Freescale SPI eTPU Function Application Note

Freescale Semiconductor
Application Note
AN2847
Rev. 0, 10/2004
Using the Serial Peripheral
Interface (SPI) eTPU Function
by: Jenifer Scott & Geoff Emerson
Freescale 32-Bit Embedded Controller Division
This eTPU Serial Peripheral Interface (SPI) application
note is intended to provide simple C interface functions
to the eTPU SPI function. The functions are useable on
any product which has an eTPU module. Example code
is available for the MPC5554 and MCF5235 devices.
This application note should be read in conjunction with
application note AN2864, “General C Functions for the
eTPU.”
1
Function Overview
The SPI function uses three eTPU channels to form a
bi-directional, synchronous serial port that can be used to
communicate with a wide variety of devices. It can be
used to add serial capabilities to a device without a serial
port, or to add further serial port(s) to a device that
already has a hardware-synchronous port. The function
requires no host CPU’s intervention once the function
has been initialized and a request for data transmission
has been made. One eTPU channel is configured to
function as the clock and the other two are configured to
function as serial transmitter (TxD, or ‘data out’) and
serial receiver (RxD, or ‘data in’). The eTPU SPI
© Freescale Semiconductor, Inc., 2004. All rights reserved.
Table of Contents
1
2
3
4
4.1
5
5.1
5.2
5.3
6
6.1
7
Function Overview...............................................1
SPI Overview.......................................................2
Basic Timing........................................................2
Using the Function ..............................................3
Notes on the Performance and Use of eTPU SPI
Function.............................................................4
C Level API for eTPU SPI Function.....................4
SPI Initialization Function ..................................5
SPI Transmit Data Function ...............................6
SPI Retrieve Received data...............................7
Examples of Function Use ..................................7
Description.........................................................8
Summary .............................................................8
SPI Overview
function provides similar functionality to the TPU3 SIOP function. Peripheral Chip Select (PCS)
functionality is not provided by the eTPU SPI function.
The main features of the function are as follows:
• Programmable baud rate period over a 23-bit range of TCR1 or TCR2 counts
• Selection of msb or lsb first shift direction
• Variable transfer size from 1 to 24 bits
• Programmable clock polarity
• Master mode only
2
SPI Overview
An SPI is primarily used to allow a microcontroller to communicate with peripheral devices. An SPI is
also capable of interprocessor communications. Peripheral devices may be as simple as an ordinary
transistor-transistor logic (TTL) shift register, or as complex as a complete subsystem, such as a liquid
crystal diode (LCD) display driver or an analogue-to-digital (A/D) converter subsystem. The SPI system
is flexible enough to interface with numerous standard product peripherals from several manufacturers.
3
Basic Timing
The basic timing arrangement for the eTPU SPI function is shown in Figure 1and Figure 2. With positive
clock polarity, the master (eTPU SPI) changes the transmitted data on the falling edge of the clock. The
received data from the slave is sampled on the rising edge of the clock. With negative clock polarity, the
master (eTPU SPI) changes the transmitted data on the rising edge of the clock. The received data from
the slave is sampled on the falling edge of the clock.
1/baud_rate
Data Out
CLK
Data In
Master &
Slave Sample
Master &
Slave Drive
Figure 1. SPI Timing when CLK has Positive Polarity
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
2
Freescale Semiconductor
Using the Function
1/baud_rate
Data Out
CLK
Data In
Master &
Slave Sample
Master &
Slave Drive
Figure 2. SPI Timing when CLK has Negative Polarity
4
Using the Function
A simple C API is provided to allow customers to use the SPI function quickly and easily. The API is
defined in Section 5, “C Level API for eTPU SPI Function.”
An initialization function call is used to set up the SPI function to match the user’s requirements.
Following initialization, the transmit function call should be used to send and receive data. The function
works in such a way that when data is transmitted on the TxD pin, data will also be sampled on the RxD
pin. The transmit function will use the SPI parameters defined during initialization.
