How to add blinking LED to FreeRTOS/EV-LM3S811

Using the FreeRTOS demo code for the EV-LM3S811, I added a simple task to blink the User LED. It was a good way to begin to understand how FreeRTOS works.

All of the changes are to the 'main.c' file. First, add some #defines (near the 'Demo Board Specifics' #defines):

#define mainUSER_LED GPIO_PIN_5

Right after that, add a #define for the blink rate (1000 ms = 1 second):

#define mainLED_DELAY ((portTickType) 1000/portTICK_RATE_MS)

Add a prototype for the task function:

static void vUserLEDTask(void *pvParameter);

In the main() function, add the call to create the task after the other demo tasks (modelled exactly after the other task create calls):

xTaskCreate(vUserLEDTask, "UserLED", configMINIMAL_STACK_SIZE, NULL, mainCHECK_TASK_PRIORITY - 1, NULL);

In the prvSetupHardware() function, add a line to configure the GPIO pin as an output, immediately after the section that configures the push button input:

GPIODirModeSet(GPIO_PORTC_BASE, mainUSER_LED, GPIO_DIR_MODE_OUT);

And finally, add the actual blinking task after the other tasks:

static void vUserLEDTask(void *pvParameter) {

for(;;) {
GPIOPinWrite(GPIO_PORTC_BASE, mainUSER_LED, mainUSER_LED); // let it shine
vTaskDelay(mainLED_DELAY);
GPIOPinWrite(GPIO_PORTC_BASE, mainUSER_LED, 0); // take a break
vTaskDelay(mainLED_DELAY);
}
}

That's it! I hope the long lines don't get too mangled. You might have to drop some of the other demo tasks to get it to fit using the code-limited linker. You could also try space optimizations. Let me know if you have any questions or suggestions about this little experiement.

Dale Wheat