTOOUT pin.
R/W
1: Clock signals are output from the RTOOUT pin.
b7 to b4
—
(Reserved)
These bits are always read as 0. The write value
should always be 0.
R/W
Figure 8.18 RCR2 (RTC Control Register 2). Source: Hardware Manual, Section 22.2.18.
number 0b01000101. So if we were to write 0x45 to the seconds counter register, then 4
would be written to the tens span and 5 would be written to the ones span. The new count
for the seconds register would be read as 45.
Keep in mind it is not a good idea to write to each span of the register individually as
the counters update on each 128 Hz count. If your code writes a new value to the register
during the same 128 Hz count it may not be acknowledged, even if is to different bits.
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
321
RCR1 enables and disables the three available RTC interrupts and the period of the periodic interrupt request. We will go over these interrupts in further detail in the advanced
concepts section, for now we are most concerned with just understanding and initially setting up the Real Time Clock.
RCR2 controls the start and reset of the Real Time Clock. By writing a 1 or 0 to the
START bit you start or stop the clock. By writing a 1 to the RESTART bit you will reset the
64 Hz counter, presecalers, and alarm registers to 0. Take note that these bits are updated in
sync with the count source, so if you write to either of these bits it won’t take effect until
the next count of the RTC’s 128 Hz clock. More details are available in the hardware manual. We will cover how to account for this in code examples.
8.3.2
Setting the RTC
Setting the Real Time Clock is relatively simple, as illustrated in Figure 8.19. After setting
and waiting for the START bit in RCR2 to clear to 0, you set a 1 to the RESET bit. After
this you can set the counter registers in any order. Then you set a 1 to the START bit in
RCR2 to get the counter started again. Be sure to wait for the bit to set to 1 before you continue with any other operations on the RTC.
Clear the START bit to 0
No
START 5 0
Write 0 to the START bit in RCR2
Wait for the START bit in RCR2 to be cleared to 0
Yes
Reset the prescaler and 64CNT
Set the year, month,
day of the week, date, hour,
minute, and second
Set the START bit to 1.
Write 1 to the RESET bit in RCR2
Settings in arbitrary order is possible
Write 1 to the START bit in RCR2
Yes
No
START 5 1
Wait for the START bit in RCR2 to be set to 1
Figure 8.19 Setting the Real Time Clock. Source: Hardware Manual, Figure 22.2.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
8.3.3
Reading the RTC
Reading the values in the RTC is a little tricky. If a carry request is performed from the
64 KHz clock to the second counter while a reading occurs, then the correct time won’t be
read. There are two ways to read the time that avoids this.
Disable the ICU carry interrupt
request
Write 0 to the IER07.EN7 bit of the ICU
Enable the RTC carry Interrupt
request
Write 1 to the CIE bit in RCR1
Clear the carry flag
Read counter register
Write 0 to the IR63.IR flag of the ICU
Read all the necessary counter registers
Yes
Carry flag 5 1?
Read the IR63.IR flag of the ICU for checking
No
(a) To read the time without using Interrupt
Clear the carry flag
Disable the ICU carry interrupt
request
Write 1 to the IER07.IEN7 bit of the ICU
Enable the RTC carry Interrupt
request
Write 1 to the CIE bit in RCR1
Clear the carry flag
Read counter register
Yes
Write 0 to the IR63.IR flag of the ICU
Write 0 to the IR63.IR flag of the ICU
Read all the necessary counter registers
Interrupt?
No
Disable the RTC carry Interrupt
Write 0 to the CIE bit in RCR1
(b) To read the time using interrupts
Figure 8.20 Reading 64 Hz Counter and Time. Source: Hardware Manual, Figure 22.4.
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
323
This flowchart from the RX62N manual illustrates the operation to take when reading
the counter values using interrupts or not using interrupts. In the non-interrupt method
you disable the carry interrupt in the ICU, but enable it in the RTC. Then you check the
interrupt flag for the carry operation after reading the registers. If a carry has occurred,
you clear the carry flag and start reading over again because the time has changed since
reading started. When using the interrupt method you start the same, but instead of checking the carry flag you use the carry interrupt to indicate that a carry has occurred between
the 64 Hz counter and the second count. The non-interrupt method is preferred as it takes
less code.
8.4
BASIC EXAMPLES
Now that we have covered the basic concepts needed to understand how the timer works in
these different modes, we will cover a few examples. For now we will demonstrate the initial setup of the clock and how to read from it.
8.4.1
Setting Up Cascaded Timers
For this demo we will be setting up Timer Unit 0 in cascaded timer mode by cascading
Timer 0 and Timer 1 together. We will call an interrupt service routine every time this cascaded counter overflows from 0xFFFF to 0x0000. In the service routine we will put a call
to a function that rotates the LEDs on the board. The resulting program will make the
LEDs on the board blink in a rotating sequence at a speed determined by how we set up
our timer.
We will start with a base HEW project that includes the iodefine.h file and other support headers for the RX62N. In this example we will use macros to control the LEDs, we
will continue assuming you have defined a similar substitute for performing the action described by the macro.
The first thing to do in our main program is to declare our only global variable.
1. int Current_LED = 1;
We will use this variable to keep track of which LED is currently lit. We will cover how
when we discuss the function that uses it.
Then we need to include our function prototypes. As you can see we will only use two
function calls, one to set up the timer and another to blink the LEDs.
1. void InitTimer(void);
2. void Rotate_LED(void);
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
After our main() loop begins we will only need to include the macro for initializing the
LEDs and our timer initialization function call. Our while(1) loop will be empty, as all operations will be handled in the timer interrupt. Note that this is generally bad programming
practice and very uncommon; however, in some cases this is the correct solution.
1. void main(void){
2.
ENABLE_LEDS;
3.
InitTimer();
4.
while(1){}
5. }
Now comes the part we are most concerned with, the timer initialization. In this function
we will set the timer registers for 16-bit cascaded mode.
1. void InitTimer(void){
2.
IEN(TMR0,OVI0) = 1;
//Enable TMR0 Overflow interrupt in ICR
3.
IPR(TMR0,OVI0) = 2;
//Set priority level of interrupt
4.
MSTP(TMR0) = 0;
//Activate TMR0 unit
5.
MSTP(TMR1) = 0;
//Activate TMR1 unit
6.
TMR1.TCCR.BIT.CSS = 1;
7.
TMR1.TCCR.BIT.CKS = 4;
//Count source is PCLK/64 for TMR1
8.
TMR0.TCCR.BIT.CSS = 3;
9.
TMR0.TCR.BIT.CCLR = 1;
//Count source is TMR1 for TMR0
10.
TMR0.TCR.BIT.OVIE = 1;
//Overflow interrupt enabled
11. }
We start on lines 2–3 by enabling the Timer 0 overflow interrupt in the ICU and setting its
priority level. Then on lines 4–5 we activate the Timer 0 and 1 units in the Module Stop
Control Register (they are off by default). On lines 6–7 we set the count source for Timer 1
as the PCLK/64 input which is just the main clock divided by 64. On lines 9–10 we set the
count source for Timer 0 as Timer 1. With the count source set, this will make Timer 0
count every time Timer 1 overflows. Now, with this set the two timers are cascaded. On line
14 we finish by setting the interrupt in the timer unit itself.
As we calculated earlier in our concepts, this setup will take the main clock of 24 MHz
and divide it by 64. Then every 65535 counts of that the Timer 0 interrupt will occur and
the interrupt routine will be called, thus rotating the current LED that is lit. This is calcu1
64 (clock division)
lated to be approximately every 174.76 ms.
*
*
24 MHz (main clock)
1
65535 (counts per interrupt)
⫽ 174.76 ms
1
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
325
The next function is used to light the LEDs on the board one at a time in a circular sequence. It uses the Current_LED variable to hold which Led is currently lit. Each time it is
called, it increments the value, and as soon as it passes 12 it restarts at 1.
1. void LED_Rotate(void){
2.
switch(Current_LED){
3.
case 1:
4.
ALL_LEDS_ON;
5.
LED6 = LED_OFF;
6.
break;
7.
case 2:
8.
ALL_LEDS_ON;
9.
LED12 = LED_OFF;
10.
break;
11.
case 3:
12.
ALL_LEDS_ON;
13.
LED3 = LED_OFF;
14.
break;
15.
case 4:
16.
ALL_LEDS_ON;
17.
LED9 = LED_OFF;
18.
break;
19.
case 5:
20.
ALL_LEDS_ON;
21.
LED5 = LED_OFF;
22.
break;
23.
case 6:
24.
ALL_LEDS_ON;
25.
LED11 = LED_OFF;
26.
break;
27.
case 7:
28.
ALL_LEDS_ON;
29.
LED2 = LED_OFF;
30.
break;
31.
case 8:
32.
ALL_LEDS_ON;
33.
LED8 = LED_OFF;
34.
break;
35.
case 9:
36.
ALL_LEDS_ON;
37.
LED4 = LED_OFF;
38.
break;
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59. }
case 10:
ALL_LEDS_ON;
LED10 = LED_OFF;
break;
case 11:
ALL_LEDS_ON;
LED1 = LED_OFF;
break;
case 12:
ALL_LEDS_ON;
LED7 = LED_OFF;
break;
default:
ALL_LEDS_OFF;
break;
}
Current_LED++;
if(Current_LED == 13){
Current_LED = 1;
}
That is all of the code we need in the main program file. Now we need to define our interrupt and put a call to our LED_Rotate() function.
1.
2.
3.
4.
#pragma interrupt (Excep_TMR0_OV0I(vect = VECT_TMR0_OVI0))
void Excep_TMR0_OV0I(void);
//TMR0_OV0I
void Excep_TMR0_OV0I(void){LED_Rotate();}
The first line of this code snippet defines an interrupt at the vector for Timer 0. Next it gives
a function definition and the function itself. Inside the function is a call to the LED_Rotate()
function. Make note that it is bad practice to include function calls inside of an ISR for many
reasons. We will go over reasons why and workarounds for this later.
We have now successfully set up a 16-bit cascaded timer on the RX62N and used it to
trigger an interrupt that rotates the board’s LEDs. By modifying the count source of
Timer 1 we can change the speed of this rotation. Later, in a more advanced example, we
will cover how to take greater control of the timer and interrupt timing using the timer constant registers and compare match events.
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
8.4.2
327
Setting Up a Timer for Pulse Output
Now we will cover an example of setting up a timer for pulse output. This requires very little code to execute. Once we have set up the timer it will begin to output our desired pulse
without any further intervention.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
void main(void);
void InitTimer(void);
void main(void){
InitTimer();
while(1){}
}
void InitTimer(void){
MSTP(TMR0) = 0;
//Activate TMR0 unit
TMR0.TCCR.BIT.CSS = 1;
//Count source is PCLK/8
TMR0.TCCR.BIT.CKS = 2;
TMR0.TCR.BIT.CCLR = 1;
//Timer resets at compare match A
TMR0.TCSR.BIT.OSA = 2;
//1-output at compare match A
TMR0.TCSR.BIT.OSB = 1;
//0-output at compare match B
TMR0.TCORA = 0x55;
//Frequency
TMR0.TCORB = 0x20;
//Duty cycle
//Pulse outputs to TMo0, which is also P22/USB_DRPD
//Can be monitored by touching a scope probe to the top
//of resistor R46, near bottom right corner of ethernet
//port. Port JN2 provides a ground.
}
As can be seen here, we have no global variables to initialize and the only function we need
is the function to set up the timer. In the timer initialization we first enable the 8-bit timer
unit on Line 8. We set the count source for Timer 0 as PCLK/8 on Lines 9 and 10.
On line 11 we set the Timer 0 to clear every time a compare match A occurs. This allows us to alter how fast the timer resets with more control than just changing the count
source.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
On Lines 12 and 13 we set the timer output to go high every time there is a compare match
A and to go low when there is a compare match B. This allows us to control the frequency using the timer constant register A, and the duty cycle using timer constant register B.
On Lines 14 and 15 we set the frequency and duty cycle by assigning a value to timer
constant registers A and B. These are randomly chosen; we will worry about getting an exact frequency and duty cycle in the advanced concept section.
When running this code the pulse will be output on signal TMO0. By referencing
the hardware manual and schematic we find that this is output to Pin 22/USB_DRPD on
the board. There is no output pin to monitor this so we will have to observe the output
waveform by touching a scope probe to the top of resistor R46 near the bottom right corner
of the Ethernet port. You can get a ground reference by connecting to pin 2 on port JN1.
Figure 8.21 Resistor R46 location.
In this example we have set up a pulse output from Timer 0 and observed the output square
wave. In a more advanced example later we will cover how to calculate and control the exact frequency of the wave and discuss how this relates to controlling external devices.
8.4.3
Setting and Reading from the Real Time Clock
In this example we will demonstrate how to set the time in the Real Time Clock. We will
then continuously read the value in the RTC and display it on the LCD.
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329
To start we will use a base project that has all of the included support files
for the graphic LCD. The only needed font file is helvr10.c. Also included is the
iodefine_RX62N.h file.
The first step in this example is to define our global variables.
1. char Year1000, Year100, Year10, Year1, Mon10, Mon1, Day10, Day1,
Day, Hour10, Hour1, Min10, Min1, Sec10, Sec1;
These will all hold the value for each of the decimal places of the date values.
Next we insert the function prototypes for the functions we will write:
1. void InitTimer(void);
2. void DisplayTime(void);
3. void GetTime(void);
Now that all of that is defined we go into our main() program.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
void main(void){
int i;
InitTimer();
}
}
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
/* use Glyph full access direct functions */
GlyphNormalScreen(G_lcd);
GlyphSetFont(G_lcd, GLYPH_FONT_HELVR10);
GlyphClearScreen(G_lcd);
while(1){
DisplayTime();
for (i = 0; i < 100000; i++){}
}
} else {
}
GlyphClose(&G_lcd);
GlyphClose(&G_lcd);
}
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
First we define the variable ‘i’ in line 2. This is used to create a delay loop between writes to
the LCD. Next we call our function initializing the timer in Line 4; this is where all of the
code is that initializes and starts the Real Time Clock. The next few lines we won’t cover in
depth, but are merely to initialize the LCD. All of the code we are concerned with is in the
while(1) loop. The function DisplayTime() is called which retrieves the time from the RTC
and then sends it to be displayed on the LCD on Line 12. The for() loop on Line 13 is merely
to create a delay so we aren’t constantly writing to the LCD, which makes the display flicker.
The else() clause on Line 15 would hold error handling code to executed in the event the LCD
did not start up correctly. We also will not go into depth on the closing function on Line 17.
The next section of code we will consider is the InitTime() function.
1. void InitTimer(void){
2.
//Set date and time on RTC
3.
4.
RTC.RCR2.BIT.START = 0;
//Write 0 to start bit in RCR2
5.
while(RTC.RCR2.BIT.START == 1){}
//Wait for start bit to
clear to 0
6.
7.
RTC.RCR2.BIT.RESET = 1;
//Write 1 to Reset bit in RCR2
8.
9.
RTC.RYRCNT.WORD = 0x2015;
//Set year, month, day of
10.
RTC.RMONCNT.BYTE = 0x10;
//week, date, hour, minute,
11.
RTC.RDAYCNT.BYTE = 0x21;
//second to 2015 Oct 21st
12.
RTC.RWKCNT.BYTE = 0x02;
//Tue 12:00:00
13.
RTC.RHRCNT.BYTE = 0x12;
14.
RTC.RMINCNT.BYTE = 0x00;
15.
RTC.RSECCNT.BYTE = 0x00;
16.
17.
RTC.RCR2.BIT.START = 1;
//Set start bit to 1 in RCR2
18.
while(RTC.RCR2.BIT.START == 0){}
//Wait for start bit to set
to 1
19.
20.
//Set carry interrupt for use later when reading time from RTC
21.
IEN(RTC,CUP) = 0;
//Disable carry interrupt in ICU
22.
RTC.RCR1.BIT.CIE = 1;
//Enable carry interrupt in the RTC
23. }
Here we set up the Real Time Clock and initialize all of the count registers to the date we
want. This follows the flowchart in Figure 8.19. Lines 4 and 5 clear and wait for the START
bit in the RCR2 register to equal to 0. The wait is necessary because the bits in this register
only update on every count of the 128 KHz clock in the RTC, and the program is executing
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
331
at a much faster 24 MHz. Next the RESET bit in RCR2 is set to 1 on Line 7. This resets the
RTC’s prescaler clocks, 64 Hz counter, and alarm registers to 0. After this is done, from
Line 9 through 15 the clock’s count registers are set to the starting date and time desired. In
this example the start time and date is 12:00 PM Tue, Oct 21, 2015. The next step is to start
the clock. In Line 17 we write a 1 to the START bit in RCR2 and then wait for it to be set
in Line 18. The code on Lines 21 and 22 disable the carry interrupt in the ICU, but enable
it in the Real Time Clock peripheral. This allows us to monitor if there has been a carry
from the 64 Hz counter to the second counter later on when we are reading the time. We
will demonstrate this later in the example.
The next function is the DisplayTime() function. This function calls the GetTime function to update the value of the time in our global variables. It then writes them to the LCD
using the sprintf() and BSP_Display() functions.
1. void DisplayTime(void){
2.
char buffer [30 ];
3.
const char DayNames [7 ][4 ] = {“Sun”, “Mon”, “Tue”, “Wed”, “Thu”,
“Fri”, “Sat”};
4.
5.
GetTime();
6.
7.
BSP_Display_String(LCD_LINE1, “RTC Example”);
8.
sprintf((char *)buffer, “%d%d%d%d %d%d / %d%d”,
9.
Year1000,
10.
Year100,
11.
Year10,
12.
Year1,
13.
Mon10,
14.
Mon1,
15.
Day10,
16.
Day1);
17.
BSP_Display_String(LCD_LINE2, buffer);
18.
BSP_Display_String(LCD_LINE3, DayNames [Day ]);
19.
sprintf((char *)buffer, “%d%d:%d%d:%d%d”,
20.
Hour10,
21.
Hour1,
22.
Min10,
23.
Min1,
24.
Sec10,
25.
Sec1);
26.
BSP_Display_String(LCD_LINE4, buffer);
27. }
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
In this function we first define two character arrays on Lines 2 and 3. The GetTime() function is called on line 5; this copies the values of the time and date into our global variable
placeholders. On line 7 we write text to the first line of the display to show the program that
is running. On Line 8 we use the sprintf() function to take date values and translate them
into ASCII text, and then we place these in an array called buffer. On Line 17 we write
these values to the second line of the screen using the BSP_Display_String function, and a
pointer to the array holding the text to write. The day of the week is written to the screen
on Line 18. On Line 19 we use sprintf() once again to write the time to an array of ASCII
characters. On Line 26 we write this to line 4 of the display.
The last function we use is the GetTime() function.
1. void GetTime(void)
2. {
3.
do {
4.
IR(RTC,CUP) = 0;
//Clear the Carry Flag
5.
Year1000 = RTC.RYRCNT.BIT.YEAR1000;
6.
Year100 = RTC.RYRCNT.BIT.YEAR100;
7.
Year10 = RTC.RYRCNT.BIT.YEAR10;
8.
Year1 = RTC.RYRCNT.BIT.YEAR1;
9.
Mon10 = RTC.RMONCNT.BIT.MON10;
10.
Mon1 = RTC.RMONCNT.BIT.MON1;
11.
Day10 = RTC.RDAYCNT.BIT.DAY10;
12.
Day1 = RTC.RDAYCNT.BIT.DAY1;
13.
Day = RTC.RWKCNT.BYTE;
14.
Hour10 = RTC.RHRCNT.BIT.HOUR10;
15.
Hour1 = RTC.RHRCNT.BIT.HOUR1;
16.
Min10 = RTC.RMINCNT.BIT.MIN10;
17.
Min1 = RTC.RMINCNT.BIT.MIN1;
18.
Sec10 = RTC.RSECCNT.BIT.SEC10;
19.
Sec1 = RTC.RSECCNT.BIT.SEC1;
20.
} while(IR(RTC,CUP) == 1);
21.
//If carry bit has been set since reading started,
try again
22. }
This function follows procedure a in Figure 8.20: Reading 64 Hz Counter and Time. The
interrupt has already been disabled in the ICU and enabled in the RTC peripheral by the
TimerInit() function. Now when there is a carry from the 64 Hz counter to the seconds
counter, the interrupt flag in the ICU will set but an interrupt will not trigger. Now we start
this function by clearing the interrupt request flag for the carry interrupt. We then read all
of the digits the RTC counter registers into separate variables from Lines 5 through 19.
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333
After we have read the time we check and make sure the interrupt request flag for the carry
interrupt hasn’t been set. If it has, that means the seconds counter has incremented and the
time held in our variables is no longer correct and we will need to call the function again.
The GetTime() function will repeat itself until it successfully reads a time without the carry
interrupt being requested.
Once all of this code is in our program we can compile it and load it onto our board.
Once run, within a second the following text should appear on the graphical LCD screen.
Timer
2015
Tue
12:00:00
Example
10/21
The time will now be displayed as a clock until the program is paused in the debugger
and/or power is removed from the board.
This example covered the basics of setting up and reading from the Real Time Clock
by setting the time and then reading it and displaying it on the boards graphical LCD as it
counts. In the advanced concepts section we will cover how to use the RTC interrupts such
as the periodic and alarm interrupts.
8.5
ADVANCED CONCEPTS
By now we should have a basic grasp on how to set up and use the more advanced features of
the 8-bit timers along with how to set up and read the real time clock. We have covered the
basics in setting up a cascaded timer, the bare minimum set up of a pulse output signal, and
how to set up and read the real time clock. Now we cover how to take more control of our
timer count duration by using the timer counter registers. We will go into more detail on the
pulse output operation by covering how to calculate and control our output frequency and
duty cycle. Also, we will cover usage of the real time clocks alarm and periodic interrupts.
8.5.1
Using a Cascaded Timer with 16-Bit Timer Constant Registers
We have covered the basics of using a cascaded 16-bit timer and have given examples of a
basic set up. However, this set up lacks a bit of control that an embedded designer would
want. Currently, with what we know, we can only count in increments of 0xFFFF (65535).
The only control we have over how fast the timer overflows is by altering the count source.
This only leaves us with the capability to count to the lengths of time in Table 8. With the
timer constant registers we can extend that functionality. We have taken note of this while
setting up the timer in pulse output mode, and now will cover it in more depth.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Each timer channel offers three interrupts: the overflow interrupt, and two timer constant interrupts. If we set a value in either of the timer constant registers and enable these
interrupts, the respective interrupt will be triggered when a compare match event occurs for
that register. A compare match event will occur when the TCNT register matches the value
in that timer constant register; i.e., compare match A when TCNT matches timer constant
register A, and compare match B when TCNT matches timer constant register B. So now
that gives us the ability to trigger interrupts at even more precise times. But we still have to
wait for the timer to finish counting to 0xFFFF and overflow and then count back to the
timer constant value before the interrupt is triggered again. This is imprecise and not practical in many situations. So, by setting in the TCR for the timer channel to reset on compare
match A or B, we can control to a much higher degree the time the counter will count to.
This describes how the compare match counters work in 8-bit mode, but what about
16-bit mode? There is only a minor difference. When we place the timer channel into
16-bit mode, the TCNT, TCORA, and TCORB registers from the two timer channels in the
unit span into one register. So now they each are practically one 16-bit register. We can still
only write to them as their 8-bit entities; so when we calculate the values we want to enter
into them, we just convert to hex and write the upper byte to the register of the channel with
a higher number and the lower byte to the other. If we wanted a value of 0x1234 in TCORA
of timer unit 1, we would enter 0x12 in TCORA of Timer 0, and 0x34 in TCORA of timer
1. For timer unit two we write the upper bytes to Timer 2’s registers and the lower bytes to
Timer 3’s registers.
As an example we have a timer set up in 16-bit cascaded timer mode with a count
source of 1/1028. If we wait for an overflow, that gives us an interrupt every 2.8 s. But what
if we want to generate an interrupt every 1 s? First we calculate what fraction of 2.8 1 is,
1
and then multiple 65535 by that:
* 65535 ⫽ 23405 (approximately). We enter this
2.8
value into the timer constant register A and enable the compare match A interrupt. Of
course, this is a 16 bit value, so we can’t enter it at one time. So we convert it to hex and enter the upper byte into TMR0.TCORA and the lower byte into TMR1.TCORA. Now we
still have the interrupt occurring every 2.8 s, but that’s because the timer is still counting to
65535 before resetting. So we set the bit CCL bit in the TCR so the timer is clear by compare match A. Thus giving us an interrupt every 1 s on compare match A.
8.5.2
Calculating and Programming Pulse Frequency and Duty Cycle in Pulse Output
Mode, and Controlling a Servo Motor
We have covered the concept of how pulse output works and demonstrated the basic register set up needed to get a pulse output. We did not go into much detail about calculating the
frequency and duty cycle of our output wave. This is not too complex but has been saved
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
335
for this section just to give time to get used to the concept of pulse output operation first. If
you understand the concepts of pulse output operation and calculating timer speeds from
the basic concepts section, this should be no problem.
For this example we will assume we are using the pulse output to control a servo motor. Common servo motors use a pulse input to determine how or where it moves to. Specifications vary by motor, as per frequency and duty cycle required. We will use specifications from an anonymously chosen motor for this example. In the case of this motor we
need a 1 ms pulse to turn full left and a pulse of 2 ms to turn full right. Usually a frequency
is not specified, however you want to have adequate space between your pulses for smooth
operation; and also not have them too spaced apart, so that when the duty cycle is updated
the servo reacts in a timely manner. 50 Hz (20 ms period) is a safe frequency for smooth
operation.
For this example we will be using the timer in 16-bit cascaded mode as well as in pulse
output mode. This gives us more precise control over the duty cycle while still allowing for
a wide period between pulses (low frequency). This is not much more complicated than
8-bit pulse output.
Our first step is to choose a speed for our prescaler. If we look at Table 8.2: Clock Division and Interrupt Times we see that PCLK/8 (3 MHz) offers almost a 21.84 ms period
between TCNT overflows. We will choose this prescaler, as choosing PCLK/32 (87.38 ms)
will provide us with a much smaller resolution between a 1 ms pulse and a 2 ms pulse.
Now we must calculate the values for the timer counter registers. First, we will calculate
the values to place in timer constant register B to obtain a pulse of 1 ms and 2 ms. Then we
must calculate the value to place in timer constant register A to obtain a 20 mS low signal
after the pulse. Note that when we change the value of TCORB, the frequency of the wave
still stays the same, so the time our wave is low is affected. However, since 1–2 ms is small
compared to 20 ms, this is negligible and we don’t have to worry about recalculating for
TCORA.
To calculate the value for TCORB we divide 1 ms and 2 ms by the length of time
2 ms
1 ms
⫽ 3000 and
⫽ 6000. For the value in TCORA
333.33 ns
333.33 ns
we add 20 ms to our maximum high period (2 ms) to get 22 ms, then divide this by the time
22 ms
for a clock tick,
⫽ 66000. In this case it gives us a value greater than our range,
333.33 ns
which is 65535. Luckily we only max out 155 ns shorter than our desired time, which is acceptable because, once again, having a precise low period is not crucial with servo motors,
only having a fair amount of low time for the control circuitry to acknowledge our high
pulse. So in the case of this application it is fine to leave the value of TCORA at 0xFFFF.
So, in all practicality, when setting up a pulse output signal we are just calculating a
timer length for the period of our wave and for each high duty cycle we desire, and then
between timer counts;
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
programing it into the timer constant registers. Also, keep in mind that with this example
1 ms and 2 ms are the maximum value pulses for our motor. If this were a 180 degree
servo, 1 ms would put it at 0 degrees, and 2 ms at 180 degrees. If we wanted any position
in between we would have to output a signal proportionally between 1 and 2 ms. 1.5 ms
would place the servo at 90 degrees, 1.75 ms at 135 degrees and so on. In the case of a continuous rotation servo, 1 and 2 ms would be full forward and backward, and any pulse
length in between would speed up or slow down the rotation; 1.5 ms would be a full stop.
8.5.3
Using the Real Time Clock’s Alarm and Periodic Interrupts
The RX62N’s real time clock peripheral includes three interrupts: the carry interrupt, periodic interrupt, and alarm interrupt. The carry interrupt we have used in a previous example,
and is triggered every time there is a carry from the 64 KHz counter to the second counter.
The periodic interrupt is an interrupt that can be set to occur on a regular interval determined
by what we set in the RCR1 register. We can alter this interval by editing three bits in the
register, allowing us seven options for interrupt intervals. The alarm interrupt gives us the
ability to choose an exact time for an interrupt to occur. For each count register there is an
alarm register. When enabled, once the values in all of the enabled registers match the real
time clocks counter registers, an interrupt will be triggered. Besides triggering an interrupt
routine the alarm interrupt also has the ability to wake the processor from low power modes.
Setting the periodic interrupt is simple in comparison to calculating and setting an 8-bit
timer to do the same task. First we must make sure that the interrupt is disabled in the ICU.
Then we set the periodic interrupt enable bit in RCR1 and set the periodic interrupt select
bits to whichever interrupt period we desire. The options are 2 seconds, 1 second, 1⁄ 2 second,
1
⁄ 4 second, 1⁄ 16 second, 1⁄ 64 second, and 1⁄ 256 second. After clearing the request flag we enable
the interrupt in the ICU and the ISR will begin triggering on the chosen interval.
Setting the alarm interrupt is a bit more complicated, but is illustrated in a flowchart in
the RX62N hardware manual. We can set all of the alarm registers and have the interrupt
only trigger at a specific date and time, or we can only enable certain registers so the interrupt triggers each time the counters match those particular alarm registers. Say we want an
interrupt to trigger at thirty minutes of every hour; we will set the minute alarm register to
thirty minutes, and then set the enable bit in the same register. After enabling and setting a
priority level for the alarm interrupt, every time the value in the minute count register
matches 30 the interrupt will occur.
First we make sure that the real time clock is running. Then we make sure the interrupt
is not enabled in the ICU, so that it doesn’t trigger accidentally while we are setting it. Now
we are able to set all of the alarm registers to the time we desire the interrupt to be triggered
at. Once done, we write a 1 to the alarm interrupt bit in the ICU. Using the periodic interrupt we will wait for the 1⁄ 64 second interrupt, this is to allow time for the alarm interrupt
enable bit to be set. We then clear the alarm interrupt request flag in the ICU in case it has
been set while we were setting the alarm. Our last step before the interrupt is ready to be
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
Clock running
Disable the ICU alarm interrupt
request
337
Check that the count is in operation
(the START bit in RCR2 is 1)
Write 0 to the IER0B.IEN4 bit of the ICU to
prevent erroneous interrupts
Set alarm time
Enable the RTC alarm interrupt
request
Use a periodic interrupt
to wait for 1/64 of a second
Write 1 to the AIE bit in RCR1
Set the PES[2:0] bits in RCR1 to 010b to wait for
periodic interrupts twice
Clear alarm flag
Always clear the IR92.IR flag of the ICU
to 0, since the flag may have been set
while the alarm time was being set
Enable the ICU alarm interrupt
request
Write 1 to the IER0B.IEN4 bit of the ICU
Monitor alarm time
(wait for interrupt or
check alarm flag)
Wait for alarm interrupt or the IR92.IR flag
of the ICU to be set to 1
Figure 8.22 Alarm interrupt setting procedure. Source: Hardware Manual, Figure 22.5.
used is to enable the interrupt in the ICU. Now we can return to our normal program, and
once the counters match the enabled alarm registers the interrupt will trigger.
8.6
ADVANCED EXAMPLES
Now that we have covered the more advanced concepts to using these features we will now
go over examples implementing these concepts in code. The code will follow along with
the examples in the earlier sections.
8.6.1
Using a Cascaded Timer with 16-Bit Timer Constant Registers
In this example our program will once again cause the LEDs on the board to blink in a rotating sequence, but this time with a 1s delay between blinks. We will implement this delay
using a 16-bit cascaded timer and its interrupt.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
We will be using the LEDs in these examples so the first part of our code will be the
definitions for the LED ports. After the LED definitions, we declare our first global variable, which will keep track of which LED is currently lit. Also we set a global variable we
will use to indicate whether the timer interrupt has triggered or not. This is known as a flag,
and such usage will be covered in more depth in a later chapter.
1. int Current_LED = 1;
2. int TimerInterruptFlag = 0;
Next we have to declare our functions.
1. void main(void);
2. void InitTimer(void);
3. void Rotate_LED(void);
Our main() function doesn’t contain much code. First we enable the LEDs with a macro on
line 3, and then we call the timer setup function on line 4. Nothing happens in our while(1)
loop until the TimerInterruptFlag variable is set by the interrupt. Note that the interrupt will
run upon the timer triggering, and there will be some time delay between when the variable
is set and the program returns to the main function and the LED is rotated. Because of this,
the timing of the LED rotation won’t be exactly one second, but that is acceptable because
LEDs aren’t time critical and can be off by a few milliseconds without hurting anything. It
is bad programming practice to include the function call in the interrupt itself because it
requires more time overhead in the ISR along with the need to save and restore all processor registers.
1. void main(void)
2. {
3.
ENABLE_LEDS;
4.
InitTimer();
5.
6.
while(1)
7.
{
8.
if(TimerInterruptFlag)
9.
{
10.
LED_Rotate();
11.
TimerInterruptFlag = 0;
12.
}
13.
}
14. }
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
339
The most important part of this example is our InitTimer() function. On lines 2 and 3 we enable and set a priority for the compare match A interrupt. We then enable timer unit 0 channels one and two (TMR0 and TMR1) on lines 5 and 6. On lines 8 and 9 the TMR1 count
source is set to PCLK/1024, which gives us a count every 42.66 ms. This is done by writing
the appropriate values to the TCCR register. Then on lines 11 and 12 we set the count source
for TMR0 to TMR1, so now TMR0 counts once every time TMR1 overflows. Now we have
a total of 2.8 s between timer overflows. In order to make the timer reset every 1 s we need
to write the appropriate value to the TCORA(timer constant A) register and set the timer to
reset on ever compare match A event. In Section 8.4.1 we calculated the needed value as
23405. We convert this into hex, separate it into a higher and lower byte, and then write the
higher byte to TMR0 and the lower byte to TMR1 on lines 14 and 15. On line 17 we set the
bit in the TCR that enables resets on compare match A event.
1. void InitTimer(void){
2.
IEN(TMR0,CMIA0) = 1;
3.
IPR(TMR0,CMIA0) = 3;
4.
5.
MSTP(TMR0) = 0;
//Activate TMR0 unit
6.
MSTP(TMR1) = 0;
//Activate TMR1 unit
7.
8.
TMR1.TCCR.BIT.CSS = 1;
9.
TMR1.TCCR.BIT.CKS = 5;
//Count source is PCLK/1024 for TMR1
10.
11.
TMR0.TCCR.BIT.CSS = 3;
12.
TMR0.TCR.BIT.CCLR = 1;
//Count source is TMR1 for TMR0
13.
14.
TMR0.TCORA = 0x5B;
//Set TCORA to 23405
15.
TMR1.TCORA = 0x6D;
//(0x5B6D hex)
16.
17.
TMR0.TCR.BIT.CMIEA = 1;
18. }
The only remaining code in our main C file is our LED_Rotate function which we have already covered.
The last code we need to consider is our interrupt. For this example, unlike our basic
example, we will be using the compare match A interrupt.
1.
2.
3.
4.
5.
#pragma interrupt (Excep_TMR0_CMI0A(vect = VECT_TMR0_CMIA0))
void Excep_TMR0_CMI0A(void);
//TMR0_CMI0A
void Excep_TMR0_CMI0A(void){LED_Rotate();}
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
If we look in the RX62N hardware manual we will see that the compare match A interrupt
is at vector 174. This code defines an interrupt routine at that vector and places the
LED_Rotate() function inside of it.
Now we have a program that once compiled and downloaded to the board will cause
the LEDs to blink in a rotating sequence. The LEDs will advance at a rate of 1 per second
as defined by our timer setup. This program demonstrates a timer function that makes use
of a 16-bit cascaded timer with a compare match interrupt and reset on compare match
event. This provides greater precision and a broader range of times to count.
8.6.2
Setting Up Pulse Output Mode to Control a Servo Motor
In this example we will use our calculations from Section 8.5.2 to write a program that will
control our theoretical servo motor. We will be setting up a timer for the pulse output mode
and then make two functions that will alter our timer setup such that the servo will rotate
left or right.
Our program will only need the default iodefine_RX62N.h file, so we won’t need any
LED definitions or code for the graphical LCD.
We begin our main program by defining our function prototypes.
1.
2.
3.
4.
void
void
void
void
main(void);
InitTimer(void);
Turn_Left(void);
Turn_Right(void);
As you can see, once again we will only need a function to set up the timer initially, then
we have two functions that when called will alter the timer setup to give us the needed
pulse output to turn left or right.
1. void main(void){
2.
float i;
3.
4.
InitTimer();
5.
6.
while(1){
7.
8.
for(i = 0; i < 10000000; i++);
9.
Turn_Left();
10.
for(i = 0; i < 10000000; i++);
11.
Turn_Right();
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
12.
13. }
341
}
Also, once again, our main program is very simple. We merely create the variable i as a
method to create a delay. Once we call the function to initialize our timer we go into our
while(1) loop. In that loop we repeatedly pause, call the function to turn left, pause again,
then call the function to turn right. This represents a very simple method of setting up motor control in C. The for() loops merely create an arbitrary delay between the duty cycle
changes which is long enough that we can observe the difference. In a normal program we
would not make a delay this way; this is merely for the sake of demonstration.
1. void InitTimer(void){
2.
MSTP(TMR0) = 0;
//Activate TMR0 unit
3.
MSTP(TMR1) = 0;
//Activate TMR1 unit
4.
5.
6.
TMR1.TCCR.BIT.CSS = 1;
7.
TMR1.TCCR.BIT.CKS = 2;
//Count source is PCLK/64 for TMR1
8.
9.
TMR0.TCCR.BIT.CSS = 3;
10.
TMR0.TCR.BIT.CCLR = 1;
//Count source is TMR1 for TMR0
11.
12.
TMR0.TCR.BIT.CCLR = 1;
//Timer resets at compare match A
13.
14.
TMR0.TCSR.BIT.OSA = 2;
//1-output at compare match A
15.
TMR0.TCSR.BIT.OSB = 1;
//0-output at compare match B
16.
17.
TMR0.TCORA = 0xFF;
//Frequency
18.
TMR1.TCORA = 0xFF;
19.
20.
TMR0.TCORB = 0x00;
//Duty cycle
21.
TMR1.TCORB = 0x00;
22.
23.
//Pulse outputs to TMo0, which is also P22/USB_DRPD
24.
//Can be monitored by touching a scope probe to the top of
resistor
25.
//R46, near bottom right corner of ethernet port. Port JN2
26.
//provides a ground.