The channel arrangement for the SPI function is fixed. The diagram and table below show this
arrangement.
eTPU
Clock_channel –1
Data In (RxD)
Clock_channel
Clock (CLK)
Clock_channel +1
Data Out (TxD)
Pin function
Channel number
Data in (RxD)
Clock_channel -1
Clock
Clock_channel
Data Out (TxD) Clock_channel +1
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
Freescale Semiconductor
3
C Level API for eTPU SPI Function
When a transfer of data is complete, the SPI function’s clock channel sends an interrupt and DMA request.
The DMA request signal for a given channel may not be connected; the connection depends on the specific
integration of the eTPU. The programmer can use either the DMA request or the interrupt request,
depending on the specific integration.
Typically an SPI will require a Chip Select signal to be asserted. This signal can be generated by using
either the General Purpose Input/Output on the host, or by using the eTPU GPIO function.
4.1
Notes on the Performance and Use of eTPU SPI
Function
Like all eTPU functions, SPI function performance in an application, to some extent, depends on the
service time (latency) of other active eTPU channels. This is due to the operational nature of the eTPU
scheduler.
When a single SPI function is in use and no other eTPU channels are active, the minimum time between
clock edges is 37 eTPU clock cycles. This is due to the time taken for the eTPU engine to calculate and
schedule the events required by the SPI function. If the time requested between clock edges is less than
this minimum, the SPI function transmits and receives data correctly, but the actual time between clock
edges will be longer then requested, as the baud rate will be limited by the eTPU’s bandwidth. When more
eTPU channels are active, performance decreases, as the eTPU engine can only service one channel at a
time. However, worst-case latency in any eTPU application can be closely estimated. To analyze the
performance of an application that appears to approach the limits of the eTPU, use the guidelines given in
the eTPU Reference Manual and the information provided in the eTPU SPI software release available from
Freescale.
Although the SPI function is a three-channel function, only the clock channel is scheduled for service. The
TXD and RxD channel hardware is used by the clock channel. All three channels share the same parameter
RAM. The use of the TxD and RxD channels does not affect he performance of the eTPU, and should
therefore not be considered in latency calculations.
For the MPC5554 with a system frequency of 132 MHz, the maximum baud rate using TCR1 with a
timebase_freq of 66 Mhz is 1.75 Mbits per second.
For the MCF5235 with a system frequency of 150MHz, the maximum baud rate using TCR1 with a
timebase_freq of 37.5 Mhz is 0.85 Mbits per second.
Maximum baud-rate is influenced by compiler efficiency. The above numbers are given for guidance only
and are subject to change. For up to date information, refer to the information provided in the eTPU SPI
software release available from Freescale.
5
C Level API for eTPU SPI Function
The following functions provide easy access for the application developer into the eTPU SPI function for
the application developer. Use of these functions eliminates the need to directly control the eTPU registers.
The API consists of three functions. These functions can be found in the etpu_spi.h and etpu_spi.c files.
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
4
Freescale Semiconductor
C Level API for eTPU SPI Function
The functions are described below and are available from Freescale. In addition, the eTPU compiler
generates a file called etpu_spi_auto.h. This file contains information relating to the eTPU SPI function
including details of how the Parameter RAM is organized and definitions for the various API interface
information.
Unless otherwise stated the function parameter macros are defined in etpu_spi_auto.h
SPI Initialization
int32_t_fs_etpu_spi_init
(uint8_t clock_channel, uint8_t priority,
uint32_t baud_rate, uint8_t shift_dir,
uint8_t polarity, uint32_t transfer_size,
uint8_t timebase, uint32_t timebase_freq);
SPI Transmit Data
void fs_etpu_spi_transmit_data (uint8_t clock_channel, uint32_t tx_data);
SPI Retrieve Received data
uint32_t fs_etpu_spi_get_data (uint8_t clock_channel);
5.1
SPI Initialization Function
Function fs_etpu_spi_init is used to initialize three eTPU channels for the eTPU SPI function. For further
transfers of data, the transmit data function call should be used.
