- Science Publishing Group

American Journal of Embedded Systems and Applications
2015; 3(3): 23-34
Published online October 12, 2015 (http://www.sciencepublishinggroup.com/j/ajesa)
doi: 10.11648/j.ajesa.20150303.11
ISSN: 2376-6069 (Print); ISSN: 2376-6085 (Online)
Fast Track Exercises to Understand ARM Cortex-M4
Architecture Using Texas Instruments’ Stellaris Launch Pad
Rajeswari Cherukuri, Raghavendra Rao Kanchi*
VLSI and Embedded System Laboratory, Department of Physics, Sri Krishnadevaraya University, Anantapuramu, India
Email address:
shahitharaji@gmail.com (R. Cherukuri),kanchiraghavendrarao@gmail.com (R. R. Kanchi)
To cite this article:
Rajeswari Cherukuri, Raghavendra Rao Kanchi. Fast Track Exercises to Understand ARM Cortex-M4 Architecture Using Texas Instruments’
Stellaris Launch Pad. American Journal of Embedded Systems and Applications. Vol. 3, No. 3, 2015, pp. 23-34.
doi: 10.11648/j.ajesa.20150303.11
Abstract: In this paper we present fast track training for students to get acquainted with ARM Cortex -M4 architecture. This is
accomplished by considering exercises and a simple project that gives not only an insight but also hands-on experience to the
students and electronics hobbyist. Microcontrollers with ARM architecture have become popular and are one of the best
microcontrollers to start working with in an introductory embedded system laboratory. Texas Instruments’ Stellaris LaunchPad is
chosen for this purpose. The tiny board contains LM4F120H5QR as the microcontroller. It is an inexpensive board which can be
purchased by the student. Further, these exercises with some more advanced projects can be introduced as a half-semester
laboratory training program.
Keywords: Embedded System Laboratory, LM4F120H5QR Microcontroller, Project-Based Exercises
1. Introduction
ARM core microcontrollers have become popular and are
being used in a wide range of applications. Reasons for
becoming popular include its ability to execute instructions at
a faster rate (few hundreds of MHz), pipelining execution,
floating point arithmetic support for digital signal processing
(DSP) applications, memory protection, and ultra low power
consumption with a better interrupt support, etc. ARM cortex
architecture supports 16-bit thumb and 32-bit mode
applications. These features are further augmented with
powerful on-chip peripherals. Present day microcontrollers
with system-on-chip (SoC) contain a CPU with ARM cortex
architecture plus Wi-Fi Network Processor Subsystem for
Internet of things (IoT) applications developed on single
silicon. Some of the examples for such microcontrollers are:
Texas Instruments’ CC3200, Nordic Semiconductors’
nRF5182 and ST Microelectronics’ STM32W108CB.
It is evident from the above facts that there is a fast growth
and improvement in the field of semiconductor
technology/electronic industry. This fact need to be backed
up with modified curriculum at the undergraduate level, since
the upcoming students are the workforce in the industrial
environment. We propose in this paper, exercises and simple
student project for undergraduate curriculum which fits to a
half-a-semester hands-on laboratory.
General areas that employ embedded systems covers every
branch of day to day science and technology, namely
communications, automotive, medical, consumer, machine
control etc. Another trend in embedded device development
is to produce families of devices with a basic functionalities
and different extra details determining peculiarities of the
device exploitation and finally the cost of the device. With
embedded systems becoming omnipresent, there is a growing
need to teach and train engineers to learn their design and
development [1].
Learning embedded system is interesting on one hand but
need efforts to learn many areas: microcontroller architecture
and programming, sensor interfacing technology etc.
Designing an embedded system laboratory is an art, and
demands talented students to take up the design challenges
keeping the time frame in their mind [2, 3]. Various methods,
means and difficulties in establishing an embedded system
design was explained by Li Tu and Jun Yang [4]. In our
laboratory students are first trained to exploit the on-chip
facilities of the microcontroller before developing any
dedicated hardware. In this direction, we have published
papers related to laboratory training to get hands-on
experience and also as take-home exercises [5-8].