27. }
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Next in our code is our timer initialization function. This will set up the timer unit 0 channels one and two for the pulse output we desire. We will use the values we calculated earlier in Section 8.5.2. First we activate the timer channels on lines 2 and 3, because we cannot alter the registers in the unit until it is activated. Our next step is to set the Timer 1
count source to the PCLK/64 prescaler on lines 6 and 7. On lines 9 and 10 we set the count
source for Timer 0 as Timer 1. We now have a 16-bit cascaded timer so any settings made
for clearing in the Timer 0 TCR are effective for the entire cascaded unit. On line 12 we set
the unit to reset on a compare match A event. We then set the timer output port to go to one
output on compare match A events, and to zero on compare match B events. Remember
that because the unit is now 16-bits, the timer constant registers are now spanned into single 16-bit registers, with the upper byte in the Timer 0 timer constant register and the lower
byte in the Timer 1 timer constant registers. Any value we want to write to the compare
match registers must first be converted to hex, and then the upper and lower bytes written
to the appropriate registers. Lines 17 and 18 set our time count for compare match A
events, thus setting the period and therefore frequency of our waveform. Lines 20 and 21
set our initial duty cycle to zero, so at this point our timer is set up but we are not yet outputting a waveform because the wave is constantly held low by the compare match B event
at time count 0x0000.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
void Turn_Left(void){
TMR0.TCORB = 0x0B;
TMR1.TCORB = 0xB8;
//Duty cycle
}
void Turn_Right(void){
TMR0.TCORB = 0x17;
TMR1.TCORB = 0x70;
//Duty cycle
}
Now all we need are our functions to turn left and right. These functions are very simple;
they merely alter the values in the Timer constant B registers so that the duty cycle is either
1 ms or 2 ms. In the Turn_Left() function we write the value for 1 ms and in the
Turn_Right() function we write the value for 2 ms.
After being compiled and downloaded to the board this program will initially not give
an output, then begin to toggle the output between a 22 ms wave with 1 ms high pulse and
2 ms high pulse after an arbitrary delay created by the for() loops in our while(1) code.
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
8.6.3
343
Using the Real Time Clock’s Alarm and Periodic Interrupts
This program example begins with the program we wrote in Section 8.3, so we already
have a program that sets the real time clock, then reads it and displays the count. Initially
the program will behave like our basic example: set the time, then begin counting, and display the time on the LCD. Then when the time reaches 12:00:15 the LEDs will be enabled
by the alarm interrupt and begin to blink in a circular pattern at a rate determined by the periodic interrupt.
For review on the code we have already written refer to Section 8.3. In this section we
will only focus on the parts we are adding to give the alarm and periodic interrupt functionality, which will not require the removal or modification of any old code.
1. void Set_Alarm(void);
2. void LED_Rotate(void);
Our first addition to the basic example is the addition of two new function prototypes.
We are adding a function to set the alarm time and also we will be using our LED_Rotate
function once again to make the LEDs rotate in a circular sequence.
1. void main(void){
2.
int i;
3.
ENABLE_LEDS;
4.
ALL_LEDS_OFF;
5.
DISABLE_LEDS;
6.
7.
InitTimer();
8.
Set_Alarm();
9.
10.
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
11.
/* use Glyph full access direct functions */
12.
GlyphNormalScreen(G_lcd);
13.
GlyphSetFont(G_lcd, GLYPH_FONT_HELVR10);
14.
GlyphClearScreen(G_lcd);
15.
while(1){
16.
for(i = 0; i < 10000; i++);
17.
DisplayTime();
18.
}
19.
}
20.
else {}
21.
22.
GlyphClose(&G_lcd);
23. }
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
As you can see, our main function is the same save for some additions. The first addition is
lines 4 through 6; this code enables the LEDs and turns them off, then disables them once
again. Initially our program doesn’t use the LEDs, so this makes sure LEDs left lit from
previous running programs are turned off and then disables them so they won’t be lit until
re-enabled by the alarm interrupt. After this our only other addition is the Set_Alarm()
function call on line 8 after we initialize the real time clock.
1. void Set_Alarm(void){
2.
3.
//Check clock running
4.
if(RTC.RCR2.BIT.START == 1){
5.
6.
//Disable ICU alarm interrupt
7.
IEN(RTC,ALM) = 0;
8.
IEN(RTC,PRD) = 1;
9.
10.
//Set alarm
11.
RTC.RSECAR.BYTE = 0x15;
12.
RTC.RMINAR.BYTE = 0x00;
13.
RTC.RHRAR.BYTE = 0x12;
14.
RTC.RWKAR.BYTE = 0x02;
15.
RTC.RDAYAR.BYTE = 0x21;
16.
RTC.RMONAR.BYTE = 0x10;
17.
RTC.RYRAR.WORD = 0x2015;
18.
19.
RTC.RSECAR.BIT.ENB = 0x01;
20.
RTC.RMINAR.BIT.ENB = 0x01;
21.
RTC.RHRAR.BIT.ENB = 0x01;
22.
RTC.RWKAR.BIT.ENB = 0x01;
23.
RTC.RDAYAR.BIT.ENB = 0x01;
24.
RTC.RMONAR.BIT.ENB = 0x01;
25.
RTC.RYRAREN.BIT.ENB = 0x01;
26.
27.
//Enable RTC alarm
28.
RTC.RCR1.BIT.AIE = 1
29.
while(RTC.RCR1.BIT.AIE == 0)
30.
31.
32.
33.
//Wait for it to be written
before continuing
;
//Use periodic interrupt to wait 1/64 second
IR(RTC,PRD) = 0;
RTC.RCR1.BIT.PES = 0x02;
//Set periodic interrupt to 1/64s
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52. }
while(IR(RTC,PRD) == 0)
;
//Clear alarm flag
IR(RTC,ALM) = 0;
345
//Wait for flag to be set
//Enable ICU alarm interrupt
IEN(RTC,ALM) = 1;
IPR(RTC,ALM) = 3;
}
else {
//error handling code
}
//Set up Periodic interrupt to trigger ISR every 0.5s
RTC.RCR1.BIT.PES = 0x05;//Set periodic interrupt to 0.5s
IR(RTC,PRD) = 0;
//Clear periodic interrupt flag
IEN(RTC,PRD) = 1;
//Enable periodic interrupt in ICU
IPR(RTC,PRD) = 4;
//Set priority level
Our most important addition to the basic program is our Set_Alarm() function. The code in
this function follows the flowchart in Figure 8.22. First on line 4 we have an if statement
that checks if the real time clock is counting, this is in case we call the function and have
forgotten to initialize the real time clock or somehow the clock has ceased to count. On line
43 we have an else statement where error handling code would be put, but we will not
worry about what to put there yet. The next step is to disable the alarm interrupt in the ICU;
this ensures we aren’t interrupted by the alarm while we are setting it. We also disable the
periodic interrupt in the ICU since we are using it to set the alarm but do not want the ISR
routine interrupting our configuration code. This is done on line 7.
With the periodic interrupt disabled, we can set the alarm registers for the time we
want the alarm interrupt to occur; this is handled on lines 11 through 25. In this example
we utilize all of the alarm registers and set it to occur fifteen seconds after the initial time
set by the clock. Take note on lines 19–25 that we set the enable bit for each of the registers, otherwise they won’t be compared. Also take note that because the year alarm register
encompasses an entire word and doesn’t have an extra bit set aside, there is a separate register we must set a 1 to in order to enable it, the RYRAREN register on line 25. After that
we set the alarm enable bit in the RCR1 register on line 28. On line 29 we get stuck in a
while loop until the bit gets set, because the RCR1 register only gets updated at the rate of
the real time clocks internal clock. On line 32 through 34 we clear the periodic interrupt request flag and then set the periodic interrupt for 1⁄ 64 of a second.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Then we have a while loop that will hold the program until the periodic interrupt sets
the request flag again. After all of this we can be assured that the alarm interrupt enable bit
has been set and we enable and set a priority for the alarm interrupt on lines 40 and 41.
That is all of the code we need to set our alarm, but in this program example we are also using the periodic interrupt, so we include code to set that up for the rest of our program as
well. On line 48 we set the periodic interrupt to occur at 0.5 second intervals. Then on lines
49 through 51 we clear the interrupt flag, and then enable it and set a priority level.
Also before the next snippet of code make sure to insert our LED_Rotate() function
from previous examples. We won’t cover it since we aren’t covering any older code.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
//RTC PRD
#pragma interrupt (Excep_RTC_PRD(vect = VECT_RTC_PRD))
void Excep_RTC_PRD(void);
//RTC_ALM
#pragma interrupt (Excep_RTC_ALM(vect = VECT_RTC_ALM))
void Excep_RTC_ALM(void);
//RTC_PRD
void Excep_RTC_PRD(void){LED_Rotate();}
//RTC_ALM
void Excep_RTC_ALM(void){ENABLE_LEDS;}
With any program using interrupt routines it is necessary to define where our interrupt is.
On lines 2, 3, 6, and 7 we define the name of our interrupt service routines and their vectors, which are given in the RX62N Hardware Manual in Section 11.3. Then on lines 10
and 13 are our service routine functions. On line 10 is our periodic interrupt routine which
will call our LED_Rotate() function, so once the LEDs are enabled they will blink in a rotating sequence at a rate of one LED per 0.5 s. On line 13 is our alarm interrupt function
that contains our macro for enabling the LEDs, so no LEDs will light up from the periodic
interrupts routine until the alarm interrupt enables them. Note once again this code includes a function call in an ISR for simplicity and illustration purposes, however, in an actual program this would be bad practice and should be avoided.
Once this program is built and downloaded to the board, at first it will seem the same
as our basic example where it begins to display the time starting with when we set the
clock to. Then after fifteen seconds the alarm interrupt will call and enable the LEDs. Afterwards the LEDs will blink in a circular sequence at a rate of one per 0.5 s for the duration of the programs running time.
CHAPTER 8 / EVENT COUNTERS, TIMERS, AND THE REAL TIME CLOCK
8.7
347
RECAP
In this chapter we covered the capabilities of the 8-bit timer peripherals on the Renesas
RX62N. We started with a brief overview of the timer concepts. Then we covered how to
cascade two 8-bit timers into one 16-bit unit. We also covered pulse output operation that
allows us to generate a steady frequency square wave whose duty cycle and frequency are
maintained by the timer unit. Additionally we covered the Real Time Clock feature, which
allows the RX62N to easily and accurately track the time and date. In the advanced concepts section we showed how to take more control of a cascaded timer by using the 16-bit
timer constant register. We then went over how to calculate and precisely control frequency
in pulse output mode, and gave an example of controlling a servo motor. For our final example we showed how to set up and use the Real Time Clock’s alarm interrupt.
8.8
REFERENCES
Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
8.9
EXERCISES
1. What registers would you use when setting up the 8-bit timer unit 0 in cascaded
mode?
2. Briefly describe three events that can happen when a compare match event occurs.
3. Explain the algorithm used and describe the purpose of the steps used when ini4.
5.
6.
7.
8.
9.
tially setting the RTC.
Give sample code that will set up a basic 1 KHz square wave with a 40% duty
cycle.
Assume you have set up a 16-bit cascaded timer and now you want its interrupt to
occur every 3 seconds. Name the registers you would write to, and the values you
would write to them.
Assume you have set up a 16-bit cascaded timer for pulse output mode, what registers and what values would you write to them to get an output that is high for
3 ms and low for 18 ms?
Name two advantages to using the timer constant registers.
Give at least one advantage to using the periodic interrupt over setting up an 8-bit
timer in order to get a 1 s recurring interrupt.
Besides triggering an ISR at the exact time specified by the real time clock alarm
registers, what is another action the alarm interrupt performs?
Chapter Nine
Using Interrupts with Peripherals
9.1
LEARNING OBJECTIVES
No doubt so far in this book you have seen interrupts mentioned several times. This book
is only meant to touch on and explain concepts having to do with embedded systems and
the peripherals of the RX62N, yet in the case of most peripherals covered so far it has been
impossible to give even a brief overview without using interrupts in some way. In this
chapter we will be covering more thoroughly exactly what interrupts are and how they
work on a microcontroller. Using interrupts in an embedded application gives a greatly increased capacity for efficiency over a purely linear program.
In the basic concepts section we will give an in depth look at how an interrupt is triggered between a peripheral and the Interrupt Control Unit, and explain the process of setting up an interrupt and what is going on when we do so. In the advanced concepts section
we will cover why keeping our code minimal in interrupts is important to prevent bugs.
Also we will cover handling the passage of data from interrupts. After a brief overview of
state machine programming design, we will pull all of this together by giving an example
of a state machine whose state is controlled via interrupts.
9.2
BASIC CONCEPTS
Basic programs will read and execute in order from beginning to end in a mostly linear
fashion save for control logic such as if() and while() loops. The problem with this is embedded systems are meant to interface with the real world, which does not often occur in
such a predictable linear manner. Almost all embedded systems will depend on an external
event and may even need to critically execute some given code immediately at that event,
and we need a means to signal this in the program, stop what we are doing, handle another
task, then return to the previous program execution. But how do we do that?
9.2.1
Using Interrupts for Tasks versus Other Methods
One method of gathering outside data into a program is via polling. For example, say you
are getting ready for work in the morning and you want to brew a pot of coffee. The coffee
349
350
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
takes at least five minutes to boil and then steep. If we were to act in a manner similar to
polling we would set the water in the pot then watch (poll) it until it is boiling. That is five
minutes of time that we are staring at a pot and not getting other things done that we could
potentially be doing. Instead, we can set a kettle and then go about our routine and don’t
worry about ‘processing’ the coffee until the kettle whistles to signal the water is boiling.
Once we are notified via this signal we ‘interrupt’ our routine to pour a cup and then return
to what we were doing. There are also alternative methods of occasionally stepping back
into the room to check if the water is boiling, which is similar to polling methods used for
keypads. In more complex situations you will need to worry about multiple interrupts occurring; e.g., the dog wants out, the phone rings, someone knocks at the door. In a situation
like this you will need some way to handle scheduling the interrupts and to make sure some
lower priority interrupts don’t interrupt more critical code that needs to execute faster. In
these situations it is handy to use a Real Time Operating System, which is covered in a later
chapter. For now we will start with the simple single interrupt method.
Start preparing breakfast:
Put water in kettle and turn on burner
Put ground coffee in filter in cone
Put cone on cup
Get milk out of fridge
Get cereal from cabinet
Water
boils and
kettle
whistles
An Interrupt Occurs
Resume breakfast preparation:
Get bowl from cabinet
Pour cereal into bowl
Get spoon
Put milk back in fridge
Interrupt Service Routine
Put down whatever is in hands
Turn off burner
Pour boiling water into coffee filter
Pick up whatever was put down
Figure 9.1 Preparing coffee flowchart.
9.3
INTERRUPTS
One good example of how interrupts are used is a robot with an IR sensor. Consider how the
robot uses the IR sensor to detect and avoid obstacles. The robot continuously polls for a signal from the IR sensor, which tells the robot when an obstacle is close. The robot may be running lots of tasks, so if it gets stuck in a long process, the polling process is halted until the
long task is executed. If the signal from the IR sensor occurs while the robot is processing, the
robot will bump into the obstacle. Interrupts are an alternative to polling in these situations.
An interrupt is an external or internal event that takes the Program Counter (PC) from
the current point of the code to a subroutine in the code called the Interrupt Service Routine
(ISR) which has a higher priority of execution. The address to the ISRs is listed out in the
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
351
Interrupt Vector Table (IVT) which is defined in each processor memory. Whenever an interrupt occurs, the processor goes to the IVT and determines the location of the ISR; it then
executes the subroutine present at that address. For example, consider the above situation of
polling the signal from the sensor for detecting the obstacle. Instead of polling the signal, we
can setup an interrupt which runs a subroutine whenever there is a change in the logic level.
When a processor is running a long task we do not need to worry that we would lose the signal from the sensor as the interrupt is set up. The subroutine will be the ISR for the interrupt,
and when the processor executes the ISR it means that an obstacle has occurred. So the
function of the subroutine should be to avoid the obstacle, either change the path or stop the
robot before bumping into the obstacle. The ISRs should contain very little code in them.
There are two types of interrupts: Maskable and Non-Maskable. Non-Maskable interrupts (NMI) are interrupts that cannot be ignored by the processor. When a non-maskable interrupt occurs, the processor should stop whatever it is executing and attend it first. The nonmaskable interrupts are usually used for non-recoverable errors and serious hardware errors
that need immediate attention. One example of a non-maskable interrupt is the reset pin.
The Interrupt Control Unit (ICU) receives signals from peripherals such as timers,
ADCs, and external pins of the microcontroller. The interrupt sources available for the
RX62N/RX621 group are listed in Table 9.1. The block diagram of the ICU is shown
Figure 9.2. This chapter deals with the interrupts generated using software and the external
pins of the microcontrollers.
The following registers are used to setup and read the status of the interrupts:
䡲
䡲
䡲
䡲
䡲
䡲
䡲
䡲
䡲
䡲
Interrupt Request Register (IRR)
Interrupt Request Enable Register (IER)
Interrupt Priority Register (IPR)
Fast Interrupt Register (FIR)
Software Interrupt Activation Register (SWINTR)
IRQ Control Register (IRQCR)
Non-Maskable Interrupt Status Register (NMISR)
Non-Maskable Interrupt Enable Register (NMIER)
Non-Maskable Interrupt Clear Register (NMICLR)
NMI Pin Interrupt Control Register (NMICR)
Interrupt Request Register n (IRn) (n ⴝ interrupt vector number)
The least significant bit of the interrupt request register indicates the status of a particular
interrupt source. The value n of the interrupt request register corresponds to different
interrupt sources in the vector table. For the interrupt sources and corresponding interrupt
vector numbers, refer to the Interrupt Vector Table of the hardware manual (Table 11.4,
RX62N Group, RX621 Group Hardware Manual).
NMI
SR
NMI
ER
[Legend]
NMIER:
NMICR:
NMICLR:
NMISR:
IRQCR:
IR
IER
Cntl
DMASR
Module data bus
DTCER
Clock
restoration
judgment
IR:
IER:
IPR:
FIR:
DTCER:
DMRSR:
IR clear
Destination switchover
to CPU
IR clear
Destination switchover
to CPU
Clear
IR clear
Interrupt request register
Interrupt request enable register
Interrupt source priority register
Fast Interrupt set register
DTC activation enable register
DMAC activation source select register
Interrupt status, destination switchover
Non-maskable interrupt enable register
NMI pin interrupt control register
Non-maskable interrupt clear register
Non-maskable interrupt status register
IRQ control register
Interrupt source
IRQ0 to IRQ15 detection
Detection
IRQCR
NMI NMI
CR CLR
Detection
Interrupt control unit
FIR
DMAC
activation
control
DTC
activation
control
DMAC response
DMAC start request
DMAC activation
enable
DTC response
DTC start request
Interrupt request
CPU priority level
Interrupt acceptance
judgment
IPR
Non-maskable Interrupt request
Clock restoration enable level
Clock restoration request
DMAC
DTC
CPU
Clock
generator
nesas Electronics America, Inc., 2010, page 11–2.
Figure 9.2 Block diagram of Interrupt Control Unit. Source: RX62N Group, RX621 Group Hardware Manual: RX62N Hardware Manual, Re-
Peripheral
module
IRQ15
IRQ0
Low power-voltage destination
Oscillation stop destination
NMI pin
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
TABLE 9.1
Specifications of ICU.
ITEM
Interrupts
Non-maskable
interrupts
353
DESCRIPTION
Peripheral
function
interrupts
䡲 Interrupts from peripheral modules
䡲 Number of sources: 146
䡲 Interrupt detection: Edge detection/level detection
Edge detection or level detection is determined for each
source of connected peripheral modules.
External pin
interrupts
䡲 Interrupts from pins IRQ15 to IRQ0
䡲 Number of sources: 16
䡲 Interrupt detection: Low level, falling edge, rising edge,
both rising and falling edges
One of these detection methods can be set for each source.
Software
interrupt
䡲 Interrupt generated by writing to a register
䡲 One interrupt source
Interrupt priority
Specified by registers.
Fast interrupt
function
Faster interrupt processing of the CPU can be set only for a
single interrupt source.
DTC/DMACA
control
䡲 The DTC and DMACA can be activated by interrupt sources.
䡲 Number of DTC activating sources: 102 (85 peripheral
function interrupts 16 external pin interrupts 1
software interrupt)
䡲 Number of DMACA activating sources: 45(41 peripheral
function interrupts 4 external pin interrupts)
䡲 Interrupt from the NMI pin
䡲 Interrupt detection: Falling edge/rising edge
NMI pin
interrupts
Power-voltage
falling detection
Interrupt during power-voltage fall detection
Oscillation stop
detection
Interrupt during oscillation stop detection
Return from power-down modes
䡲 Sleep mode: Return is initiated by non-maskable interrupts
or any other interrupt source.
䡲 All-module clock stop mode: Return is initiated by
non-maskable interrupts, IRQ15 to IRQ0 interrupts,
WDT interrupts, timer interrupts, USB resume interrupts,
or RTC alarm interrupts.
䡲 Software standby mode: Return is initiated by
non-maskable interrupts, IRQ15 to IRQ0 interrupts
USB resume interrupts, or RTC alarm interrupts.
Source: RX62N Group, RX621 Group Hardware Manual,Table 11.1.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
TABLE 9.2
BIT
Bit Description of Interrupt Request Register.
SYMBOL
BIT NAME
DESCRIPTION
R/W
b0
IR
Interrupt status flag
0: No interrupt request is generated
R/W*
b7 to b1
—
(Reserved)
These bits are read as 0. The write
value should always be 0.
R/W
Note: *For edge-detected sources, only 0 can be written to this bit, which clears the flag, and
writing 1 to the bit is prohibited. Writing is not possible if the source is level-detected.
Source: RX62N Group, RX621 Group Hardware Manual, Section 11.2.1.
IR Flag (Interrupt Status Flag)
When a particular interrupt request is generated, the corresponding vector number IR flag
will be set to 1. The interrupt request detection can be set to edge detection or level detection for each interrupt by using the bits in IRQCRi (i 0 to 15).
Interrupt Request Enable Register m (IERm) (m 02 to 1Fh):
Address: 0008 7202h to 0008 721Fh
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
IEN7
IEN6
IEN5
IEN4
IEN3
IEN2
IEN1
IEN1
0
0
0
0
0
0
0
0
Figure 9.3 Interrupt Request Enable Register.
Source: RX62N Group, RX621 Group Hardware Manual,
Section 11.2.2.
The Interrupt Request Enable Register (IERm) is used to enable and disable the interrupt
requests to the CPU.
IENj bits (Interrupt Request Enable) ( j 0 to 7): When the IENj bit is set to 1, the CPU
accepts that particular interrupt request and handles the interrupt. When this bit is set to 0,
the CPU ignores that particular request. The m and j values in IERm and IENj are for enabling and disabling particular interrupts that can be referenced in the Interrupt Vector Table
in the hardware manual (Table 11.4, RX62N Group, RX621 Group Hardware Manual).
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
355
EXAMPLE
External pin interrupt IRQ0 is referred using the IER register as IER08.IEN0.
The Timer1 overflow interrupt OVI1 is referred using the IER register as IER16.IEN
Interrupt Priority Register m (IPRm) (m ⴝ 00 to 8Fh)
The Interrupt Priority Register is used to set the priority for each interrupt source. The interrupt source should be disabled while setting the priority level. The possible priority levels are listed in Table 9.3. Each interrupt source has its own reserved IPR bits. For the IPR
bits of each interrupt source, refer to the Interrupt Vector Table in the hardware manual
(Table 11.4, RX62N Group, RX621 Group Hardware Manual). The interrupt sources with
a higher priority than the priority level set by IPL [3⬊0] bits in PSW are accepted. If the interrupt priority level of two interrupts are the same and are requested at the same time, then
the interrupt source with the smallest vector number will have the higher priority.
TABLE 9.3
BIT
SYMBOL
b3 to b0
IPR[3⬊0]
Bit Description of Interrupt Priority Register.
BIT NAME
DESCRIPTION
Interrupt
Priority Level
b3 b0
Select
0 0 0 0: Level 0 (interrupt prohibited)
R/W
R/W
0 0 0 1: Level 1
0 0 1 0: Level 2
:
1 1 1 1: Level 15 (highest)
b7 to b4
—
(Reserved)
This bit is read as 0. The write value
should always be 0.
Source: RX62N Group, RX621 Group Hardware Manual, Section 11.2.3.
R/W
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Fast Interrupt Register (FIR)
Address: 0008 72F0h
Value after reset:
b15
b14
b13
b12
b11
b10
b9
b8
FIEN
—
—
—
—
—
—
—
0
0
0
0
0
0
0
0
b7
b6
b5
b4
b3
b2
b1
b0
0
0
0
FVCT[7:0]
Value after reset:
0
0
0
0
0
Figure 9.4 Fast Interrupt Register. Source: RX62N Group, RX621 Group Hardware Manual, Section 11.2.5.
This FIR register is used to set a particular interrupt source as a fast interrupt. The fast interrupt function cannot be used to trigger the peripherals like DTC, DMAC, etc. The fast
interrupt function should not be set up for reserved interrupts in the interrupt vector table.
FVCT [7⬊0]: These bits are used to mention the interrupt vector number of the interrupt
source, which should function as a fast interrupt.
FIEN: This bit should be set to 1 for the interrupt source mentioned in FVCT [7⬊0] to function as a fast interrupt.
Software Interrupt Activation Register (SWINTR)
TABLE 9.4
BIT
b0
Bit Description of SWINTR.
SYMBOL
BIT NAME
DESCRIPTION
SWINT
Software Interrupt
This bit is read as 0.
Activation
Writing 1 issues a software
interrupt request.
R/W
R/W*
Writing 0 to this bit has no effect.
b7 to b1
—
(Reserved)
These bits are read as 0. The write
value should always be 0.
Note: Only 1 can be written. This bit is read as 0.
Source: RX62N Group, RX621 Group Hardware Manual, Section 11.2.5.
R/W
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357
The Software Interrupt Activation Register (SWINTR) is used to create a software interrupt request.
When the SWINT bit is set to 1, the interrupt occurs in vector 27 and the interrupt request for vector 27 is also set to 1. If the DTC Activation Enable Register 27 (DTCER) is
set to 0, then a CPU interrupt is generated. If it is cleared to 0, then a DTC activation request is generated.
IRQ Control Register i (IRQCRi) (i ⴝ 0 to 15)
IRQ Control Register i (IRQCRi) (i 0 to 15)
Address: 0008 7500h to 0008 750Fh
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
IRQMD[1:0]
—
—
0
0
0
0
0
0
0
0
Figure 9.5 IRQ Control Register. Source: RX62N Group, RX621 Group Hardware Manual, page 336.
The IRQ Control Register (IRQCRi) is used to select the type of external interrupts, which
are either edge detection or level detection. The IRQMD [1⬊0] bits in the IRQCR are used
to set up the type of external interrupts. These settings should only be done when the interrupt is disabled and after the interrupt is set up. The interrupt request bit for the particular
external interrupt should be cleared and the interrupt enable bit should be set to 1.
IRQMD [1⬊0]: The possible values for the IRQMD [1⬊0] bits and the corresponding
setting for the interrupts are shown in Table 9.5.
Non-Maskable Interrupt Enable Register (NMIER)
The Non-Maskable Interrupt Enable Register (NMIER) is an 8-bit register that is used to
enable or disable the NMI interrupts. The NMIER has control over three NMI interrupts:
oscillation stop detection, power-voltage detection, and NMI pin interrupts.
Address: 0008 7581h
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
Figure 9.6 Non-Maskable Interrupt Enable Register (NMIER).
Hardware Manual, Section 11.2.10.
b2
b1
b0
OSTEN LVDEN NMIEN
0
0
0
Source: RX62N Group, RX621 Group
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
TABLE 9.5
BIT
SYMBOL
b1, b0
—
b3, b2
IRQMD[1:0]
Bit Description for IRQ Control Register.
BIT NAME
DESCRIPTION
R/W
(Reserved)
These bits are read as 0. The
write value should always be 0.
R/W
IRQ Detection Sense
b3 b2
Select
0 0: Low level
0 1: Falling edge
1 0: Rising edge
1 1: Rising and falling edges
b7 to b4
—
(Reserved)
These bits are read as 0. The
write value should always be 0.
R/W
Source: RX62N Group, RX621 Group Hardware Manual, Section 11.2.8.
NMIEN (Non-Maskable interrupt enable) bit: When this bit is set to 1, the interrupt request from the NMI pin will be sent to the CPU; otherwise the request will be ignored.
LVDEN (Power-voltage falling detection enable) bit: When this bit is set to 1, the power
voltage falling detection interrupt request will be sent to the CPU; otherwise the request
will be ignored.
OSTEN (Oscillation stop detection enable) bit: When this bit is set to 1, the oscillation
stop detection interrupt request will be sent to the CPU; otherwise the request will be
ignored.
NOTE:
For all of the bits described in Figure 9.6, writing “1” is accepted only once—subsequently
writing 0 or 1 to these bits is disabled. In other words, we cannot disable the NMI interrupts after enabling them.
Non-Maskable Interrupt Status Register (NMISR)
The Non-Maskable Interrupt Status register is a read only 8-bit register. This register is
used to read the status of three non-maskable interrupts: oscillation stop detection interrupt
(OSTST), power-voltage falling detection interrupt (LVDST), and non-maskable pin interrupt (NMIST).
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
359
Address: 0008 7580h
Value after reset:
b7
b6
b5
b4
b3
—
—
—
—
—
0
0
0
0
0
Figure 9.7 Non-Maskable Interrupt Status Register (NMISR).
b2
b1
b0
OSTST LVDST
0
0
NMIST
0
Source: RX62N Group, RX621 Group
Hardware Manual, Section 11.2.9.
Figure 9.7 shows the following about the Non-Maskable Interrupt Status Register:
䡲
䡲
䡲
NMIST (NMI status flag) bit: This bit is set to 1 when the edge specified by the
NMIMD bit in the NMICR occurs at the NMI pin. When this is bit is set to 1, the
interrupt request from the NMI pin will be generated to the CPU. This bit is
cleared to zero only when the NMICLR bit in NMICLR register is set to 1.
LVDST (Power-voltage falling detection status flag) bit: This bit is set to “1” when
the power-voltage falling detection interrupt is generated and is cleared to 0, and
when the interrupt is cleared by the interrupt source.
OSTST (Oscillation stop detection status flag) bit: This bit is set to 1 when the oscillation stop detection interrupt is generated and is cleared to 0, and when the
OSTCLR bit in NMICLR register is set to 1.
Non-Maskable Interrupt Clear Register (NMICLR)
The Non-Maskable Interrupt Clear Register (NMICLR) is an 8-bit register that is used to
clear the status flags of the NMI interrupts. The status flags of NMI pin and the oscillation
stop detection interrupts can be cleared by this register.
Address: 0008 7582h
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
—
OSTCLR
—
NMICLR
0
0
0
0
0
0
0
0
Figure 9.8 Non-Maskable Interrupt Clear Register (NMICLR).
Source: RX62N Group, RX621 Group
Hardware Manual, Section 11.2.11.
Figure 9.8 shows the following:
䡲
NMICLR (NMI clear) bit: When this bit is set to 1, the NMIST flag in the NMISR
register will be cleared to 0.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
OSTCLR (OST clear) bit: When this bit is set to 1, the OSTST flag in the NMISR
register will be cleared to 0.
NOTE:
We do not need to clear the NMICLR and the OSTCLR bits to 0. As soon as the corresponding status flag goes to 0, the NMICLR and the OSTCLR bits are also cleared to 0.
NMI Pin Interrupt Control Register (NMICR)
The NMI Pin Interrupt Control Register (NMICR) is an 8-bit register in which only one bit
is used to set the type of edge detection of the interrupt to either the falling edge or the rising edge. The edge detection should be set before enabling the NMI interrupt.
Figure 9.9 illustrates how to address the NMI Pin Interrupt Control Register (NMICR).
When this bit is set to 1, the interrupt request is generated on the rising edge input to the
NMI pin. When this bit is cleared to 0, the interrupt request is generated on the falling edge
input to the NMI pin.
Address: 0008 7583h
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
NMIMD
—
—
—
0
0
0
0
0
0
0
0
Figure 9.9 NMI Pin Interrupt Control Register (NMICR).
Source: RX62N Group, RX621 Group Hard-
ware Manual, Section 11.2.12.
9.3.1
Interrupt Vector Table
The Interrupt Vector Table (IVT) in an RX62N microcontroller has 256 interrupts, with
each interrupt source occupying four bytes in the table. In total, the size of IVT is 1024 bytes
(4 bytes 256 sources). Each address space specifies the location of the interrupt service
routine for the interrupt. When the CPU accepts an interrupt, it acquires the four byte address from the IVT and executes the code specified at that particular interrupt service routine. Refer to Table 11.4 located in the hardware manual of the RX62N microcontroller for
the vector address for the interrupt sources.
9.3.2
Interrupt Operation
The interrupt control unit (ICU) performs the following operations while setting up the
interrupts:
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
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䡲
䡲
䡲
361
Detecting the interrupts.
Enabling and disabling the interrupts.
Selecting the interrupt destination.
Determining the priority.
The ICU first detects the interrupts. Detecting the interrupt requests is by way of either
edge detection of the interrupt signal (edge triggered interrupts), or level detection of the
interrupt signal (level triggered interrupts).
Edge Detection
The interrupt status flag is set to 1 when the microcontroller responds to the interrupt request, and the bit is cleared to 0 when the particular module or I/O pin interrupt request is
accepted. Figure 9.10 shows how the interrupt status flag operates for edge triggered interrupts. The IR flag for the particular interrupt is set to 1 as soon as the interrupt signal goes
high. If the interrupt is a CPU interrupt, the IR flag is cleared to 0 when the interrupt is accepted by the CPU. If the interrupt is a DMACA or DTC activation interrupt, the IR flag is
cleared to 0 once the transfer by the DTC or DMACA has been completed.
Interrupt Signal
IRn.IR flag
Acceptance of the interrupt by the
CPU or completion of transfer by
the DTC or DMACA
Figure 9.10 Interrupt status flag for edge triggered interrupts. Source: RX62N Group, RX621 Group
Hardware Manual, page 11–40.
If the source of the interrupt generation is disabled and after the interrupt status flag
goes high, the IR flag remains in the high state. For example after the IR flag for DTC activation interrupt goes high, if the DTC is disabled, then the IR flag of the DTC activation interrupt remains in the high state until the DTC is enabled and the transfer is done. Figure 9.9
shows how the IR flag operates when the source of the interrupt is disabled.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Source for interrupt generation
is enabled/disabled
Interrupt Signal
IRn.IR flag
IRn.IR flag is not cleared even when the source is disabled
Figure 9.11 Interrupt status flag when the source of the interrupt is disabled.
Source: RX62N
Group, RX621 Group Hardware Manual, Figure 11.4.
Level Detection
The interrupt status flag remains set to 1 when the interrupt is requested and being sent to
the destination. The bit is cleared to 0 when the source of the interrupt request is cleared.
Figure 9.11 shows the operation of the IR flag for level-triggered interrupts. As shown in
Figure 9.12, the IR flag remains in the high state until the source of the device requesting
the interrupt is cleared.
Interrupt source cleared
Interrupt Signal
IRn.IR flag
IRn.IR flag cleared
Figure 9.12 Interrupt status flag for level triggered interrupts. Source: RX62N Group, RX621 Group
Hardware Manual, Figure 11.5.
The edge detection and the level detection of the interrupts can be selected using the
IRQMD [1⬊0] bits in IRQ control register. When the level detection is selected for the interrupt requests, the interrupt status flag should not be cleared to 0.
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
363
After detecting the interrupts, the ICU checks to see if the interrupt is disabled or enabled. Enabling and disabling the interrupts can be performed by using the bits in IERm
register. Refer to Table 11.4 of the hardware manual for information about the corresponding bit for each interrupt. If the interrupt is disabled, the ICU ignores the interrupt. If the
interrupt is enabled, the ICU checks for the destination of the interrupt. The possible destinations for the interrupt would be the CPU, or DTC or DMACA activation. The destination
for any interrupt is the CPU by default. The destination of the interrupt can be modified using the bits in the DTCER and DMRCR registers. For the interrupt vector number of a particular interrupt, refer to Table 11.4 of the hardware manual (Table 11.4, RX62N Group,
RX621 Group Hardware Manual).
If two or more interrupts occur at the same time, the ICU fetches the interrupt requests based upon the interrupt priority set up by the IPR register. An interrupt selected as
a fast interrupt will have the highest priority. After that, the highest value in the IPR [3⬊0]
bits of IPRm will have the next highest priority. If interrupts with same priority level occur at the same time, the interrupt source with smallest vector number will have higher
priority.
9.3.3
Setting Up an Interrupt for a Peripheral
All interrupts in the RX62N are handled via the Interrupt Control Unit (ICU). When
setting up an interrupt there are two places where we make configuration settings, in the
peripheral itself and in the ICU. When an interrupt occurs a signal is sent from the peripheral to the ICU, the ICU then processes the request and sends the interrupts to the
CPU as needed.
Setting Up an Interrupt
The steps to set up an interrupt for a peripheral are as follows:
1. The peripheral or port pin must be enabled and configured.
2. Set an interrupt priority for the interrupt source (IPR macro) to a value greater than
zero (zero disabled).
3. Enable the interrupt in the peripheral (local enable bit).
4. Enable the interrupt in the ICU (IEN macro). (Conrad, J.)
NOTE:
The procedure is slightly different for setting an I/O pin as an interrupt; refer to section
Registers Set in the ICU for an Interrupt under the definition for the IRQCRi register.)
Figure 9.13
Peripheral
module
NMI
ER
[Legend]
NMIER:
NMICR:
NMICLR:
NMISR:
IRQCR:
IR
IER
Cntl
DMASR
Module data bus
DTCER
Clock
restoration
judgment
IR:
IER:
IPR:
FIR:
DTCER:
DMRSR:
IR clear
Destination switchover
to CPU
IR clear
Destination switchover
to CPU
Clear
IR clear
Interrupt request register
Interrupt request enable register
Interrupt source priority register
Fast Interrupt set register
DTC activation enable register
DMAC activation source select register
Interrupt status, destination switchover
Non-maskable interrupt enable register
NMI pin interrupt control register
Non-maskable interrupt clear register
Non-maskable interrupt status register
IRQ control register
Interrupt source
IRQ0 to IRQ15 detection
Detection
IRQCR
NMI NMI
CR CLR
Detection
NMI
SR
Interrupt control unit
FIR
DMAC
activation
control
DTC
activation
control
DMAC response
DMAC start request
DMAC activation
enable
DTC response
DTC start request
Interrupt request
CPU priority level
Interrupt acceptance
judgment
IPR
Non-maskable Interrupt request
Clock restoration enable level
Clock restoration request
DMAC
DTC
CPU
Clock
generator
Interrupt Control Unit Block Diagram. Source: RX62N Group, RX621 Group Hardware Manual, Figure 11.1.