This function dynamically allocates parameter RAM. If dynamic allocation is not required, then the clock
channel’s Channel Parameter Base Address field should be written with a non-zero value before calling
the fs_etpu_spi_init function.
Dynamic allocation of parameter RAM occurs if the channel has a zero in its Channel Parameter Base
Address field. The Channel Parameter Base Address field is updated by the API with a non-zero value to
point to the parameter RAM allocated to the channel. The fs_etpu_spi_init API will not allocate new
parameter RAM if the channel has a non-zero value in its Channel Parameter Base Address field; this
means that channel has already been assigned. The channel can be reconfigured to transmit/receive data
with a different set of transmit/receive parameters by calling the fs_etpu_spi_init function again.
This function has the following parameters:
• clock_channel: The SPI clock channel number. For devices with two eTPUs, this parameter
should be assigned a value of 1-30 for eTPU_A and 65-94 for eTPU_B. For products with a single
eTPU, this parameter should be assigned a value of 1-30. Operation is not guaranteed if channels
0, 31, 64, or 95 are used as clock_channel.
• priority: The priority to assign to the eTPU SPI clock channel. The following eTPU priority
definitions are found in the utilities file etpu_util.h. This parameter should be assigned one of the
following values:
— FS_ETPU_PRIORITY_HIGH
— FS_ETPU_PRIORITY_MIDDLE
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
Freescale Semiconductor
5
C Level API for eTPU SPI Function
•
•
•
•
•
•
5.2
— FS_ETPU_PRIORITY_LOW
— FS_ETPU_PRIORITY_DISABLED
baud_rate: This is the required rate of data transmission. Maximum baud rate is dependant upon
system frequency, timebase frequency and eTPU loading; see Section 4.1, “Notes on the
Performance and Use of eTPU SPI Function.”
The eTPU microcode schedules an event every ‘half period’ of the programmed eTPU SPI
baud_rate. The half period is calculated by the initialization API according to the following
formula:
half_period = timebase_freq/(2* baud_rate).
If this formula resolves to a non-integer value, then the API will effectively round down
half_period. This will result in an error in the baud_rate. The accuracy of data transfers is
unaffected by this error.
shift_dir: Selection of msb (most significant bit) or lsb (least significant bit) first shift direction.
This parameter should be assigned one of the following values:
— FS_ETPU_SPI_SHIFT_DIR_MSB
— FS_ETPU_SPI_SHIFT_DIR_LSB
Polarity: This is the polarity of the channel. This parameter should be assigned one of the
following values:
— FS_ETPU_SPI_CLK_POL_POS
— FS_ETPU_SPI_CLK_POL_NEG
When polarity is FS_ETPU_SPI_CLK_POL_POS, the eTPU SPI function samples the RxD pin on
the rising edge of the clock channel and changes the TxD pin on the falling edge of the clock
channel.
When polarity is FS_ETPU_SPI_CLK_POL_NEG, the eTPU SPI function samples the RxD pin
on the falling edge of the clock channel and changes the TxD pin on the rising edge of the clock
channel.
transfer_size: This is the size of the data to be transferred. This parameter should be assigned a
value of between 1 and 24 decimal.
timebase: This is the timebase to use as a reference for the SPI clock signal. This parameter
should be assigned one of the following values (definitions are found in the utilities file
etpu_util.h):
— FS_ETPU_TCR1
— FS_ETPU_TCR2
timebase_freq: This is the pre-scaled frequency of the timebase (either TCR1/TCR2), supplied by
the eTPU to the function
SPI Transmit Data Function
Function fs_etpu_spi_transmit_data is used only after the SPI function has been initialized using the
fs_etpu_spi_init function. The configuration selected at initialization will be used for data transfers using
this function call.
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
6
Freescale Semiconductor
Examples of Function Use
This function call is used to transmit and/or receive data. When the function transmits a data bit, a
corresponding data bit is received. The SPI function can be used to transmit data only by using the transmit
API function call and ignoring the received data.