The Stellaris LM4F120 LaunchPad is a low-cost evaluation
board from Texas Instruments [9]. It is built around ARM
24
Rajeswari Cherukuri and Raghavendra Rao Kanchi: Fast Track Exercises to Understand ARM Cortex-M4
Architecture Using Texas Instruments’ Stellaris Launch Pad
Cortex M4-F based microcontroller. This processor provides
multiple interfaces using AMBAR technology. It provides
high-speed, low-latency memory access. Further, the
processor has a memory protection unit to enable memory
control and security privilege levels. The memory is organized
in such a way that code, data and stack are served exclusively
in a manner of task-by-task. When the on-chip peripherals of
the microprocessor unit is looked at, it has a variety of
peripherals (section 2).To understand the functionality of
these peripherals for interfacing, we explained a series of
exercises related to this. By performing exercises related to
module A, the student will have an understanding of the
Input/Output interfacing of LEDs, push button, seven segment
displays, LCD module and mechanical device like stepper
motor. Module B gives an opportunity to exploit the on-chip
peripherals like: analog-to-digital converter (ADC), Universal
Asynchronous Receiver- Transmitter (UART), Pulse Width
Modulation (PWM), Inter- Integrated Circuit (I2C). Spoon
feeding is avoided by leaving certain on-chip peripherals:
Synchronous Serial Interface (SSI), Controller Area Network
(CAN), Universal Serial Bus (USB) controller, analog
comparator unexplained. The student can have a go, to
understand these peripherals by developing suitable hardware
and software, by which partial assessment of a student is made.
At the end semester, students are supplied with a questionnaire
to give their feedback. Results of this are included at the end of
the paper (Section-5), which shows that students found it more
convenient to use the Stellaris LaunchPad in getting hands-on
training on exploiting the on-chip peripherals of ARM
Cortex-M4 architecture in general and the on-board facilities
provided by LaunchPad in particular.
The exercises are described in the order of increasing
complexity, starting with a LED blinking (Hello World!) to
temperature measurement by interfacing a sensor to the
LaunchPad. The systematic approach by learn-while-doing,
not only increases confidence in the student, but light up the
spark of innovation by thinking new ways of using the
microcontroller.
The paper is organized as follows: Section 2 gives brief
description on the architectural details of LM4F120H5QR
microcontroller. The programming procedure of the
controller using Code Composer Studio (CCS) is described in
Section 3. Section 4 gives the hardware and software details
of the experiments developed in the present study. Section 5
gives the student feedback and survey. Conclusions are
included in Section 6.
EPROM, 32Kbytes of SRAM, and 2Kbytes of EEPROM for
memory [9].
Key features of the LM4F120H5QR microcontrollers
include:
IEEE754-compliant, single-precision floating-point
capability at 80 MHz
SIMD instructions
256Kbytes of embedded flash memory and 32Kbytes of
SRAM
Low-power modes including power-saving hibernate
32-bit ARM cortex-M4F architecture optimized for
small-footprint embedded applications.
Thumb-2 mixed 16-/32-bit instruction set
Harvard architecture characterized by separate buses for
instruction and data.
Efficient processor core, system and memories
Memory protection unit (MPU) to provide a privileged
mode for protected operating system functionally
Serial wire Debug and serial wire trace reduce the
number of pins required for debugging and tracing
Ultra-low power consumption with integrated sleep
modes
LM4F120H5QR microcontroller operates at 3.3V. In
active mode controller uses 50mA at 3.3V and in idle
mode it uses 12mA at 3.3V
Two 12-bit 1MSPS ADCs and 24 analog input channels
Two CAN controllers
Optional full-speed USB 2.0 with device, host, and OTG
Advanced motion control capability, with as many as 16
motion control PWM outputs
Eight UARTs, six I2C modules, and four SPI/SSI ports,
JTAG and ARM serial wire Debug facility is provided.
2. Architecture Description of
LM4F120H5QR Controller
The TI Stellaris LM4F120H5QR microcontroller is based
on an 80MHz version of the ARM Cortex-M4F processor core.
The ARM Cortex-M4F processor core is a full-fledged 32-bit
processor core and the “F” designates the inclusion of a
hardware floating point unit. The TI LM4F120H5QR
microcontroller also incorporates 256Kbytes of Flash
Figure 1. The pin diagram of LM4F120H5R microcontroller (courtesy:
Texas Instruments, USA).
American Journal of Embedded Systems and Applications 2015; 3(3): 23-34
Texas Instruments user manual gives a detailed description
on LM4F120H5QR [10]. Also, there is a text book available
on the market [11].
Figure 2. Block diagram of LM4F120H5QR microcontroller (courtesy: Texas Instruments, USA).