IRQ15
IRQ0
Low power-voltage destination
Oscillation stop destination
NMI pin
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As can be seen, first off the peripheral must be enabled and configured; it can’t signal
an interrupt if it isn’t on or configured to operate. The next steps don’t necessarily need to
be handled in the given order. A priority must be set for the interrupt in the ICU, you may
have noticed in previous chapters we have done this using the IPR() macro. Using the provided macros from Renesas simplifies the process by only having us need to know the
name of the peripheral and its interrupt in order to set its priority and enable it in the ICU.
These can be found, along with the vector numbers for the interrupts, in the RX62N hardware manual or in Appendix A: Interrupt Vector Table of this text. We must also enable the
interrupt in the peripheral itself. Where this is done is dependent on the peripheral, and
could vary from setting an enable bit in a control register to a variety of settings in a separate register specifically for the interrupt. The interrupt must also be enabled in the ICU itself in order for the ICU to send it to the CPU.
Besides enabling the registers for the interrupt we need to define the Interrupt Service
Routine to be used when the interrupt is triggered. The vector for each interrupt is available
in the Interrupt Vector Table. In the case of the interrupts we will be using, the location the
vector points to is variable and can be defined using a #pragma and another macro feature
provided by Renesas. We put the code we want to run as an ISR in a subroutine, and then
we define the subroutine as an interrupt and place a pointer to its memory address with
the following code, where SUBROUTINE_NAME is the name of the subroutine and
VECTORNUMBER is the number of the vector located in the Interrupt Vector Table.
1. #pragma interrupt (SUBROUTINE_NAME(vect = VECTORNUMBER))
2. void SUBROUTINE_NAME(void);
We place this code at the beginning of our program or in a separate .h file. Then we put the
code for our ISR in the subroutine with the rest of our program’s functions or in a separate
.c file allocated for our interrupt code.
1. //Name of Interrupt
2. void SUBROUTINE_NAME(void){
3.
//ISR Code
4. }
Registers Set in the ICU for an Interrupt
Each of the following registers is not a single register, but a representation of a type of register. In the RX62N there are several of these. The one which services the interrupt we will
use is determinable by looking in the Interrupt Vector Table. However, we need not worry
about any details besides the abbreviation for the peripheral, the abbreviation for the interrupt, and the vector number, because everything is handled in the Renesas IR(), IPR(), and
IEN() macros. We will cover the registers here just to help understand the interrupt process.
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Interrupt Request Register n (IRn) (n interrupt vector number)
Address: 0008 7010h to 0008 70FDh
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
—
—
—
—
—
—
—
IR
0
0
0
0
0
0
0
0
BIT
SYMBOL
BIT NAME
DESCRIPTION
R/W
b0
IR
Interrupt status flag
0: No interrupt request is generated
R/W*
1: An interrupt request is generated
b7 to b1
—
(Reserved)
These bits are read as 0. The write
value should always be 0.
R/W
Note: *For edge-detected sources, only 0 can be written to this bit, which clears the flag, and
writing 1 to the bit is prohibited. Writing is not possible if the source is level-detected.
Figure 9.14 Interrupt Request Register.
Source: RX62N Group, RX621 Group Hardware Manual, Section
11.2.1.
The Interrupt Request Register (shown in Figure 9.14) is merely a flag holder that indicates a request signal has been sent from the peripheral. When a signal is received in the
ICU, the Interrupt Status Flag bit will be set to 1, and will return to 0 when the CPU accepts the interrupt. In the event that an interrupt is enabled in a peripheral and not in the
ICU, this flag can still be set. It is possible to clear this register to 0 before an interrupt occurs by writing a 0 to it.
To clear a flag via the IR() macro we merely enter the code as:
1. IR(“PERIPHERAL”, “INTERRUPT”) = 0;
Where PERIPHERAL is the abbreviation of the peripheral and INTERRUPT is the abbreviation for the interrupt name (available in the Interrupt Vector Table). To check a flag via
the IR() macro we enter the code as:
1. VARIABLE = IR(“PERIPHERAL”, “INTERRUPT”);
or
1. if(IR(“PERIPHERAL”, “INTERRUPT”)) == 1){
2.
//Code if flag is set
3. }
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Interrupt Request Register m (IERm) (m 02h to 1Fh)
Address: 0008 7202h to 0008 721Fh
Value after reset:
b7
b6
b5
b4
b3
b2
b1
b0
IEN7
IEN6
IEN5
IEN4
IEN3
IEN2
IEN1
IEN0
0
0
0
0
0
0
0
0
BIT
SYMBOL
BIT NAME
DESCRIPTION
R/W
b0
IEN0
Interrupt Request Enable 0
0: Interrupt request is disabled
R/W
b1
IEN1
Interrupt Request Enable 1
1: Interrupt request is enabled
R/W
b2
IEN2
Interrupt Request Enable 2
R/W
b3
IEN3
Interrupt Request Enable 3
R/W
b4
IEN4
Interrupt Request Enable 4
R/W
b5
IEN5
Interrupt Request Enable 5
R/W
b6
IEN6
Interrupt Request Enable 6
R/W
b7
IEN7
Interrupt Request Enable 7
R/W
Note: Write 0 to the bit that corresponds to the vector number for reservation. These bits are
read as 0.
Figure 9.15 Interrupt Request Enable Register. Source: RX62N Group, RX621 Group Hardware Manual,
Section 11.2.2.
The Interrupt request enable register (shown in Figure 9.15) enables whether the ICU will
process the interrupt request flag once it is set by a signal from the peripheral. The address
of the IEN register and the bit of the register that needs to be set for each interrupt is once
again available in the Interrupt Vector Table, but we don’t need to worry about that. We
only need to know the IEN() macro, which operates just like the IR() macro.
To set or clear the bit corresponding to an interrupt in the IER register we only need to
enter the following code, where PERIPHERAL and INTERRUPT are the abbreviations for
the peripheral in the Interrupt Vector Table.
1. IEN(“INTERRUPT”, “PERIPHERAL”) = 1;
2. //‘1’ to enable, or ‘0’ to disable
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Interrupt Request Register m (IPRm) (m 00h to 8Fh)
Address: 0008 7300h to 0008 738Fh
Value after reset:
b7
b6
b5
b4
—
—
—
—
0
0
0
0
b3
b2
b1
b0
IPR[3:0]
0
0
0
BIT
SYMBOL
BIT NAME
DESCRIPTION
b3 to b0
IPR[3:0]
Interrupt Priority Level
b3 b0
Select
0 0 0 0: Level 0 (interrupt
prohibited)
0
R/W
R/W
0 0 0 1: Level 1
0 0 1 0: Level 2
:
1 1 1 1: Level 15 (highest)
b7 to b4
—
(Reserved)
This bit is read as 0. The write
value should always be 0.
R/W
Figure 9.16 Interrupt Priority Register. Source: RX62N Group, RX621 Group Hardware Manual, Section 11.2.3.
The Interrupt Priority Register (shown in Figure 9.16) allows the priority of the interrupt to be
specified. A priority level from one to fifteen is allowed, fifteen being the highest. Interrupts
with higher priority are handled first. If interrupts occur simultaneously with the same priority,
the interrupt with the lower vector number is handled first. If a priority level isn’t set, the interrupt will not be handled.
In case you are using an I/O pin to trigger an interrupt, you would use this register to determine how it is triggered. The number of the IRQ register for each I/O pin corresponds to
the number of the interrupt request pin. Please refer to the RX62N schematic to determine
where to connect to that pin physically. The only pins we are concerned with in this book are
the pins connected to Switch 1, 2, and 3 which are IRQ pins; and 8, 9, and 10, respectively.
Take note you must also enable the port as an input when using it to trigger an interrupt. It is
important when setting up an I/O pin as an interrupt to do it in this order:
1.
2.
3.
4.
5.
Clear the IEN bit.
Enable or confirm the I/O pin as an input.
Set the detection method in the IRQCR register.
Clear the IR flag.
Set the IEN bit.
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369
Take note of Step 2. Alongside writing the ports data direction register to set it as an input,
you must also write a 1 to the input buffer control register (ICR; RX62N Group, RX621
Group Hardware Manual, page 641) in the I/O registers. This must be done any time you
are using an input pin to control a peripheral, in this case the peripheral is the ICU. You will
have to refer to the schematic to see which port number and bit correspond to the IRQ input, and then write to that ICR bit. In the case of the three on board switches 1, 2, and 3, the
ports are PORT4.0, PORT4.1 and PORT4.2 respectively. So for switch one you would
write a 1 to PORT4.ICR.BIT.0.
9.3.4
How an Interrupt Operates
So, now that we know how to set up an interrupt and a bit of the inner workings of the ICU,
we will briefly explain the process of what happens when an interrupt is triggered. When
conditions are met in a peripheral to trigger an interrupt, the first process that happens is
the sending of the request to, and the processing of that request by, the ICU.
Conditions met for interrupt in peripheral, peripheral flag set.
Signal sent to ICU, peripheral flag cleared.
IR flag set in ICU.
If the interrupt is enabled in the ICU and no higher priority interrupts are currently
running, the interrupt is sent to the CPU.
5. Interrupt accepted by CPU, IR flag cleared.
1.
2.
3.
4.
Once the interrupt is sent to the CPU the following process occurs in the program:
1.
2.
3.
4.
5.
Finish processing current instruction.
Save program counter and flags to memory.
Run interrupt service routine.
Restore program counter and flags from stack.
Resume main program.
The stack is a dynamically allocated resource that contains current working data to do with
our program. If too many interrupts occur, the stack can fill up pretty quickly and may
overflow. This can become a problem if not well monitored. Another reason to keep ISRs
small and short is so that they get back to the main program quickly and don’t interfere
with other interrupts.
This, of course, is just a very basic overview of the process that occurs. The detailed order of this process and instructions used to perform it are more complex and processor specific. But hopefully this gives an overview and helps you understand the process involved
with setting up and using interrupts.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
9.4
BASIC EXAMPLES
9.4.1
Polling a Switch for Input versus Using an Interrupt
Aim: Demonstrate checking the status of a hardware switch via polling and with an
interrupt.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0, RX62N
Development kit.
Details: In this example, we will setup the RX62N processor to check the status of switch
one (SW1). If the switch is pressed, the lit LED will rotate clockwise once until the switch
is pressed again. We will first do this via a polling method, and then with an interrupt. We
will compare and contrast the differences.
Procedure: First we will set up SW1 and check it with a polling method.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
#include “iodefine_RX62N.h”
//Function definitions
void main(void);
void LED_Rotate(void);
//Define global variables
int Current_LED;
void main(void){
ENABLE_LEDS
ENABLE_SWITCHES
Current_LED = 1;
20.
21.
22.
23. }
while(1){
if(SW1 == 0){
LED_Rotate();
while(SW1 == 0)
}
}
;
//Note that this code does not handle
switch debouncing.
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
371
All of this should be familiar; the LED_Rotate function rotates the LEDs one step in a clockwise sequence every time it is called. Current_LED is used to keep track of which LED is currently lit. For more reference on how to implement this function, refer to Chapter 8 where it is
first used.
Lines 17 through 22 are where we check the status of SW1. SW1 is active low so once
it is pressed the input will become a zero. Every time the program cycles through the
while(1) loop it will check if SW1 is a zero yet. If it is a zero it will rotate the LED clockwise and then get stuck in the while (SW 0); until the switch is released. Note that on
line 19 there is a comment noting that this code does not account for debouncing.
Debouncing accounts for how a switch will, for a brief time after being pressed, rapidly
switch back and forth (or “bounce”) between an ON and OFF position rather than cleanly
switching between states. Usually this state is accounted for by calling a brief timer loop
before checking ON or OFF, and indicating pressed or depressed. This method was left out
in this example for simplicity.
Another method would be to replace lines 16 through 22 with the following code:
1. while(1){
2.
while(SW1 == 1);
3.
LED_Rotate();
4.
while(SW1 == 0)
5.
;
6.
}
7. }
With this method, we avoid problem number one of the last method by pausing the program until the switch is pressed. This solves that problem, but now this makes problem
number two even worse. The program will be hung up entirely and no other calculations
will be performed until the switch is pressed and released each time the while(1) loop repeats. To solve both problems we will use an interrupt.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
#include “iodefine_RX62N.h”
//Define SW1 interrupt
#pragma interrupt(SW1_Int(vect = VECT_IRQ8))
void SW1_Int(void);
//Function definitions
void main(void);
void LED_Rotate(void);
void EnableIRQ8(void);
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
//Define global variables
int Switch_Press = 0;
int Current_LED;
void main(void)
{
ENABLE_LEDS
EnableIRQ8();
Current_LED = 1;
while(1)
{
if(Switch_Press)
{
LED_Rotate();
Switch_Press = 0;
}
}
}
First take note of the addition on lines 3 through 5. SW1 is connected to IRQ8, if we look
up IRQ8 in the Interrupt Vector Table we will see that it is at vector 72. This code defines
the ISR for IRQ8 as SW1_Int and places a pointer to its memory address at vector 72, and
also defines the function SW1_Int. Also on line 10 we define a new function EnableIRQ8
which is called on line 19 to perform all of the necessary operations to set up the switch to
trigger an interrupt. In our while(1) loop nothing will happen unless the Switch_Press flag
is set in the switches interrupt routine. If it does, the LED_Rotate function is called and the
flag is reset to 0.
1. void EnableIRQ8(void){
2.
IEN( ,IRQ8) = 0;
3.
PORT4.ICR.BIT.B0 = 1;
4.
ICU.IRQCR [8 ].BIT.IRQMD = 0x01;
5.
ENABLE_SWITCHES
6.
IPR( ,IRQ8) = 0x03;
7.
IR( ,IRQ8) = 0;
8.
IEN( ,IRQ8) = 1;
9. }
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
373
You may notice this code follows the procedure defined for setting a switch for an interrupt
in Section 9.3.3 in the description of the IRQCRi register. First, as a precaution we disable
the interrupt in the ICU in case it has been enabled in our program. This is on line 2. Then
on line 3 we write a 1 to the input control register on Port4.0, the port that SW1 is connected to. This passes a signal to the ICU when the switch is pressed. Then we set the triggering method for IRQ8 on line 4. The switch is active when low, and it goes from a one to
zero when pressed, so we set the trigger as a falling edge. Line 5 is our macro to set up the
switches as inputs. By default the ports are inputs when the program starts, and we have
also already called this macro in the main program; but this is a precautionary measure in
case we decide to put this function in other programs where this hasn’t already been done.
Now that all of this is done, all we have to do is set up the interrupt in the ICU by defining
its priority level, clearing the request flag in case it has been generated during setup, and
then enabling the interrupt on lines 7 through 9.
1. void SW1_Int(void)
2. {
3.
Switch_Press = 1;
4. }
Our last piece of code is for the SW1 Interrupt Subroutine. This sets the flag indicating the
interrupt was triggered then returns to the main function. Because we set the trigger for the
interrupt as a falling edge on the switch, it will only trigger when the button is pushed.
Once the button is pushed, the subroutine is called and whatever code we want to address
is executed. The switch is not ignored. Also, there is no waiting because the main program
is halted for only as long as it takes to address the ISR. Though the setup is slightly more
complex, the interrupt method is superior in efficiency.
9.4.2
Setting up the ADC with an Interrupt
Aim: Demonstrate using the interrupt with a peripheral.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0, RX62N
Development kit, RX62N Graphical LCD Code package.
Details: In this example, we will set up the RX62N processor to read the value of the potentiometer. Our program will use an interrupt, a device interrupt as a trigger, and a subroutine. TMR0 will trigger the A/D conversion every one second. When the A/D conversion is done it will call a subroutine to store the conversion in a variable. The main program
will use this variable to display the conversion value on the LCD.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Procedure: First we need to set up our definitions and global variables:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
#include “iodefine_RX62N.h”
//Glyph Includes
#include <stdlib.h>
#include <stdio.h>
#include “src\Glyph\Glyph.h”
//Define interrupt for AD1
#pragma interrupt (AD1_Interrupt(vect = VECT_AD1_ADI1))
void AD1_Interrupt(void);
//Function definitions
void main(void);
void InitADC(void);
void InitTimer(void);
void LED_Rotate(void);
void BSP_Display_String(int8_t aLine, char *aText);
#define LCD_LINE1 0
#define LCD_LINE2 1
#define LCD_LINE3 2
#define LCD_LINE4 3
//Define global variables
T_glyphHandle G_lcd;
int Current_LED;
int ADCResult = 0;
char buffer [30 ];
From line 1 to 6 we have included all I/O files for the RX62N and the LCD. On line 8 through
10 we define our interrupt function for the A/D conversion done interrupt, and place a pointer
at its vector in the interrupt table. Notice in our function definitions on lines 13 to 17 that we
have made a function for initializing the ADC and timer. Also note on line 26 that we have
made the global variable ADCResult, where we will hold the value read from the A/D conversion. The array on line 27 will be used to store the ASCII conversion of the ADCResult
that is sent to the LCD.
Next is our main function and while(1) loop:
1. void main(void)
2. {
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26. }
375
float i;
InitADC();
InitTimer();
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
/* use Glyph full access direct functions */
GlyphNormalScreen(G_lcd);
GlyphSetFont(G_lcd, GLYPH_FONT_HELVR10);
GlyphClearScreen(G_lcd);
BSP_Display_String(LCD_LINE1, “ADC Int Example”);
BSP_Display_String(LCD_LINE2, “Potentiometer Value:”);
while(1){
for(i = 0; i < 100000; i++);
sprintf(buffer, “%d”, ADCResult);
BSP_Display_String(LCD_LINE3, buffer);
}
}
else {}
GlyphClose(&G_lcd);
We create the variable i on line 3 to make our arbitrary delay loop on line 17. On lines
4 and 5 we call our functions to set up the timer and the AD converter. The code from
lines 7 through 11 are initialization for the LCD. In lines 13 and 14 we display on the
LCD some information concerning the program that is running. Then in our while(1) loop,
repeatedly, after an arbitrary delay, we will convert our value from the A/D conversion to
an ASCII string and write it to line 3 of the LCD. The rest of the code is LCD control code.
1. void InitADC(void){
2.
MSTP(AD1) = 0;
3.
AD1.ADCSR.BIT.ADIE = 1;
4.
AD1.ADCSR.BIT.ADST = 0;
5.
AD1.ADCSR.BIT.CH = 0x000;
6.
7.
AD1.ADCR.BIT.MODE = 0;
8.
AD1.ADCR.BIT.CKS = 3;
9.
AD1.ADCR.BIT.TRGS = 2;
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
10.
11.
12.
13. }
IPR(AD1,ADI1) = 0x03;
IR(AD1,ADI1) = 0;
IEN(AD1,ADI1) = 1;
This is our function to set up the AD converter to read the value from the potentiometer. We
will set it up to do a single conversion every time it receives a trigger from TMR0. First we
enable the peripheral on line 2. Then on line 3 we enable the interrupt in the A/D peripheral;
this will trigger the interrupt service routine every time a conversion finishes. We set the
conversion to not start yet on line 4, and then select channel AN4 on line 5. It is indicated in
the RX62N schematic that AN4 corresponds to the pin that is connected to the potentiometer. On line 7 we set the mode to single conversion, so every time the converter is triggered
it will do one conversion then stop. We select the clock source for the AD converter as the
peripheral clock on line 8. On line 9 we select the trigger as a Compare Match A event on
TMR0. Every time a Compare Match A event occurs in TMR0 a signal will be sent to the
A/D converter. This requires some set up in TMR0 as well; we will see that code shortly. On
lines 10 through 12 we have the code to set the priority level, clear the request flag, and then
enable the interrupt in the ICU.
1. void InitTimer(void){
2.
MSTP(TMR0) = 0;
3.
MSTP(TMR1) = 0;
4.
5.
TMR1.TCCR.BIT.CSS = 1;
6.
TMR1.TCCR.BIT.CKS = 5;
7.
8.
TMR0.TCCR.BIT.CSS = 3;
9.
TMR0.TCR.BIT.CCLR = 1;
10.
11.
TMR0.TCORA = 0x5B;
12.
TMR1.TCORA = 0x6D;
13.
14.
TMR0.TCSR.BIT.ADTE = 1;
15. }
Here is our code to set up a 16-bit cascaded timer that resets and generates a Compare
Match A signal every one second. The code from lines 3 through 13 configures the timer to
generate a one second interval; details are in the timer chapter of this text. The only code
we need to examine here is on line 14, where we set the unit to send a trigger to the A/D
converter every time there is a Compare Match A or every one second.
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
377
1. void AD1_Interrupt(void){
2.
ADCResult = AD1.ADDRA;
3. }
Our last bit of code is our interrupt subroutine for the A/D conversion. Every time a conversion finishes this routine will interrupt to write the latest conversion value to our variable, and then the program will return to its previous task.
So, to review, this program begins by initializing the A/D converter and the TMR0.
TMR0’s interrupt routine is not enabled, but the Compare Match A interrupt in the peripheral will send a signal to the A/D converter every one second. Once triggered the A/D conversion will begin, and once finished it will trigger its own interrupt. This interrupts the
main program for long enough to write the conversion value to a variable, then returns. Inside the main program there is a constant loop writing the A/D conversion to the LCD after
a short delay. When run, the LCD screen should display “ADC Int Example” on line 1 of
the LCD and “Potentiometer Value:” on line 2. On roughly one second intervals the screen
should update with a new value for the potentiometer.
This example illustrates two uses of interrupts, and an alternative use of interrupt signals to triggering subroutines. By now you should be pretty familiar with the process of
setting up an interrupt to trigger a subroutine as well as the concept of using them to trigger processes in other peripherals.
9.5
ADVANCED CONCEPTS
9.5.1
Minimizing the Amount of Code in Interrupts
In example 9.4.1, Polling a Switch for Input versus Using an Interrupt, it was pointed out
that excessive function calls, or code in general, inside of an interrupt routine is bad. If a
function call is made in an interrupt routine it requires that all the processor register information be stored to the stack, which makes the compiler blind to register usage. Also, as
mentioned several times in this book, it just simply adds more time and over head to the interrupt, and we want to avoid this as much as possible.
So how do we do this? Often an ISR is used only to set flags or alter very small
amounts of data. Then these flags or data are used to alter something in the main program.
A flag can be a global variable that is toggled between one and zero. Once the program returns from the interrupt, some control statement will eventually use this as an indicator to
change the program flow in some way.
For example, say we have a program that is constantly checking the value of a thermistor but we only want it to update the value on the LCD screen every second. We would
set up a timer to interrupt periodically every second, and when it interrupts it writes a one
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
to a variable named Timer_Flag. In our main program there is an if statement that checks
the timer flag. When the Timer_Flag variable is 1 the function to write the value to the
LCD is called. This way we still get the benefits of the interrupt, but keep our code in
the interrupt minimal.
9.5.2
Brief Introduction to State Machines
In the next section we will cover how to make an interrupt controlled state machine. But
first, in this section we need to give a brief overview of what a state machine is and how to
program one. State machines are simply a method that makes it easier to abstract a process
we want to perform in real life and convert it into a program.
So far we have thought of programs as sequential processes. One process is executed,
then some others, repeat. Sometimes that flow is altered slightly due to something happening, such as an interrupt or control loops, but with an embedded system we still will restart
in our while(1) loop eventually and the program will repeat and execute the same processes
again. With state machines we think of our program as having ‘states.’ In each state there is
a different flow of operations to perform. Depending on some change in data or a triggering event, the state will change. The program will continue to perform the functions in this
state until conditions are met to go into another state. We will implement the state machine
by making a variable to represent the current state of the machine, and then using a switch
statement to check that variable in the while(1) loop. If the variable is changed the state
will change, otherwise the code in the current state will continue to run repeatedly. We can
also make states that perform one task and then immediately switch to another state without to another state by default.
In order to better understand a state machine, let’s imagine a vending machine as a
state machine. The vending machine can be in a ‘state’ depending on what task it needs to
perform at the current moment. In each state the program is focused on a particular function such as accepting money, returning change, or vending drinks. In the case of the coin
return state, it will return the proper amount of coins and then by default return to the Accept Money state. The same for the vend state, which automatically goes to the Coin Return state (which we assume simultaneously checks to see if coins are needed to be returned at all). In the case of the Accept Money state, the state will not change until a
selection is made or the coin return button is pressed. In the case of the Check Correct
Change state it will immediately go to either state 4 or 1, depending on if the right amount
of change was deposited for the selection. This is how a state machine works on a very basic level. A full implementation of a vending machine state machine would require many
more states such as “jammed coin,” “machine tilt,” “coolant problem,” “out of order,” etc.
In order to address the real world well embedded systems must get very intricate. This is
just a simple illustrative example.
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
379
Switch(State)
Accept
Money
Check Correct
Change
Coin
Return
Vend
State 1
State 2
State 3
State 4
1. Get_Money()
2. if(selection_
made)
3. {State = 2}
4. if(coin_
return)
5. {State = 3}
1. Determine_
Proper_
Change()
2. if(proper_
change)
3. State = 4
4. Else {
5. Output
“incorrect
change”
6. {State = 1}
1. Return_Change
2. {State = 1}
1. Vend
(selection)
2. {State = 3}
Figure 9.17 Vending machine state machine example.
9.5.3
State Machines and Using Them with Interrupts
So now that we know what a basic state machine looks like, we are going to demonstrate
how to implement one effectively using interrupts to switch states. You’ll notice in the vending machine examples that different actions triggered a state change, such as coin_return or
selection made. These actions were represented as a variable of some sort and were checked
by an If statement; if these variables were a one or higher the state was changed. Do these
variables look familiar to something else we talked about in this chapter? These are simply
the flags we talked about in Section 9.5.1, Minimizing the Amount of Code in Interrupts. So
by setting flags with an interrupt we can have code in our states check these flags and
change states based on input. Once again let’s use an example to illustrate.
For this example let’s use the RX62N. We will make a state machine that will have three
states. In one state the machine will rotate the LEDs in a circular sequence. In the second
state we will display the value of the potentiometer on the LCD. In the third state the LCD
will display the number of seconds elapsed since the program has started. Each time switch
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Switch(State)
Rotate
LEDs
Display A/D of
Potentiometer
Display
Seconds
State 1
State 2
State 3
1. if(Second_Flag){
2.
DisplayLEDs();
3.
Second_Flag = 0;
4. }
1. if(AD_Flag){
2.
DisplayADC();
3.
Second_Flag = 0
4. }
1. if(Second_Flag){
2.
DisplaySec();
3.
Second_Flag = 0;
4. }
Figure 9.18 RX62N state machine example with interrupts.
one is pressed the board will cycle to the next state, once it goes beyond state three it will return to state one. We will make it that each state performs its actions at one second intervals.
With state machines this implementation is very simple. We only need three states as
specified. The flag indicating which state is currently active is rotated using the ISR for
switch one, defaulting to state one on start. Every second the timer will interrupt and set a
flag that a second has passed, this flag will trigger actions in States 1 and 3. Note that the
DisplayLEDs function in State 1 will include a function call to rotate the LEDs as well as
display information on the LCD, thus rotating the LEDs. In the case of State 2 we are using
the A/D converter, so we will use a flag set by its own ISR to trigger this state’s actions. This
will occur on roughly one second intervals since the A/D itself will be set to be triggered by
a signal from the Timer device. This is a full, very basic state machine that uses interrupts to
switch states. We will give a coding example of this in the advanced examples section.
9.6
ADVANCED EXAMPLES
9.6.1
Using an ADC Interrupt with Flags to Process Data
Aim: Demonstrate using flags with an interrupt to minimize the time spent in an ISR.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0, RX62N
Development kit.
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
381
Details: In this example, we will set up the A/D converter once again to perform a conversion, except in this example the A/D will trigger an interrupt when the conversion is
done. This interrupt will set a flag that is checked in the main code to trigger, writing the
new data to the LCD.
Procedure: The code is mostly the same as our example in Section 9.4.2, Setting up the
ADC with an Interrupt, except with modifications so that it now operates around the A/D
interrupt. Our variable and function prototypes are mostly the same.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
#include “iodefine_RX62N.h”
//Glyph Includes
#include <stdlib.h>
#include <stdio.h>.
#include “src\Glyph\Glyph.h”
//Define interrupt for AD1
#pragma interrupt (AD1_Interrupt(vect = VECT_AD1_ADI1))
void AD1_Interrupt(void);
//Function definitions
void main(void);
void InitADC(void);
void InitTimer(void);
void LED_Rotate(void);
void BSP_Display_String(int8_t aLine, char *aText);
#define LCD_LINE1 0
#define LCD_LINE2 1
#define LCD_LINE3 2
#define LCD_LINE4 3
//Define global variables
T_glyphHandle G_lcd;
int Current_LED;
int ADCResult = 0;
char AD_Flag = 0;
char buffer [30 ];
The only difference here is we have added the AD_Flag variable on line 27. It is initialized
to zero to indicate the interrupt has not been triggered yet.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
1. void main(void){
2.
ENABLE_LEDS
3.
InitADC();
4.
InitTimer();
5.
6.
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
7.
/* use Glyph full access direct functions */
8.
GlyphNormalScreen(G_lcd);
9.
GlyphSetFont(G_lcd, GLYPH_FONT_HELVR10);
10.
GlyphClearScreen(G_lcd);
11.
12.
BSP_Display_String(LCD_LINE1, “ADC Int Flag Example”);
13.
BSP_Display_String(LCD_LINE2, “Potentiometer Value:”);
14.
15.
while(1){
16.
if(AD_Flag){
17.
ADCResult = AD1.ADDRA;
18.
sprintf(buffer, “%d”, ADCResult);
19.
BSP_Display_String(LCD_LINE3, buffer);
20.
AD_Flag = 0;
21.
}
22.
}
23.
}
24.
else{}
25.
26.
GlyphClose(&G_lcd);
27.
28. }
Our main code has only been modified so all code to do with reading the A/D conversion
value and writing it to the LCD has been placed in an If statement. When the AD_Flag variable becomes a 1 or higher this will cue the code to execute, then the flag will be reset to 0.
The code will not execute again until the flag has been set to 1 again.
We won’t cover the InitADC or InitTimer functions again as they are identical to a previous example. We are once again setting a one second interval timer. The timer generates
a Compare Match A signal after one second that resets the timer and sends a signal to the
AD converter to start converting. Once done, the A/D converter will trigger its own interrupt that will call an ISR.
1. void AD1_Interrupt(void){
2.
AD_Flag = 1;
//Set A/D conversion flag
3. }
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
383
Now the A/D conversion ISR will set the flag to one, indicating the conversion is done.
Conclusion: We have effectively altered our old program to use an interrupt and a flag to
indicate data is ready from an external device. The flag now triggers the execution of a
large amount of code in the main program. Keeping this code out of the interrupt service
routine improves responsiveness for other ISRs.
9.6.2
A Simple State Machine Controlled by Interrupts
Aim: Demonstrate a state machine whose state is altered by an interrupt.
Requirements: PC with High-performance Embedded Workshop 4.0 or 4.0, RX62N
Development kit, RX62N Graphical LCD Code package.
Details: In this example, we will set up a state machine on the RX62N. When SW1 is
pressed, the machine will rotate states. In State 1 the LEDs will blink clockwise at a rate of
one LED per second. In State 2 the LCD will display the current ADC reading across the
board’s potentiometer every second. In State 3 the LCD will display the number of seconds
elapsed since the program started. If the switch is pressed again the state will rotate back to
State 1.
Procedure: First we once again need to set up our definitions and global variables:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
#include “iodefine_RX62N.h”
//Glyph Includes
#include <stdlib.h>
#include <stdio.h>
#include “src\Glyph\Glyph.h”
//Define SW1 interrupt
#pragma interrupt (SW1_Int(vect = VECT_IRQ8))
void SW1_Int(void);
//Define interrupt for TMR0 Compare Match A
#pragma interrupt (TMR0_CompareMatchA_Interrupt
(vect = VECT_TMR0_CMIA0))
14. void TMR0_CompareMatchA_Interrupt(void);
15.
16. //Define interrupt for AD1
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
#pragma interrupt (AD1_Interrupt(vect = VECT_AD1_ADI1))
void AD1_Interrupt(void);
//Function definitions
void main(void);
void InitADC(void);
void InitTimer(void);
void EnableIRQ8(void);
void LED_Rotate(void);
void DisplaySec(void);
void DisplayADC(void);
void DisplayLEDs(void);
void BSP_Display_String(int8_t aLine, char *aText);
#define LCD_LINE1 0
#define LCD_LINE2 1
#define LCD_LINE3 2
#define LCD_LINE4 3
//Define global variables
T_glyphHandle G_lcd;
int Current_LED;
int State = 1;
int Second_Flag;
int AD_Flag;
int SecCount;
int ADCResult = 0;
char buffer [30 ];
For this example we will use three ISRs. One each for the switch interrupt, the A/D conversion interrupt, and the TMR0 interrupt. These are defined on lines 8 through 18. On
lines 22 to 24 we define our functions to set up each of these peripherals. We have also defined functions to call to display these on lines 26 through 28. On line 38 we create our
state variable; altering this variable will alter which state we are in. On lines 39 to 40 we
create flags for each interrupt, so when the interrupt is triggered the ISRs will set these
flags, and then the main program will use these to trigger code to handle the events. On
line 41 we create a global variable that counts the number of seconds the program has run.
Now we have our main program code, which is very simple.
1. void main(void){
2.
ENABLE_LEDS
3.
InitADC();
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
385
InitTimer();
EnableIRQ8();
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
/* use Glyph full access direct functions */
GlyphNormalScreen(G_lcd);
GlyphSetFont(G_lcd, GLYPH_FONT_HELVR10);
GlyphClearScreen(G_lcd);
BSP_Display_String(LCD_LINE1, “State Machine”);
while(1){
switch(State){
case 1:
if(Second_Flag){
DisplayLEDs();
Second_Flag = 0;
}
break;
case 2:
if(AD_Flag){
DisplayADC();
AD_Flag = 0;
}
break;
case 3:
if(Second_Flag){
DisplaySec();
Second_Flag = 0;
}
break;
default:
//In the off chance that the State variable is set
to something other than 1 through 3
//we will be informed via this default state.
BSP_Display_String(LCD_LINE1, “Error”);
break;
}
}
}
else{}
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
45.
46.
47. }
GlyphClose(&G_lcd);
First on lines 2 through 5 we call our macros and functions to enable the LEDs and each of
our peripherals (the A/D, timer and SW1). After the code to set up the LCD we enter our
while(1) loop, where the only code we have is our state machine. This is implemented via
a switch statement that uses the state variable to control it. In State 1 we will check the
Second_Flag; every time it is set we will call the DisplayLEDs function which will update
the LCD to display our state and then rotate the LEDs. In State 2 we check the A/D conversion finish flag, as the A/D conversion itself is trigger by the timer interrupt and we
don’t want to write the A/D value until the conversion is finished. When the flag is set, we
will call the DisplayADC function which updates the LCD for the state and displays the
conversion of the voltage across the potentiometer. In State 3 we check the second flag and
once it is set we call the DisplaySec function, which updates our LCD for the state and displays the number of seconds elapsed on the screen.
Now we will go over out peripheral setup functions.
1. void InitADC(void){
2.
MSTP(AD1) = 0;
3.
AD1.ADCSR.BIT.ADIE = 1;
4.
AD1.ADCSR.BIT.ADST = 0;
5.
AD1.ADCSR.BIT.CH = 0x000;
6.
7.
AD1.ADCR.BIT.MODE = 0;
8.
AD1.ADCR.BIT.CKS = 3;
9.
AD1.ADCR.BIT.TRGS = 2;
10.
11.
IPR(AD1,ADI1) = 0x03;
12.
IR(AD1,ADI1) = 0;
13.
IEN(AD1,ADI1) = 1;
14. }
15.
16. void InitTimer(void){
17.
MSTP(TMR0) = 0;
18.
MSTP(TMR1) = 0;
19.
20.
TMR1.TCCR.BIT.CSS = 1;
21.
TMR1.TCCR.BIT.CKS = 5;
22.
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
387
23.
TMR0.TCCR.BIT.CSS = 3;
24.
TMR0.TCR.BIT.CCLR = 1;
25.
26.
TMR0.TCORA = 0x5B;
27.
TMR1.TCORA = 0x6D;
28.
29.
TMR0.TCSR.BIT.ADTE = 1;
30.
TMR0.TCR.BIT.CMIEA = 1;
31.
32.
IPR(TMR0,CMIA0) = 3;
33.
IR(TMR0,CMIA0) = 0;
34.
IEN(TMR0,CMIA0) = 1;
35.
36. }
37.
38. void EnableIRQ8(void){
39.
IEN( ,IRQ8) = 0;
40.
PORT4.ICR.BIT.B0 = 1;
41.
ICU.IRQCR [8 ].BIT.IRQMD = 0x01;
42.
ENABLE_SWITCHES
43.
IPR( ,IRQ8) = 0x03;
44.
IR( ,IRQ8) = 0;
45.
IEN( ,IRQ8) = 1;
46. }
Each of these peripherals is set up as in previous examples so we won’t have to review the
code extensively. AD1 is set up to be triggered every time TMR0 sends it a Compare
Match A signal, once triggered it will convert the voltage across the board’s potentiometer
and then trigger its ISR. TMR0 will generate a Compare Match A signal and trigger its
ISR every second. SW1 will trigger its ISR every time it is pressed via IRQ8.
1.
2.
3.
4.
5.
6.
7.
8.
9.
void DisplayLEDs(void)
{
LED_Rotate();
BSP_Display_String(LCD_LINE2, “State 1”);
BSP_Display_String(LCD_LINE3, “Rotating LEDs”);
BSP_Display_String(LCD_LINE4, “ ”);
}
void DisplayADC(void){
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
10.
ADCResult = AD1.ADDRA;
11.
sprintf(buffer, “%d”, ADCResult);
12.
BSP_Display_String(LCD_LINE2, “State 2”);
13.
BSP_Display_String(LCD_LINE3, “Potentiometer Value:”);
14.
BSP_Display_String(LCD_LINE4, buffer);
15. }
16.
17. void DisplaySec(void){
18.
sprintf(buffer, “%d”, SecCount);
19.
BSP_Display_String(LCD_LINE2, “State 3”);
20.
BSP_Display_String(LCD_LINE3, “Seconds Count:”);
21.
BSP_Display_String(LCD_LINE4, buffer);
22. }
Our display functions are quite similar. As said before, each one updates the LCD and performs necessary actions based on which interrupt it is related to. The DisplayLEDs function calls the LED_Rotate function. The DisplayADC function updates the variable that
contains the conversion result, and converts it to ASCII before sending it to the LCD. The
DisplaySec function merely converts the seconds count variable to ASCII as the variable is
updated in the ISR.
