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FreeRTOS V8.0.1 - Copyright (C) 2014 Real Time Engineers Ltd.
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FreeRTOS is free software; you can redistribute it and/or modify it under
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This simple demo project runs on the STM32 Discovery board, which is
populated with an STM32F100RB Cortex-M3 microcontroller. The discovery board
makes an ideal low cost evaluation platform, but the 8K of RAM provided on the
STM32F100RB does not allow the simple application to demonstrate all of all the
FreeRTOS kernel features. Therefore, this simple demo only actively
demonstrates task, queue, timer and interrupt functionality. In addition, the
demo is configured to include malloc failure, idle and stack overflow hook
The idle hook function:
The idle hook function queries the amount of FreeRTOS heap space that is
remaining (see vApplicationIdleHook() defined in this file). The demo
application is configured to use 7K of the available 8K of RAM as the FreeRTOS
heap. Memory is only allocated from this heap during initialisation, and this
demo only actually uses 1.6K bytes of the configured 7K available - leaving 5.4K
bytes of heap space unallocated.
The main() Function:
main() creates one software timer, one queue, and two tasks. It then starts the
The Queue Send Task:
The queue send task is implemented by the prvQueueSendTask() function in this
file. prvQueueSendTask() sits in a loop that causes it to repeatedly block for
200 milliseconds, before sending the value 100 to the queue that was created
within main(). Once the value is sent, the task loops back around to block for
another 200 milliseconds.
The Queue Receive Task:
The queue receive task is implemented by the prvQueueReceiveTask() function
in this file. prvQueueReceiveTask() sits in a loop where it repeatedly blocks
on attempts to read data from the queue that was created within main(). When
data is received, the task checks the value of the data, and if the value equals
the expected 100, toggles the green LED. The 'block time' parameter passed to
the queue receive function specifies that the task should be held in the Blocked
state indefinitely to wait for data to be available on the queue. The queue
receive task will only leave the Blocked state when the queue send task writes
to the queue. As the queue send task writes to the queue every 200
milliseconds, the queue receive task leaves the Blocked state every 200
milliseconds, and therefore toggles the green LED every 200 milliseconds.
The LED Software Timer and the Button Interrupt:
The user button B1 is configured to generate an interrupt each time it is
pressed. The interrupt service routine switches the red LED on, and resets the
LED software timer. The LED timer has a 5000 millisecond (5 second) period, and
uses a callback function that is defined to just turn the red LED off.
Therefore, pressing the user button will turn the red LED on, and the LED will
remain on until a full five seconds pass without the button being pressed.
/* Kernel includes. */
#include "FreeRTOS.h"
#include "task.h"
#include "queue.h"
#include "timers.h"
/* STM32 Library includes. */
#include "stm32f10x.h"
#include "STM32vldiscovery.h"
/* Priorities at which the tasks are created. */
/* The rate at which data is sent to the queue, specified in milliseconds, and
converted to ticks using the portTICK_PERIOD_MS constant. */
#define mainQUEUE_SEND_FREQUENCY_MS ( 200 / portTICK_PERIOD_MS )
/* The number of items the queue can hold. This is 1 as the receive task
will remove items as they are added, meaning the send task should always find
the queue empty. */
#define mainQUEUE_LENGTH ( 1 )
* Setup the NVIC, LED outputs, and button inputs.
static void prvSetupHardware( void );
* The tasks as described in the comments at the top of this file.
static void prvQueueReceiveTask( void *pvParameters );
static void prvQueueSendTask( void *pvParameters );
* The LED timer callback function. This does nothing but switch the red LED
* off.
static void vLEDTimerCallback( TimerHandle_t xTimer );
/* The queue used by both tasks. */
static QueueHandle_t xQueue = NULL;
/* The LED software timer. This uses vLEDTimerCallback() as its callback
* function.