The data will be justified to the left by this API call if the function has been configured to send/receive
data msb first. For example, if the API is used to transmit 4 bits with msb first and tx_data= 0xFC 8431,
the API would left justify the tx_data parameter to be 0x10 0000. The transmitted data would come out of
the TxD channel in the following bit order: 0,0,0,1.
If the same data is transmitted lsb first, no left justification would be performed, and the transmitted data
would come out of the TxD channel in the following bit order: 1,0,0,0.
This function has two parameters:
• clock_channel: The SPI clock channel number. For devices with two eTPUs, this parameter
should be assigned a value of 1-30 for eTPU_A and 65-94 for eTPU_B. For products with a single
eTPU, this parameter should be assigned a value of 1-30. Operation is not guaranteed if channels
0, 31, 64, or 95 are used as clock_channel.
• tx_data: This is the data to be transmitted. It will be placed in the data register to be accessed by
the SPI function. Note that although tx_data is a 32-bit parameter, the eTPU SPI function is
capable of transferring between 1 and 24 bits. The number of bits to be transferred is defined by
parameter transfer_size in the fs_etpu_spi_init function.
It is imperative that the function is allowed to finish sending/receiving data before the channel is used to
send/receive data again; otherwise, the sent/received data may be corrupted. The function sends interrupt
and DMA requests when it has finished processing.
5.3
SPI Retrieve Received data
Function fs_etpu_spi_get_data is used to retrieve data which the SPI function has received.
This function has only one parameter:
• clock_channel: The SPI clock channel number. For products with two eTPUs, this parameter
should be assigned a value of 1-30 for eTPU_A and 65-94 for eTPU_B. For products with a single
eTPU, this parameter should be assigned a value of 1-30. Operation is not guaranteed if channels
0, 31, 64, or 95 are used as clock_channel.
This function retrieves the number of bits that the function was configured to receive by fs_etpu_spi_init
from the eTPU Parameter RAM.
6
Examples of Function Use
Example code showing use of the eTPU SPI function is available from Freescale for both the MPC5500
and the MCF523x families of devices.
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
Freescale Semiconductor
7
Summary
6.1
Description
This section describes a simple use of the SPI function and how to initialize the eTPU module and assign
the eTPU SPI function to an eTPU channel. Examples are given for the MPC5500 series parts and the
MCF523x series parts.
6.1.1
MPC5500 Example Code
The example consists of two files:
• spi_ppc_example.h
• spi_ppc_example.c
File spi_ppc_example.c contains the main() routine. This routine initializes the MPC5554 device for 128
MHz CPU operation and initializes the eTPU according to the information in the my_etpu_config struct
(stored in file spi_ppc_example.h). The pins used in this example are configured for eTPU operation, and
then the SPI function is initialized on channel 3 (ETUA2=RxD, ETPUA3=CLK ETPUA4=TxD). Eight
bits of data (0xCC) are then transmitted from the TxD pin and received on the RxD pin. In order to observe
the transmitted data being received, the TxD pin should be shorted to the RxD pin.
6.1.2
MCF523x Example Code
The example consists of four files:
• spi_mcf_example.h
• spi_mcf_example.c
• spi_mcf_example_global_etpu_gct.h
• spi_mcf_example_global_etpu_gct.c
File spi_mcf_example.c contains the main() routine. This routine initializes the MCF5235 device for 100
MHz CPU operation and initializes the eTPU according to the information in the my_etpu_config struct
(stored in file spi_mcf_example_global_etpu_gct.c). The SPI function is initialized on channel 9
(ETUA8=RxD, ETPUA9=CLK ETPUA10=TxD). Eight bits of data (0xCC) are then transmitted from the
TxD pin and received on the RxD pin. In order to observe the transmitted data being received, the TxD pin
should be shorted to the RxD pin.