Now we will cover our interrupt functions themselves.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
//Timer 0 Compare Match A Interrupt
void TMR0_CompareMatchA_Interrupt(void){
Second_Flag = 1;
SecCount++;
}
//AD1 Conversion Finished Interrupt
void AD1_Interrupt(void){
AD_Flag = 1;
}
//SW1 Interrupt
void SW1_Int(void){
State++;
if(State >= 4){
State = 1;
}
}
CHAPTER 9 / USING INTERRUPTS WITH PERIPHERALS
389
Each ISR is kept very simple. The TMR0 ISR merely sets the second flag and increments
the count of the number of seconds. The AD1 interrupt only sets its flag. The SW1 interrupt
increments the state, if it is 4 or greater the state is reset to 1.
Once compiled and run the state machine should start off in State 1. The LEDs will
once again rotate on a one second interval with the state displayed on the LCD. Once SW1
is pressed, the state will increment to State 2 where the A/D conversion result from the potentiometer will update on the LCD every one second along with the state information.
When SW1 is pressed again, the seconds count will be displayed on the screen along with
State 3’s info.
9.7
RECAP
In this chapter we have made a broad overview of the interrupt features on the RX62N and
how they can be used with the different peripherals. We started by covering reasons for using an interrupt for tasks as compared to other techniques. Then we covered the full
process of setting up an interrupt as it may apply to any peripheral. In the advanced concepts section we went over the reasons for keeping code minimal in interrupts. Then an example of a full implementation of interrupts was presented by introducing state machines
and then describing a state machine controlled purely by peripheral interrupts.
9.8
REFERENCES
Conrad, James. ECGR 4101 Class Lecture; Topic: “Interrupts, and Using Them in C.” Charlotte, NC:
Department of Electrical and Computer Engineering, University of North Carolina at Charlotte; July,
2010. Lecture.
RX62N Group, RX621 Group Hardware Manual: RX62N Hardware Manual. Renesas Electronics America,
Inc., Feb, 2010. Print.
9.9
EXERCISES
1. You want to set up one of the switches on the RX62N board to trigger an interrupt.
List the registers you need to modify and the values you need to assign to them.
2. List at least three advantages of using an interrupt to signal data ready from a device rather than polling.
3. List at least five examples of an application where using an interrupt to signal data
from a processor peripheral would greatly speed up a program.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
4. Choose one of these examples and write pseudocode explaining how you would
5.
6.
7.
8.
9.
program this. Include descriptions of the interrupt function, your interrupt initialization function, and your main function.
Explain how you would use a flag to signal and process data from a device with an
interrupt.
Why would you use a flag to signal processing of the data in the main program instead of placing all of the code in the interrupt?
What advantages does a state machine approach have over a purely sequential approach to embedded programming?
Give some examples of where a state machine would be a good choice of design
approach.
Choose one of those examples and make a simple state machine design such as the
one in Section 9.5.2, Brief Introduction to State Machines.
Chapter Ten
Floating Point Unit and Operations
10.1
LEARNING OBJECTIVES
All microprocessors can store and operate on integers. However, often we wish to operate
on real numbers. We can represent these values with fixed-point or floating-point approaches. Fixed-point math is nearly as fast as integer math. Its main drawback is that the
designer must understand the sizes of the smallest and largest data values in order to determine the appropriate fixed-point representation. Floating-point math automatically adjusts
the scaling to account for large and small values.
Generally floating-point math is emulated in software, but some microprocessors have
special hardware called a Floating Point Unit (FPU) for executing these operations natively,
greatly increasing the speed. Though the FPU varies with the microcontroller, or with different families of microcontrollers, we will be discussing the FPU in the RX62N microcontroller and comparing it with the software emulation of a FPU on the QSK62P board.
In this chapter the reader will learn:
䡲
䡲
䡲
10.2
The Instruction Set Architecture (ISA) of the RX62N Floating Point Unit
Differences between a fixed point and a floating point operation
Handling floating point exceptions
BASIC CONCEPTS
10.2.1 Floating Point Basics
Floating Point Representation
Before taking a look at the FPU in the RX62N, let’s look at the basics of floating point.
Consider a floating point number, say 241.3247810. It denotes the following.
102
101
100
2
4
1
ⴢ
101
102
103
104
105
3
2
4
7
8
Figure 10.1 Decimal floating point representation.
391
392
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
The number in the box is the significand, 10 is the base and the power to which 10 is raised
is the exponent.
We can represent the above number in exponential form as 2.4132478 102.
Consider a binary number, say 1011.01102. The number can be represented as:
23
22
21
20
1
0
1
1
ⴢ
21
22
23
24
0
1
1
0
Figure 10.2 Binary floating point representation.
We can represent the above binary number in exponential form as 1.0110110 23.
From the above notations, we can generalize the floating point expression as:
(1)sign Significand BaseExponent
Though the decimal floating point representation is simple, it cannot be used by microcontrollers to work on floating point numbers. Since they work on binary digits, the
IEEE 754 Floating Point Standard was introduced to represent decimal numbers as binary
numbers.
IEEE 754 Floating Point Standard
In order to standardize floating point arithmetic, the IEEE 754 floating point standard was
first introduced in 1985. Though the current version of IEEE 754 is IEEE 754–2008, it includes the original information in IEEE 754–1985 as well.
The binary floating point numbers represented by IEEE 754 are in sign magnitude form
where the most significant bit is the sign bit followed by the biased exponent and significand
without the most significant bit. The field representation of IEEE 754 is as follows.
Sign
Exponent
Significand
Figure 10.3 IEEE 754 floating point representation.
The IEEE 754 defines four formats for representing floating point values.
䡲
䡲
Single-Precision (32 bit)
Double Precision (64 bit)
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
䡲
䡲
393
Single Extended Precision ( 43 bit, not commonly used)
Double Extended Precision ( 79 bit, not commonly used)
The IEEE 754 Floating Point Standard
Though the number of bits varies in each precision, the format for representing the floating
point number is the same. The format for representing a floating point number according to
IEEE 754 is as follows.
(1)sign (1 Significand) 2Exponent-Bias
Since we will not be using Single Extended Precision and Double Extended Precision, we
will look at Single Precision and Double Precision in detail.
Single Precision (32 bits)
Single Precision consists of 4 bytes (or) 32 bits, where the 32 bits are divided into the following fields.
1 bit
8 bits
23 bits
Sign
Exponent
Significand
Figure 10.4 IEEE 754 single precision floating point representation.
In order to obtain the Single Precision representation, a few general steps are to be
followed.
䡲
䡲
䡲
䡲
䡲
Convert the decimal into a binary number.
Express the binary number in normalized exponential notation. Since we are representing binary numbers, the power will be raised to 2, which is the base.
Since we need to represent the exponent as an 8 bit binary number, we add 127 to
the exponent in the normalized notation if the number we need to represent is
positive.
If the number we need to represent is negative, we subtract the exponent in the normalized notation from 127.
Having done that, we add the significand bits by extending it to 23 bits.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
EXAMPLE 1
A decimal number can be represented as a Single Precision number as follows. Consider a
number, say 10.010
10.010 1010 20 or 1.010 23
In the above number 1.010 23, the significand is 010 as the number before the decimal
point will always be 1. Since the significand here does not have a specific pattern of repetition, the 23 bit significand field will be the significand appended with zeroes at the end.
From the above number:
Sign Bit: 0 (Since the number is positive).
Exponent: 127 3 130. For simplification, let’s split 130 as 128 2. As 128 is
nothing but 8-bit or 100000002
12810 210 100000002 000102 100000102
Significand: 0100 0000 0000 0000 0000 000 (010 appended with zeroes)
From the Single Precision field representation, we can represent this number as:
1 bit
8 bits
23 bits
0
10000010
0100 0000 0000 0000 0000 000
Figure 10.5 Example 1; single precision conversion.
EXAMPLE 2
Consider a negative floating point number, say 0.110.
0.110 0.000110011 20 or 1.10011 24
In the binary number 1.10011, the 0011 pattern is repeated. Since the number has a pattern
which gets repeated, the significand is 1 followed by a pattern of 0011.
Therefore, from the above number:
Sign Bit: 1 (Since the number is negative)
Exponent: 127 4 123
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
395
Since 123 is less than 128, we cannot adopt the technique used in Example 10.1.
We know 12310 0111 10112
Significant: 1001 1001 1001 1001 1001 100
From the Single Precision field representation, we can represent this number as,
1 bit
8 bits
23 bits
1
0111 1011
1001 1001 1001 1001 1001 100
Figure 10.6 Example 2; single precision conversion.
Double Precision (64 bits)
Double Precision consists of 8 bytes (or) 64 bits, where the 64 bits are divided into the following fields.
1 bit
11 bits
52 bits
Sign
Exponent
Significand
Figure 10.7 IEEE 754 double precision floating point representation.
Obtaining the Double Precision numbers, follow the same steps we adopted for Single Precision numbers but with different bits.
In order to obtain the Double Precision representation, the following steps are adopted:
䡲
䡲
䡲
䡲
䡲
Convert the decimal into a binary number.
Express the binary number in normalized exponential notation. Since we are representing binary numbers, the power will be raised to 2, which is the base.
Since we need to represent the exponent as an 11 bit binary number, we add
1023 to the exponent in the normalized notation if the number we need to represent is positive.
If the number we need to represent is negative, we subtract the exponent in the normalized notation from 1023.
Having done that, we add the significand bits which is 52 bits wide.
396
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
EXAMPLE 3
Consider Example 10.1. To represent the number 1010 to a Double Precision number, we
do the following.
10 1010 20 or 1.010 23
In the above number 1.010 23, the significand is 010 as the number before the decimal
point will always be 1. Since the significand here does not have a specific pattern of repetition, the 52 bit significand field will be the significand appended with zeroes at the end.
From the above number,
Sign Bit: 0 (Since the number is positive).
Exponent: 1023 3 102610 100000000102
Significand: 0100 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000
(010 appended with zeroes)
From the Double Precision field representation, we can represent this number as:
1 bit
11 bits
52 bits
0
10000000010
0100 0000 0000 0000 0000 0000
0000 0000 0000 0000 0000 0000
0000
Figure 10.8 Example 3; double precision conversion.
EXAMPLE 4
Consider Example 10.2. To represent the number 0.110 to a Double Precision number, we
do the following:
0.1 0.00011 20 or 1.10011 24
Therefore, from the above number,
Sign Bit: 1 (Since the number is negative)
Exponent: 1023 4 1019
101910 011111110112
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
397
Significand: 1001 1001 1001 1001 1001 1001 1001 1001 1001 1001 1001 1001 1010
From the Double Precision field representation, we can represent this number as:
1 bit
11 bits
52 bits
1
01111111011
1001 1001 1001 1001 1001 1001
1001 1001 1001 1001 1001 1001
1010
Figure 10.9 Example 4; double precision conversion.
10.2.2 Pipelining Basics
In order to understand the floating point operations in microcontrollers and the difference
between fixed point and floating point operations, it is necessary to take a look at the some
of the basics of pipelining.
Pipelining is the technique adopted for increasing the instruction throughout and reducing the number of clock cycles required to execute an instruction by microprocessors. It is a
method of realizing temporal parallelism, an assembly line processing technique. The instruction is broken down into a sequence of sub-tasks, each of which can be executed concurrently with other stages in the pipeline. The basic instruction cycle consists of five stages:
䡲
䡲
䡲
䡲
䡲
Instruction Fetch
Instruction Decode
Execute
Memory Access
Write Back
IF
ID
EX
MEM
WB
Figure 10.10 A basic pipeline.
Instruction Fetch
䡲
䡲
The Instruction Fetch (IF) cycle fetches the current instruction from the memory
into the program counter (PC).
It updates the PC to the next sequential instruction.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Instruction Decode
䡲
䡲
䡲
The Instruction Decode cycle (ID) decodes the instruction and reads the registers
corresponding to the specified register source.
It performs an equality test of registers for a possible branch.
The decoding is done in parallel with reading registers.
Execution
The Execution (EX) cycle does the following:
䡲
䡲
䡲
Memory Reference—Calculates effective address.
Register—Register Operation—ALU performs the operation specified by the
ALU opcode on the values read from the register file.
Register-Immediate Operation—Operation specified by the ALU on the value read
from the register and the sign-extended immediate.
Memory Access
The Memory Access (MEM) cycle does the following operations:
䡲
䡲
Load—A read operation performed by the memory using the calculated effective
address.
Store—A write operation performed by the memory from the register read from
the register file using the effective address.
Write-Back
䡲
The Write-Back (WB) cycle writes the result into the register file, whether it
comes from the memory system (load) or from the ALU (ALU instruction).
10.2.3 Floating Point in RX62N
In order to handle floating point operations, RX62N has the following:
䡲
䡲
䡲
䡲
A Floating Point Unit
Floating Point Instructions
Floating Point Registers
Floating Point Exceptions
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
399
Floating Point Unit
The Floating Point Unit (FPU) in RX62N operates on Single Precision floating point operands
(32-bit) and the data-types and floating point exceptions conform to the IEEE 754 standard.
This implementation facilitates the FPU to operate directly on the CPU registers rather than
the dedicated register sets, thereby avoiding extra load/store operations and improving the performance. Figure 10.11 shows the floating point unit architecture in RX62N.
General
register
Traditional
FPU operation
using
dedicated
data registers
General register
No load/store
instruction
needed
RX operation
using general
registers
Floatingpoint unit
Load/store
Dedicated
data register
Floatingpoint unit
Figure 10.11 Architecture used by RX62N with dedicated registers for floating point
operations.
Floating Point Registers
The RX62N uses a single floating point register, Floating-Point Status Word (FPSW) to indicate the results of the floating-point operations. It is a 32-bit register consisting of flags,
bits representing modes for rounding off floating point numbers, exception enable/disable
bits and reserved bits. Figure 10.12 shows the FPSW bits and Table 10.1 shows the bit definitions for the FPSW.
Value after reset:
Value after reset:
b31
b30
b29
b28
b27
b26
b25
b24
b23
b22
b21
b20
b19
b18
b17
b16
FS
FX
FU
FZ
FO
FV
—
—
—
—
—
—
—
—
—
—
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
b15
b14
b13
b12
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
—
EX
EU
EZ
EO
EV
—
DN
CE
CX
CU
CZ
CO
CV
RM[1:0]
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
Figure 10.12 Floating-point status word. Source: Software Manual, Renesas 32-Bit Microcomputer, RX Family/RX600
Series, Renesas Electronics America, Inc., 2010, Section 2.2.2.8.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
TABLE 10.1
BIT
SYMBOL
b1, b0
RM[1⬊0]
Floating-Point Status Word Bit Definition.
BIT NAME
Floating-point
rounding-mode
setting bits
DESCRIPTION
b1 b0
R/W
R/W
0 0: Round to the nearest value
0 1: Round towards 0
1 0: Round towards ⬁
1 1: Round towards ⬁
b2
CV
Invalid operation
cause flag
0: No invalid operation has been
encountered.
R/(W)*1
1: Invalid operation has been encountered.
b3
b4
b5
b6
CO
CZ
CU
CX
Overflow cause
flag
0: No overflow has occurred.
Division-by-zero
cause flag
0: No division-by-zero has occurred.
Underflow cause
flag
0: No underflow has occurred.
Inexact cause flag
0: No inexact exception has been generated.
R/(W)*1
1: Overflow has occurred.
R/(W)*1
1: Division-by-zero has occurred.
R/(W)*1
1: Underflow has occurred.
R/(W)*1
1: Inexact exception has been generated.
b7
b8
b9
CE
DN
—
R/(W)*1
Unimplemented
processing cause
flag
0: No unimplemented processing has been
encountered.
0 flush bit of
denormalized
number
0: A denormalized number is handled as a
denormalized number.
R/W
1: A denormalized number is handled
as 0.*2
R/W
Reserved
When writing, write 0 to this bit. The value
read is always 0.
R/W
1: Unimplemented processing has been
encountered.
Source: Software Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series, Renesas Electronics America, Inc., 2010,
Section 2.2.2.8.
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
401
Floating Point Instructions
The RX62N uses eight floating point instructions to perform floating point operations. All
floating point instructions work on single precision floating point operands conforming to
IEEE754 standard. The floating point instructions are as follows:
FADD
Function: Adds two floating point operands and stores the result in the register file.
Operations performed: Immediate-Register and Register-Register.
Number of cycles taken: Four.
FADD Operation:
FADD R2, R4
IF
D
(mop) fadd-1
E
D
E
D
(mop) fadd-2
E
D
(mop) fadd-3
E
WB
(mop) fadd-4
Write to R4
Figure 10.13 FADD Operation (Register-Register, Immediate-Register). Source: Hardware Manual,
Renesas 32-Bit Microcomputer, RX Family/RX600 Series, Renesas Electronics America, Inc., 2010, Figure 2.19.
FSUB
Function: Subtracts the second floating point operand from the first floating point
operand and stores the result in the register file.
Operation performed: Immediate-Register, Register-Register.
Number of cycles taken: Four.
FSUB Operation:
FSUB R2, R3
IF
D
(mop) fsub-1
E
D
E
D
(mop) fsub-2
E
D
(mop) fsub-3
E
WB
(mop) fsub-4
Write to R3
Figure 10.14 FSUB Operation (Register-Register, Immediate-Register). Source: Hardware Manual.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
TABLE 10.1
Floating-Point Status Word Bit Definition.—Continued
BIT
SYMBOL
BIT NAME
b10
EV
Invalid operation
exception enable
bit
0: Invalid operation exception is masked.
Overflow
exception enable
bit
0: Overflow exception is masked.
Division-by-zero
exception enable
bit
0: Division-by-zero exception is masked.
Underflow
exception enable
bit
0: Underflow exception is masked.
Inexact exception
enable bit
0: Inexact exception is masked.
Reserved
When writing, write 0 to these bits. The value
read is always 0.
R/W
Invalid operation
flag
0: No invalid operation has been
encountered.
R/W
b11
b12
b13
B14
EO
EZ
EU
EX
b25 to
b15
—
b26
FV*3
DESCRIPTION
R/W
R/W
1: Invalid operation exception is enabled.
R/W
1: Overflow exception is enabled.
R/W
1: Division-by-zero exception is enabled.
R/W
1: Underflow exception is enabled.
R/W
1: Inexact exception is enabled.
1: Invalid operation has been
encountered.*8
b27
FO*4
Overflow flag
0: No overflow has occurred.
R/W
*8
1: Overflow has occurred.
b28
FZ*5
b29
*6
FU
Division-by-zero
flag
0: No division-by-zero has occurred.
Underflow flag
0: No underflow has occurred.
R/W
1: Division-by-zero has occured
R/W
1: Underflow has occurred.*8
b30
FX*7
Inexact flag
0: No inexact exception has been generated.
R/W
*8
1: Inexact exception has been generated.
b31
FS
Floating-point
error summary
flag
This bit reflects the logical OR of the FU, FZ,
FO, and FV flags.
R
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
403
FCMP
Function: Compares the floating point operands and updates the status register based on
the results. The difference between FSUB and FCMP is that, FCMP does not store the result anywhere.
Operation performed: Immediate-Register, Register-Register.
Number of cycles taken: Four.
FSUB Operation:
FSUB R2, R3
IF
D
(mop) fsub-1
E
D
E
D
(mop) fsub-2
E
D
(mop) fsub-3
E
WB
(mop) fsub-4
Write to R3
Figure 10.15 FSUB Operation (Register-Register, Immediate-Register). Source: Hardware Manual.
Floating Point Exceptions
The floating point exceptions are basically exceptions which arise due to inappropriate
floating point operations. According to IEEE 754 standard, there are five floating-point exceptions as follows:
䡲
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Overflow
Underflow
Inexact
Division-by-zero
Invalid Operation
Overflow
This exception occurs when the result of a floating-point operation is too large. Under such
circumstances, the result cannot be represented as a single-precision floating point number
(32 bit) or a double precision floating point number (64 bit).
䡲
The limits for signed single precision floating point numbers are 3.4E 38 to
3.4E 38.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
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The limits for unsigned single precision floating point numbers are 0 to 6.8E38.
The limits for signed double precision floating point numbers are 1.7E 308 to
1.7E 308.
The limits for unsigned double precision floating point numbers are 0 to
3.4E 308.
If the result exceeds these limits, an overflow exception is raised.
Underflow
This exception occurs when the result is too small to be represented as a normalized
floating-point number.
Inexact
This exception occurs when the result is not a single-precision floating point number.
Rounding off the result and using it as a single-precision floating point number may cause
this exception.
Divide-By-Zero
This exception occurs when a floating point number is divided by zero.
Invalid Operation
This exception occurs when the result is ill-defined. For example, an operation leading to a
result which is ⬁ (Infinty) or NaN (Not a number) could cause this exception.
For example, 1.0 / 0.0 ⬁, 0.0 / 0.0 NaN.
10.3
BASIC EXAMPLES
10.3.1 Operations Explaining Floating Point Exceptions
Before working on the RX62N’s FPU, it is important to take a look at the operations causing Floating Point Exceptions, so that they can be handled efficiently. The Floating-point
error summary flag (FS) notifies the programmer that an error (overflow, underflow, invalid
operation, inexact, or division-by-zero) has occurred.
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
405
EXAMPLE 1
Overflow Exception
Consider the following example:
1. float a, c;
2. a = 999999969999999923.235;
3. c = a * 9999999999999969999999923.235;
The above operation causes an Overflow exception. To observe this exception, the contents
of the FPSW can be viewed.
Click on the
(Registers icon) in the CPU Toolbox.
Figure 10.16 CPU toolbox.
For the above example, the FPSW was C8000100, where the Radix is Hexadecimal.
C8000100
0000
0000
0001
DN 5 1
0000
0000
0000
1000
FO 5 1
1100
FX 5 1
FS 5 1
Figure 10.17 Example 1; FPSW.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
From the above example:
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䡲
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DN 1, where a denormalized number is handled as 0.
FO 1, where an overflow exception has occurred.
FX 1, where an inexact exception has been generated.
FS 1, where the logical OR of the exception flags, except inexact exception, is 1;
meaning an overflow/underflow/divide-by-zero/invalid operation exception flag
has been set.
EXAMPLE 2
Underflow Exception
Consider the following example:
1. float a, c;
2. a = 0.00000000000000000000000000000005623;
3. c = a * 0.00000000000000000000000001235431435234;
The above operation causes an Underflow Exception. The FPSW has the following value.
A0000120
0000
0010
CU 5 1
0001
DN 5 1
0000
0000
0000
0000
1010
FU 5 1
FS 5 1
Figure 10.18 Example 2; FPSW.
From the above example:
䡲
䡲
CU 1, where an underflow operation has occurred.
DN 1, where a denormalized number is handled as 0.
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
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407
FU 1, where an underflow exception has occurred and the underflow flag has
been set.
FS 1, where the logical OR of the exception flags, except inexact exception, is 1;
meaning an overflow/underflow/divide-by-zero/invalid operation exception flag
has been set.
EXAMPLE 3
Divide-by-Zero Exception
Consider the following example:
1. float a, c;
2. a = 1.2;
3. c = a / 0;
The above code returns a divide-by-zero exception and the FPSW has the following value.
90000100
0000
0000
0001
DN 5 1
0000
0000
0000
0000
1001
FZ 5 1
FS 5 1
Figure 10.19 Example 3; FPSW.
From the above example:
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䡲
䡲
DN 1, where a denormalized number is handled as 0.
FZ 1, where Division-by-zero flag has been set.
FS 1, where the Floating-point error summary flag has been set.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
EXAMPLE 4
Invalid Operation
Consider the following example:
1. float c;
2. c = 0.0 / 0.0;
The above code returns an Invalid Operation and the FPSW has the following value.
84000104
0100
CV 5 1
0000
0001
DN 5 1
0000
0000
0000
0100
1000
FV 5 1
FS 5 1
Figure 10.20 Example 4; FPSW.
From the above example:
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䡲
䡲
䡲
10.4
CV 1, where an invalid operation has occurred.
DN 1, where a denormalized number is handled as 0.
FV 1, where an invalid operation exception has occurred and the invalid operation flag has been set.
FS 1, where the the floating-point error summary flag has been set.
ADVANCED CONCEPTS OF RX62N FLOATING POINT UNIT
10.4.1 FPSW in Detail
In order to perform complex floating point operations and handle floating point exceptions,
a detailed knowledge about the FPSW is important. The bits in the FPSW can be categorized as follows:
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
409
Rounding-Modes
Using the RM bits in the FPSW, the floating point value or the result can be rounded to
0, ⬁, ⬁ or the nearest value. The bits b0 and b1 in the RM represent the roundingmode. By default, the values are rounded towards the nearest absolute value. Consider
Table 10.2, for RM bit definitions.
TABLE 10.2
BIT
SYMBOL
b1, b0
RM[1⬊0]
RM Bit Definitions in FPSW.
BIT NAME
Floating-point rounding-mode
setting bits
DESCRIPTION
b1 b0
0 0: Round to the nearest value
0 1: Round towards 0
1 0: Round towards ⬁
1 1: Round towards ⬁
Source: Software Manual, page 24.
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Round to the nearest value: With this rounding-mode, the inexact value or the inexact result is rounded to the nearest absolute value. If two absolute values are
equally close, the result is the one with the even alternative.
Round towards 0: With this rounding mode, the inexact value or the inexact result
is rounded to the smallest available absolute value in the direction of zero.
Round towards ⬁: The inexact value is rounded to the nearest available value in
the direction of ⬁.
Round towards ⬁: The inexact value is rounded to the nearest available value in
the direction of ⬁.
Cause Flags
In order to handle the floating point exceptions and floating point exceptions that are generated upon detection of unimplemented processing, the cause flags are used. When a
cause flag is set to 1, it means a corresponding exception has occurred. The bit that has
been set to 1 is cleared to 0 when an FPU instruction is executed.
The Cause Flags in the FPSW are:
䡲
䡲
Invalid Operation Exception Cause Flag (CV)
Overflow Exception Cause Flag (CO)
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
䡲
䡲
Underflow Exception Cause Flag (CU)
Divide-By-Zero Exception Cause Flag (CZ)
Inexact Exception Cause Flag (CX)
Unimplemented Processing Cause Flag (CE)
Exception Flags
The Exception Flags are used to indicate the occurrence of exceptions. If the exception flag
is set to 1, it means the corresponding error has occurred. The exception flags available in
the FPSW are:
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䡲
䡲
Invalid Operation Flag (FV)
Overflow Flag (FO)
Underflow Flag (FU)
Division-by-zero flag (FZ)
Inexact Flag (FX)
Exception Handling Enable Bits
When any of the five floating point exceptions occur, the bit decides whether the CPU will
start handling the exception. When the bit is set to 0, the exception handling is masked.
When the bit is set to 1, exception handling is enabled.
The Exception Handling bits in the FPSW are:
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䡲
䡲
䡲
䡲
Invalid Operation Exception Enable bit (EV)
Overflow Exception Enable bit (EO)
Underflow Exception Enable bit (EU)
Divide-by-zero Exception Enable bit (EZ)
Inexact Exception Enable bit (EX)
Denormalized Number Bit
A denormalized number is a number of the form 1 an, where a is the base of the number (2 for decimal numbers and 10 for binary numbers) and n is the exponent.
When the denormalized number bit (DN) is set to 1, a denormalized number is handled
as 0. When the DN bit is set to 0, the denormalized number is handled as a denormalized
number.
From the basic examples, it can be seen that the DN bit is set to 1 when an Overflow,
Underflow, Invalid Operation, or a Divide-by-zero exception occurs. This denotes that the
result of the operation cannot be handled as a denormalized number.
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
411
Floating Point Error Summary Flag
The Floating Point Error Summary flag (FS) bit represents the logical OR of the following
Exception flags:
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䡲
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Invalid Operation Exception
Overflow Exception
Underflow Exception
Divide-by-Zero Exception
Since the occurrence of inexact operation is common and is taken care of by the RM bits
under certain circumstances, the FS bit does not reflect the occurrence of an inexact
operation.
Reserved Bits
The reserved bits are restricted for the programmer, as they are used by the microcontroller
itself. The reserved bits have a value of 0.
10.4.2 Floating Point Exception Handling Procedure
Though the floating-point exceptions appear similar to other exceptions, the handling routine for the floating-point exceptions vary slightly from that of other instructions. Floatingpoint exceptions are of the lowest priority and handling the exceptions can be classified as
follows:
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䡲
䡲
䡲
Acceptance of the exception
Hardware pre-processing
Processing of the user-written code
Hardware post-processing
Acceptance of the Exception
When a floating-point exception occurs, the CPU suspends the execution of the current
instruction and stores the PC value of the instruction that is generated by the exception
on the Stack. It is for this reason; the floating-point instruction is of instruction canceling type.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Hardware Pre-Processing
The following steps take place during hardware pre-processing:
䡲
䡲
䡲
䡲
Preserving the PSW
The value of the PSW is stored in the stack.
PSW V Stack
Updating the PSW
The following bits are updated:
▫ IV0
▫ UV0
▫ PM V 0
Preserving the PC
The value of the PC is stored in the stack.
PC V Stack
Updating the PC
The PC is updated with branch-destination address fetched from the vector address
FFFFFFE4h in the fixed vector table. The processing is then shifted to the exception handling routine.
Processing of User-Written Program Code
The following steps take place while processing user-written code.
䡲
䡲
䡲
䡲
Preserving general purpose registers
The contents of the general purpose registers are stored in the stack.
General purpose registers V Stack
User code execution
Corresponding user code is executed. In general, the code is inserted in the
Excep_FloatingPoint() interrupt/function.
General Purpose registers restoration
The contents of the general purpose registers are stored in the stack.
Stack V General purpose registers
RTE Execution
After restoring the contents of the general-purpose registers, the Return from Exception (RTE) is executed. This marks the end of exception handling. Following
this step will be hardware post-processing.
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
413
Gereation of an exception event request
Exception request
Instruction Instruction Instruction
A
B
C
The program is suspended
and the exception
is accepted
(For exceptions other than the fast interrupt)
PC V Preserved on the stack (ISP)
PSW V Preserved on the stack (ISP)
U50
I50
PM 5 0
.. .. .
• Instruction canceling type
(UND, PIE, ACE, and FPE)
• Instruction suspending type
(Reception of an EI during execution of the RMPA
instruction or a string manipulation instruction)
• Instruction completion type
(EI and TRAP)
Transition to the user mode when the
PM bit in the PSW is 1
Hardware pre-processing
(For the fast interrupt)
PC V BPC
PSW V BPSW
U50
I50
PM 5 0
Restarting of the program
Instruction Instruction
C
D
Switch to the
supervisor mode
(For the fast interrupt)
BPC V PC
BPSW V PSW
(For exceptions other than the fast interrupt)
Stack V PC
Stack V PSW
Hardware post-processing
Read the
vector.
Branch to the
start of the
handler.
Exception handling
routine other than
the non-maskable
interrupt
Non-maskable
interrupt
[Legend]
UND:
PIE:
ACE:
FPE:
EI:
TRAP:
Processing of user-written program code
Generalpurpose
registers
preserved on
the stack
Non-maskable
interrupt processing
Handler
processing
Restoration
of generalpurpose
registers
(For the fast interrupt)
RTFI instruction
(For exceptions other than
the fast interrupt)
RTE instruction
End of the program or resetting of the system
Undefined instruction exception
Privileged instuction exception
Access exception
Floating-point exception
Interrupt
Unconditional trap
Figure 10.21 Exception handling procedure. Source: Software Manual, page 258.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Hardware Post-Processing
The following steps take place during hardware post-processing:
䡲
䡲
Restoring PC
The contents of the PC are restored from the Stack.
Stack V PC.
Restoring PSW
The contents of the PC are restored from the Stack.
Stack V PC.
Following the exception handling routine, the program is restarted. Figure 10.21 explains
the exception handling procedure.
10.5
ADVANCED EXAMPLES
10.5.1 Fixed-Point and Floating-Point Operation Time Calculation
This example calculates the time taken for a single fixed-point operation and the time taken
for a single floating point operation based on switch presses. For example, if Switch 1 is
pressed, an Integer operation is carried out and the time taken for the operation is displayed.
In order to calculate the operation time, we need a timer. Let’s say we are using Timer 0
(TMR0), with a clock source of PCLK/2 (to be more precise). In order to calculate the time
taken, we initialize the timer and reset the Timer Counter (TCNT). The following would be
the function to initialize the timer.
1. void Init_Timer(void)
2. {
3.
MSTP(TMR0) = 0;
//Activate TMR0
4.
TMR0.TCCR.BIT.CSS = 1;
//Count source is PCLK/2
5.
TMR0.TCCR.BIT.CKS = 1;
6.
TMR0.TCNT = 0x00;
//Reset TCNT
7. }
We will also need a function to reset the timer, which will deactivate the timer unit and reset the timer counter.
1. void Reset_Timer(void)
2. {
3.
MSTP(TMR0) = 1;
//Deactivate TMR0
4.
TMR0.TCNT = 0x00;
//Reset TCNT
5. }
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
The following code would be the main function:
1. void main(void)
2. {
3.
char str [30 ];
4.
int i;
5.
long int int1, int2, int3;
6.
float float1, float2, float3;
7.
double double1, double2, double3;
8.
9.
int1 = 2; int2 = 3;
10.
float1 = 2.0; float2 = 3.0;
11.
double1 = 2.0; double2 = 3.0;
12.
13.
ENABLE_LEDS;
14.
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
15.
/* use Glyph full access direct functions */
16.
GlyphNormalScreen(G_lcd);
17.
GlyphSetFont(G_lcd, GLYPH_FONT_6_BY_13);
18.
GlyphClearScreen(G_lcd);
19.
}
20.
while(1)
21.
{
22.
if(SW1 == 0)
//If SW1 pressed
23.
{
24.
Init_Timer();
25.
for(i = 0; i < 10; i++)
26.
int3 = (int1 * int2);
27.
sprintf((char *)str, “C:%d”, TMR0.TCNT);
28.
Reset_Timer();
29.
BSP_Display_String(LCD_LINE3, str);
30.
}
31.
32.
else if(SW2 == 0)
33.
{
34.
Init_Timer();
35.
for(i = 0; i < 10; i++)
36.
float3 = (float1 * float2);
37.
sprintf((char *)str, “C:%d”, TMR0.TCNT);
38.
Reset_Timer();
39.
BSP_Display_String(LCD_LINE3, str);
415
416
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62. }
}
else if(SW3 == 0)
{
Init_Timer();
for(i = 0; i < 10; i++)
double3 = (double1 * double2);
sprintf((char *)str, “C:%d”, TMR0.TCNT);
Reset_Timer();
BSP_Display_String(LCD_LINE3, str);
}
}
else
{
sprintf((char *)str, “Press any Switch”);
BSP_Display_String(LCD_LINE1, str);
sprintf((char *)str, “to continue!”);
BSP_Display_String(LCD_LINE2, str);
}
GlyphClose(&G_lcd);
In the previous code, consider the snippet from Line 22 to Line 30:
22. if(SW1 == 0)
//If SW1 pressed
23. {
24.
Init_Timer();
25.
for(i = 0; i < 10; i++)
26.
int3 = (int1 * int2);
27.
sprintf((char *)str, “C:%d”, TMR0.TCNT);
28.
Reset_Timer();
29.
BSP_Display_String(LCD_LINE3, str);
30. }
Line 24 initiates the timer and starts counting. Line 25 and line 26 perform integer multiplication for ten iterations. Since the time taken for iteration would be less, we consider ten
iterations and divide the result by ten. Similar to the above code snippet, the multiplication
operation is performed for float and double, and the value of the counter is found.
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
417
From the above code, it was found that the operations performed take the following
time:
Int
Timer Count 80
Time Taken Since we use
Timer Count
PCLK
a10 b
2
PCLK
clock and we perform ten iterations, we divide the timer count by
2
PCLK
(PCLK 16.5 MHz here).
2
Therefore,
10 and
Time Taken 80
0.9696 microseconds
16.5
a10 b
2
Float
Timer Count 90
Therefore,
Time Taken 90
1.0909 microseconds
16.5
a10 b
2
Double
Timer Count 90
Therefore,
Time Taken 90
1.0909 microseconds
16.5
a10 b
2
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
From the above example, the time taken for a floating point operation in the RX62N processor was found to be 1.0909 micro-seconds.
To observe the floating point instructions, one could follow the Source Address and
view the corresponding Disassembly by clicking the
(View Disassembly) icon.
For example, consider the following figure.
266
227
FFFFCFFA
FFFFD006
f(i – 0; i < 10; i++)
float3 = (float1 * float2);
Figure 10.22 Code snippet in view source tab.
The above code generates the following assembly code after building/compilation:
FFFFD006
FFFFD009
FFFFD00B
FFFFD00E
FFFFD011
FFFFD014
FFFFD016
FFFFD019
FFFFD01C
FFFFD01E
ED0E0C
AB0D
FC8FF5E
E70E0E
ED0E08
621E
E70E08
ED0E08
61AE
29E8
MOV.L
MOV.L
FMUL
MOV.L
MOV.L
ADD
MOV.L
MOV.L
CMP
BLT.B
30H [R0 ],R14
34H [R0 ],R5
R5,R14
R14,38H [R0 ]
20H [RO ],R14
#1H,R14
R14,20H [R0 ]
20H [R0 ],R14
#0AH,R14
0FFFFD006H
Figure 10.23 Assembly code in view disassembly tab.
10.5.2 Matrix Multiplication Time Calculation
Similar to the above example, let’s examine the time taken to calculate a simple 3 3 matrix.
In order to choose between int, float, and double, let’s use the following code for userfriendliness:
1. void Init_Display()
2. {
3.
char str [30 ];
4.
sprintf((char *)str, “Matrix Mult”);
5.
BSP_Display_String(LCD_LINE1, str);
6.
7.
sprintf((char *)str, “SW1: Int”);
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
8.
9.
10.
11.
12.
13.
14.
15. }
419
BSP_Display_String(LCD_LINE2,str);
sprintf((char *)str, “SW2: Float”);
BSP_Display_String(LCD_LINE3,str);
sprintf((char *)str, “SW3: Double”);
BSP_Display_String(LCD_LINE4,str);
The previous code allows the user to choose the operation to perform. Pressing SW1 performs matrix multiplication with integer variables, whereas pressing SW2 and SW3 performs matrix multiplication using single precision and double precision floating point
variables.
16. void int_Multiply(int matA [3 ] [3 ], int matB [3 ] [3 ], int
matC [3 ] [3 ],)
17. {
18.
int i, j, k;
19.
for(i = 0; i < 3; i++)
20.
for(j = 0; j < 3; j++)
21.
for(k = 0; k < 3; k++)
22.
matC [i ] [j ] += matA [i ] [k ] * matB [k ] [j ];
23. }
24.
25. void float_Multiply(float matA [3 ] [3 ], float matB [3 ] [3 ], float
matC [3 ] [3 ])
26. {
27.
int i, j, k;
28.
for(i = 0; i < 3; i++)
29.
for(j = 0; j < 3; j++)
30.
for(k = 0; k < 3; k++)
31.
matC [i ] [j ] += matA [i ] [k ] * matB [k ] [j ];
32. }
33. void dbl_Multiply(double matA [3 ] [3 ], double matB [3 ] [3 ], double
matC [3 ] [3 ])
34. {
35.
int i, j, k;
36.
for(i = 0; i < 3; i++)
37.
for(j = 0; j < 3; j++)
38.
for(k = 0; k < 3; k++)
39.
matC [i ] [j ] += matA [i ] [k ] * matB [k ] [j ];
40. }
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
In the previous code, lines 16 through 23 perform matrix multiplication using integers,
lines 24 through 31 perform matrix multiplication using single-precision floating-point
numbers, and lines 32 through 39 perform matrix multiplication using double precision
floating-point numbers.