25
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Rajeswari Cherukuri and Raghavendra Rao Kanchi: Fast Track Exercises to Understand ARM Cortex-M4
Architecture Using Texas Instruments’ Stellaris Launch Pad
3. Programming Procedure [12]
The main aim of using microcontrollers is to use it in
dedicated or stand-alone applications. As such, the software
developed for such application has to be stored in the
microcontroller’s application memory permanently. This
method of storing is otherwise known as programming. The
LM4F120H5QR microcontroller can be programmed using
one of the two programming hardware options which are
given below.
Using Joint Test Action Group (JTAG)
Using Serial Wire Debug (SWD)
In the present work, the on-board microcontroller is
programmed using JTAG (USB Emulator connector). The
application program can be developed either in assembly or
embedded C. We used CCS integrated development
environment (IDE) in the present work.
In order to give the flavor of CCS, the example of Blink
program is considered.
After installing the CCS software, the shortcut icon on
desktop can be clicked. A new project can be selected from the
drop-down menu, by giving project name, file name and the
location. The project can be saved in the StellarisWare
workspace. Further the device to be programmed and the in
circuit debug (ICD) interface are to be selected. Now, an
empty project space with the filename with .C extension will
be created. The program to be run is entered in the file, and
after completion the file can be saved with a name, e.g., LED_
Blink. C if the program is developed in C and with an
extension of .asm if the program is developed in assembly
language. Next in the project explorer window, the LED Blink
project with its properties can be selected. The properties
include path and inclusion of appropriate library files.
Pressing OK button will finish the project explorer. Now the
current project can be built. After building the project without
errors, the next step is debugging. After successful debugging,
pressing of Run button dumps the .HEX file on to the
microcontroller. Now, the microcontroller can be run in the
stand-alone mode for that specific application for which the
software is developed. Some screenshots which are related to
create a new project, built, debug, and run the project are
shown in figures 3, 4, and 5 respectively.
Figure 3. Creating a new project window (courtesy: Texas Instruments, USA).
American Journal of Embedded Systems and Applications 2015; 3(3): 23-34
Figure 4. Saving C file with LED_ Blink (courtesy: Texas Instruments, USA).
Figure 5. Debugging and running the LED_ Blink program (courtesy: Texas Instruments, USA).
27
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Rajeswari Cherukuri and Raghavendra Rao Kanchi: Fast Track Exercises to Understand ARM Cortex-M4
Architecture Using Texas Instruments’ Stellaris Launch Pad
4. Details of Individual Exercises
The total exercises developed and described in this paper
are divided into three modules: A, B and C. The first module
explains the basic input/output interfacing. Module B
corresponds to the exercises for exploitation of the on-chip
peripherals (partially). Temperature measurement using a
copper-constantan thermocouple interfaced with Stellaris
LaunchPad is described in module C. Photograph of the
Stellaris Launchpad with the on-board components is shown
in figure 6.
Figure 6. Stellaris LaunchPad development board (courtesy: Texas Instruments, USA).
Module A: Basic I/O Interfacing
This module contains interfacing exercises, relating to I/O
programming. Interfacing exercises starts with LED blinking
program, seven segment, push button, four digit seven
segment multiplexed display, stepper motor, and LCD display.
Ex. A 1: LED Blinking
The first exercise is LED toggling. This is the basic
experiment in embedded systems. LED is the most commonly
used component, usually for displaying the digital status of
I/O pins.
To get acquainted with GPIO pins of the controller, LEDs
are connected to port pins PB0 to PB 7 of PORTB with current
limiting resistors (220Ω), mounted on a bread board. The
program is developed in embedded C using CCS.
The software starts with first enabling the clock to the port
by setting the register RCGCGPIO to 02. Declaring the GPIO
port as output port, setting the drive strength and pull-up for
each of the pins, enabling GPIO pins as digital I/O s are done
by setting the registers: GPIODIR, GPIODR8R, GPIOPUR,
and GPIODEN to FF. Now, alternate pins of PORTB are made
high followed by a delay. Next, other four pins of PORTB are
made high followed by a delay. The last two steps are kept in
an infinite loop; as a result, alternate LEDs of PORTB blinks.
The outcome of this basic experiment is to understand the
I/O pin characteristics of the microcontroller and connecting
the LED in positive or negative logic through the current
limiting resistors.
Figure A1 shows the photograph of this exercise.