7
Summary
This applications note provides the user with a description of the Serial Peripheral Interface (SPI) eTPU
function and details on how to use the function. The simple C interface functions for the eTPU SPI function
that are provided in the API enable easy implementation of the SPI function in user applications. The
functions are targeted for the MPC5500 and the MCF53x families of devices, but they can be used with
any device that has an eTPU.
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
8
Freescale Semiconductor
THIS PAGE INTENTIONALLY LEFT BLANK
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
Freescale Semiconductor
9
THIS PAGE INTENTIONALLY LEFT BLANK
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
10
Freescale Semiconductor
THIS PAGE INTENTIONALLY LEFT BLANK
Using the Serial Peripheral Interface (SPI) eTPU Function, Rev. 0
Freescale Semiconductor
11
How to Reach Us:
Home Page:
www.freescale.com
E-mail:
[email protected]
USA/Europe or Locations Not Listed:
Freescale Semiconductor
Technical Information Center, CH370
1300 N. Alma School Road
Chandler, Arizona 85224
+1-800-521-6274 or +1-480-768-2130
[email protected]
Europe, Middle East, and Africa:
Freescale Halbleiter Deutschland GmbH
Technical Information Center
Schatzbogen 7
81829 Muenchen, Germany
+44 1296 380 456 (English)
+46 8 52200080 (English)
+49 89 92103 559 (German)
+33 1 69 35 48 48 (French)
[email protected]
Japan:
Freescale Semiconductor Japan Ltd.
Technical Information Center
3-20-1, Minami-Azabu, Minato-ku
Tokyo 106-0047, Japan
0120 191014 or +81 3 3440 3569
[email protected]
Asia/Pacific:
Freescale Semiconductor Hong Kong Ltd.
Technical Information Center
2 Dai King Street
Tai Po Industrial Estate
Tai Po, N.T., Hong Kong
+800 2666 8080
[email protected]
For Literature Requests Only:
Freescale Semiconductor Literature Distribution Center
P.O. Box 5405
Denver, Colorado 80217
1-800-441-2447 or 303-675-2140
Fax: 303-675-2150
[email protected]
Information in this document is provided solely to enable system and
software implementers to use Freescale Semiconductor products. There are
no express or implied copyright licenses granted hereunder to design or
fabricate any integrated circuits or integrated circuits based on the
information in this document.
Freescale Semiconductor reserves the right to make changes without further
notice to any products herein. Freescale Semiconductor makes no warranty,
representation or guarantee regarding the suitability of its products for any
particular purpose, nor does Freescale Semiconductor assume any liability
arising out of the application or use of any product or circuit, and specifically
disclaims any and all liability, including without limitation consequential or
incidental damages. “Typical” parameters that may be provided in Freescale
Semiconductor data sheets and/or specifications can and do vary in different
applications and actual performance may vary over time. All operating
parameters, including “Typicals”, must be validated for each customer
application by customer’s technical experts. Freescale Semiconductor does
not convey any license under its patent rights nor the rights of others.
Freescale Semiconductor products are not designed, intended, or authorized
for use as components in systems intended for surgical implant into the body,
or other applications intended to support or sustain life, or for any other
application in which the failure of the Freescale Semiconductor product could
create a situation where personal injury or death may occur. Should Buyer
purchase or use Freescale Semiconductor products for any such unintended
or unauthorized application, Buyer shall indemnify and hold Freescale
Semiconductor and its officers, employees, subsidiaries, affiliates, and
distributors harmless against all claims, costs, damages, and expenses, and
reasonable attorney fees arising out of, directly or indirectly, any claim of
personal injury or death associated with such unintended or unauthorized
use, even if such claim alleges that Freescale Semiconductor was negligent
regarding the design or manufacture of the part.
Freescale™ and the Freescale logo are trademarks of Freescale
Semiconductor, Inc. All other product or service names are the property
of their respective owners.© Freescale Semiconductor, Inc. 2004. All rights
reserved.
AN2847
Rev. 0
10/2004
">