We use the Init_Timer() and Reset_Timer() functions discussed in the previous example to activate and deactivate the timer unit.
The main function would be as follows:
41. void main(void)
42. {
43.
char str [30 ];
44.
int i, j;
45.
int Timer_Count;
46.
float time;
47.
int int_matA [3 ] [3 ], int_matB [3 ] [3 ];
48.
int int_matC [3 ] [3 ],
49.
float float_matA [3 ] [3 ], float_matB [3 ] [3 ];
50.
float float_matC [3 ] [3 ],
51.
double dbl_matA [3 ] [3 ], dbl_matB [3 ] [3 ];
52.
double dbl_matC [3 ] [3 ],
53.
for(i = 0; i < 3; i++)
54.
for(j = 0; j < 3; j++)
55.
int_matA [i ] [j ] = j * 2;
56.
for(i = 0; i < 3; i++)
57.
for(j = 0; j < 3; j++)
58.
int_matB [i ] [j ] = (9 - j) * 2;
59.
for(i = 0; i < 3; i++)
60.
for(j = 0; j < 3; j++)
61.
float_matA [i ] [j ] = j * 1.1;
62.
for(i = 0; i < 3; i++)
63.
for(j = 0; j < 3; j++)
64.
float_matB [i ] [j ] = (9 - j) * 1.1;
65.
for(i = 0; i < 3; i++)
66.
for(j = 0; j < 3; j++)
67.
dbl_matA [i ] [j ] = j * 1.1;
68.
for(i = 0; i < 3; i++)
69.
for(j = 0; j < 3; j++)
70.
dbl_matB [i ] [j ] = (9 - j) * 1.1;
71.
if(GlyphOpen(&G_lcd, 0) == GLYPH_ERROR_NONE){
72.
/* use Glyph full access direct functions */
73.
GlyphNormalScreen(G_lcd);
74.
GlyphSetFont(G_lcd, GLYPH_FONT_6_BY_13);
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
103.
104.
105.
106.
107.
108.
109.
110.
111.
112.
113.
114.
115. }
GlyphClearScreen(G_lcd);
}
Init_Display();
while(1)
{
if(SW1 == 0)
{
GlyphClearScreen(G_lcd);
Init_Timer();
int_Multiply(int_matA, int_matB, int_matC);
Timer_Count = TMR0.TCNT;
Reset_Timer();
sprintf((char *)str, “Count:%d”, Timer_Count);
BSP_Display_String(LCD_LINE3, str);
Timer_Count = 0;
}
if(SW2 == 0)
{
GlyphClearScreen(G_lcd);
Init_Timer();
float_Multiply(float_matA, float_matB, float_matC);
Timer_Count = TMR0.TCNT;
Reset_Timer();
sprintf((char *)str, “Count:%d”, Timer_Count);
BSP_Display_String(LCD_LINE3,str);
Timer_Count = 0;
}
if(SW3 == 0)
{
GlyphClearScreen(G_lcd);
Init_Timer();
dbl_Multiply(dbl_matA, dbl_matB, dbl_matC);
Timer_Count = TMR0.TCNT;
Reset_Timer();
sprintf((char *)str, “Count:%d”, Timer_Count);
BSP_Display_String(LCD_LINE3, str);
Timer_Count = 0;
}
}
GlyphClose(&G_lcd);
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
In the above code lines 52 through 69 initialize the matrices in corresponding data-type.
When switch 1 is pressed, the code enters line 79. The integer matrix multiplication is performed at line 83 and the corresponding count is measured as the previous example.
From the previous example, the following results were observed:
Int
Timer Count 112
Time Taken 111
1.3454 microseconds
16.5
a10 b
2
Float
Timer Count 197
Time Taken 197
2.3878 microseconds
16.5
a10 b
2
Double
Timer Count 198
Time Taken 198
2.4 microseconds
16.5
a10 b
2
From the example, time taken to perform matrix multiplication of two 3 3 matrices was
found. Also, a slight difference in time taken to perform single-precision and doubleprecision floating point matrix multiplication operation was observed.
10.6
RECAP
In this chapter, the Floating Point Unit (FPU) used in the Renesas RX62N was analyzed in
detail, where the floating point instructions, floating point exceptions and floating point
registers were discussed.
CHAPTER 10 / FLOATING POINT UNIT AND OPERATIONS
423
By applying this knowledge about the FPU, the RX62N board can be used in signal
processing, image processing applications, and applications that require precise round-off
(for example, in applications involving currency, floating-point rounding off errors should
be considered in order to value currency as $$.cc where “$$” denotes the dollar value and
“cc” denotes the cent value) with an understanding of the time-memory tradeoff between a
microcontroller with an FPU and one without an FPU.
10.7
REFERENCES
Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
Software Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
10.8
EXERCISES
1. Write a C program to identify different Floating Point Exceptions.
2. Consider the following operations:
Addition: 2.0 3.0
Multiplication: 2.0 * 3.0
Division: 2.0/3.0
Do different operations involving floating-point (addition, multiplication, and division) take the same time to complete? Justify your answer. Use single-precision
floating point numbers for the operations. Use Switch 1 (SW1), Switch 2 (SW2),
and Switch 3 (SW3) to perform Addition, Multiplication, and Division respectively and display the time taken as the result.
3. Write a C program on the RX62N to calculate the time taken to perform the operations stated in problem 10.7.2. Use single-precision floating point numbers for
the operations.
4. Implement problem 10.7.3 using double precision floating point numbers. Does it
take the same time as single precision floating point numbers? Justify your answer.
5. Identify the floating point instructions involved in single precision and double precision operations in problems 10.7.3 and 10.7.4 from the disassembly. Do they
look alike? Explain your answer.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
6. Write a C program on the RX62N to calculate the time taken to perform the in-
verse of the given matrix A. (Note: The inverse of the matrix should be calculated
in a different function other than “main.”)
1
A3
1
2
6
2
0
1
1
7. Multiply the inverted A matrix with B matrix given below. Identify the floating
point exceptions involved. (Note: Matrix Multiplication should be done in a different function other than “main.”)
0.001
B 3.143
0.917
2.400
2.743
0.008
0.120
4.901
2.001
Chapter Eleven
Watchdog Timer and Brown-Out Detector
11.1
LEARNING OBJECTIVES
Embedded systems are expected to work correctly. However, it is very difficult (even impossible) to completely test a system in all possible environments. Hence embedded system designers usually rely on a watchdog timer (WDT) to reset the processor if the program runs out of control. They also use a brown-out (or low-voltage) detector to hold the
processor in reset if the supply voltage is too low for correct operation.
This chapter presents information on:
䡲
䡲
䡲
䡲
11.2
Basic watchdog timer concepts
How application software and the WDT should interact
How to configure the RX62N WDT
Concepts for the brown-out detector
BASIC CONCEPTS OF WATCHDOG TIMER
Many embedded systems are built to operate without an operator, so there should be a
mechanism that monitors the system for unexpected errors due to some hardware fault, an
unusual endless loop, or other fatal software bug. The watchdog timer serves the purpose
of automatically monitoring and recovering the system from such situations.
The watchdog timer is an internal hardware timer peripheral in the CPU or an external
device which resets the processor if it is not reset within a given period of time. The application software needs to periodically reset the watchdog timer. If the application software
does not do this soon enough, the WDT overflows and the overflow signal is used to reset
the system. So, the watchdog timer can only help the system recover from faults which prevent the timely refresh of the WDT.
In a multitasking system, it is a best practice to have each task check in with a task
which monitors system-wide task progress. This monitor task will only reset the WDT if
all tasks are making adequate progress.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
One should never build a system in which the WDT is reset automatically by a task
or ISR which operates autonomously of the rest of the system. This defeats the purpose of
the WDT.
11.2.1 Watchdog Timer (WDT)
The Watchdog timer in RX62N microcontroller is an 8-bit timer which outputs an overflow
signal (WDTOVF), if the timer overflow occurs during general program flow, and it can
also be set up to reset the processor whenever the overflow signal occurs. The watchdog
timer can also be used as an interval timer which generates an interrupt each time the
counter overflows.
11.2.2 Register Descriptions
The registers used for the watchdog timer are listed in Table 11.2. The Timer control/status
register (TCSR) is used for selecting the timer operation and clock source for the timer.
The Timer counter (TCNT) contains the count value for the timer. The Reset control/status
register (RSTCSR) is used to reset the timer. Window A and Window B registers are used
for writing data into TCNT, TCSR and RSTCSR.
TABLE 11.1
ITEM
Specifications of WDT.
SPECIFICATIONS
Count clocks
PCLK/4, PCLK/64, PCLK/128, PCLK/512, PCLK/2048, PCLK/8192,
PCLK/32768, and PCLK/131072
Number of channels
8 bits ⫻ 1 channel
Count clear
Write to TCNT
Operating modes
Switchable between watchdog timer mode and interval timer mode
Watchdog timer mode
Outputs a WDTOVF# signal when the counter overflows.
Selectable whether or not to internally reset the RX62N/RX621 at the
same time.
Interval timer mode
Generates an interval timer interrupt (WOVI) when the counter overflows.
Source: Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America, Inc.,
2010, Table 23.1.
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
Overflow
WOVI
(Interrupt request signal)
PCLK/4
PCLK/64
PCLK/128
PCLK/512
PCLK/2048
PCLK/8192
PCLK/32768
PCLK/131072
Interrupt
control
Clock
Clock
selection
WDTOVF#
(Overflow signal)
Reset control
Internal reset signal*
Internal clocks
RSTCSR
TCNT
TCSR
Internal
main bus
Peripheral bus
interface
Peripheral bus
WINB
[Legend]
TCSR:
TCNT:
RSTCSR:
WINA:
WINB:
427
WINA
Timer control/status register
Timer counter
Reset control/status register
Write window A register
Write window B register
Note:* An internal reset signal can be generated depending on the register setting.
Figure 11.1 Block diagram of the WDT. Source: Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600
Series, Renesas Electronics America, Inc., 2010, Figure 23.1.
TABLE 11.2
REGISTER NAME
Timer control/status register
SYMBOL
TCSR
WDT Registers.
VALUE AFTER
RESET
ADDRESS
x8h
0008 8028h*1
8
*1
ACCESS SIZE
Timer counter
TCNT
00h
0008 8029h
8
Reset control/satus register
RSTCSR
1Fh
0008 802Bh*1
8
*2
16
*2
16
Write window A register
Write window B register
Notes: 1. Read-only register
2. Write-only register
Source: Hardware Manual, Table 23.3.
WINA
WINB
—
—
0008 8028h
0008 802Ah
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Window A Register (WINA): WINA is a 16-bit write-only register which is used to write
the data into Timer Counter (TCNT) register and Timer Control/Status register (TCSR). To
write to this register, use word access. The address of the WINA register is 0008 8082h.
Window B Register (WINB): WINB is a 16-bit write-only register and is used to write
the data into Reset Control/Status register (RSTCSR). To write to this register, use word
access. The address of WINB register is 0008 802Ah.
Timer Counter Register (TCNT)
The timer counter register (TCNT) is an 8-bit register which contains the maximum upcount value for the internal clock. To write any value into TCNT register, data should
be written into WINA register by word access. The value of the register after reset would
be 00h. The address of the TCNT register is 0008 8029h.
The following is a code snippet to write data into the TCNT register:
1. void write_TCNT (void){
2.
WINAL* = count_value;
3.
WINAH* = 0x5Ah;
4. }
Explanation of the Code
Line 2: WINAL = count_value;
The count value for the timer is set in the lower byte of the WINA register.
Line 3: WINAH = 0x5Ah;
To write the required data into the TCNT register, the upper byte of the
WINA register is set to 5Ah.
Timer Control/Status Register (TCSR)
Timer Control/Status Register is an 8-bit register which is used to select the clock source
for the timer and type of operation of the timer.
*In the code snippets, for easy explanation of settings for WINA and WINB registers, they are not used through
word access. WINAL/WINBL is the lower byte of the word and WINAH/WINBH is the upper byte of the
word. The actual way of setting the registers will be in the code examples.
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
429
Address: 0008 8028h
Value after reset:
b7
b6
b5
b4
b3
—
TMS
TME
—
—
0
0
0
0
0
b2
b1
b0
CKS[2:0]
0
0
0
[Legend] x: Undefined
Figure 11.2 Timer Control/Status Register (TCSR). Source: Hardware Manual, page 23–4.
Bit Description of TCSR
CKS [2:0] Bits: These bits are used to select the clock input to the timer in timer mode.
TME Bit (Timer Enable): This bit is used to start or stop the counting. When the bit is set
to 1, TCNT starts counting. When the bit is cleared to 0, TCNT stops counting and is initialized to 00h.
TMS Bit (Timer Select): This bit is used to select the operation of WDT as a Watchdog
timer or Interval timer. When this bit is cleared to 0, Interval timer mode is selected and as
the TCNT overflows, an interval timer interrupt is generated. When this bit is set to 1,
Watchdog timer mode is selected and as the TCNT overflows WDTOVF signal goes high.
The importance of using the clock source:
Problem 1: Design an embedded system using RX62N microcontroller with a delay of
326.4 ms to a watchdog timer. (Given PCLK ⫽ 50 MHZ)
Solution: The highest possible value the Timer count register (TCNT) can count up to
255 (FFh). So the delay we get with PCLK as the clock source is:
Delay ⫽
255
⫽ (255 / 50) ms ⫽ 5.1 ms
(PCLK)
So with a maximum value in the TCNT register we only get a delay of 5.1 ms. To increase
the delay the clock source frequency should be decreased.
Because 326.4 ms/5.1 ms ⫽ 64, the clock source frequency should be reduced to 1⁄ 64 of
the original clock source PCLK.
If PLCK/64 is used as a clock source:
Delay ⫽ (255/(PCLK/64)) ⫽ ((255 * 64)/PCLK) ⫽ ((255 * 64)/50) ms ⫽ 326.4 ms
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
430
TABLE 11.3
BIT
SYMBOL
BIT NAME
b2 to b0
CKS[2⬊0]
Clock select
Bit Description of TCSR.
DESCRIPTION
b2 b0
R/W
R/W
0 0 0: PCLK/4 (cycle: 20.4 ms)
0 0 1: PCLK/64 (cycle: 326.4 ms)
0 1 0: PCLK/128 (cycle: 652.8 ms)
0 1 1: PCLK/512 (cycle: 2.6 ms)
1 0 0: PCLK/2048 (cycle: 10.4 ms)
1 0 1: PCLK/8192 (cycle: 41.8 ms)
1 1 0: PCLK/32768 (cycle: 167.1 ms)
1 1 1: PCLK/131072 (cycle: 668.5 ms)
Note: The overflow cycle for PCLK ⫽ 50 MHz is
indicated in parentheses.
b4, b3
—
b5
TME
(Reserved)
These bits are always read as 1. The write value
should always be 1.
R/W
Timer enable
0: TCNT stops counting and is initialized to 00h.
R/W
1: TCNT starts counting.
b6
TMS
Timer Mode
Select
0: Interval timer mode
R/W
When TCNT overflows, an interval timer interrupt
(WOVI) is requested.
1: Watchdog timer mode
When TCNT overflows, WDTOVF# is output.
b7
—
(Reserved)
If read, an undefined value will be read. The write
value should always be 1.
R/W
Source: Hardware Manual, page 23–4.
The following is a code snippet to start the timer in WDT mode with a clock source of 1⁄ 64:
To write data to the TCSR register, data should be written into the WINA register by word
access.
1. void write_TCNT (void){
2.
WINAL = data;
3.
WINAH = 0xA5h;
4. }
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
431
Explanation of the Code
Line 2: WINAL = data;
The value in data variable to—the timer counting in WDT mode with a
clock source of 1⁄ 64 —is F9h, so data = F9h.
Line 3: WINAH = 0xA5h;
To write the required data into the TCNT register, the upper byte of the
WINA register is set to A5h.
Reset Control/Status Register (RSTCSR)
Reset Control/Status Register is an 8-bit register which is used to control the internal reset
signal when TCNT overflows and to select the type of internal reset signal. After the reset
signal from the RES pin or a deep software standby reset, the register value is set to 1Fh but
the value does not change when the WDT internal reset signal occurs.
Address: 0008 802Bh
b7
b6
b5
b4
b3
b2
b1
b0
WOVF
RSTE
—
—
—
—
—
—
0
0
0
0
0
0
0
0
Value after reset:
Figure 11.3 Reset Control/Status Register. Source: Hardware Manual, page 23–5.
Bit Description of RSTCSR
RSTE Bit (Reset Enable): This bit is used to enable or disable the internal reset of the microcontroller when TCNT overflows in watchdog timer mode. When the bit is set to 1, the
internal reset of the microcontroller will be enabled.
WOVF Flag (Watchdog Timer Overflow): This bit is used to check the overflow of
TCNT in watchdog timer mode. This bit cannot be set to 1 in interval timer mode. The
WOVF flag is set to 1 when the TCNT overflows (changed from FFh to 00h) in watchdog
timer mode. WOVF flag should be cleared to 0 by the software when it is read as 1.
The following is a code snippet to start the timer in WDT mode with a clock source
1
of ⁄ 4, LSI internally reset and writing 0 to the WOVF flag:
To write data to the TCSR register, data should be written into the WINA register by word
access. To write data to the RSTCSR data should be written into the WINB register by
word access.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
1. void write_RSTCSR (void){
2.
WINAL = data;
3.
WINAH = 0xA5h;
4.
WINBL = data1;
5.
WINBH = 0x5Ah;
6.
while((RSTCSR&0x80) != 0x80)
7.
;
8.
WINBL = data2;
9.
WINBH = 0x5Ah;
10. }
Explanation of the Code
Line 2: WINAL = data;
The value in data variable to start counting the timer in WDT mode with a
clock source of 1⁄ 4 is F8h.
Line 3: WINAH = 0x5Ah;
To write the required data into the TCNT register, the upper byte of the
WINA register is set to 5Ah.
Line 4: WINBL = data1;
The value in the data1 variable to make the microcontroller reset internally
is 5Fh.
Line 5: WINBH = 0x5Ah;
To write the required data into the RSTCSR, the upper byte of the WINB
register is set to 5Ah.
Line 7: while((RSTCSR&0x80) != 0x80);
The program waits here until the WOVF flag is set.
Line 8: WINBL = data2;
When the WOVF flag is set, the program comes out of the while loop and
clears the WOVF flag. To clear the flag, a value of 00h is written in the lower
byte of the WINB register through the local variable data2. data2 ⫽ 00h.
Line 9: WINBH = 0x5Ah;
To write into RSTCR, the upper byte of the WINB register should be set to
a value of A5h.
11.2.3 Operation of WDT
Watchdog Timer Mode: To use the watchdog timer mode, the TMS bit and the TME bit
should be set to 1. In watchdog timer mode, the TCNT overflows either when a system
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
433
goes unresponsive due to a software bugs or any other error. When the TCNT overflows,
the WDTOVF signal goes high for 257 cycles of PCLK when the RSTE bit in RSTCSR is
set to 1, and WDTOVF signal goes high for 256 cycles of PCLK when RSTE is cleared to
0. This signal can be used to reset the MCU internally in watchdog timer mode. TCNT
overflows must be prevented in the software by rewriting the value of TCNT to 00h before
overflow occurs. If TCNT overflows and the RSTE bit in RSTCSR is set to 1, the internal
reset signal that resets the RX62N/RX621 and the WDTOVF signal are generated at the
same time. If the external reset from the RES pin and the reset from the WDT occur at the
same time, the RES pin gets the highest priority and the WOVF flag in RSTCSR is cleared
to 0. The software should rewrite the TCNT value to 00h before the overflow occurs.
Figure 11.4 shows an example of how the WDT operates. At the first arrow the TMS
and TME bit are set to 1. At the next three arrows, the WDT is refreshed. WDT overflow
occurs at WOVF arrow point so the internal reset signal goes high for 1027 cycles and the
WDTOVF signal toggles for 257 or 256 cycles depending on the RSTE bit in RSTCSR.
TCNT value
Overflow
FFh
Time
00h
TMS 5 1
TME 5 1
Write 00h to
TCNT
WOVF 5 1
TMS 5 1
TME 5 1
Write 00h to
TCNT
Generating WDTOVF#
and internal reset
WDTOVF# signal
257 cycles*2
Internal reset signal*1
1027 cycles
Notes: 1. An internal reset signal is generated if TCNT overflows when the RSTE bit in RSTCSR is set to 1.
2. The WDTOVF# signal is output for 256 cycles when RSTE bit in RSTCSR is set to 0.
Figure 11.4 Watchdog timer mode operation. Source: Hardware Manual, page 23–7.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
11.3
BASIC CODE EXAMPLES
11.3.1 Example 1: Setting Up Watchdog Timer Mode
In this example code a subroutine is provided with the watchdog timer set up for a delay
time of FFh; i.e., equal to 5.1 ms. (PCLK ⫽ 50 MHZ)
1. void Init_WDT(void){
2.
WDT.WRITE.WINA = 0x5A00;
3.
WDT.WRITE.WINB = 0x5A5F;
4.
WDT.WRITE.WINA = 0xA5FD;
5. }
//Writing data into TCNT
//Writing data into RSTCSR
//Writing data into TCSR
Explanation of the Code
Line 2: WDT.WRITE.WINA = 0x5A00;
A value of 00h is written into the TCNT register. Since we cannot directly
write value into TCNT register, WINA register is used to write the value.
To write data into the TCNT register, the upper byte of the word of WINA
register should be set to 5Ah and then the data is written to the lower byte
of the word of WINA register.
Line 3: WDT.WRITE.WINB = 0x5A5F;
A value of 5F is written into the RSTCSR using WINB register. To write
data into the RSTCSR the upper byte of the word of WINB register should
be set to 5Ah, and then the data is written to the lower byte of the word of
WINB register. The internal reset enable (RSTE) pin is set to 1 to reset the
microcontroller on the overflow of the watchdog timer.
Line 4: WDT.WRITE.WINA = 0xA5FD;
A value of FD is written into TCSR using the WINA register. To write data
into the TCSR the upper byte of the word of the WINA register should be
set to 5Ah and then the data is written to the lower byte of the word of the
WINA register. The CKS [2⬊0] bits are set to a value of 7 selecting the
prescaler division factor as 131072 with clock source as PCLK. The
TMS bit in this register is set to 1 to select the watchdog timer mode, and
the timer start enable bit is set to 1 to start counting.
11.3.2 Example 2: Application of a Watchdog Timer
Consider a software bug which leads the program into an infinite loop. This example shows
how the watchdog timer brings the program out of the infinite loop.
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
435
1. void main(){
2.
int i;
3.
ENABLE_LEDS;
4.
while(1){
5.
Init_WDT(void);
6.
ALL_LEDS_OFF();
7.
for(i = 0; i < 10000000; i++){
8.
i––;
9.
}
10.
ALL_LEDS_ON();
11.
WDT.WRITE.WINA = 0x5A00;
//Clearing data into TCNT
12.
}
13. }
In the above program, the LEDs should switch on and switch off with some delay, but due
to the software bug the program enters into an infinite loop which eventually causes the
overflow of the watchdog timer—and the overflow causes the internal reset of the microcontroller. If there is no infinite loop, the count of the watchdog timer is reset frequently to
prevent the overflow.
Explanation of the Code
Line 3:
ENABLE_LEDS;
This macro enables the LEDs.
Line 5:
Init_WDT(void);
Calls the subroutine to initialize the watchdog timer, which resets the
system as the overflow occurs.
Line 6:
ALL_LEDS_OFF();
Switches off all the LEDs.
Lines 7–9: These are the lines with the bug which takes the program into an infinite
loop. We start the loop, decrement the counter variable, and then
increment the counter variable—the counter variable will not be anything
other than ⫺1 or 0.
Line 10:
ALL_LEDS_ON();
Switches on all the LEDs.
Line 11:
WDT.WRITE.WINA = 0x5A00;
This line is used to clear the value of TCNT periodically if the program
executes without the infinite loop. If this line is not executed then the TCNT
is not cleared to zero, which forces the overflow of the watchdog timer.
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11.4
ADVANCED CONCEPTS OF THE WATCHDOG TIMER
11.4.1 Interval Timer Mode
To use WDT as an interval timer mode, set the TMS bit to 0 and the TME bit to 1 in TCSR.
In interval timer mode, a timer interrupt WOVI is generated each time the TCNT overflows.
As the TCNT overflows periodically, the timer interrupt is an interval timer interrupt.
TCNT value
Overflow
FFh
Overflow
Overflow
Overflow
Time
00h
TMS 5 0
TME 5 1
WOVI
WOVI
WOVI
WOVI
WOVI: An interval timer interrupt request is generated.
Figure 11.5 Interval timer mode operation. Source: Hardware Manual, page 23–8.
11.4.2 Independent Watchdog Timer (IWDT)
The independent watchdog timer (IWDT) is a watchdog timer for use independent of the
conventional watchdog timer, which is for detecting programs with runaway execution and
system crashes (Hardware Manual, page 1184). The IWDT is a 14-bit down counter which
resets the system if an underflow of the timer count value occurs. The timer count value
must be refreshed before the counter underflows.
Registers Used to Set Up IWDT: Table 11.5 shows the list of registers used to set up the
IWDT.
IWDT Refresh Register (IWDTRR): The IWDT refresh register (IWDTRR) is used to
refresh the timer down count value of the IWDT. The down count value of the IWDT is refreshed by passing 00h and FFh as a sequence to the IWDTRR. After the writing of FFh to
IWDTRR, refreshing the down counter takes up to four cycles of the signal for counting.
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
TABLE 11.4
ITEM
437
Specification of IWDT.
SPECIFICATIONS
Clock for counting
OCOCLK, OCOCLK/16, OCOCLK/32, OCOCLK/64, OCOCLK/128,
OCOCLK/256
Counter operation
Counting down by a 14-bit down-counter
Conditions for starting
the counter
Counting can be started by refreshing the down-counter (write FFh
after 00h has been written to the IWDTRR register).
Conditions for stopping
the counter
䡲 Pin reset (the down-counter and other registers return to their initial
values)
䡲 Generation of an underflow
Window facility
A refresh-permitted period and fresh-prohibited period may be set.
Reset-output sources
of the IWDT
Underflow of the down-counter
Reading the value
of the IWDT counter
The value reached in counting by the down-counter can be read out
from a register (the IWDTSR).
Source: Hardware Manual, Table 24.1.
IWDT reset
output
OCOCLK
PCLK
IWDT control circuit
I
W
D
T
R
R
I
W
D
T
C
R
14-bit down counter
I
W
D
T
S
R
OCOCLK
OCOCLK/16
Count clock
Clock
selection
OCOCLK/32
OCOCLK/64
OCOCLK/128
OCOCLK/256
Internal bus
[Legend]
IWDTRR: IWDT refresh register
IWDTCR: IWDT control register
IWDTSR: IWDT status register
Figure 11.6 Block diagram of IWDT. Source: Hardware Manual, figure 24.1.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
List of Registers.
TABLE 11.5
REGISTER NAME
SYMBOL
IWDT refresh register
IWDTRR
IWDT control register
IWDT status register
VALUE AFTER RESET
ADDRESS
ACCESS SIZE
FFh
0008 8030h
8
IWDTCR
3303h
0008 8032h
16
IWDTSR
0000h
0008 8034h
16
Source: Hardware Manual, Table 24.2.
After the counter value has been refreshed and the reset signal has been generated and released, the timer starts to count down from the value set up in the TOPS [1⬊0] bits in IWDT
Control Register (IWDTCR).
IWDT Control Register (IWDTCR): The IWDTCR is a sixteen bit register in which
only six bits are used for setting up the IWDT. The IWDT Control register (IWDTCR) is
used to specify the time-out period for the down count of the timer. The time-out period in
the bits TOPS [1⬊0] can only be changed between the release from the reset state and the
first time the counter is refreshed. The writing to the IWDTCR is locked otherwise, because we don’t want to change the time out period of the timer after the counting has
started. The writing is only unlocked by the reset signal generated by the IWDT.
Address: 0008 8032h
Value after reset:
b15
b14
b13
b12
b11
b10
b9
b8
—
—
—
—
—
—
—
—
0
0
1
1
0
0
1
1
b7
b6
b5
b4
b3
b2
b1
b0
CKS[3:0]
Value after reset:
0
0
0
TOPS[1:0]
0
0
0
1
1
Figure 11.7 IWDT Control Register (IWDTCR).
Bit Description for IWDTCR
TOPS [1⬊0]: These bits in the IWDTCR are used to select the time-out period for the down
count of the timer. The different possible values of the time-out period are 1024, 4096,
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
TABLE 11.6
BIT
SYMBOL
BIT NAME
b1, b0
TOPS[1⬊0]
Time-out
period
selection
439
Bit Description for IWDTCR.
DESCRIPTION
b1 b0
R/W
R/W
0 0: 1024 cycles (03FFh)
0 1: 4096 cycles (0FFFh)
1 0: 8192 cycles (1FFFh)
1 1: 16384 cycles (3FFFh)
b3, b2
—
b7 to b4
CKS[3⬊0]
(Reserved)
These bits are read as 0. The write value should be 0.
R/W
Clock
selection
b7 b4
R/W
0 0 – –: OCOCLK
0 1 0 0: OCOCLK/16
0 1 0 1: OCOCLK/32
0 1 1 0: OCOCLK/64
0 1 1 1: OCOCLK/128
1 – – –: OCOCLK/256
b9, b8
—
(Reserved)
These bits are read as 1. The write value should be 1.
R/W
b11, b10
—
(Reserved)
These bits are read as 0. The write value should be 0.
R/W
b13, b12
—
(Reserved)
These bits are read as 1. The write value should be 1.
R/W
b15, b14
—
(Reserved)
These bits are read as 0. The write value should be 0.
R/W
Source: Hardware Manual.
8192 and 16384. The number of cycles for the time-out period is determined by the clock
source selected by the CKS [3⬊0] bits.
CKS [3⬊0]: These bits are used to select the clock source for the IWDT. A minimum of
1024 cycles to a maximum of 4194304 cycles time-out period of the LOCO signal can be
selected with the combination of TOPS [1⬊0] and CKS [3⬊0] bits. The different combinations of the time-out period is shown in Table 11.7.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
TABLE 11.7
Different Combinations of TOPS [1⬊0] and CKS [3⬊0], with Corresponding
Number of Cycles of the LOCO Signal.
CKS[3⬊0]
0
0
0
0
0
1
0
1
1
1
1
—
—
0
0
1
1
—
TOPS[1⬊0]
—
0
1
0
1
—
0
0
0
COUNT
CLOCK
CYCLES OF
THE LOCO
SIGNAL
1024
1024
1
4096
4096
1
0
8192
8192
1
1
16384
16384
0
0
1024
16384
0
1
4096
65536
1
0
8192
131072
1
1
16384
262144
0
0
1024
32768
0
1
4096
131072
1
0
8192
262144
1
1
16384
524288
0
0
1024
65536
0
1
4096
262144
1
0
8192
524288
1
1
16384
1048576
0
0
1024
131072
0
1
4096
524288
1
0
8192
1048576
1
1
16384
2097152
0
0
1024
262144
0
1
4096
1048576
1
0
8192
2097152
1
1
16384
4194304
Source: Hardware Manual, Table 24.3.
OCOCLK
TIME-OUT PERIOD
(NUMBER OF CYCLES)
OCOCLK/16
OCOCLK/32
OCOCLK/64
OCOCLK/128
OCOCLK/256
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
441
IWDT Status Register (IWDTSR): The IWDTSR is a sixteen bit register which contains
the underflow information and the counter value of the down counter. This register is initialized only by the IWDT reset source.
Address: 0008 8034h
b15
b14
—
UNDFF
0
0
0
0
0
b7
b6
b5
b4
b3
Value after reset:
b13
b12
b11
b10
b9
b8
0
0
0
b2
b1
b0
0
0
0
CNTVAL[13:0]
CNTVAL[13:0]
Value after reset:
0
0
0
0
0
Figure 11.8 IWDT Status Register (IWDTSR). Source: Hardware Manual.
Bit Description of IWDTSR
CNTVAL [13⬊0]: These bits of IWDTSR can be read to check the count value of the
down counter.
UNDFF: This bit of IWDTSR shows the state of underflow. If this bit is set to 1, the down
counter has underflowed. If this bit is cleared to 0, the down counter has not underflowed.
Operation of Independent Watchdog Timer
The TOPS [1⬊0] bits of IWDTCR are used to select the time out period of the IWDT. The
writing to IWDTCR is unlocked only after the reset from the IWDT. When the IWDT is refreshed, the timer counts down from the value set in the TOPS [1⬊0] bits.
In the normal execution of the program, the IWDT is refreshed at regular intervals.
If the refresh of the IWDT does not occur, that shows that the program has entered into
an infinite loop, has gotten stuck in a long process, or is not working in the desired manner. The underflow flag is set to 1 and the reset source from the IWDT is activated to reset the system. After the output of the reset signal, the down counter is initialized and
the writing to the IWDTCR is unlocked. After the system has been re-booted, counting
down is again started by refreshing the counter. Figure 11.9 shows an example of the
operation of the IWDT.
Reset output
from the IWDT
Underflow flag
Refreshing the
counter
(1) Initial value
(2) Set value
IWDTCR
register
Reset input
to the IWDT
0%
25%
50%
75%
100%
(2)
Counting starts
The status is cleared
Underflow
Writing to the
register is valid.
(2)
Figure 11.9 Operation of IWDT. Source: Hardware Manual, Figure 24.2.
Counting starts
Writing to the
register is valid.
(1)
Value in the down-counter
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CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
11.5
443
COMPLEX EXAMPLES
11.5.1 Example 1: Interval Timer Mode of a Watchdog Timer
In the next example of code a subroutine has been provided for setting up the WDT as an
interval timer. This function should be called before the main function to initialize the
WDT in interval timer mode. The interval timer has been set up for a clock with a prescaler
division factor of 8192 and an interrupt occurs as the timer overflows. Therefore, code can
be added to the ISR if needed.
1. void init_WDT_intervaltimer(){
2.
IEN(WDT,WOVI) = 0;
3.
IPR(WDT,WOVI) = 3;
4.
IEN(WDT,WOVI) = 1;
5.
WDT.WRITE.WINA = 0x5AFF;
//Writing data into TCNT
6.
WDT.WRITE.WINB = 0x5A1F;
//Writing data into RSTCSR
7.
WDT.WRITE.WINA = 0xA53D;
//Starting the timer
8. }
Explanation of the Code
Line 2: IEN (WDT, WOVI) = 0;
When setting the priority level for an interrupt, the interrupt source should be
disabled. So this instruction disables the WDT overflow interrupt (WOVI).
Line 3: IPR (WDT, WOVI) = 3;
This instruction sets a priority level of 3 to the WDT overflow interrupt (WOVI).
Line 4: IEN (WDT, WOVI) = 1;
This instruction enables the WDT overflow interrupt.
Line 5: WDT.WRITE.WINA = 0x5AFF;
This instruction writes the timer count value to the timer counter register
(TCNT) of WDT through WINA register.
Line 6: WDT.WRITE.WINB = 0x5A1F;
This instruction writes a value of 1Fh to RSTCSR register. The internal reset
enable bit (RSTE) in RSTCSR is disabled.
Line 7: WDT.WRITE.WINA = 0xA53D;
This instruction is used to write the 3Dh value to the TCSR register. The
CKS [2⬊0] bits are set to 101b for a prescaler division factor of 8192. The
timer mode select (TMS) bit is cleared to 0, which selects the interval timer
mode of WDT. The timer enable (TME) bit is set to 1 which starts the timer.
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11.5.2 Example 2: Setting Up of IWDT
The following is the subroutine to set up the watchdog timer for a clock source of
OCOCLK/16 with a time out period of 4096 cycles. The IWDT down counts from the value
set up by the bits in IWDTCR register and as the underflow occurs the system will reset.
1. void Init_IWDT(void){
2.
IWDT.IWDTCR.BIT.CKS = 4;
3.
IWDT.IWDTCR.BIT.TOPS = 1;
4. }
We can also use a single instruction by writing a word into the IWDTCR register.
IWDT.IWDTCR.WORD = 0x3340;
Explanation of the Code
Line 2: IWDT.IWDTCR.BIT.CKS = 4;
This line is used to set up the value for CKS [3⬊0] bits in IWDTCR register;
for selecting a prescaler division factor of 16 for clock source OCOCLK, a
value 0100b should be written to CKS [3⬊0] bits.
Line 3: IWDT.IWDTCR.BIT.TOPS = 1;
This line is used to set up the value for TOPS [1⬊0] bits in IWDTCR
register. For selecting a timeout period of 4096 cycles, a value 01b should
be written to TOPS [1⬊0] bits.
11.6
BROWNOUT CONDITION
11.6.1 How Brownout Occurs
A brownout condition in a microcontroller occurs when the supply voltage for the microcontroller temporarily goes below a threshold value (Vdet). Below this threshold value, the
microcontroller may malfunction. There is also a blackout condition in which the microcontroller will have a total loss of electricity. In a brownout condition, some operations
may work but in a blackout condition none of the operations will be active.
11.6.2 Automatically Detecting a Brownout Condition
The main purpose of automatically detecting the brownout condition is to prevent the corruption of processor critical information. Whenever the brownout condition is detected, the
CHAPTER 11 / WATCHDOG TIMER AND BROWN-OUT DETECTOR
445
internal reset from the voltage detection circuit should keep the processor in reset condition
until the voltage increases above the threshold value (Vdet).
The RX62N MCU group provides two low-voltage detection (LVD) circuits based on
analog comparators. Each compares the supply voltage Vcc against a fixed reference voltage (Vdet1 or Vdet2). If the supply voltage is not above the reference voltage, the LVD can
reset the processor or generate an interrupt, based on the LVD configuration. Because
there are two LVD comparators, one can be configured to warn of a likely impending
power failure (when Vdet2 is reached) using an interrupt. This will trigger the saving of
critical data and putting outputs into safe states (e.g. turning off motors). The second LVD
can be configured to reset the processor when Vdet1 is reached.
11.7
RECAP
A watchdog timer is one of the tools in the microcontroller, which gets the system out of
unexpected errors or infinite loops. The watchdog timer count is refreshed frequently so
that the overflow does not occur in the general flow of the program. When the overflow occurs, it implies that the timer count has been not refreshed and the program is not functioning in the way it should. So the watchdog timer resets the system whenever it overflows.
The RX62N/RX621 group has two watchdog timers, WDT and IWDT. The WDT can be
used in watchdog timer mode and interval timer mode. The registers are used to set up the
WDT and IWDT. WINA and WINB registers are used to write data to WDT registers. To
refresh the timer count for IWDT, two length sequence 00h and FFh should be written to
the timer counter register of IWDT.