Figure A1. Stellaris LaunchPad interfaced with LEDs.
Ex. A 2: Seven segment Display
This exercise explains the interfacing of a common anode
type seven segment display with PORTB to display
hexadecimal numbers 0 through F. A seven segment display
with current limiting resistors is assembled on a bread board
American Journal of Embedded Systems and Applications 2015; 3(3): 23-34
with eight wires for connecting to PORTB.
Software initially enables the GPIO pins as digital I/O by
setting the registers mentioned in the previous exercise to FF,
and setting PORTB as output. An array of sixteen elements to
hold the HEX data corresponding to numbers 0 through F is
initialized. Contents of array are sent to PORTB sequentially
with delay. This program is kept in a loop. Figure A2 shows
the seven segment displaying number 7 during the process of
execution.
The outcome of the experiment is that the student will come
to know about two types of displays: common anode, common
cathode, and its usage in display circuits. As for as the
software is concerned, student learns the initialization of
arrays in embedded C using CCS.
29
particular. Figure A3 shows the pushbutton connected on a
bread board and the display showing count 0 at the beginning.
Figure A3. Stellaris LaunchPad interfaced with seven segment display and
push button.
Figure A2. Stellaris LaunchPad interfaced with seven segment display., Hex
value ‘7’ is displayed on the seven segment display.
Ex. A 3: Debouncing a pushbutton
Mechanical switches have a problem called bouncing in the
electronic domain, especially when used as a input to the
microprocessor/microcontroller. Bouncing can be eliminated
by either hardware or software. Hardware uses cross coupled
NAND gates (basic RS flip-flop) or IC MAX6816, while the
software needs programming (delay). In this exercise software
debouncing is done by connecting a push button to PD2 of
PORTD. A seven segment display connected to PORTB
shows the number of times the button is pressed. Hardware is
developed on a bread board by connecting pushbutton to
PORTD and seven segment display to PORTB.
Program starts by loading the registers GPIODIR,
GPIODR8R, GPIOPUR, GPIODEN to FF, which sets the
direction of PORTB as output, drive strength and pull-up for
each pin, enables the GPIO pins as digital I/O. GPIO register
of PORTD is loaded with FB, since the pushbutton is
connected to PD2. The count which reflects the number of
times the button is pushed/pressed is displayed on the seven
segment display.
The outcome of the experiment is that the student learns the
necessity for debouncing a mechanical switch in general and
the method of debouncing the button through software, in
Ex. A 4: Four-digit multiplexed seven segment displays
In exercise A 3, a push button is interfaced with PORTD2,
and the number of times the button is pressed is displayed on
the single digit display. If the number of pushes crosses nine,
then the display starts once again from zero. This problem is
overcome in this exercise using a four-digit multiplexed
display.
This exercise will serve two purposes, namely, the true
count of the button pressing is displayed and multiplexing of
display is implemented that results in average current drawn
by the displays with less intensity/brightness.
All eight digit pins of each of the four seven segment
displays are made common and connected to PORTB
(PB0-PB7). Selection of one among four digits is
accomplished using four pins of PORTE. Initialization of
ports is done accordingly, through software. Further, the main
software is developed for multiplexed display with the same
debounce program explained in exercise A 2. A four-digit
module available commercially is used in this exercise. Figure
A4 shows the photograph of the interface.
The outcome of the experiment is that the student learns
about what is multiplexing? How to multiplex displays What
are the advantages of multiplexing seven segment displays?
Figure A4. Stellaris LaunchPad interfaced with seven segment multiplexed
display.
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Rajeswari Cherukuri and Raghavendra Rao Kanchi: Fast Track Exercises to Understand ARM Cortex-M4
Architecture Using Texas Instruments’ Stellaris Launch Pad
Ex. A 5: Stepper Motor Interface
Motors can be broadly classified into two categories: ac
motors, dc motors. Further, dc motors can be classified into
two types: continuous rotation motors, stepper motors.
Nevertheless, all motors are mechanical devices and are
power hungry. Hence, if one wants to drive a stepper motor
with microcontroller, he should be careful with the power
driving capability of the port pins to which it is connected. It is
always a good idea to use a buffer (current amplifier such as
Darlington pair) between the microcontroller pins and the
motor winding. In the present work a dc stepper motor
working at 5V is taken. Its winding resistance is 15Ω. We have
chosen ULN2003 as the power driver.
