This application uses both module_spi_master and module_spi_slave to create a loopback between 2 threads.
Note: Jumpers are required on the board to run this demo, as described in SPI H/W Development Platforms.
The Makefile is found in the top level directory of the application. It uses the general XMOS makefile in module_xcommon which compiles all the source files in the application and the modules that the application uses. We only have to add a couple of configuration options.
Firstly, this application is for an XK-1 development board so the TARGET variable needs to be set in the Makefile:
# The TARGET variable determines what target system the application is
# compiled for. It either refers to an XN file in the source directories
# or a valid argument for the --target option when compiling.
TARGET = XK-1
Secondly, the application name must be set:
# The APP_NAME variable determines the name of the final .xe file. It should
# not include the .xe postfix. If left blank the name will default to
# the project name
APP_NAME = app_spi_loopback_demo
Finally, the application will use both the SPI master and slave modules. We state that the application uses them as follows:
# The USED_MODULES variable lists other module used by the application.
USED_MODULES = module_spi_master module_spi_slave
The spi_conf.h file is found in the src/ directory of the application. This file contains a series of #defines that configure the SPI component. The possible #defines that can be set are described in Configuration Defines.
If not set, default values in the spi_master and spi_slave header files will be used.
As both master and slave modules can run in all the SPI modes, within this application any mode can be selected. Changing the #define SPI_MODE ensures that both master and slave are run in the same mode as one another.
The maximum frequency sclk supported by the slave module differs for each SPI mode, #define DEFAULT_SPI_CLOCK_DIV sets the highest frequency that will work in any SPI mode. #define SPI_CLOCK_DIV sets the frequency actually used by the application.
// Copyright (c) 2011, XMOS Ltd., All rights reserved
// This software is freely distributable under a derivative of the
// University of Illinois/NCSA Open Source License posted in
// LICENSE.txt and at <http://github.xcore.com/>
#define DEFAULT_SPI_CLOCK_DIV 58 // Maximum frequency suitable for SPI slave in any SPI mode
#define SPI_CLOCK_DIV 2 //DEFAULT_SPI_CLOCK_DIV
#define SPI_MODE 3
// Ensure that master and slave always operate in the same mode
#define SPI_MASTER_MODE SPI_MODE
#define SPI_SLAVE_MODE SPI_MODE
The application comes configured to run in SPI mode 3, with an SPI clock divider of 2 (giving a SPI clock frequency of 25MHz). The demo can be recompiled and run in other SPI modes, with different clock dividers.
To make use of the SPI master and slave modules app_spi_loopback_demo must contain the following lines:
#include "spi_master.h"
#include "spi_slave.h"
This application is contained in spi_loopback_demo.xc. Within this file is the main() function which starts the SPI master and slave running in parallel threads by calling the functions run_master() and run_slave(). These run functions initialise the interface modules and run the demo a set number of times. The master_demo() function checks that the data returned from the slave is correct. The interfaces are shut down after the final run of the demo.