11.8
REFERENCES
Hardware Manual, Renesas 32-Bit Microcomputer, RX Family/RX600 Series. Renesas Electronics America,
Inc., 2010. Print.
11.9
EXERCISES
1. List the registers used to set up the WDT and describe the importance of the
registers.
2. List the registers used to set up the IWDT and describe the importance of
the registers.
3. What registers used to write data into RSTCR, TCNT, and TCSR registers with
pseudo code?
4. Draw a flowchart explaining when and how a WDT resets the system.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
5. What is the maximum interval time of the WDT in interval timer mode? Show
with calculations.
6. Write pseudo code to reset the microcontroller when a brownout condition
7.
8.
9.
10.
11.
occurs (use the pins available on the microcontroller to detect the brownout
condition).
Write the Code to set up the WDT in watchdog timer mode with a 167.1 ms
clock, with no internal reset, and to start the counting of the timer.
Write the Code to refresh the timer counter register of the IWDT.
Write the Code to set up the WDT to reset the microcontroller every 1s.
Write the Code to set up the IWDT to reset the microcontroller every 1s.
Write a program to create a software bug, and reset the microcontroller using
IWDT when the bug occurs.
Chapter Twelve
Designing Responsive and Real-Time Systems
12.1
LEARNING OBJECTIVES
Most embedded systems have multiple independent tasks running at the same time. Which
activity should the microprocessor perform first? This decision determines how responsive
the system is, which then affects how determines how fast a processor we must use, how
much time we have for running intensive control algorithms, how much energy we can
save, and many other factors. In this chapter we will discuss how the microprocessor
schedules its tasks.
12.2
MOTIVATION
Consider an embedded system which controls a doorbell in a house. When a person at the
front door presses the switch, the bell should ring inside the house. The system’s responsiveness describes how long it takes from pressing the switch to sounding the bell. It is
easy to create a very responsive embedded system with only one task. The scheduling approach shown below is an obvious and simple approach.
1. void main (void){
2.
init_system();
3.
while(1){
4.
if(switch == PRESSED){
5.
Ring_The_Bell();
6.
}
7.
}
8. }
Our doorbell is very responsive. In fact, we like it so much that we decide to add in a smoke
detector and a very loud beeper so we can be warned about a possible fire. We also add a
burglar detector and another alarm bell. This results in the code shown on the next page.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
1. void main (void){
2.
init_system();
3.
while(1){
4.
if(switch == PRESSED){
5.
Ring_The_Doorbell();
6.
}
7.
if(Burglar_Detected() == TRUE){
8.
Sound_The_Burglar_Alarm();
9.
}
10.
if(Smoke_Detected() == TRUE){
11.
Sound_The_Fire_Alarm();
12.
}
13.
}
14. }
Going from one task to three tasks has complicated the situation significantly.1 How should
we share the processor’s time between these tasks?
䡲
䡲
䡲
䡲
䡲
䡲
How long of a delay are we willing to accept between smoke detection and the fire
alarm sounding? And the delay between the switch being pressed and the doorbell
sounding?
Should the system try to detect smoke or burglars while the doorbell is playing?
Should the doorbell work while the smoke alarm is being sounded? What about
when the burglar alarm is sounding?
Which subsystem should the processor check first: the doorbell, the smoke detector, or the burglar detector? Or should it just alternate between them?
Should the doorbell switch be checked as often as the smoke and burglar detectors,
or at a different rate?
What if the person at the door presses the switch again before the doorbell finishes
sounding? Should that be detected?
Now that we have to share the processor, we have to worry about how long the bell rings
and the alarms sound. If we use a doorbell ringtone which lasts for thirty seconds, then
Ring_The_Bell will take at least thirty seconds to run. During this time, we won’t know if
our house is burning or being robbed. Similarly, what if the firemen come when the alarm
is sounding? How quickly should the doorbell respond in that case?
1
In fact, any number of tasks greater than one complicates the situation!
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
12.3
449
SCHEDULING FUNDAMENTALS
This example reveals the two fundamental issues in scheduling for responsive systems.
䡲
䡲
If we have multiple tasks ready to run, which one do we run first? This decision defines the ordering of task execution.
Do we allow one task to interrupt or preempt another task (or even itself)?
Both of these decisions will determine the system’s responsiveness (measured by response
time):
䡲
䡲
䡲
How long will it take for the most important task to start running? To finish
running? Does this depend on how long any other tasks take to run, and how often they run?
How long will it take for the least important task to start running? To finish
running? We expect it will depend on how long all the other tasks take to run, and
how often they run.
If we allow tasks to preempt each other, then a task may start running very soon
but finish much later, after multiple possible preemptions.
These response times in turn affect many performance-related issues, such as these:
䡲
䡲
䡲
䡲
How fast must the processor’s clock rate be to ensure that nothing happens “late”?
How much time do we have available for running compute-intensive algorithms?
How much energy can we save by putting the processor to sleep?
How much power can we save by slowing down the processor?
Figure 12.1 shows a visual representation of some arbitrary scheduling activity. Task A
is released (becomes ready to run) at the first vertical bar. There is some latency between the release and when the task starts running, due to other processing in the system and scheduler overhead. Similarly, there is a response time which measures how
long it takes task A to complete its processing. Some scheduling approaches allow a
task to be preempted (delayed) after it has started running, which will increase the response time.
12.3.1 Task Ordering
The first factor affecting response time is the order in which we run tasks. We could
always follow the same order by using a static schedule. The code shown for the Doorbell/
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Task A
Current Task
Task Time
Scheduler
Task A
Latency
Response Time
Time
Figure 12.1 Diagram and definitions of scheduler concepts.
Friend rings doorbell
Burglar breaks in
Fire breaks out
Doorbell
Burglar Alarm
Fire Alarm
Burglar Alarm
Fire Alarm
Fire Alarm
Fire Alarm
Fire Alarm
Fire Alarm
Fire Alarm
Fire Alarm
Fire Alarm
Fire Alarm
30 seconds
60 seconds
Doorbell
30 seconds
Fire Alarm
Negligible
delay
Figure 12.2 Doorbell/fire alarm/burglar alarm system behavior with different scheduling
approaches.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
451
Fire Alarm/Burglar Alarm uses a static schedule. Figure 12.2a shows an interesting case. If
a burglar broke in and a fire broke out just after someone pressed the switch to ring
the doorbell; we wouldn’t find out about the burglar for almost thirty seconds and the
fire for about sixty seconds. We probably do not want these large delays for such critical
notifications.
We can change the order based on current conditions (e.g., if the house is on fire) using
a dynamic schedule. An obvious way to do this is to reschedule after finishing each task.
A dynamic schedule lets us improve the responsiveness of some tasks at the price of delaying other tasks. For example, let’s prioritize fire detection over burglar detection over
the doorbell.
1. void main (void){
2.
init_system();
3.
while(1){
4.
if(Smoke_Detected() == TRUE){
5.
Sound_The_Fire_Alarm();
6.
} else if (Burglar_Detected() == TRUE) {
7.
Sound_The_Burglar_Alarm();
8.
} else if (switch == PRESSED) {
9.
Ring_The_Doorbell();
10.
}
11.
}
12. }
Notice how this code is different—there are else clauses added, which change the
schedule to a dynamic one. As long as smoke is detected, Sound_The_Fire_Alarm()
will run repeatedly. The burglar alarm and doorbell will be ignored until no more
smoke is detected. Similarly, burglar detection will disable the doorbell. This is shown
in Figure 12.2b.
This strict prioritization may or may not be appropriate for a given system. We may
want to ensure some fairness, perhaps by limiting how often a task can run. Later in this
chapter we present a periodic table-based approach which is much better than this hardcoded design.
12.3.2 Task Preemption
The second aspect to consider is whether one task can preempt another task. Consider our
thirty-second doorbell ringtone—the task Ring_The_Doorbell will run to completion
without stopping or yielding the processor.
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What if a burglar breaks the window a split second after an accomplice rings the doorbell? In this worst-case scenario, we won’t find out about the burglar (or a possible fire) for
thirty seconds.2 Let’s say we’d like to find out within one second. We have several options:
䡲
䡲
䡲
䡲
Limit the maximum duration for the doorbell ringtone to one second.
Add another microprocessor which is dedicated to playing the doorbell ringtone.
This will raise system costs.
Break the Ring_The_Doorbell function into thirty separate pieces (e.g., with a
state machine or separate functions), each of which takes only one second to run.
This code will be hard to maintain.
Allow the smoke and burglar detection code to preempt Ring_The_Doorbell. We
will need to use a more sophisticated task scheduler which can (1) preempt and resume tasks, and (2) detect events which trigger switching and starting tasks. We will
not need to break apart any source code. This will make code maintenance easier.
However, we introduce the vulnerability to race conditions for shared data, and we
also will need more memory (enough to hold each task’s stack simultaneously).
Let’s apply this preemption option to our system. We assign the highest priority to fire detection, then burglar detection, and then the doorbell. Now we have the response timeline
shown in Figure 12.2c. The system starts sounding the doorbell after the switch is pressed,
but as soon as the fire is detected, the scheduler preempts the Ring_The_Doorbell and
starts running Sound_The_Fire_Alarm. We find out about the fire essentially immediately,
without having to wait for the doorbell to finish sounding.
As with the previous example, we have strict prioritization without control of how often tasks can run. As long as smoke is detected, Sound_The_Fire_Alarm() will run repeatedly. The burglar alarm and doorbell will be ignored until no more smoke is detected. Similarly, burglar detection will disable the doorbell.
12.3.3 Fairness and Prioritization
These examples all show one weakness of our system: prioritizing some tasks over others can
lead to starvation of lower priority tasks (they may never get to run). For some systems this is
acceptable, but for others it is not. Here are two ways of providing some kind of fairness:
䡲
2
We can allow multiple tasks to share the same priority level. If both tasks are ready
to run, we alternate between executing each of them (whether by allowing each
task to run to completion, or by preempting each periodically).
Imagine what Thomas Crown, James Bond, or Jason Bourne could do in that time!
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
䡲
453
We can limit how often each task can run by defining the task frequency. This is
the common approach used for designers of real-time systems. Note that we can
still allow only one task per priority level.
12.3.4 Response Time and Preemption
For the two non-preemptive examples in Figure 12.2, notice how the response time for the
fire alarm and the burglar alarm depends on how long the doorbell sounds. However, for
the preemptive approach those response times are independent of how long the doorbell
sounds. This is the major benefit of a preemptive scheduling approach: it makes a task’s response time essentially independent of all processing by lower priority tasks.3 Instead,
only higher priority tasks can delay that task.
In Figure 12.3 we present these relationships in a graph. Tasks and ISRs are nodes,
while edges (or arcs) are timing dependences. For example, the edge from B to C indicates
Non-Preemptive
Static Scheduling
Non-Preemptive
Dynamic Scheduling
Preemptive
Dynamic Scheduling
ISRs
ISRs
ISRs
A
A
A
B
B
B
C
C
Task B’s response
time depends on
Task C’s duration
9 dependences
- Higher priority tasks and ISRs
- Lower priority tasks
Task C is
slowest task
8 dependences
- Higher priority tasks and ISRs
- Slowest task
C
6 dependences
- Only higher priority tasks
and ISRs
Figure 12.3 Timing dependences of different scheduling approaches.
3
There are exceptions when tasks can communicate with each other with semaphores and other such mechanisms, but that is beyond the scope of this introductory text.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
that task B’s response time depends on task C’s duration. We can now compare timing dependences for these three classes of scheduler.
䡲
䡲
䡲
With the non-preemptive static scheduler, each task’s response time depends on
the duration of all other tasks and ISRs, so there are nine dependences.4
With the non-preemptive dynamic scheduler, we assign priorities to tasks
(A B C). In general, a task no longer depends on lower priority tasks, so we
have more timing independence and isolation. This accounts for six dependences.
The exception is the slowest or longest duration task, which is C in this example.
If task C has started running, it will delay any other task, regardless of priority. So
the higher priority tasks A and B each have a dependence edge leading to task C in
Figure 12.3, which results in a total of eight dependences.
With the preemptive dynamic scheduler, we also prioritize the tasks (A B C).
Because a task can preempt any lower priority task, the slowest task no longer matters. Each task can be preempted by an ISR, so there are three dependence edges to
begin with. Task A cannot be preempted by B or C, so it adds no new edges. Task
B can be preempted by task A, which adds one edge. Finally, task C can be preempted by task A or B, which adds two more edges. As a result we have only six
dependences. Most importantly, these dependence edges all point upwards.5 This
means that in order to determine the response time for a task, we only need to consider higher priority tasks. This makes the analysis much easier.
The real-time system research and development communities have developed extensive precise mathematical methods for calculating worst-case response times, determining if deadlines can ever be missed, and other characteristics of a system. These methods consider semaphores, task interactions, scheduler overhead, and all sorts of other complexities of practical
implementations. We do not discuss them here as they are beyond the scope of this text.
12.3.5 Stack Memory Requirements
The non-preemptive scheduling approaches do not require as much data memory as the
preemptive approaches. In particular, the non-preemptive approach requires only one call
stack, while a preemptive approach typically requires one call stack per task.6
4
Of course, if task code can disable interrupts, then there will be three more edges leading from the ISRs back
to the tasks! That would be a total of twelve dependences, which is quite a few to handle.
5
6
This is called a DAG or directed acyclic graph.
There are several ways to reduce the number of stacks needed for preemptive scheduling, but they are beyond
the scope of this text.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
455
The function call stack holds a function’s state information such as return address and
limited lifetime variables (e.g., automatic variables, which only last for the duration of a
function). Without task preemption, task execution does not overlap in time, so all tasks
can share the same stack. Preemption allows tasks to preempt each other at essentially any
point in time. Trying to reuse the same stack space for different tasks would lead to corruption of this information on the stack. For example, task B is running. Function B3 in
task B calls function B4. The scheduler then preempts task B to run the higher priority task
A, which was running function A2. Function A2 completes and it expects to return to function A1, which called A2. However, the call stack has function B3’s information on the
stack, so task A will start executing function B3! And so the system fails to operate
correctly.
As a result of these memory requirements for preemptive scheduling approaches, there
are many cost-sensitive embedded systems which use a non-preemptive scheduler to minimize RAM sizes and therefore costs.
12.3.6 Interrupts
Interrupts are a special case of preemption with dedicated hardware and compiler support.
They can be added to any of these scheduling approaches in order to provide faster, timecritical processing. In fact, for many systems only interrupt service routines are needed for
the application’s work. The main loop is simply an infinite loop which keeps putting the
processor into a low-power idle mode.
When designing a system which splits between ISRs and task code, one must strike a
balance. The more work which is placed in an ISR, the slower the response time for other
processing (whether tasks or other ISRs7). The standard approach is to perform timecritical processing in the ISR (e.g., unloading a character from the UART received data
buffer) and deferring remaining work for task code (pushing that character in a FIFO from
which the task will eventually read). ISR execution duration affects the response time for
other code, so it is included in the response time calculations described in Section 12.3.4
and in Figure 12.3.
There are many good texts which suggest approaches for architecting ISRs; please see
the references list.
7
It is possible to make ISRs interruptable, but this introduces many new ways to build the system wrong.
Hence it is discouraged.
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12.4
TASK MANAGEMENT
12.4.1 Task States
A task will be in one of several possible states. The scheduler and the task code itself both
affect which state is active. With a non-preemptive dynamic scheduler, a task can be in
any one of the states8 shown in Figure 12.4a:
Scheduler Tick
ISR or other task
marks this task
as Ready
Ready
Scheduler selects
highest priority
ready task and
starts it running
Waiting
Scheduler Tick
ISR or other task
marks this task
as Ready
Ready
Scheduler
finds a
higher
priority
ready task
Waiting
Scheduler selects
highest priority
ready task and
starts it running
Task function
completes
Task function
completes
Running
Non-preemptive Dynamic Scheduler
Running
Preemptive Dynamic Scheduler
Figure 12.4 Task states and transitions for different schedulers.
䡲
䡲
䡲
8
Waiting for the scheduler to decide that this task is ready to run. For example, a
task which asked the scheduler to delay it for 500 ms will be in this state for that
amount of time.
Ready to start running but not running yet. There may be a higher-priority task
which is running. As this task has not started running, no automatic variables have
been initialized, and there is no activation record.
Running on the processor. The task runs to the completion of the task function,
at which point the scheduler resumes execution and the task is moved to the waiting state. Automatic variables have been initialized, and there is at least one activation record on the stack frame for this task. A single processor system can have
only one task in this state.
We consider preemption by an ISR as a separate state. However, since it operates automatically and saves and
restores system context, we consider it as a separate enhancement to the RTC scheduler and leave it out of our
diagrams. In fact, the scheduler relies on a tick ISR to track time and move tasks between certain states.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
457
Consider a task which needs to write a block of data to flash memory. After issuing a write
command to the flash memory controller, it may take some significant amount of time
(e.g., 10 ms) to program the block. We have two options with a non-preemptive kernel:
䡲
䡲
Our task can use a busy wait loop until the flash block programming is complete.
The task remains in the running state while programming. This approach delays
other processing and wastes processor cycles.
We can break the task into a state machine so that task state one issues the write
command, task state two checks to see if the programming is done, and task state
three continues with the task’s processing. The task executes task state two each
time it is called as long as programming is not done. The task spends most of its
time waiting, with occasional brief periods running when executing the code for
task state two. This approach complicates program design but is practical for
smaller systems. However, it grows unwieldy for complex systems.
Allowing tasks to preempt each other reduces response time and simplifies application design. With preemption, each task need not be built with a run-to-completion structure. Instead, the task can yield the processor to other tasks, or it can be preempted by a higherpriority task with more urgent processing. For example, our task can tell the scheduler
“I don’t have anything else to do for the next 10 ms, so you can run a different task.” The
scheduler then will save the state of this task, and swap in the state of the next highest priority task which is ready to run. This introduces another way to move from running to waiting, as well as a way to move from running to ready. We examine these in detail next.
12.4.2 Transitions between States
We now examine the ways in which a task can move between the various states. These
rules govern how the system behaves, and therefore set some ground rules for how we
should design our system.
䡲
䡲
The transition from ready to running:
▫ In a non-preemptive system, when the scheduler is ready to run a task, it selects the highest priority ready task and moves it to the running state, typically
by calling it as a subroutine (as there is no context to restore).
▫ In a preemptive system, when the kernel is ready to run a task, it selects the
highest priority ready task and moves it to the running state by restoring its
context to the processor.
The transition from running to waiting:
▫ In a non-preemptive system, the only way a task can move from running to
waiting is if it completes (returns from the task function). At this point there is
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
no more execution context for the task (return addresses, automatic variables),
so there is no data to save or restore.
▫ In a preemptive system, the task can yield the processor.9 For example, it can
request a delay (“Hey, RTOS! Wake me up in at least 10 ms!”) or it can wait or
pend on an event (“Hey, RTOS! Wake me up when I get a message in my
mailbox called foo!”). This makes application programming much easier, as
mentioned before. At this point there still is execution context, so the kernel
must save it for later restoration.
The transition from waiting to ready:
▫ In a non-preemptive system such as the RTC scheduler above, the timer tick
ISR moves the task by setting the run flag. Alternatively, another task can set
the run flag to request for this task to run.
▫ In a preemptive system, the kernel is notified that some event has occurred.
For example, time delay has expired, or a task has sent a message to the mailbox called foo. The kernel knows which task is waiting for this event, so it
moves that particular task from the waiting state to the ready state.
The transition from running to ready:
▫ In a non-preemptive system this transition does not exist, as a task cannot be
preempted.
▫ In a preemptive system, when the kernel determines a higher priority task is
ready to run, it will save the context of the currently running task, and move
that task to the ready state.
12.4.3 Context Switching for Preemptive Systems
In preemptive systems, some of these state transitions require the scheduler to save a task’s
execution context and restore another task’s context to ensure programs execute correctly.
This is called context switching and involves accessing the processor’s general-purpose
registers.
Figure 12.5 shows a view of a processor and its memory as it is executing task A in a
system with two tasks (A and B). The CPU uses the program counter PC to fetch the next
instruction to execute, and various pointer registers refer to locations in memory such as
the task’s stack, etc. The CPU also has general purpose registers which are used to hold the
programs data and intermediate computation results.
In order to perform a context switch from task A to task B correctly, we must first
copy all of this task-specific processor register information to a storage location (e.g., task
9
What happens if the task function finishes executing depends on the RTOS. The task could move to the waiting state, or to a terminated state.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
Memory
0x000000
Figure 12.5 Saving task
A’s context from the CPU.
global data
CPU
R0
R1
A0
A1
FLG USP
R2
R3
PC
FB
ISP
heap
SB
TCB A
R0
R1
A0
A1
FLG USP
R2
R3
PC
FB
ISP
B Stack
SB
A Stack
Task A
instructions
Task B
0xFFFFFF
Memory
0x000000
global data
CPU
R0
R1
A0
A1
FLG USP
R2
R3
PC
FB
ISP
heap
SB
TCB A
R0
R1
A0
A1
FLG USP
R2
R3
PC
FB
ISP
B Stack
SB
A Stack
Task A
TCB B
R2
instructions
R0
R1
R3
A0
A1
FLG USP
PC
FB
ISP
Task B
SB
0xFFFFFF
Figure 12.6 Restoring
task B’s context to the CPU.
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EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
control block (TCB) A). Second, we must copy all of the data from TCB B into the CPU’s
registers. This operation is shown in Figure 12.6. Now the CPU will be able to resume execution of task B where it left off.
12.5
SHARING DATA SAFELY
Preemption among tasks introduces a vulnerability to data race conditions. Now a task can
be considered to be as bug-prone and difficult to debug as an ISR! The system can fail in
new ways when:
䡲
䡲
Multiple tasks or ISRs share data,10 or
Multiple instances of a function can execute concurrently.
In order to prevent these failures we need to be careful when designing our system.
12.5.1 Data Shared Objects
If a data object is accessed by code which can be interrupted (is not atomic), then there is a
risk of data corruption. Atomic code is the smallest part of a program that executes without
interruption. Generally a single machine instruction is atomic,11 but sequences of instructions are not atomic unless interrupts are disabled.
Consider an example where task A starts modifying object O. Task B preempts it before it finishes. At this point in time object O is corrupted, as it is only partially updated. If
task B needs to read or write O, the computation results will be incorrect and the system
will likely fail.
1. unsigned time_minutes, time_seconds;
2. void task1 (void){
3.
time_seconds++;
4.
if(time_seconds >= 60){
5.
time_minutes++;
6.
time_seconds = 0;
7.
}
8. }
10
Hardware registers which change outside of the program’s control also introduce problems but we do not discuss them further here.
11
Some instruction sets have long instructions (e.g., string copy, block move) which can be interrupted, in
which case those instructions are not atomic.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
461
9. void task2 (void){
10.
unsigned elapsed_sec;
11.
elapsed_seconds = time_minutes * 60 + time_seconds;
12. }
Here is a more specific example. Our shared object is a pair of variables which measure the
current time in minutes and seconds. Task1 runs once per second to increment the seconds,
and possibly the minutes as well. Task2 calculates how many total seconds have elapsed
since time zero. There are data races possible:
䡲
䡲
If task1 is preempted between lines 4 and 5 or lines 5 and 6, then when task2 runs
it will only have a partially updated version of the current time, and elapsed_
seconds will be incorrect.
If task2 is preempted during line 11, then it is possible that timeinutes is read before task1 updates it and time_seconds is read after task 1 updates it. Again, this
leads to a corrupted elapsed_seconds value.
12.5.2 Function Reentrancy
Another type of shared data problem comes with the use of non-reentrant functions. In this
case, the problem arises from multiple instances of the same function accessing the same
object. Consider the following example:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
void task1 ( ){
. . . . . . . . .
swap(&x, &y);
. . . . . . . . .
}
void task2 ( ){
. . . . . . . . .
swap(&p, &q);
. . . . . . . . .
}
int Temp;
void swap (*i, *j ){
Temp = *j;
*j = *i;
*i = Temp;
}
. . . . . .
. . . . . .
. . . . . .
. . . . . .
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Suppose task1 is running and calls the swap function. After line 13 is executed, task2 becomes ready. If task2 has a higher priority, task1 is suspended and task2 is serviced. Later,
task1 resumes to line 14. Since Temp is a shared variable, it is not stored in the TASK subroutine shared data stack. When task1 line 15 is executed, variable x (of task1 pointed by
variable pointer i) gets the wrong value. Such function executions should not be suspended
in between or shared by more than one task. Such functions are called non-reentrant. The
code which can have multiple simultaneous, interleaved, or nested invocations which will
not interfere with each other is called reentrant code. These types of code are important for
parallel processing, recursive functions or subroutines, and for interrupt handling. An example of a reentrant code is as follows:
1. void swap (*i, *j ){
2.
static int Temp;
3.
Temp = *j;
4.
*j = *i;
5.
*i = Temp;
6. }
Since the variable Temp is declared within the function, if any other task interrupts the execution of the swap function, the variable Temp will be stored in the corresponding task’s
stack and will be retrieved when the task resumes its function. In most cases, especially in
a multi-processing environment, the non-reentrant functions should be eliminated. A function can be checked for its reentrancy based on these three rules:
1. A reentrant function may not use variables in a non-atomic way unless they are
stored on the stack of the calling task or are the private variables of that task.
2. A reentrant function may not call other functions which are not reentrant.
3. A reentrant function may not use the hardware in a non-atomic way.
12.5.3 High-Level Languages and Atomicity
We can identify some but not all non-atomic operations by examining high-level source
code. Since the processor executes machine code rather than a high-level language such as
C or Java, we can’t identify all possible non-atomic operations just by examining the
C source code. Something may seem atomic in C but actually be implemented by multiple
machine instructions. We need to examine the assembly code to know for sure. Let’s examine the following function and determine whether it is reentrant or not:
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
463
EXAMPLE 1
1. static int event_count;
2. void event_counter (void){
3.
++event_count;
4. }
Example 1 in assembly language:
1.
2.
3.
4.
5.
MOV.L #0000100CH, R4
MOV.L [R4 ], R5
ADD #1H, R5
MOV.L R5, [R4 ]
RTS
Consider example 1, and then apply the first rule. Does it use shared variable event_count in
an atomic way? The ++event_count operation is not atomic, and that single line of C code is
implemented with three lines of assembly code (lines two through four). The processor loads
R4 with a pointer to event_count, copies the value of event_count into register R5, adds 1 to
R5, and then stores it back into memory. Hence, example 1 is non-reentrant.
However, what if the processor instruction set supports in-place memory operations?
The RX architecture does not, but many others do. In that case, the assembly code could
look like this:
Example 1 in assembly language, compiled for a different processor architecture:
1. MOV.L #0000100CH, A0
2. ADD #1H, [A0 ]
3. RTS
This code is reentrant, since there is only one instruction needed to update the value of the
event count. Instruction 1 is only loading a pointer to the event count, so interrupting between 1 and 2 does not cause a problem.
EXAMPLE 2
1. void add_sum (int *j){
2.
++(*j);
3.
DisplayString(LCDLINE1, Int_to_ascii(*j);
4. }
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Now consider example 2. Even though line 2 in this example is not atomic, the variable *j
is task’s private variable, hence rule 1 is not breached. But consider line 3. Is the function
DisplayString reentrant? That depends on the code of DisplayString, which depends
on the user. Unless we are sure that the DisplayString function is reentrant, example 2 is
considered to be non-reentrant. So every time a user codes a function, he has to make sure
the function is reentrant to avoid erroneous results.
12.5.4 Shared-Data Solutions and Protection
In the previous section, we discussed the problems of using shared data in a RTOS environment. In this section we shall study some methods to protect the shared data. The solutions provided in this section may not be ideal for all applications. The user must judge
which solution may work best for the application.
Disable Interrupts
One of the easiest methods is to disable the interrupts during the critical section of the task.
Disabling the interrupts may not take more than one machine cycle to execute, but will increase the worst case response time of all other code, including other interrupt service routines. Once the critical section, or shared variable section, of the code is executed, the interrupt masking be restored to its previous state (either enabled or disabled). The user must
be cautious while disabling or enabling interrupts, because if interrupts are disabled for too
long, the system may fail to meet the timing requirements. See Chapter 9, Using Interrupts
with Peripherals, to find out how to disable and restore interrupt masking state. A simple
example of disabling interrupts is as follows:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
#define TRUE 1
#define FALSE 0
static int error;
static int error_count;
void error_counter ( ){
if(error == TRUE){
SAVE_INT_STATE;
DISABLE_INTS;
error_count++;
error = FALSE;
RESTORE_INT_STATE;
}
}
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
465
Disabling and restoring the interrupt masking state requires only one or a few machine cycles. Disabling interrupts must take place only at critical sections to avoid increasing response time excessively. Also, while restoring the interrupt masking state the user must
keep in mind the need to enable only those interrupts that were active (enabled) before they
were disabled. Determining the interrupt masking status can be achieved by referring to the
interrupt mask register. The Interrupt mask register keeps track of which interrupts are
enabled and disabled.
Use a Lock
Another solution is to associate every shared variable with a lock variable, which is also
declared globally. If a function uses the shared variable, then it sets the lock variable
and once it has finished process, it resets the lock variable. Every function must test the
lock variable before accessing it. If the lock variable is already set, the task should inform the scheduler to be rescheduled once the variable becomes available. Since only
one variable has to be checked every time before accessing the data, using lock variables simplifies the data structure and I/O devices access. Consider the following example for using a lock:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
unsigned int var;
char lock_var;
void task_var ( ){
unsigned int sum;
if(lock_var == 0){
lock_var = 1;
var = var + sum;
lock_var = 0;
}
else {
/* message to scheduler to check var
and reschedule */
}
}
Since it takes more than one clock cycle to check whether a variable is available and use a
lock on it, the interrupts have to be disabled. Once again when the lock has to be released,
the interrupts should be disabled since locking and releasing the variable is a critical part of
the code. Interrupts must be enabled whenever possible to lower the interrupt service response time. If the variable is not available, the scheduler is informed about the lock and
the task goes into a waiting state.
466
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Microprocessors such as the Renesas RX support Bit Test and Set instructions can perform a test and set in one atomic machine instruction, and therefore do not require an
interrupt disable/enable lock around semaphore usage.
The challenge with this approach is determining what to do in lines 11 and 12 if there
is no scheduler support. There may be no easy way to tell the scheduler to reschedule this
task when the lock variable becomes available again.
RTOS-Provided Semaphore
Most operating systems provide locks to shared variables through the use of semaphores.
A semaphore is a mechanism that uses most of the multitasking kernels to protect shared
data and to synchronize two tasks. A semaphore is very much similar to the variable lock
process explained in the Section 12.4.3. The main difference is that the OS takes care of
initializing and handling the locks, so the implementation is much more likely to be correct
than if you try to create your own lock.
There are two types of semaphores—binary semaphores and counting semaphores.
Binary semaphores take two values, 0 or 1. A counting semaphore takes a value between
0 and 2N 1, where N is the number of bits used for the semaphore. In this book we consider only the binary semaphore. A semaphore usually has three tasks: initialization/create,
wait, and signal.
A non-zero number or value is assigned to the semaphore once it is created. At this
point no task is waiting for the semaphore. Once a task requires a data, the task performs a
wait operation on the semaphore. The OS checks the value of the semaphore; for example,
if the semaphore is available (semaphore value is non-zero), the OS changes the value of
the semaphore to zero and assigns the semaphore to the task. If the semaphore value is zero
during the wait operation, the task that requested the wait operation is placed on the semaphore’s waiting list. Once the semaphore becomes available based on the priority of the
tasks waiting for it, the OS decides which task to assign to the semaphore.
The tasks added to the semaphore’s waiting list wait only for a certain amount of time.
If the time expires, the task sends an error code to the semaphore seeking function and resumes its work. When the task has attained the semaphore and all its operations are complete, the task performs a signal operation, announcing that the semaphore is free. The OS
checks if any other task is waiting for the semaphore and then transfers the semaphore to
the task without changing the semaphore’s value. If no task is waiting for the semaphore,
the semaphore is incremented to a non-zero number. The wait operation is also referred to
as Take or Pend or P and signal operation is referred to as Release or Post or V. The following example shows how wait and signal operations are performed:
1.
2.
3.
4.
typedef int semaphore;
float temp;
semaphore var_temp
void Task1 (void){
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
467
5.
wait (var_temp);
6.
temp = (9/5)(temp + 32); /* Celsius into Fahrenheit */
7.
Signal (var_temp);
8. }
9. void Task2 (void){
10.
wait(var_temp);
11.
temp = ADDR0; /* Read ADC value from thermistor */
12.
temp = ADCtotemp_conversion();
13.
Signal (var_temp);
14. }
In the previous example two tasks share the variable temp. The Task2 subroutine reads the
temperature value from a thermistor and saves it on temp, while Task1 converts the temperature from Celsius to Fahrenheit. Just before the tasks enter the critical section, they request the semaphore and only then perform the operation on the shared variable.
RTOS-Provided Messages
The RTOS provides other mechanisms besides semaphores for allowing tasks to communicate, such as message queues and mailboxes. It may be possible to structure your program to
use messages to pass information rather than sharing data objects directly. We leave further
discussion of this approach to the many RTOS-oriented books and articles already available.
Disable Task Switching
If no other method seems to work, one unattractive option is to disable the scheduler. If the
scheduler is disabled, the task switching does not take place and the critical sections or shared
data can be protected by other tasks. This method is counter-productive; disabling the scheduler increases response times and makes analysis much more difficult. This is considered bad
practice and must be properly justified; hence consider this method as a last resort.
12.6
NONPREEMPTIVE DYNAMIC SCHEDULER
12.6.1 Concepts
We will now examine a flexible nonpreemptive scheduler for periodic and aperiodic tasks.
We call it the RTC (run-to-completion) scheduler. This simple tick-based scheduler is quite
flexible and offers the following major benefits:
䡲
We can configure the system to run each task with a given period (e.g., every
40 ms) measured in time ticks. This simplifies the creation of multi-rate systems.
468
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
䡲
䡲
We can define task priorities, allowing us to design the system’s response (which
tasks are executed earlier) when there are multiple tasks ready to run.
We can selectively enable and disable tasks.
This scheduler has three fundamental parts.
䡲
䡲
䡲
Task Table: This table holds information on each task, including:
▫ The address of the task’s root function.
▫ The period with which the task should run (e.g., 10 ticks).
▫ The time delay until the next time the task should run (measured in ticks).
▫ A flag indicating whether the task is ready to run.
Tick ISR: Once per time tick (say each 1 millisecond) a hardware timer triggers
an interrupt. The interrupt service routine decrements the time delay (timer) until
the next run. If this reaches zero, then the task is ready to release, so the ISR sets
its run flag.
Task Dispatcher: The other part of the scheduler is what actually runs the tasks. It
is simply an infinite loop which examines each task’s run flag. If it finds a task with
the run flag set to 1, the scheduler will clear the run flag back to 0, execute the
task, and then go back to examining the run flags (starting with the highestpriority task in the table).
Figure 12.7 shows a simple example of how this works with three tasks. Task 1 becomes
active every twenty time intervals, and takes one time interval to complete. Task 2 is active
every ten time intervals, and takes two time intervals to complete. Task 3 becomes active
every five time intervals and takes one time interval to complete.
If more than one task becomes ready simultaneously (as seen at elapsed time ten), the
higher priority task is serviced first. When the higher priority task finishes, the next highest
ready task is executed. This repeats until there are no ready tasks.
Another example of a run-to-completion dynamic scheduling with interrupts is shown
in Figure 12.8. A new task, Task 4, is added, which becomes active every three time intervals and runs for one time interval.
As shown in Figure 12.8, at time 20, tasks T1, T2, T3 all become active and T2 is
run based on priority. At time 21, task T4 becomes active and is scheduled to run at
time 22. T1 runs at time 23, but before T3 gets a chance to run, T4 becomes active
again and gains the processor. At time 25, T3 misses a turn since T3 becomes active
again and the T3 is serviced as if it were active only once. This is an example of an overload situation which leads to one of the tasks missing its turn.12
12
We could use a counter rather than a flag for the run variable, to allow for processing backlogs. In this case
the ISR would increment run rather than set it, and the scheduler function would decrement it rather than clear
it. This could be useful in some situations, but it would complicate the analysis.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
Priority
2
1
3
Task 1
Task 2
Task 3
Elapsed time 0
Task executed
Task T1
Task T2
Task T3
1
Length
1
2
1
2
3
4
Frequency
20
10
5
5
T3
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
T2
T3
T3
T2
T1 T3
T3
20 19 18 17 16 15 14 13 12 11 10
10 9 8 7 6 5 4 3 2 1 10
5 4 3 2 1 5 4 3 2 1 5
Run T1
Run T2
Run T3
9
9
4
R
W W
R
R Running on processor
469
8
8
3
7
7
2
6
6
1
R
5
5
5
4
4
4
3
3
3
2
2
2
1
1
1
20 19 18 17 16 15
10 9 8 7 6 5
5 4 3 2 1 5
W W R
R
W W W
R
R
R
W Ready and waiting for processor
Figure 12.7 Simple run-to-completion dynamic scheduling.
Priority
2
1
3
0
Task 1
Task 2
Task 3
Task 4
Elapsed time 0
Task executed
Task T1
Task T2
Task T3
Task T4
1
Length
1
2
1
1
2
3
T4
4
Frequency
20
10
5
3
5 6
T3 T4
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
T4
T2
T4 T3
T4 T3
T4
T2
T4 T1 T4 T3
20 19 18 17 16 15 14 13 12 11 10
10 9 8 7 6 5 4 3 2 1 10
5 4 3 2 1 5 4 3 2 1 5
3 2 1 3 2 1 3 2 1 3 2
Run T1
Run T2
Run T3
Run T4
R
R
R Running on processor
R
R
9
9
4
1
8
8
3
3
R
W W W
R
7
7
2
2
R
6
6
1
1
5
5
5
3
W
R
4
4
4
2
3
3
3
1
2
2
2
3
R
R
1
1
1
2
20 19 18 17 16 15
10 9 8 7 6 5
5 4 3 2 1 5
1 3 2 1 3 2
W W W R
R
W W W W W
W R
R
W Ready and waiting for processor
Figure 12.8 Complex run-to-completion dynamic scheduling.