Winding of the stepper motor are connected to PORTB via
ULN2003. The IC ULN2003 is placed on the bread board and
jumpers are connected between the port pins and the motor. As
the name indicates, stepper motor rotates in steps. The
stepping angle per step varies from one motor to another motor.
Motor stepping angle and speed can be controlled by software.
Software initialization is same as in exercise A 1.
REGISTERB is initialized with 88H, and rotated right/left
each time outputting the contents of REGISTERB, with delay
in between. This rotates the shaft of the motor
clockwise/anticlockwise. Figure A5 shows the photograph of
this exercise.
Outcome of this exercise include the understanding of the
working of stepper motor which is a mechanical device
(having inertia), and its interfacing with microcontroller.
Understanding its I/O pins driving capability (current sourcing
and sinking) of ports I/O pins is an additional advantage.
Figure A5. Stellaris LaunchPad interfaced with stepper motor.
Ex. A 6: LCD Interface
Liquid Crystal Display (LCD) has the greatest advantage of
low power consumption and occupies less space compared to
the seven segment display used in the previous exercises (A
3and A 4). Of course, it has a couple of major draw backs like
the display appears clearly at a particular angle with a small
distance, and needs more commands in software for its
initialization. In the present work, a 16X2 LCD display is used
for displaying characters [13]. A 10kΩ trim pot is used for
brightness control of the backlight LED of the LCD module.
The module is mounted on a bread board and connection
between the LaunchPad pins and display are accomplished
using jumper wires.
LCD module can be used in two modes: 8-bit mode and
4-bit mode. The 4-bit is also known as economical mode. In
the present study, 4-bit mode is selected. PORTB is initialized
as output port. RB4 to RB7 of PORTB pins are used for
sending data to LCD, and RB2, RB3 are used as LCD control
pins.
Besides setting the register for digital I/O, LCD commands
are sent to choose 16 characters, 2 lines. Program contains two
arrays: one consisting of characters: “STELLARIS” another
array: “LAUNCHPAD”. The data in the first and second
arrays are output on first and second lines of LCD,
respectively. Figure A6 shows the photograph of this exercise
From this exercise, the student learns the LCD functioning
and its pros and cons compared with LED display. Total
schematic diagram related to module A is shown in figure 7.
Figure A6. Stellaris LaunchPad interfaced with LCD.
Exploitation of on-chip peripherals is discussed in the
following module.
Module B: Interfacing Experiments to exploit the on-chip
Peripherals
This module gives the information about interfacing of the
on-chip peripherals (partially) like Analog to Digital converter
(ADC), Pulse Width Modulation (PWM), Universal
Asynchronous Receivers/Transmitter (UART), and Inter
Integrated Circuit (I2C).
Ex. B1: UART Echo Exercise
The microcontroller LM4F120H5QR has eight on-chip
UARTs: UART0 to UART7. Baud rate is selectable. In the
present exercise, UART0 is chosen with a baud rate of 115200
with 8-N-1protocol.
The software needs the inclusion of library functions like:
memmap.h, types.h, systcl.h, uart.h, gpio.h. All the
peripherals related to UART0 are enabled, which includes the
clock. The GPIO pinmuxing is configured for UART function
(PORTA0 corresponds to RX and PORTA1 corresponds to
TX). Program is developed to transmit the character typed on
the keyboard serially on TX/RX lines to echo it on the
hyperterminal of the laptop. The program is kept in a closed
loop. The characters typed on the keyboard are displayed on
the monitor of the laptop.
The outcome of this exercise include the selection and
programming of the on-chip UART for serial data
transmission to any peripheral connected to the
American Journal of Embedded Systems and Applications 2015; 3(3): 23-34
microcontroller over TX and RX lines. Figure B1 shows the
31
photograph of this exercise.
Figure 7. Total hardware for experiments A1 to A6 (Module A).
done continuously and the data stored in the register
ADCDATA is read and sent to laptop through UART. The
digital value is displayed on the hyperterminal of the laptop.
The outcome of this exercise is that the student understands
about the important ADC signals like: start-of-conversion
(SOC), end-of-conversion (EOC), conversion time, ADC
selection, input analog channel selection, clock selection for
ADC. These are in addition to the serial transmission of ADC
data to laptop with the knowledge of exercise B1. Figure B2
shows the photograph of this exercise.
Figure B1. Photograph of UART Echo.
Ex. B2: Measurement of Analog Voltage using on-Chip
ADC
The microcontroller used in the present work has two
on-chip ADCs, each having twelve analog input channels. In
the present exercise, ADC0 with analog input channel AN0 is
used. The converted digital data equivalent to the analog input
is sent to the laptop using the on-chip UART (Ex.B1).
The software starts with the inclusion of all required files
like: memmap.h, types.h, adc.h, gpio.h, sysctl.h, uartstudio.h.
UART0 is chosen to establish a serial link with the laptop in
order to display the digital data. ADC0 is initialized for a
single-ended and for a single sample. Sampling of the data is
Figure B2. Photograph of ADC Interfacing.
32
Rajeswari Cherukuri and Raghavendra Rao Kanchi: Fast Track Exercises to Understand ARM Cortex-M4
Architecture Using Texas Instruments’ Stellaris Launch Pad
Ex. B3: Realization of PWM using LED
The microcontroller has twelve capture compare (CCP)
PWM channels. They can be used in 16/32/64-bit modes. In
the present work, CCP0 is used for producing PWM.
Modulated output is obtained at PORTB6. An LED is
connected to PORTB6 through a 150Ω resistor to observe the
PWM. The same can be connected to the CRO in order to
observe the waveform.
The software includes all files mentioned in the above
exercises with an additional file:timer.h. Variables are defined
that determines the duty cycle of the PWM pulses. The CCP0
peripheral is configured appropriately and enabled. The
corresponding timer: TIMER0 is also enabled and configured
as 16-bit periodic timer. It is loaded with 1000 and that of
timer match is loaded with 250. Program with these inputs
produces a PWM at PB6.
The outcome of this exercise is that the student gets to know
about the various functionalities of the on-chip timer in
general and production of PWM signals using CCP0 in
particular.
Figure B 3 shows the photograph of this exercise
microcontroller used here has an additional feature of I2C
loopback mode that is useful for debugging I2C operation
through software. This mode internally connects the I2C0
master and slave terminals, so that data sent by master can be
received by the slave. The software can select the data transfer
rate. If the verification of I2C operation has to be done by
interfacing with external peripheral that supports I2C
communication, then, PORTB2 and PORTB3 pins have to be
connected to Vcc through external pull-up resistors.
An array of data is initialized, and the SLAVE ADDRESS is
selected. Data is placed in DATA REGISTER. The RECEIVE
BUFFER and DATA DIRECTION REGISTERS are
initialized. After sending each data, the program waits for an
acknowledgement from the slave. The data received by the
slave is displayed on the hyperterminal of the laptop. After
resetting the receive buffer, the direction of data transfer is
changed so that the master reads the data that is sent from the
data buffer of the slave. This is done after a dummy read
(receive) by the master so that junk data will be avoided. After
dummy acknowledge, the program waits for a send request
from the master to the slave. Data read by the master is also
sent to the laptop’s hyperterminal. Thus the data
communicated between master-to-slave and vice versa on
I2C0 lines can be verified physically on the hyperterminal.
Figure B4 shows the photograph of this exercise
Figure B3. Photograph of PWM interfacing.
Ex. B4: I2C (Inter-Integrated Circuit)
In general I2C bus provides bi-directional data transfer
through a two-wire design. This communication doesn’t need
level converters as in serial transmission using UART. The
microcontroller presents four I2C modules (I2C0-I2C3) on the
chip itself. The present exercise uses I2C0 module. The I2C
module contains a master and a slave. Master and slave can be
used in loopback mode to transfer data between master and
slave by giving a common clock. In the present experiment, a
loop back mode is accomplished besides transmitting the data
to hyperterminal of the laptop using the on-chip UART0. This
avoids interfacing with an external device having I2C pins.
The software starts with the inclusion of header files
including the files that supports I2C and UART. I2C0, UART0
and clock modules are enabled. The GPIO PINMUX is
configured for both I2C and UART functions (PORTB2 I2C0SCL, PORTB3 - I2C0SDA; PORTA0 - UART0RX,
PORTA1 - UART0TX). As a matter of fact, the Stellaris
Figure B4. Photograph of I2C module interfacing.
Module C: Sensor Interfacing with Stellaris LaunchPad
(LM4F120H5QR)
Ex. C1: Temperature measurement using copper-constantan
thermocouple sensor interfaced with microcontroller
Temperature measurement is an attractive exercise which
involves sensor interfacing. There are different types of
temperature sensors available on the market, like
thermocouple, semiconductor (pn-junction sensors) and IC
sensors.