R
470
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Priority
2
1
3
0
Task 1
Task 2
Task 3
Task 4
Elapsed time 0
Task executed
Task T1
Task T2
Task T3
Task T4
20
10
5
3
Length
1
2
1
2
Frequency
20
10
5
3
1
2
3 4 5 6 7
T4 T3 T4
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
T4
T2
T4
T4 T3 T4
T2
T4
T4 T1 T4 T3 T4
19
9
4
2
18
8
3
1
17
7
2
3
12
2
2
1
11
1
1
3
Run T1
Run T2
Run T3
Run T4
16
6
1
2
15
5
5
1
14
4
4
3
R
R
R Running on processor
R
13
3
3
2
10
10
5
2
9
9
4
1
8
8
3
3
7
7
2
2
6
6
1
1
5
5
5
3
4
4
4
2
3
3
3
1
2
2
2
3
W R
W W W W W W W R
R
W R
R
R
1 20 19
1 10 9
1 5 4
2 1 3
18
8
3
2
17
7
2
1
16
6
1
3
15
5
5
2
14
4
4
1
13
3
3
3
12
2
2
2
11
1
1
1
10
10
5
3
W W W W W W R
R
W
W W W W W W W W W R W
W R
R
R
R
W Ready and waiting for processor
Figure 12.9 Overload example of run-to-completion dynamic scheduling.
Figure 12.9 shows a complex overloaded example where the scheduler fails to service
every task that is ready.
12.6.2 Implementation
Task Table
A scheduler uses a table to store information on each task. Each task has been assigned a
timer value. A task becomes active at regular intervals based on this value. This timer value
is decremented each tick by the timer tick ISR. Once the timer value reaches zero, the task
becomes ready to run. To reset this value after it has reached zero, an initial Timer Value
variable is used to store the time at which the task has to be active. Two variables, enabled
and run, are used to signal when a task is enabled and when it is ready to run. Variables
enabled and run are used to indicate to the scheduler if a task is enabled and if it is ready to
run. The function pointer *task indicates to the scheduler which function to perform.
The task’s priority is defined by its position within this array. Entry 0 has the highest
priority; whenever the scheduler needs to find a task to run, it begins at entry 0 and then
works its way through the table.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
471
The scheduler’s task table is defined as follows:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
#define MAX_TASKS 10
#define NULL ((void *)0)
typedef struct {
int initialTimerValue;
int timer;
int run;
int enabled;
void (* task)(void);
} task_t;
task_t GBL_task_table [MAX_TASKS ];
Before running the scheduler, the application must initialize the task table as follows:
1. void init_Task_Timers(void){
2.
int i;
3.
/* Initialize all tasks */
4.
for(i = 0; i < MAX_TASKS; i++){
5.
GBL_task_table [i ].initialTimerValue = 0;
6.
GBL_task_table [i ].run = 0;
7.
GBL_task_table [i ].timer = 0;
8.
GBL_task_table [i ].enabled = 0;
9.
GBL_task_table [i ].task = NULL;
10.
}
11. }
Managing Tasks
Once the initialization is completed, tasks must be added to the task structure. The new
tasks can be added before starting the scheduler or during the scheduler’s execution time.
When adding a task, the following must be specified: the time interval in which the task has
to be active, its priority, and the function on which the task has to operate. The following
code shows how adding a task is added:
1. int Add_Task(void (*task)(void), int time, int priority){
2.
/* Check for valid priority */
3.
if(priority >= MAX_TASKS || priority < 0)
4.
return 0;
5.
/* Check to see if we are overwriting an already scheduled
task */
6.
if(GBL_task_table [priority ].task != NULL)
472
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
7.
8.
9.
10.
11.
12.
13.
14.
15. }
return 0;
/* Schedule the task */
GBL_task_table [priority ].task = task;
GBL_task_table [priority ].run = 0;
GBL_task_table [priority ].timer = time;
GBL_task_table [priority ].enabled = 1;
GBL_task_table [priority ].initialTimerValue = time;
return 1;
We can remove an existing task:
1. void removeTask(void (* task)(void)){
2.
int i;
3.
for(i = 0; i < MAX_TASKS; i++){
4.
if(GBL_task_table [i ].task == task){
5.
GBL_task_table [i ].task = NULL;
6.
GBL_task_table [i ].timer = 0;
7.
GBL_task_table [i ].initialTimerValue = 0;
8.
GBL_task_table [i ].run = enabled = 0;
9.
return;
10.
}
11.
}
12. }
We can also selectively enable or disable a task by changing its enabled flag:
1.
2.
3.
4.
5.
6.
7.
void Enable_Task(int task_number){
GBL_task_table [task_number ].enabled = 1;
}
void Disable_Task(int task_number){
GBL_task_table [task_number ].enabled = 0;
}
Finally, we can change the period with which a task runs:
1. void Reschedule_Task(int task_number, int new_timer_val){
2.
GBL_task_table [task_number ].initialTimerValue =
3.
new_timer_val;
4.
GBL_task_table [task_number ].timer = new_timer_val;
5. }
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
473
Tick Timer Configuration and ISR
A run-to-completion dynamic scheduler uses a timer to help determine when tasks are
ready to run (are released). A timer is set up to generate an interrupt at regular intervals.
Within the interrupt service routine the timer value for each task is decremented. When the
timer value reaches zero, the task becomes ready to run. In this code we have configured
the 8-bit timer to generate an interrupt every 0.5 milliseconds. For details on how to set up
a timer see Chapter 8.
1. void Init_RTC_Scheduler(void){
2.
IEN(TMR0,CMIA0) = 0;
3.
IPR(TMR0,CMIA0) = 3;
4.
MSTP(TMR0) = 0;
5.
TMR0.TCNT = 0x00;
6.
TMR0.TCORA = 78;
7.
TMR0.TCSR.BYTE = 0xE2;
8.
IEN(TMR0,CMIA0) = 1;
9.
TMR0.TCCR.BYTE = 0x0C;
10.
TMR0.TCR.BYTE = 0x48;
11. }
In the next example Timer 0 is set to compare the match mode with timer constant A. An
interrupt occurs every 0.5 millisecond. The timer is configured in a continuous mode and
resets every time a compare match is made.
1. void Excep_TMR0_CMI0A(void){
2.
int i;
3.
for(i = 0; i < MAX_TASKS; i++){
4.
if(GBL_task_table [i ].task != NULL) &&
5.
(GBL_task_table [i ].enabled == 1) &&
6.
(GBL_task_table [i ].timer > 0))
7.
{
8.
if(––GBL_task_table [i ].timer == 0){
9.
GBL_task_table [i ].run = 1;
10.
GBL_task_table [i ].timer =
11.
GBL_task_table [i ].initialTimerValue;
12.
}
13.
}
14.
}
15. }
474
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
Scheduler
The scheduler looks for ready tasks starting at the top of the table (highest priority task). It
runs every ready task it finds, calling it as a function (in line 16).
1. void Run_RTC_Scheduler(void){
2.
int i;
3.
/* Loop forever */
4.
while(1){
5.
/* Check each task */
6.
for(i = 0; i < MAX_TASKS; i++){
7.
/* check if valid task */
8.
if(GBL_task_table [i ].task != NULL){
9.
/* check if enabled */
10.
if(GBL_task_table [i ].enabled == 1){
11.
/* check if ready to run */
12.
if(GBL_task_table [i ].run == 1){
13.
/* Reset the run flag */
14.
GBL_task_table [i ].run = 0;
15.
/* Run the task */
16.
GBL_task_table [i ].task();
17.
/* break out of loop to start at entry 0 */
18.
break;
19.
}
20.
}
21.
}
22.
}
23.
}
24. }
12.6.3 Example Application using RTC Scheduler
Let’s use the RTC scheduler to create a toy with red and green LEDs flashing at various frequencies. The grnLED task toggles a green LED (on board LED 6) every one second, and
the redLED task toggles a red LED (on board led 12) every 0.25 seconds. The grn_redLED
task toggles one red LED and one green LED (on board led 7 and led 8 respectively) every
0.5 seconds.
The tasks and the main program are shown below:
1. void grnLED(void){
2.
if(LED3 == LED_ON)
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
12.7
475
LED3 = LED_OFF;
else
LED3 = LED_ON;
}
void redLED(void){
if(LED4 == LED_ON)
LED4 = LED_OFF;
else
LED4 = LED_ON;
}
void grn_redLED(void){
if(LED5 == LED_ON)
LED5 = LED9 = LED_OFF;
else
LED5 = LED9 = LED_ON;
}
void main(void){
ENABLE_LEDS;
init_Task_Timers();
Add_Task(grnLED,10000,0);
Add_Task(redLED,2500,1);
Add_Task(grn_redLED,5000,2)
Init_RTC_Scheduler();
Run_RTC_Scheduler();
}
REFERENCES
Simon, David E. An Embedded Software Primer. Indianapolis: Addison-Wesley Professional, 1999. Print.
Labrosse, J. MicroC/OS II: The Real-Time Kernel, 2nd Ed. Lawrence, KS: Newnes, 2002. Print.
Labrosse, J., Ganssle, J., Oshana, R., Walls, C., Curtis, K., Andrews, J., Katz, D., Gentile, R., Hyder, K., and
B. Perrin. Embedded Software: Know it All. Burlington, MA: Newnes, 2008. Print.
Labrosse, J. MicroC/OS-III: The Real-Time Kernel, or a High Performance, Scalable, ROMable, Preemptive,
Multitasking Kernel for Microprocessors, Microcontrollers & DSPs. Weston, FL: Micrium Press, 2009.
Print.
476
EMBEDDED SYSTEMS USING THE RENESAS RX62N MICROCONTROLLER
12.8
EXERCISES
1. For some task sets, changing from static to dynamic task ordering in a scheduler
2.
3.
4.
5.
6.
will provide a major response time improvement for the highest priority task,
while for other task sets it will not. Give an example of each and explain the
difference.
For some task sets, adding preemption to a scheduler will provide a major response time improvement for the highest priority task, while for other task sets it
will not. Give an example of each and explain the difference.
Write C code to implement run-to-completion dynamic scheduling without interrupts to poll the following tasks:
a. If switch 1 is pressed Toggle the RED LEDs.
b. If switch 2 is pressed read the temperature value from the onboard thermistor
and display on LCD.
c. If switch 3 is pressed read the potentiometer value and display on the LCD.
d. If no switch is pressed Toggle the GREEN LEDs.
Write an algorithm which implements the below functionality using run-tocompletion dynamic scheduling with interrupts:
a. Toggle RED LEDs every 0.5 seconds.
b. Toggle GREEN LEDs every 0.25 seconds.
c. Read temperature value from onboard thermistor and display on LCD every
1.0 seconds.
d. Read potentiometer value and display on LCD every 2.5 seconds.
Write a C code to implement round-robin with interrupts algorithm to perform the
following tasks:
a. Toggle RED LEDs every 0.5 seconds.
b. Toggle GREEN LEDs every 0.25 seconds.
c. Read temperature value from onboard thermistor and display on LCD every
1.0 seconds.
d. Read potentiometer value and display on LCD every 2.5 seconds.
Fill in the following table to show which tasks the processor will execute and when,
as well as scheduler table contents. Assume that timer tick interrupts occur every
1 millisecond, all tasks take 1.2 milliseconds to complete, and initialTimerValue for
tasks A, B, and C are 2, 4, and 5 respectively. Note that the entries in the table in column “Right before n” (e.g., timer, run, enabled) show the variable’s value right before the timer tick interrupt occurs. This means that a task will run on the tick when
its timer reaches 0 (but show the value after the tick and after the ISR executes). Assume task A has the highest priority, followed by task B, and then C.
CHAPTER 12 / DESIGNING RESPONSIVE AND REAL-TIME SYSTEMS
RIGHT
BEFORE
N
TASK
NAME
A
B
C
timer
2
run
0
enabled
1
timer
3
run
0
enabled
1
timer
1
run
0
enabled
1
Activity
—
N
N
ⴙ
1
N
ⴙ
2
N
ⴙ
3
N
ⴙ
4
N
ⴙ
5
N
ⴙ
6
N
ⴙ
7
N
ⴙ
8
N
ⴙ
9
N
ⴙ
10
N
ⴙ
11
N
ⴙ
12
477
N
ⴙ
13
7. Fill in the table in Exercise 4, if timer tick interrupts occur every 0.5 milliseconds
and all tasks take 1.25 milliseconds to complete.
Appendix A
Interrupt Vector Table
Source of
Interrupt
Priority Generation
Name
Vector
Adress
Offset
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
—
Reserved
0
0000
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
1
0004
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
2
0008
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
3
000C
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
4
0010
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
5
0014
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
6
0018
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
7
001C
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
8
0020
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
9 to 15
0024 to 003C
—
⫻
⫻
⫻
⫻
⫻
—
—
BUSERR
16
0040
䡩
⫻
⫻
⫻
⫻
IER02. IEN0 IPR00
—
Reserved
17
0044
—
⫻
⫻
⫻
⫻
⫻
IER02. IEN1
—
—
Reserved
18
0048
—
⫻
⫻
⫻
⫻
⫻
IER02. IEN2
—
—
Reserved
19
004C
—
⫻
⫻
⫻
⫻
⫻
IER02. IEN3
—
—
Reserved
20
0050
—
⫻
⫻
⫻
⫻
⫻
IER02. IEN4
—
FIFERR
21
0054
䡩
⫻
⫻
⫻
⫻
IER02. IEN5 IPR01
Reserved
22
0058
⫻
⫻
⫻
⫻
⫻
IER02. IEN6
FRDYI
23
005C
䡩
⫻
⫻
⫻
⫻
IER02. IEN7 IPR02
—
Reserved
24
0060
—
⫻
⫻
⫻
⫻
⫻
IER03. IEN0
—
—
Reserved
25
0064
—
⫻
⫻
⫻
⫻
⫻
IER03. IEN1
—
—
Reserved
26
0068
—
⫻
⫻
⫻
⫻
⫻
IER03. IEN2
—
SWINT
27
006C
Edge
䡩
䡩
⫻
⫻
⫻
IER03. IEN3 IPR03
CMT Unit 0 CMI0
28
0070
Edge
䡩
䡩
䡩
⫻
⫻
IER03. IEN4 IPR04
CMI1
29
0074
Edge
䡩
䡩
䡩
⫻
⫻
IER03. IEN5 IPR05
High
Bus error
FCU
ICU
Low
Vector
No.
Selectable
Interrupt
Request
Destination
Level
Level
—
Edge
䡩: Selectable ⫻: Not Selectable
Source: RX62N Group, RX621 Group Hardware Manual, page 342-355.
479
—
480
APPENDIX A
Source of
Interrupt
Priority Generation
High
Vector
Adress
Offset
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
CMT Unit 1 CMI2
30
0078
Edge
䡩
䡩
䡩
⫻
⫻
IER03. IEN6 IPR06
CMI3
31
007C
Edge
䡩
䡩
䡩
⫻
⫻
IER03. IEN7 IPR07
Ether
EINT
32
0080
Level
䡩
⫻
⫻
⫻
⫻
IER04. IEN0 IPR08
USB0
D0FIFO0
36
0090
Edge
䡩
䡩
䡩
⫻
⫻
IER04.IEN4 IPR0C
D1FIFO0
37
0094
Edge
䡩
䡩
䡩
⫻
⫻
IER04.IEN5 IPR0D
USBI0
38
0098
Edge
䡩
⫻
⫻
⫻
⫻
IER04.IEN6 IPR0E
D0FIFO1
40
00A0
Edge
䡩
䡩
䡩
⫻
⫻
IER05. IEN0 IPR10
D1FIFO1
41
00A4
Edge
䡩
䡩
䡩
⫻
⫻
IER05. IEN1 IPR11
USBI1
42
00A8
Edge
䡩
⫻
⫻
⫻
⫻
IER05. IEN2 IPR12
SPEI0
44
00B0
Level
䡩
⫻
⫻
⫻
⫻
IER05. IEN4 IPR14
SPRI0
45
00B4
Edge
䡩
䡩
䡩
⫻
⫻
IER05. IEN5
SPTI0
46
00B8
Edge
䡩
䡩
䡩
⫻
⫻
IER05. IEN6
SPII0
47
00BC
Level
䡩
⫻
⫻
⫻
⫻
IER05. IEN7
SPEI1
48
00C0
Level
䡩
⫻
⫻
⫻
⫻
IER06. IEN0 IPR15
SPRI1
49
00C4
Edge
䡩
䡩
䡩
⫻
⫻
IER06. IEN1
SPTI1
50
00C8
Edge
䡩
䡩
䡩
⫻
⫻
IER06. IEN2
Level
USB1
RSPI0
RSPI1
SPII1
51
00CC
䡩
⫻
⫻
⫻
⫻
IER06. IEN3
—
Reserved
52
00D0
—
⫻
⫻
⫻
⫻
⫻
IER06. IEN4
—
—
Reserved
53
00D4
—
⫻
⫻
⫻
⫻
⫻
IER06. IEN5
—
—
Reserved
54
00D8
—
⫻
⫻
⫻
⫻
⫻
IER06. IEN6
—
—
Reserved
55
00DC
—
⫻
⫻
⫻
⫻
⫻
IER06. IEN7
—
ERS0
56
00E0
Edge
䡩
⫻
⫻
⫻
⫻
IER07. IEN0 IPR18
RXF0
57
00E4
Edge
䡩
⫻
⫻
⫻
⫻
IER07. IEN1
TXF0
58
00E8
Edge
䡩
⫻
⫻
⫻
⫻
IER07. IEN2
RXM0
59
00EC
Edge
䡩
⫻
⫻
⫻
⫻
IER07. IEN3
TXM0
60
00F0
Edge
䡩
⫻
⫻
⫻
⫻
IER07. IEN4
PRD
62
00F8
Edge
䡩
⫻
⫻
⫻
⫻
IER07. IEN6 IPR1E
CUP
63
00FC
Edge
䡩
⫻
⫻
⫻
⫻
IER07. IEN7 IPR1F
External pins IRQ0
64
0100
Edge/level
䡩
䡩
䡩
䡩
䡩
IER08. IEN0 IPR20
IRQ1
65
0104
Edge/level
䡩
䡩
䡩
䡩
䡩
IER08. IEN1 IPR21
CAN0
RTC
Low
Name
Vector
No.
Selectable
Interrupt
Request
Destination
APPENDIX A
Source of
Interrupt
Priority Generation
Vector
Adress
Offset
Selectable
Interrupt
Request
Destination
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
IRQ2
66
0108
Edge/level
䡩
䡩
䡩
䡩
䡩
IER08. IEN2 IPR22
IRQ3
67
010C
Edge/level
䡩
䡩
䡩
䡩
䡩
IER08. IEN3 IPR23
IRQ4
68
0110
Edge/level
䡩
䡩
⫻
䡩
䡩
IER08. IEN4 IPR24
IRQ5
69
0114
Edge/level
䡩
䡩
⫻
䡩
䡩
IER08. IEN5 IPR25
IRQ6
70
0118
Edge/level
䡩
䡩
⫻
䡩
䡩
IER08. IEN6 IPR26
IRQ7
71
011C
Edge/level
䡩
䡩
⫻
䡩
䡩
IER08. IEN7 IPR27
IRQ8
72
0120
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN0 IPR28
IRQ9
73
0124
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN1 IPR29
External pins IRQ10
74
0128
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN2 IPR2A
IRQ11
75
012C
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN3 IPR2B
IRQ12
76
0130
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN4 IPR2C
IRQ13
77
0134
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN5 IPR2D
IRQ14
78
0138
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN6 IPR2E
IRQ15
79
013C
Edge/level
䡩
䡩
⫻
䡩
䡩
IER09. IEN7 IPR2F
—
Reserved
80 to 87
0140 to 015C
—
⫻
⫻
⫻
⫻
⫻
—
—
—
Reserved
88
0160
—
⫻
⫻
⫻
⫻
⫻
IER0B. IEN0
—
—
Reserved
—
—
High
89
0164
⫻
⫻
⫻
⫻
⫻
IER0B. IEN1
USB_resume USBR0
90
0168
Level
䡩
⫻
⫻
䡩
䡩
IER0B. IEN2 IPR3A
USBR1
91
016C
Level
䡩
⫻
⫻
䡩
䡩
IER0B. IEN3 IPR3B
ALM
92
0170
Edge
䡩
⫻
⫻
䡩
䡩
IER0B. IEN4 IPR3C
Reserved
93
0174
—
⫻
⫻
⫻
⫻
⫻
IER0B. IEN5
—
Reserved
94
0178
—
⫻
⫻
⫻
⫻
⫻
IER0B. IEN6
—
Reserved
95
017C
—
⫻
⫻
⫻
⫻
⫻
IER0B. IEN7
—
WOVI
96
0180
䡩
⫻
⫻
⫻
䡩
IER0C. IEN0 IPR40
RTC
WDT
Low
Name
Vector
No.
481
Edge
Reserved
97
0184
⫻
⫻
⫻
⫻
⫻
IER0C. IEN1
AD0
ADI0
98
0188
Edge
䡩
䡩
䡩
⫻
⫻
IER0C. IEN2 IPR44
AD1
ADI1
99
018C
Edge
䡩
䡩
䡩
⫻
⫻
IER0C. IEN3 IPR45
—
Reserved
100
0190
—
⫻
⫻
⫻
⫻
⫻
IER0C. IEN4
—
—
Reserved
101
0194
—
⫻
⫻
⫻
⫻
⫻
IER0C. IEN5
—
S12AD
ADI12_0
102
0198
䡩
䡩
䡩
⫻
⫻
IER0C. IEN6 IPR48
—
Edge
—
482
APPENDIX A
Source of
Interrupt
Priority Generation
High
—
MTU0
MTU1
MTU2
MTU2
MTU3
MTU4
MTU5
Low
MTU6
Name
Vector
No.
Vector
Adress
Offset
Selectable
Interrupt
Request
Destination
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
—
—
Reserved
103 to 113 019C to 01C4
⫻
⫻
⫻
⫻
⫻
TGIA0
114
01C8
Edge
䡩
䡩
䡩
⫻
⫻
IER0E. IEN2 IPR51
TGIB0
115
01CC
Edge
䡩
䡩
⫻
⫻
⫻
IER0E. IEN3
TGIC0
116
01D0
Edge
䡩
䡩
⫻
⫻
⫻
IER0E. IEN4
TGID0
117
01D4
Edge
䡩
䡩
⫻
⫻
⫻
IER0E. IEN5
TCIV0
118
01D8
Edge
䡩
⫻
⫻
⫻
⫻
IER0E. IEN6 IPR52
TGIE0
119
01DC
Edge
䡩
⫻
⫻
⫻
⫻
IER0E. IEN7
TGIF0
120
01E0
Edge
䡩
⫻
⫻
⫻
⫻
IER0F. IEN0
TGIA1
121
01E4
Edge
䡩
䡩
䡩
⫻
⫻
IER0F. IEN1 IPR53
TGIB1
122
01E8
Edge
䡩
䡩
⫻
⫻
⫻
IER0F. IEN2
TCIV1
123
01EC
Edge
䡩
⫻
⫻
⫻
⫻
IER0F. IEN3 IPR54
TCIU1
124
01F0
Edge
䡩
⫻
⫻
⫻
⫻
IER0F. IEN4
TGIA2
125
01F4
Edge
䡩
䡩
䡩
⫻
⫻
IER0F. IEN5 IPR55
TGIB2
126
01F8
Edge
䡩
䡩
⫻
⫻
⫻
IER0F. IEN6
TCIV2
127
01FC
Edge
䡩
⫻
⫻
⫻
⫻
IER0F. IEN7 IPR56
TCIU2
128
0200
Edge
䡩
⫻
⫻
⫻
⫻
IER10. IEN0
TGIA3
129
0204
Edge
䡩
䡩
䡩
⫻
⫻
IER10. IEN1 IPR57
TGIB3
130
0208
Edge
䡩
䡩
⫻
⫻
⫻
IER0E. IEN2
TGIC3
131
020C
Edge
䡩
䡩
⫻
⫻
⫻
IER10. IEN3
TGID3
132
0210
Edge
䡩
䡩
⫻
⫻
⫻
IER10. IEN4
TGIV3
133
0214
Edge
䡩
⫻
⫻
⫻
⫻
IER10. IEN5 IPR58
TGIA4
134
0218
Edge
䡩
䡩
䡩
⫻
⫻
IER10. IEN6 IPR59
TGIB4
135
021C
Edge
䡩
䡩
⫻
⫻
⫻
IER10. IEN7
TGIC4
136
0220
Edge
䡩
䡩
⫻
⫻
⫻
IER11. IEN0
TGID4
137
0224
Edge
䡩
䡩
⫻
⫻
⫻
IER11. IEN1
TCIV4
138
0228
Edge
䡩
䡩
⫻
⫻
⫻
IER11. IEN2 IPR5A
TGIU5
139
022C
Edge
䡩
䡩
⫻
⫻
⫻
IER11. IEN3 IPR5B
TGIV5
140
0230
Edge
䡩
䡩
⫻
⫻
⫻
IER11. IEN4
TGIW5
141
021C
Edge
䡩
䡩
⫻
⫻
⫻
IER10. IEN7
TGIA6
142
0238
Edge
䡩
䡩
䡩
⫻
⫻
IER11. IEN6 IPR5C
—
APPENDIX A
Source of
Interrupt
Priority Generation
High
MTU6
MTU7
MTU8
MTU9
MTU10
MTU11
POE
Low
Name
Vector
No.
Vector
Adress
Offset
483
Selectable
Interrupt
Request
Destination
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
TGIB6
143
023C
Edge
䡩
䡩
⫻
⫻
⫻
IER11. IEN7
TGIC6
144
0240
Edge
䡩
䡩
⫻
⫻
⫻
IER12. IEN0
TGID6
145
0244
Edge
䡩
䡩
⫻
⫻
⫻
IER12. IEN1 IPR5C
TCIV6
146
0248
Edge
䡩
⫻
⫻
⫻
⫻
IER12. IEN2 IPR5D
TGIE6
147
024C
Edge
䡩
⫻
⫻
⫻
⫻
IER12. IEN3
TGIF6
148
0250
Edge
䡩
⫻
⫻
⫻
⫻
IER12. IEN4
TGIA7
149
0254
Edge
䡩
䡩
䡩
⫻
⫻
IER12. IEN5 IPR5E
TGIB7
150
0258
Edge
䡩
䡩
⫻
⫻
⫻
IER12. IEN6
TCIV7
151
025C
Edge
䡩
⫻
⫻
⫻
⫻
IER12. IEN7 IPR5F
TCIU7
152
0260
Edge
䡩
⫻
⫻
⫻
⫻
IER13. IEN0
TGIA8
153
0264
Edge
䡩
䡩
䡩
⫻
⫻
IER13. IEN1 IPR60
TGIB8
154
0268
Edge
䡩
䡩
⫻
⫻
⫻
IER13. IEN2
TCIV8
155
026C
Edge
䡩
⫻
⫻
⫻
⫻
IER13. IEN3 IPR61
TCIU8
156
0270
Edge
䡩
⫻
⫻
⫻
⫻
IER13. IEN4
TGIA9
157
0274
Edge
䡩
䡩
䡩
⫻
⫻
IER13. IEN5 IPR62
TGIB9
158
0278
Edge
䡩
䡩
⫻
⫻
⫻
IER13. IEN6
TGIC9
159
027C
Edge
䡩
䡩
⫻
⫻
⫻
IER13. IEN7
TGID9
160
0280
Edge
䡩
䡩
⫻
⫻
⫻
IER14. IEN0
TCIV9
161
0284
Edge
䡩
⫻
⫻
⫻
⫻
IER14. IEN1 IPR63
TGIA10
162
0288
Edge
䡩
䡩
䡩
⫻
⫻
IER14. IEN2 IPR64
TGIB10
163
028C
Edge
䡩
䡩
⫻
⫻
⫻
IER14. IEN3
TGIC10
164
0290
Edge
䡩
䡩
⫻
⫻
⫻
IER14. IEN4
TGID10
165
0294
Edge
䡩
䡩
⫻
⫻
⫻
IER14. IEN5
TCIV10
166
0298
Edge
䡩
䡩
⫻
⫻
⫻
IER14. IEN6 IPR65
TGIU11
167
029C
Edge
䡩
䡩
⫻
⫻
⫻
IER14. IEN7 IPR66
TGIV11
168
02A0
Edge
䡩
䡩
⫻
⫻
⫻
IER15. IEN0
TGIW11
169
02A4
Edge
䡩
䡩
⫻
⫻
⫻
IER15. IEN1
OEI1
170
02A8
Level
䡩
⫻
⫻
⫻
⫻
IER15. IEN2
OEI2
171
02AC
Level
䡩
⫻
⫻
⫻
⫻
IER15. IEN3
OEI3
172
0280
Level
䡩
⫻
⫻
⫻
⫻
IER15. IEN4
484
APPENDIX A
Source of
Interrupt
Priority Generation
Vector
Adress
Offset
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
OEI4
173
02B4
Level
䡩
⫻
⫻
⫻
⫻
IER15. IEN5
CMIA0
174
02B8
Edge
䡩
䡩
⫻
⫻
䡩
IER15. IEN6 IPR68
CMIB0
175
02BC
Edge
䡩
䡩
⫻
⫻
䡩
IER15. IEN7
OVI0
176
02C0
Edge
䡩
⫻
⫻
⫻
䡩
IER16. IEN0
CMIA1
177
02C4
Edge
䡩
䡩
⫻
⫻
䡩
IER16. IEN1 IPR69
CMIB1
178
02C8
Edge
䡩
䡩
⫻
⫻
䡩
IER16. IEN2
OVI1
179
02CC
Edge
䡩
⫻
⫻
⫻
䡩
IER16. IEN3
CMIA2
180
02D0
Edge
䡩
䡩
⫻
⫻
䡩
IER16. IEN4 IPR6A
CMIB2
181
02D4
Edge
䡩
䡩
⫻
⫻
䡩
IER16. IEN5
OVI2
182
02D8
Edge
䡩
⫻
⫻
⫻
䡩
IER16. IEN6
CMIA3
183
02DC
Edge
䡩
䡩
⫻
⫻
䡩
IER16. IEN7 IPR6B
CMIB3
184
02E0
Edge
䡩
䡩
⫻
⫻
䡩
IER17. IEN0
OVI3
185
02E4
Edge
䡩
⫻
⫻
⫻
䡩
IER17. IEN1
—
Reserved
186
02E8
—
⫻
⫻
⫻
⫻
⫻
IER17. IEN2
—
Reserved
187
02EC
—
⫻
⫻
⫻
⫻
⫻
IER17. IEN3
—
Reserved
188
02F0
—
⫻
⫻
⫻
⫻
⫻
IER17. IEN4
—
Reserved
189
02F4
—
⫻
⫻
⫻
⫻
⫻
IER17. IEN5
—
Reserved
190
02F8
—
⫻
⫻
⫻
⫻
⫻
IER17. IEN6
—
Reserved
191
02FC
—
⫻
⫻
⫻
⫻
⫻
IER17. IEN7
—
Reserved
192
0300
—
⫻
⫻
⫻
⫻
⫻
IER18. IEN0
—
Reserved
193
0304
—
⫻
⫻
⫻
⫻
⫻
IER18. IEN1
—
Reserved
194
0308
—
⫻
⫻
⫻
⫻
⫻
IER18. IEN2
—
Reserved
195
030C
—
⫻
⫻
⫻
⫻
⫻
IER18. IEN3
—
Reserved
196
0310
—
⫻
⫻
⫻
⫻
⫻
IER18. IEN4
—
Reserved
197
0314
—
⫻
⫻
⫻
⫻
⫻
IER18. IEN5
DMAC0I
198
0318
Edge
䡩
䡩
⫻
⫻
⫻
IER18. IEN6 IPR70
DMAC1I
199
031C
Edge
䡩
䡩
⫻
⫻
⫻
IER18. IEN7 IPR71
DMAC2I
200
0320
Edge
䡩
䡩
⫻
⫻
⫻
IER19. IEN0 IPR72
DMAC3I
201
0324
Edge
䡩
䡩
⫻
⫻
⫻
IER19. IEN1 IPR73
EXDMAC0I 202
0328
Edge
䡩
䡩
⫻
⫻
⫻
IER19. IEN2 IPR74
High
TMR0
TMR1
TMR2
TMR3
DMACA
Low
Name
Vector
No.
Selectable
Interrupt
Request
Destination
EXDMAC
APPENDIX A
Source of
Interrupt
Priority Generation
Vector
Adress
Offset
Selectable
Interrupt
Request
Destination
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
EXDMAC1I 203
032C
䡩
䡩
⫻
⫻
⫻
IER19. IEN3 IPR75
Reserved
204
0330
—
⫻
⫻
⫻
⫻
⫻
IER19. IEN4
Reserved
205
0334
—
⫻
⫻
⫻
⫻
⫻
IER19. IEN5
—
Reserved
206
0338
—
⫻
⫻
⫻
⫻
⫻
IER19. IEN6
—
Reserved
207
033C
—
⫻
⫻
⫻
⫻
⫻
IER19. IEN7
—
Reserved
208
0340
—
⫻
⫻
⫻
⫻
⫻
IER1A. IEN0
—
Reserved
209
0344
—
⫻
⫻
⫻
⫻
⫻
IER1A. IEN1
—
Reserved
210
0348
—
⫻
⫻
⫻
⫻
⫻
IER1A. IEN2
—
Reserved
211
034C
—
⫻
⫻
⫻
⫻
⫻
IER1A. IEN3
—
Reserved
212
0350
—
⫻
⫻
⫻
⫻
⫻
IER1A. IEN4
—
Reserved
213
0354
—
⫻
⫻
⫻
⫻
⫻
IER1A. IEN5
ERI0
214
0358
Level
䡩
⫻
⫻
⫻
⫻
IER1A. IEN6 IPR80
RXI0
215
035C
Edge
䡩
䡩
䡩
⫻
⫻
IER1A. IEN7
TXI0
216
0360
Edge
䡩
䡩
䡩
⫻
⫻
IER1B. IEN0
TEI0
217
0364
Level
䡩
⫻
⫻
⫻
⫻
IER1B. IEN1
ERI1
218
0368
Level
䡩
⫻
⫻
⫻
⫻
IER1B. IEN2 IPR81
RXI1
219
036C
Edge
䡩
䡩
䡩
⫻
⫻
IER1B. IEN3
TXI1
220
0370
Edge
䡩
䡩
䡩
⫻
⫻
IER1B. IEN4
TEI1
221
0374
Level
䡩
⫻
⫻
⫻
⫻
IER1B. IEN5
ERI2
222
0378
Level
䡩
⫻
⫻
⫻
⫻
IER1B. IEN6 IPR82
RXI2
223
037C
Edge
䡩
䡩
䡩
⫻
⫻
IER1B. IEN7
TXI2
224
0380
Edge
䡩
䡩
䡩
⫻
⫻
IER1C. IEN0
TEI2
225
0384
Level
䡩
⫻
⫻
⫻
⫻
IER1C. IEN1
ERI3
226
0388
Level
䡩
⫻
⫻
⫻
⫻
IER1C. IEN2 IPR83
RXI3
227
038C
Edge
䡩
䡩
䡩
⫻
⫻
IER1C. IEN3
TXI3
228
0390
Edge
䡩
䡩
䡩
⫻
⫻
IER1C. IEN4
TEI3
229
0394
Level
䡩
⫻
⫻
⫻
⫻
IER1C. IEN5
Reserved
230
0398
—
⫻
⫻
⫻
⫻
⫻
IER1C. IEN6
Reserved
231
039C
—
⫻
⫻
⫻
⫻
⫻
IER1C. IEN7
Reserved
232
03A0
—
⫻
⫻
⫻
⫻
⫻
IER1D. IEN0
High
SCI0
SCI1
SCI2
SCI3
—
Low
Name
Vector
No.
485
—
Edge
—
—
486
APPENDIX A
Source of
Interrupt
Priority Generation
Vector
Adress
Offset
Form of
Sstb
Sacs
Detection CPU DTC DMA Return Return
IER
IPR
Reserved
233
03A4
⫻
⫻
⫻
⫻
⫻
IER1D. IEN1
ERI5
234
03A8
Level
䡩
⫻
⫻
⫻
⫻
IER1D. IEN2 IPR85
RXI5
235
03AC
Edge
䡩
䡩
䡩
⫻
⫻
IER1D. IEN3
TXI5
236
03B0
Edge
䡩
䡩
䡩
⫻
⫻
IER1D. IEN4
TEI5
237
03B4
Level
䡩
⫻
⫻
⫻
⫻
IER1D. IEN5
ERI6
238
03B8
Level
䡩
⫻
⫻
⫻
⫻
IER1D. IEN6 IPR86
RXI6
239
03BC
Edge
䡩
䡩
䡩
⫻
⫻
IER1D. IEN7
TXI6
240
03C0
Edge
䡩
䡩
䡩
⫻
⫻
IER1E. IEN0
TEI6
241
03C4
Level
䡩
⫻
⫻
⫻
⫻
IER1E. IEN1
Reserved
242
03C8
—
⫻
⫻
⫻
⫻
⫻
IER1E. IEN2
—
Reserved
243
03CC
—
⫻
⫻
⫻
⫻
⫻
IER1E. IEN3
—
Reserved
244
03D0
—
⫻
⫻
⫻
⫻
⫻
IER1E. IEN4
—
Reserved
245
03D4
—
⫻
⫻
⫻
⫻
⫻
IER1E. IEN5
—
ICEEI0
246
03D8
Level
䡩
⫻
⫻
⫻
⫻
IER1E. IEN6 IPR88
ICRXI0
247
03DC
Edge
䡩
䡩
䡩
⫻
⫻
IER1E. IEN7 IPR89
ICTXI0
248
03E0
Edge
䡩
䡩
䡩
⫻
⫻
IER1F. IEN0 IPR8A
ICTEI0
249
03E4
Level
䡩
⫻
⫻
⫻
⫻
IER1F. IEN1 IPR8B
ICEEI1
250
03E8
Level
䡩
⫻
⫻
⫻
⫻
IER1F. IEN2 IPR8C
ICRXI1
251
03EC
Edge
䡩
䡩
䡩
⫻
⫻
IER1F. IEN3 IPR8D
ICTXI1
252
03F0
Edge
䡩
䡩
䡩
⫻
⫻
IER1F. IEN4 IPR8E
ICTEI1
253
03F4
Level
䡩
⫻
⫻
⫻
⫻
IER1F. IEN5 IPR8F
—
Reserved
254
03F8
—
⫻
⫻
⫻
⫻
⫻
IER1F. IEN6 IPR90
—
Reserved
255
03FC
—
⫻
⫻
⫻
⫻
⫻
IER1F. IEN7 IPR91
High
SCI5
SCI6
—
RIIC0
RIIC1
Low
Name
Vector
No.