In the present study, copper-constantan thermocouple is
used as a temperature sensor. As the output of the
thermocouple is in the range of millivolt, it is necessary to
amplify the signal before interfacing with microcontroller.
Analog Device’s AD595 thermocouple amplifier is used to
boost the output of the thermocouple [14]. Output from the
American Journal of Embedded Systems and Applications 2015; 3(3): 23-34
33
thermocouple is filtered for noise signal before connecting it
to the amplifier. Figure 8 shows the schematic of this exercise.
The software starts with all header files mentioned in
exercise B2. UART0 and ADC0 are used in the present
exercise to display the temperature and to convert the analog
output of AD595 to digital data, respectively. Analog input
channel AN0 is fed from the output of the AD595. After
conversion of the analog voltage equivalent to the equivalent
digital value, a look up table converts this digital value to an
equivalent temperature in oC. This value is displayed on the
hyperterminal of the UART. Figure C1 shows the photograph
of this exercise.
Figure C1. Photograph of temperature sensor interfacing with Stellaris
LaunchPad.
Figure 8. Hardware Schematic of AD595 thermocouple amplifier.
5. Student Feedback and Survey
We got the feedback from the students by asking them to fill up
a questionnaire. The results of the feedback are shown in Table 1.
Student’s response over a length of three years is shown in
Figure 9.
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Rajeswari Cherukuri and Raghavendra Rao Kanchi: Fast Track Exercises to Understand ARM Cortex-M4
Architecture Using Texas Instruments’ Stellaris Launch Pad
Table 1. The Average scores of the survey for exercises.
Questions
(a). What was your understanding about the
lecture on ARM cortex-M4 based system
design?
(b). Are you satisfied with the ARM Cortex-M4
(TIs’Stellaris LM4F120H5QR) lab kit?
(c). What was your understanding about
hardware interfacing and software development?
(d). Are you satisfied with the hands-on
experience and the type of sensor based
exercise?
Score (1-5)
2012
2013
2014
4.6
4.7
4.8
4.8
4.9
4.8
4.7
4.8
4.6
4.8
4.7
4.8
C. Rajeswari is thankful to University Grants Commission
(U.G.C), New Delhi, for sanctioning of Junior Research
Fellowship (B.S.R).
Software for the above programs can be obtained from
author on request.
References
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David Lawrence, Didier Buchs, and Armin Wellig, “Using In
instrumentation for Quality Assessment of Resilient software
in Embedded systems” I. Majzik and M. Vieira (Eds):
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Sheng Hongyu, and Wei Gaung, on the “Embedded Training
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Pang Ling, An Lei, “The discussion about teaching of
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Aruna. Kommu and Raghavendra Rao Kanchi “Design and
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[7]
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[9]
Datasheet, http://www.ti.com/ds/2/405/lm4f120h5qr-12404.pdf.
1-poor, 5-Exellent
Figure 9. Students respondse over a length of three years.
6. Conclusion
In this paper, we have designed and developed certain
exercises to get acquainted with the microcontroller
LM4F120H5QR using the Texas Instruments’ Stellaris
Launch Pad board. The Launch Pad presents majority of the
pins of the microcontroller brought to the on-board connectors.
The exercises relating to the Input/Output interfacing,
exploitation of on-chip peripherals such as: ADC, UART,
PWM, I2C and a thermocouple interface for temperature
measurement are described. Still there are un attempted
on-chip peripherals: SSI and USB interface. Successful
attempt of these exercises with advanced projects will increase
the confidence in the student to think and develop embedded
system design, which is essential in the present scenario.
[10] User Manual, http://www.ti.com/lit/ug/spmu289c/spmu289c.pdf.
[11] Workbook,
http://www.ti.com/Stellaris_Launchpad_start_files/Stellarislau
nchpadworkbook.pdf.
[12] http://www.ti.com/tool/ccstudio.
Acknowledgements
The facility created by the Department of Science and
Technology (DST), New Delhi by sanctioning the FIST
program (Phase-I) is acknowledged.
[13] http://www.sparkfun.com/datasheets/LCD/ADM1602K-NSWFBS-5V.pdf.
[14] http://www.analog/media/en/technical_documentation/data_sh
eets/AD594-595.pdf.
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