Selectable
Interrupt
Request
Destination
—
Index
A
A/D control extended
register, 173
A/D control/status register, 173
A/D conversion start, 171, 180
A/D converted value addition
count select register
(ADADC), 172–73
A/D converted value addition
mode select register
(ADADS), 171–72
A/D converter(s), 24–25, 161
10-bit converter, ex, 188–90
10-bit converter, fig, 179
10-bit converter and, 168,
178–83
12-bit converter, ex, 186–88
12-bit converter, fig, 169
12-bit converter and, 168–78
ADADC converters,
tab, 173
clock selection, tab, 171
operation of, 175–78
trigger selection, tab, 174
ADSSR settings, tab, 166
channels of, 168
concepts of, 161–63
conversion chart, 2-bit, fig, 24
conversion speed, ex, 166
conversion speed of, 165
conversion time, 166
conversion timing, fig, 165
default peripherals of, 168
digital value, ex, 166
frequencies of, 162–63, 170
header files and, 128–29
mathematical calculation of,
165–67
MCU architecture and, 41
output code and, 24, 25, 162
readings, fig, 25
reference voltage of, 162
resolution of, 162
sample and hold circuit,
fig, 163
sampling state register
and, 165
step size, ex, 167
successive approximation,
fig, 164
successive approximation and,
163–65
A/D data placement register, 181
A/D data registers n, 170, 178
A/D scan conversion end
interrupt, 180
A/D scan conversion end
interrupt enable (ADIE),
171, 175, 178, 180
A/D scan conversion mode
select, 171
A/D self-diagnostic register,
181–82
A/D start bit, 171, 180
A/D start trigger select register,
173–75
AAS0, 233
AAS1, 233
AAS2, 233
Accumulator (ACC), 52
ACKBR, 230
ACKBT, 230
ACKWP, 230
Actuator, 20
ADADC, 172–73
ADADS, 171–72
ADANS, 171, 175, 178
ADCER, 173
ADCR, 180–81
ADCS, 171
487
ADCSR, 170–71, 178, 179
ADDIAGR, 181–82
ADDPR, 181
ADDRn, 170, 178
ADI, 180
ADIE, 171, 175, 178, 180
ADSSTR, 165, 166
ADST, 171, 180
ADSTRGR, 173–75
Agile development method(s),
157–58
Air to fuel mass ratio, 3
AL, 234
Alarm interrupt, 336
Algorithm(s)
I2C and, 269–75
for SPI, 266–68
ALIE, 232
ALU, 37, 38, 66
Amplifier(s), 31
Analog signal(s), 24–28
Analog to digital converter. See
A/D converter(s)
Anode, 16
ANSI standards, 87
Arithmetic and logic unit (ALU),
37, 38, 66
Assembler, 87
Assembly language, 151
Asynchronous, 41, 194
Atomic code, 460
Automobiles, MCU and, 2–3
B
Backup PC (BPC), 45, 48
Backup PSW (BPSW), 45, 48
Battery(ies), 29
Baud rate, 194
BBSY, 225, 226
BC, 228
488
INDEX
BCLK. See external bus clock
BCWP, 228
BEREN, 63
Better Embedded System
Software (Koopman), 142
Bi-endian, 88
Big bang test(s), 154
Big up-front design, 144, 155
Binary number, multi-bit, 24
Bit rate register (BRR), 200, 204
Bit(s). See individual bits
Bitwise operation(s), 54
Black box testing, 152, 153
Boot mode, 73
BPC, 45, 48
BPSW, 45, 48
BRDV, 219
Brownout condition, 444–45
Brownout detector, 425
BRR, 200, 204
Buffer function, 62
Bus(es), 194
configuration of, fig, 60
CPU and, 57–58, 58–59
description of, 58–63
error monitoring and, 63
error monitoring enable
register, 63
error types of, 63–64
external bus and, 62–63
internal main and, 58, 59
internal peripheral bus and,
58, 61
of MCU board, 57–64
memory and, 58, 59
operand and, 57
peripheral modules, tab, 61
priority of, tab, 59
specifications of, 57–58
types of, 57–58
Button connection, fig, 17
BYP, 66
Bypass process, 66
Byte addressing, 75–76
C
C/C⫹⫹ compiler, 87
features of, 88
header files of, 95–96
C/C⫹⫹ function, 88
C Flag, 46
C language, 85, 151
C⫹⫹ language, 151
C program, 85
Call walker, 88
CAN, 3, 12, 41
Capacitors
debounding solutions and, 18
loads of, 30, 31
power supplies and, 29
Carry flag, 46
Carry interrupt, 323, 336
CAS latency, 62
Cascading timer(s), 310–11,
323–26, 333–34, 337–40.
See also event counter(s);
pulse output operation;
timer(s)
Cathode, 16
Cause flag(s), 51, 409–11
Ceramic resonator(s), 31
Channel select register
(ADANS), 171, 175, 178
Chartplotter, fig, 144
Chip select, 126
Chip(s), 2, 8
Circuit(s), reset, 11
Cj, 48
CKS, 227, 439
CKS bit, 429
Clear box testing, 152, 153–54
Clock enable bit(s), 202
Clock generation circuit, 38
Clock signal generator(s), 11
ceramic resonators and, 31
crystal clock generator chip,
fig, 31
electrical and, 30
external IC chips and, 31
mechanical and, 30–31
QUART/USARTz crystals
and, 30
RC, fig, 30
Clock synchronous, 41
CM, 202
CMOS, 15
CNTVAL, 441
Coding standard(s), 151
Coil driver, fig, 22
Common expression, 87
Communication and
networking, 5
Communication format(s), 41
Communication function(s), 39
Communication mode (CM), 202
Communication protocol, 2, 5
Compare match timer, 39
Compilation mechanism, 85–86
Compiler package
assembler and, 87
C/C⫹⫹ compiler and, 87
HEW and, 88
IDE and, 88
optimizing linkage editor
and, 87
simulator debugger and, 88
standard library generator
and, 87
utilities and, 88
Compiler(s), 85
embedded systems and, 87
input/output, tab, 86
optimization of, 88
Computer(s), 35–38
components of, 36–38
example, fig, 36
functions of, 35–36
IAS and, 37–38
von Neumann, John and,
37–38
Conditional assembly
function, 87
Config.h, 118
INDEX
Const variable, 152
Constraint(s), of embedded
systems, 6
Contact bounce, 18
Continuous scan mode, 177–78
Control area network (CAN), 3,
12, 41
Control hazard, 67
Control mechanism(s), 36
Control method(s), 1
Control mode(s), 4
Control system(s), 4
Control unit, 37, 38
Controller(s)
CAN module and, 41
DMAs and, 38–39
ethernet and, 39
I2C bus interfaces and, 41
USB 2.0 host/funciton module
and, 39
Conversion rate, 162–63
Conversion time (tCONV), 165
Converter(s). See individual
converters
Cost, 2, 3, 6
Counter(s). See cascading
timer(s); event counter;
pulse output operation;
timer(s)
CPHA, 218
CPU, 36
bus error type and, 64
bus-master modules and, 63
components of, 37
features of, fig, 43
MCU architecture and, 38,
42–52
PSW, fig, 45
register sets of, 43–52
CRC calculator, 41
Crystal oscillator, 8
CSC (area controller), 62
Current-limiting resistor, 16
Current rating(s), 29
D
D/A control register (DACR),
184, 185
D/A data placement register, 184
D/A data register, 184
D/C converter(s), 26–28, 161
4-bit binary weighted, fig, 26
binary weighted and, 26–27
ex, 190–91
MCU architecture and, 41
operation of, fig, 185
output voltage, formula of, 28
pulse width modulation
and, 28
R-2R and, 27–28
registers of, 183–84
resistor networks and,
26–28
successive approximation
and, 163
D flip-flop, 198
DACR, 184, 185
DADPR, 184
DADRm, 184
DADRn, 185
Data, computers and
arrangement, fig, 57
arrangement of, 56–57
control and, 36
movement and, 35–36
processing and, 35
storage and, 35
types of, 52–55
Data acquisition, 194
Data direction register (DDR),
12–13, 20
Data flash memory, 58
Data hazard, 67
Data movement block, 35
Data register (DR), 12, 13–14
A/D converters and, 170, 175
BIT syntax of, 14
LEDs and, 20
pin selection and, 13
489
Data sharing, 460–67
disabling interrupts and,
464–65
function reentrancy and,
461–62
lock use and, 465–66
messages and, 467
protection and, 464–67
semaphores and, 466–67
source code and, 462–64
task switching and, 467
Data transfer controller, 39
DC motor(s), 20–21, 28, 312
DCLS, 228
DDR, 12–13, 20
Debouncing solution, 18
Debugger, 89
Debugging
I/O registers and, 115–17
I/O registers selection,
fig, 116
I/O window and, 114–15
memory address and, 110–12
memory and, 112–14
memory window and, 109
operating memory of, 108–9
options in HEW and, 106
sessions and, 106–8
tools for, 89
Debugging function, 88
Decomposition, 144
Default session, 94
Denormalized number
bit(s), 410
Design margin, 152
DID, 233
DIDE, 231
Digital converters. See A/D
converter(s)
Digital signals, 11–23
Digital to analog conversion. See
D/C converter(s)
Direct current motor(s), 20–21,
28, 312
490
INDEX
Direct memory access (DMA),
38–39
Divide-by-zero exception, 404,
407, 410
DMA, 38–39
DMACA, 59, 63
DN flag, 51
Double precision, 395–97
DR. See data register
Driving motor and coil(s), 20–22
DTC, 59
DTCER, 129
Dual slope integrating, 163
Duplex communication, 194
Dynamic schedule, 451
E
E stage, 66, 398
EDMAC, 58, 59
EIN GreenEval Zigbee Module,
7–8
Ej, 48, 52
Electromechanical control(s), 1
Embedded product lifecycle,
fig, 143
Embedded system(s)
attributes of, 5–6
benefits of, 2–4
constraints of, 6
designing of, 6–7
EIN GreenEval Zigbee Module
and, 7–8
functions of, 4–5
manufacturing of, 6–7
summary of, 9
Enable bit (Ej), 48, 52
ENABLE_LEDS, 19
ENABLE_SWITCHES, 20
Endianness, 55–56, 72
Enum keyword, 119–20
Enumeration(s), 129–30
Error signal flag bit, 203
ETHERC, 58
Ethernet controller(s), 39
Event counter(s). See also
cascading timer(s); pulse
output operation; timer(s)
clock input to TCNT, tab, 308
concepts of, 302–10
specification of timers,
tab, 303
TCCR description, tab, 307
TCNT, fig, 305
TCR description, fig/tab, 306
TCSR, fig, 309
TCSR description, tab, 309
timer unit 0, fig, 304
Evolutionary prototype, 158
Exception cause bit (Cj), 48
Exception flag(s), 410
Exception handle bit, 51–52
Exception handling enable
bit(s), 410
EXDMA controller, 39, 62
Execution stage (E stage),
66, 398
Extended function(s), 87
External bus clock (BCLK), 38, 61
error type and, 63–64
specifications and, 58
External trigger, 174, 175
Extreme programming, 157
F
FADD, 401
Fast interrupt vector register,
45, 48
Fault handling, 5
Fault tolerant system(s), 194
FCMP, 403
FEM, 8
FIEN, 356
FIFO data structures
I2C and, 269
UART/USART and, 262–64
File inclusion function, 87
Finite state machine, 149–50
FINTV, 45, 48
FIR, 351, 356
5PE20V chip, 8
Fixed point math, 391
time calculation, ex, 414–18
Flag status bit (Fj), 48, 52
FLASH chip, 8
Flash conversion, 163
Floating point. See also FPU
data type and, 53–54
exception handling and, 411–14
exceptions, ex, 404–8
exceptions of, 403–4
FPSW bit definition, tab,
400, 402
instructions of, 401–3
math of, 391–97
matrix multiplication, ex,
418–22
registers of, 399–400
representation of, 391–92
in RX62N, 398–404
standard of, 392–97
time calculation, ex, 414–18
Floating point error summary
flag, 411
Floating point status word
(FPSW), 45, 48–52,
399–400, 402, 408–11
Floating-point summary bit (FS
bit), 52, 234
Flyback diode, 22
FMPE, 230
FO flag, 52
Format and save data task, 148
Formula(s)
of A/D conversion time, 166
of A/D converters digital
output, 166–67
of A/D converters output
code, 25
of battery life, 29
of frequency, 311
of output voltage for D/C
converters, 28
INDEX
of quanitzation error, 162
of resistor, 16
of resolution, 24
of TCORA, 335
of TCORB, 335
of timers, 301–2
FPSW. See floating point status
word (FPSW)
FPU, 399. See also floating point
concepts of, 391–404
FWSP and, 51
math basics of, 391–97
MCU architecture and, 38
Front end module (FEM), 8
FS bit, 52, 234
FSUB, 401
FU flag, 52
Full duplex mode, 194, 206
FV flag, 52
FVCT, 356
FZ flag, 52
G
Ganssle, Jack G., 141, 142, 144,
145, 146, 151, 152
GCAE, 231, 233
Generic API for Graphics LCD
(Glyph), 118, 120
Glyph.h, 118–23
GUI display function, 88
H
H-bridge, 312
H-bridge motor driver, fig, 21
Half duplex communication, 194
Hardware post-processing, 414
Hardware preprocessing, 412
Hazards(s), of pipelining, 67
Header file(s), 94
C/C⫹⫹ compiler and, 95–96
config.h, 118
creation of, ex, 102–6
description of types used,
118–30
editing operations of, tab, 103
glyph.h, 118–23
iodefine_RX62N.h, 127–30
register description, tab, 129
library types, tab, 95
macros, tab, 96
preamble.h, 123–24
removal of, fig, 105
sbrk.h, 126
st7579_lcd.h, 124–25
stacksct.h, 127
typedef.h, 126
used in demo program, tab, 96
vect.h, 126–27
YRDKRX62N_RSPI0.h,
125–26
HEW. See high performance
embedded workshop
(HEW)
Hierarchical system(s), 35
High performance embedded
workshop (HEW), 88
concepts of, 89–94
configuration of, 94
configuration selection, fig, 93
creation of, 90–91
creation/running of, ex, 97–101
debugging options and,
106–17
fig, 89
opening of, 91
overview of, 89
project and, 89
sessions of, 94
windows of, 92–93
workspace and, 89
HOA, 233
HOAE, 231
I
I Bit, 46
I/O. See input/output (I/O)
I2C. See inter integrated
circuit (I2C)
491
IAS computer, 37
IC. See integrated circuit
ICBRH, 235
ICBRL, 235
ICCR1, 224
ICCR2, 225–27
ICDRR, 236
ICDRS, 236
ICDRT, 235
ICFER, 230–31
ICIER, 232
ICLK, 58
ICMR1, 227–28
ICMR2, 228–29
ICMR3, 229–30
ICR. See input buffer control
register (ICR)
ICSER, 231–32
ICSR1, 232–33
ICSR2, 233–34
ICU. See interrupt control unit
ID Stage, 66, 398
IDE, 88
Idle mode, 5
IDLNF, 213
IEEE 754, 392–97, 399,
401, 403
IEN register, 64
IENj, 354
IER, 351
IER (interrupt request enable
register), 129
IERm, 354, 367
IF Stage, 65–66, 397
IGAEN, 63
Illegal address access, 63
Independent watchdog timer
(IWDT), 39, 436–42
Inexact exception, 404, 410
Input buffer control register
(ICR), 12
A/D converters and, 168
example of, fig, 15
PORT and, 14
492
INDEX
Input/output (I/O)
computers and, 36, 38
MCU architecture and, 39
pins and, 16, 18–19, 20
ports, 11–12
registers and, 76–79
Input sample time (tSPL), 165
Instruction decode stage (ID
stage), 66, 398
Instruction fetch stage (IF stage),
65–66, 397
Instruction set architecture
(ISA), 391
compilers and, 87
RX CPU and, 42
INTB, 45
Integer, data type, 53
Integrated circuit (IC), 2
external chips and, 31
high voltage sensors and, 22
stepper motors and, 21
Integration test(s), 152, 154
Inter integrated circuit (I2C), 194,
297. See also Renesas
inter integrated chip
algorithms and, 269–75
bus interface and, 196–97
buses and, 41
concept of, 221–23
data transfers and, 268–75
master receiver mode, fig,
274–75
master transmitter mode and
module of, fig, 272
operation of, fig, 271
start/stop condition,
fig, 222
Interconnection(s), 37
Internal clock module, 38
Internal clock signal(s), 39
Interrupt control unit (ICU), 351,
360–63. See also
interrupt(s)
fig, 364
setting up interrupts and,
363–71
triggering of interrupt, 369
Interrupt enable (I bit), 46
Interrupt flag register, 465
Interrupt register (IR), 129
Interrupt service routine
(ISR), 149
header files and, 126
monitor and, 89
responsiveness and, 453–54,
455, 458
UART/USART and, 263–64
Interrupt source priority register
(IPR), 129, 351
Interrupt stack pointer (ISP),
42–43, 45
Interrupt vector table, 360
Interruption function
description, 87
Interrupt(s), 350–51. See also
individual interrupts
A/D converters, setting up, ex,
373–77
code, amounts of, 377
concepts of, 349–50
control unit, fig, 352
flags to process data, ex,
380–83
flowchart example, fig, 350
ICU, fig, 364
IRR, tab, 354
maskable and, 351
non-maskable and, 351
operation of, 360–63
polling, ex, 370–73
registers of, 351–60, 365–71
responsiveness and, 455
setting up and, 363–71
specifications of ICU,
tab, 353
state machine, ex, 383–89
state machine and, 378–80
status flag, figs, 361–62
triggering of, 369
vector table and, 360
Invalid operation exception, 404,
408, 410
Iodefine.h, 130
Iodefine_RX62N.h, 12, 14,
127–30
IPL bit, 46–47
IPR, 129, 351
IPRm, 355, 368
IR flag, 354
IR1, 129
IRN, 351
IRn, 366
IRQCR, 351
IRQCRi, 354, 357
IRR, 351
ISA. See instruction set
architecture (ISA)
ISO standards, 87
ISP, 42–43, 45
ISR. See interrupt service routine
Iterative process, 156
IWDT, 39, 436–42
IWDTCR, 438–39
IWDTRR, 436–38
IWDTSR, 441
J
J-link debugger, 117–18
K
Keypad(s), 22–23
Koopman, Phil, 141, 142, 143,
145, 148, 151, 152
L
L293 IC, 21
Language specification, 88
LC, 30
Lean development, 157
LED_OFF, 20
LEDs
as outputs, 16–17, 20
INDEX
pulse width modulation
and, 28
RSK_RX62N, 19
sinking current, fig, 17
sourcing current, fig, 16
switches as inputs and, 19–20
YRD RX62N, 19
Library file(s), 87
LIFO data structure, 262
Light-emitting diodes. See LEDs
Limp-home modes, 4
Linker, 85, 86, 88
Load modules, 88
Logic, 17, 22, 23
LSBF, 219
LVDEN, 358
LVDST, 359
M
M stage, 398
Macro function, 87
Magic number(s), 151
MALE, 231
Map viewer, 88
Master algorithm, 266–67
Master device(s), 206, 207
Master in slave out (MISO),
206, 207
Master out slave in (MOSI), 206
Master receiver, 223
Master/slave selectable
communication
format, 41
Master transmitter, 222
Matrix multiplication, ex, 418–22
MCU. See microcontroller(s)
Memory
computers and, 36
contents as waveforms, ex,
135–36
MCU architecture and, 38
Memory access (M stage),
66, 398
Memory block, fig, 75
Memory map, fig, 77
Microcontroller board
A/D converter and, 41
architecture terms, definitions
of, 41–42
bus error monitoring, 63
bus error types and, 63–64
bus specifications and, 57–64
clock generation circuit
and, 38
communication function
and, 39
components of, 38–52
CPU and, 38, 42–52
CRC calculator and, 41
D/A converter and, 41
data arrangement and, 56–57
data types and, 52–55
DMA and, 38–39
endianness and, 55–56
external bus extension
and, 38
I/O ports and, 39
I/O registers and, 76–79
memory and, 38
memory map of, 76–77
memory organization of,
75–76
operating modes and, 71–74
pipelining and, 65–71
register sets and, 42–52
reset and, 38
terms and, 41–42
timers and, 39
voltage detection circuit
and, 38
Microcontroller(s) (MCU), 1–2,
11–33
board organization and, 35–84
dependability and, 4
digital I/O ports and, 11–12
economies and, 2–3
EIN GreenEval Zigbee Module
and, 7–8
493
embedded systems and, 6
features of, 4
Microprocessor, 1, 2
MISO, 206, 207
MISOE bit, 220
Mode pins, operating modes,
tab, 72
MODF, 213
MODFEN, 210
Module tree, 88
Monitor, 89
MOSI, 206
MOSIE bit, 220
Motor control circuitry, 21
Motorola, 206
MOVIFE, 212
MOVIFV, 212
MST, 225, 226
MSTPCRA, 130
MSTPCRB, 130
MSTPCRC, 130
MSTPCRD, 130
MSTPRA, 168
MSTPRB, 168
MSTR, 210
MTU, 174, 175
MTWP, 227
Multifunction timer pulse unit,
39, 174, 175
Multiprocessor bit, 203
Multiprocessor communication,
201–2, 264–68
Multiprocessor interrupt enable
bit, 203
N
NACKE, 231
NACKF, 234
NAKI, 232
NAKIE, 232
NALE, 231
Nested union(s), 128
NFE, 231
9 bit wake-up mode, 201
494
INDEX
NMEA flowchart, fig, 150
NMI, 351
NMICLR, 351, 359
NMICR, 351, 360
NMIEN, 358
NMIER, 351, 357–58
NMISR, 351, 358–59
NMIST, 359
NMOS, 15
Node(s), 2
Non-preemptive dynamic
scheduler, 454, 456
concepts of, 467–70
implementation and, 470–74
RTC scheduler, ex, 474–75
scheduling, figs, 469–70
task management and, 471–73
task table and, 468, 470–74
tick ISR and, 468, 473
Non-preemptive static
scheduler, 454
Non-reentrant function(s), 461,
462, 463
Nyquist frequency, 163, 183
O
O flag, 46
Object code, 85
ODR, 12, 15
On-chip ROM disabled extended
mode, 73
On-chip ROM enabled extended
mode, 73
1-bit A/D converter(s), 25
Open drain control register,
12, 15
Operation code, 5
Optimizing linkage editor, 87
Oscillating digital output, 27
OSTEN, 358
OSTST, 359
Output. See input/output
Overflow exception, 403,
405, 410
Overflow flag (O flag), 46
Overrun error flag, 203
OVRF, 213
P
P-channel transistor(s), 15
Parallel communication, 193
Parallel computation, 194
Parallel in serial out, 199
Parity bit, 194, 202
Parity enable, 202
Parity error flag bit, 203
PC, 45
PCB, 6–7
PCLK. See peripheral module
clock (PCLK)
PCR, 12, 16
PERF, 213
Periodic interrupt, 336
Peripheral module clock
(PCLK)
A/D converters and, 165, 170
bus specifications and, 58
clock generation circuit and,
38, 39
header files and, 126
UART/USART and, 201
Peripheral module(s), 12
Peripheral modules(s), 58
PFGSPI, 219–20
Philips Electronics, 221
Piezoelectric ceramic element, 31
Piezoelectric effect, 30
Pipeline processing
block of memory layout,
fig, 75
byte addressing, fig, 76
concepts of, 397–98
configuration and operation of,
fig, 67
CPU and, 42, 65–71
example of, fig, 397
flow with stalls, figs, 68–69
I/O registers and, 76–79
memory organization of,
75–76
operating modes of, 71–74
operation of, 67–71
stages of, 65–66
word addressing, fig, 76
PISO, 199
PM bit, 46
Polling, 349–51
Port function control register G,
219–20
Port output enable timer, 39
PORT register(s), 12–13, 14–15
PORTx.DDR.BIT.BN, 13
PORTx.DR.BIT.Bn, 14
PORTx.ICR.BIT.Bn, 15
PORTx.ODR.BIT.Bn, 15
PORTx.PCR.BIT.Bn, 16
PORTx.PCR.BYTE, 16
PORTx.PORT.BIT.Bn, 14
Power-on reset, 38
Power supply(ies), 11, 28–29
Preamble.h, 118, 123–24
Preemptive dynamic
scheduler, 454
Preprocessor, 85, 86
Preprocessor #define, 152
Primary user interface task, 148
Printed circuit board (PCB), 6–7
Process NMEA data task,
148, 149
Processor interrupt priority level
(IPL bit), 46–47
Processor mode select (PM
bit), 46
Processor status word (PSW), 43,
45–47
Processor(s)
compilation mechanism and,
85–86
embedded architecture and, 87
input/output, tab, 86
Program code, 412
Program counter, 45
INDEX
Program performance evaluation
function, 88
Programmable pulse generator
timer, 39
Prototyping, 2, 158
PSPIS bit, 220
PSW, 43, 45–47
PTE, 211
Pull-up MOS control register
(PCR), 12, 16
Pull-up resistor, 17
Pulse output operation, 311–13.
See also cascading
timer(s); event counter(s);
timer(s)
example of, fig, 313
frequency and, 311, 334–36
setting up of, ex, 327–28
setting up/servo motor, ex,
340–42
square wave attributes, fig, 312
Pulse width modulation (PWM)
D/C converters and, 28
fig, 28
Q
Quantization error, 162
QUART/USARTz crystal, 30, 31
R
R-2R D/C converter(s), 27–28
R64CNT, 314, 317
Radix, 131–32
RAM
buses and, 57–59, 63
controllers and, 39
MCU architecture and, 38
RC, 30, 31
RCR1, 319, 321
RCR2, 320, 321
RDAYCNT, 317
RDR, 200, 205
RDRF, 234
RDRFS, 230
Real time clock (RTC), 313–23
interrupts, ex, 343–46
interrupts of, 323, 336–37
reading of, 322–23
registers of, 314–21
scheduler and, 467
setting of, 321
setting up/reading, ex, 328–33
Receive data register, 200, 205
Receive enable bit, 203
Receive interrupt bit, 203
Reentrant function(s)
Reference voltage, 24
Register(s), 12. See also
individual bits; individual
registers
A/D converters and, 168,
170–75, 178–82
ACC and, 52
control and, 43–52
CPU and, 37, 42–52
CPU and, fig, 44
D/C converters and, 183–84
general-purpose and, 42–43
header files and, 129–30
interrupts and, 351–60
IWDT and, 436–42
operating modes and, tab, 72
of RIIC, 224–36
RTC and, 314–21
SPI and, 208–20
UART/USART and, 200–203
viewing CPU contents of, ex,
130–35
WDT and, 426–32
Regression test(s), 152, 154
Relay(s), 21
Renesas inter integrated chip
(RIIC), 196–97. See also
inter integrated circuit
(I2C)
bit counter indications,
tab, 228
clock source selection, tab, 227
495
registers of, 224–36
transmission/reception, ex,
248–61
Renesas serial peripheral
interface (RSPI). See
serial peripheral interface
Reserved bit(s), 411
DDR and, 13
Reset circuit, 31
Reset pin(s), 38
Resistor-capacitor (RC), 30, 31
Resistor(s)
debouncing circuits and, 18
formula of, 16
networks and, 26–28
Resolution, of A/D
converter(s), 162
Resolution formula, 24
Resonant oscillator, 31
Responsiveness, 447
context and, figs, 459
context switching and, 458–60
dynamic schedule and, 451
interrupts and, 455
prioritization and, 452–53
scheduler classes and, 454
scheduling, figs, 450
scheduling approach and,
447–48
scheduling concepts of,
447–55
stack memory and, 454–55
state transitions and, 457–58
static schedule and, 449
task ordering and, 449–51
task preemption and, 449,
451–52, 457
task states of, 456–57
timing and, 449, 453–54
R5FF36B3, 8
RHRCNT, 314
fig, 318
fig and tab, 316
RIE, 232
496
INDEX
RIIC. See Renesas inter
integrated chip
Risk reduction, 141–42
RM bit(s), 51, 409
RMINCNT, 314
fig and tab, 315
RMONCNT, 317
ROM
buses and, 58–59, 63
MCU architecture and, 38
RS, 226
RS-232, 200, 297
RSECCNT, 314
fig and tab, 315
RSK_RX62N LEDs, 19
RSPCKE bit, 220
RSPI. See serial peripheral
interface
RSTCSR, 426, 431
RSTE bit, 431
RTC. See real time clock
RWKCNT, 314, 316
RX compiler package. See
compiler package
RYAREN, 317
RYRCNT, 317, 318
S
S flag, 46
SALE, 231
Sample and hold circuit, fig, 163
Sampling frequency, 162–63
SAR0E, 232
SAR1E, 232
SAR2E, 231
SARLm, 234
SARUm, 234
Sbrk.h, 126
Scan mode, 182
Scanning matrix keypad(s),
22–23
SCI, 196
SCL, 221, 222
SCLE, 231
SCLK. See serial clock
SCMR, 200, 201
SCR, 200, 202–3
Scrum, 157–58
SDA, 221, 222
SDCLK, 58, 61
SDDL, 228
SDRAM, 58, 61
controller and, 62
external bus and, 62
pipeline processing and, 76
Secondary user interface
task, 148
Semaphore(s), 466–67
SEMR, 200
Sensor(s)
A/D converters and, 24–25
driving motor, coils and, 22
Sequencing, 4
Serial clock (SCLK)
SPI and, 206, 207, 208
UART/USART and, 202
Serial communication
concepts of, 193–95
I2C and, 221–36, 248–61
data transfer and, 268–75
interface controllers and, 41
interfacing and, 196–97
modes and, 41
peripheral interface and, 41
protocols of, tab, 298
SPI and, 205–20
ex, 242–48
multiprocessor
communication, ex,
280–97
multiprocessor
communication and,
264–68
terminologies of, 194–95
UART/USART and, 198–205,
236–42
data structures, ex, 276–79
data structures for, 262–64
Serial communication interface
(SCI), 196
Serial control register, 200, 202–3
Serial extended mode
register, 200
Serial in parallel out, 199
Serial mode register, 200
UART/USART and, 201–2
Serial peripheral bit rate register,
214–15
Serial peripheral clock delay
register, 217
Serial peripheral command
register, 218–19
Serial peripheral control register,
208–10
fig, 210
Serial peripheral data control
register, 215–16
Serial peripheral data register
(SPDR), 213–14,
216, 266
Serial peripheral interface (SPI),
8, 194, 196, 205–20, 297
algorithms and, 266–68
bit rate settings, ex, 215
block diagram of, fig, 243
configurations of, 208
functioning of, 207–8
master/slave, fig, 209–10
multiprocessor communication
and, 264–68, 280–97
registers of, 208–20
single master single slave
mode, 220
transmission, ex, 242–48
Serial peripheral next access
delay register, 218
Serial peripheral pin control
register, 212
Serial peripheral sequence
control, 214
Serial peripheral sequence
status, 214
INDEX
Serial peripheral status, 212–13
Serial port, 194
Serial status register (SSR), 203
Servo motor, 312, 335
Servos, 21
754410 IC, 21
SH-4 simulator, 94
Shift register, 198–99, 201
Sign flag, 46
Signal processing, 5
SimDebug_SH-4, 94
Simplex communication, 194
SimSessionSH-4, 94
Simulator debugger, 88
Single-chip mode, 73
Single mode, 182
Single-precision, 392–95
Single scan mode, 175–76, 183
SIPO, 199
64 Hz counter, 314, 317
Slave algorithm, 267–68
Slave device, 206, 207, 297
Slave receiver, 223
Slave select (SSL), 206, 217
Slave select line negation delay,
217–18
Slave select polarity, 211
Slave transmitter, 223
Smart card interface, 41, 200, 297
Smart card mode register,
200, 201
Smart transducer(s), 194
SMBus communication
format, 41
SMDS, 230
SMR, 200, 201–2
Software configuration
management, 152
Software engineering
agile development methods
and, 157–58
chartplotter, fig, 144
coding and, 146–47
designing and, 146–47
development of lifecycle
models and, 155–58
development plan and, 142
development stages of, 142–55
embedded product lifecycle,
fig, 143
finite state machine, fig, 150
implementation of, 151–52
iterative process and, 156
peer reviews and, 147
processing and, 148–49
prototyping and, 158
requirements of, 145–46
risk reduction and, 141–42
spiral process and, 156–57
subsystem design and, 149–51
system architecture, fig, 147
system architecture and,
147–49
testing of, 152–55
V model, fig, 143
V model and, 143
waterfall process and, 155
Software trigger, 174
SP, 226
SPB, 219
SPBR, 214–15
SPCKD, 217
SPCMDx, 218–19
SPCR, 208–10
SPCR2, 210–11
SPDCR, 215–16
SPDR, 213–14, 216, 266
SPE, 210
SPEIE, 210
SPI. See serial peripheral
interface
SPIE, 232
SPIIE, 211
Spiral process, 156–57
SPLP, 212
SPLP2, 212
SPMS, 208
SPND, 218
497
SPNDEN, 219
SPOE, 211
SPOM, 212
SPPCR, 212
SPPE, 211
SPRI, 266
SPRIE, 210
SPRIx, 264
SPSCR, 214
SPSR, 212–13
SPSSR, 214
SPTI, 266
SPTIE, 210
SPTIx, 264
SSL. See slave select
SSL0E bit, 220
SSL1E bit, 220
SSL2E bit, 220
SSL3E bit, 220
SSLA, 219
SSLKP, 219
SSLND, 217–18
SSLP, 211
SSR, 200
ST, 226
st7579 graphics display, 126
st7579_lcd.h, 124–25
Stack memory, 454–55
Stack pointer select (U bit), 46
Stack value display function, 88
Stacksct.h, 127
Standard library, 87, 94
Standard library generator, 87
START bit, 194, 199, 234
State machine(s), 378–80
State of responsiveness, 456–58
Static analysis, 151
Static schedule, 449
Stepper motor(s), 21
STI, 232
STOP bit, 194, 200, 202, 234
String(s), data type, 54–55
Struct, 121
Structural hazard, 67
498
INDEX
Structure, 12
Successive approximation,
163–65
Successive conversion time
(tSAM), 165
SVA, 234
SWINTR, 351, 356–57
Switch(es), 17–20
Synchronous, 194
System command description, 87
System interconnection, 36
T
T_Comm_API, 122
T_glyphhandle, 119
T_glyphVersionInfo, 121
T_glyphworkspace, 122
T_LCD_API, 121
Task dispatcher, 468
Task table, 468, 470–71
TCCR, 307
TCNT, 305, 308, 312, 313,
426, 428
TCORA, 307, 313, 335
TCORB, 307, 313, 335
TCR, 306
TCSR, 307, 309, 426, 428–31
TDR. See transmit data register
TDRE, 234
TEIE, 232
10-bit A/D converter(s), 168,
178–83
channel selection and, 180
diagram of, fig, 179
ex, 188–90
MCU architecture and, 41
operation of, 182–83
registers of, 178–82
test voltage setting, tab, 182
trigger selection and, 181
10-bit D/A converter(s), 183–85
TEND, 234
Testing, software, 152–55
32-bit RX CPU, 38
Throw away prototype, 158
Tick ISR, 468
TIE, 232
Time out, 63–64
Timer control register
description, tab, 306
fig, 306
Timer counter control
register, 307
Timer(s), 39, 301–2. See also
event counter(s); pulse
output operation
TME bit, 429
TMOE, 231
TMOF, 234
TMOH, 229
TMOIE, 232
TMOL, 229
TMOS, 229
TMR, 174, 175, 303
TMS bit, 429
TOEN, 63–64
Top-down design, 144
TOPS, 438–40
Trace(s), 6, 7
Transducer(s), 11
Transformer(s), 29
Transistor(s), 22
Transmit data register (TDR),
200, 201, 203, 205
Transmit end flag bit, 203
Transmit end interrupt enable
bit, 202
Transmit interrupt enable bit, 203
Triac(s), 21
TRS, 225
TSam, 165
12-bit A/D converter(s), 168–78
continuous scan mode and,
177–78
diagram of, fig, 169
ex, 186–88
MCU architecture and, 41
registers and, 170–75
single-cycle scan mode and,
175–76, 178
trigger selection, tab, 174
2.4 GHz radio, 8
TXMD, 210, 211
Typedef.h, 126
U
U Bit, 46
UART receive data ISR, 149
UNDEF, 441
Underflow exception, 403,
406, 410
Union, 12
Unit test(s), 152, 153
Universal asynchronous
transmitter/receiver
(UART/USART),
194, 297
data structures, ex, 279
registers and, 200–203
SCI and, 196
shift register and, 198–99
transmission/receiving, ex,
236–42
USB, 12, 58
2.0 host/funciton module
and, 39
boot mode, 73
User stack point (USP), 43, 45
Utilities, 88
V
V model, 143
fig, 143
Vect.h, 126–27
Vector(s), 129–30
header files and, 126
Voltage
A/D converters and, 24
analog comparator and, 25
D/C converters and, 27–28
detection circuit and, 38
driving motors, coils and, 22
INDEX
LEDs as outputs and, 16
microprocessor and, 28
monitoring reset and, 38
regulator of, 29
serial communication and, 200
Voltage- mode binary weighted
D/C converter(s), 27
Von Neumann, John, 37–38
Von Neumann machine, fig, 37
W
WAIT, 230
Watchdog timer (WDT)
brownout condition and,
444–45
concepts of, 425–35
independent timer and, 436–42
operation of, 441–42
registers of, tab, 438
setting up, ex, 444
interval timer mode, ex, 443
interval timer mode and, 436
MCU architecture and, 39
operation of, 432–35
registers of, 426–32
registers of, tab, 427
reset and, 38
specifications of, tab, 426
timer mode, ex, 434–35
timer mode and, 433
Waterfall process, 155
WB stage, 66, 398
WDT. See watchdog timer
WDTOVF, 426
While (1) loop, 20, 378
White box testing, 152, 153–54
WINA, 428
WINB, 428
499
Wired-OR connection, 15
Word addressing, 75–76
WOVF flag, 431–32
Write-back stage (WB stage),
66, 398
X
XCHG instruction, 59
Y
Y Renesas development kit
(RDK), 125
YRD RX62N LEDs, 19
YRDKRX62N_RSPI0.h, 125–26
Z
Zero flag (Z flag), 46
Zigbee radio, 7
Product Development from Start to Success™
Product Development Engineering
Since 1990, we have designed some of the most exciting technologies for Fortune 500 and small
companies alike in the medical, video and portable wireless markets. We specialize in product
development services from start to success, including electrical, software, mechanical and industrial design services.
Paragon has been developing products around Renesas seminconductors since its inception.
At Paragon Innovations, we get excited about technology.
Medical
Wireless/Portable
Video
• Infusion pumps
• Insulin pumps
• Video projectors
• Pulse oximeters
• Electropora on devices
• Gas compressor lubrica on
monitor
• Extreme off axis
projec on
• Surgical lasers
• GPS based tracking devices
• Rear Projec on HDTV
• Con nuous Cardiac
Output Monitor
• GSM telephony
• Video compression
• Insulin pumps
• CDMA telephony
• Video scaling
• Breathalyzers
• Electropora on devices
• Set top box
• Wireless & bar coding
devices
• Panasonic PDA
• Flight Informa on
Display Systems
• Smart phone medical
applica ons
• Pneumothorax detec on
• Ear effusion
• Breathalyzers
• Weather sta ons
• Automo ve OBD-II Products
• Airline Video Docking
Systems (VDOCKS)
• LED displays
How often do you experience this?
Innovation Delivered™
Contact us for more information:
www.ParagonInnovations.com
866-242-1062
[email protected]
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