static TimerHandle_t xLEDTimer = NULL;
int main(void)
/* Configure the NVIC, LED outputs and button inputs. */
/* Create the queue. */
xQueue = xQueueCreate( mainQUEUE_LENGTH, sizeof( unsigned long ) );
if( xQueue != NULL )
/* Start the two tasks as described in the comments at the top of this
file. */
xTaskCreate( prvQueueReceiveTask, "Rx", configMINIMAL_STACK_SIZE, NULL, mainQUEUE_RECEIVE_TASK_PRIORITY, NULL );
xTaskCreate( prvQueueSendTask, "TX", configMINIMAL_STACK_SIZE, NULL, mainQUEUE_SEND_TASK_PRIORITY, NULL );
/* Create the software timer that is responsible for turning off the LED
if the button is not pushed within 5000ms, as described at the top of
this file. */
xLEDTimer = xTimerCreate( "LEDTimer", /* A text name, purely to help debugging. */
( 5000 / portTICK_PERIOD_MS ),/* The timer period, in this case 5000ms (5s). */
pdFALSE, /* This is a one shot timer, so xAutoReload is set to pdFALSE. */
( void * ) 0, /* The ID is not used, so can be set to anything. */
vLEDTimerCallback /* The callback function that switches the LED off. */
/* Start the tasks and timer running. */
/* If all is well, the scheduler will now be running, and the following line
will never be reached. If the following line does execute, then there was
insufficient FreeRTOS heap memory available for the idle and/or timer tasks
to be created. See the memory management section on the FreeRTOS web site
for more details. */
for( ;; );
static void vLEDTimerCallback( TimerHandle_t xTimer )
/* The timer has expired - so no button pushes have occurred in the last
five seconds - turn the LED off. NOTE - accessing the LED port should use
a critical section because it is accessed from multiple tasks, and the
button interrupt - in this trivial case, for simplicity, the critical
section is omitted. */
STM32vldiscovery_LEDOff( LED4 );
/* The ISR executed when the user button is pushed. */
void EXTI0_IRQHandler( void )
portBASE_TYPE xHigherPriorityTaskWoken = pdFALSE;
/* The button was pushed, so ensure the LED is on before resetting the
LED timer. The LED timer will turn the LED off if the button is not
pushed within 5000ms. */
STM32vldiscovery_LEDOn( LED4 );
/* This interrupt safe FreeRTOS function can be called from this interrupt
because the interrupt priority is below the
configMAX_SYSCALL_INTERRUPT_PRIORITY setting in FreeRTOSConfig.h. */
xTimerResetFromISR( xLEDTimer, &xHigherPriorityTaskWoken );
/* Clear the interrupt before leaving. */
EXTI_ClearITPendingBit( EXTI_Line0 );
/* If calling xTimerResetFromISR() caused a task (in this case the timer
service/daemon task) to unblock, and the unblocked task has a priority
higher than or equal to the task that was interrupted, then
xHigherPriorityTaskWoken will now be set to pdTRUE, and calling
portEND_SWITCHING_ISR() will ensure the unblocked task runs next. */
portEND_SWITCHING_ISR( xHigherPriorityTaskWoken );
static void prvQueueSendTask( void *pvParameters )
TickType_t xNextWakeTime;
const unsigned long ulValueToSend = 100UL;
/* Initialise xNextWakeTime - this only needs to be done once. */
xNextWakeTime = xTaskGetTickCount();
for( ;; )
/* Place this task in the blocked state until it is time to run again.
The block time is specified in ticks, the constant used converts ticks
to ms. While in the Blocked state this task will not consume any CPU
time. */
vTaskDelayUntil( &xNextWakeTime, mainQUEUE_SEND_FREQUENCY_MS );
/* Send to the queue - causing the queue receive task to unblock and
toggle an LED. 0 is used as the block time so the sending operation
will not block - it shouldn't need to block as the queue should always
be empty at this point in the code. */
xQueueSend( xQueue, &ulValueToSend, 0 );
static void prvQueueReceiveTask( void *pvParameters )
unsigned long ulReceivedValue;
for( ;; )
/* Wait until something arrives in the queue - this task will block
indefinitely provided INCLUDE_vTaskSuspend is set to 1 in
FreeRTOSConfig.h. */
xQueueReceive( xQueue, &ulReceivedValue, portMAX_DELAY );
/* To get here something must have been received from the queue, but
is it the expected value? If it is, toggle the green LED. */
if( ulReceivedValue == 100UL )
/* NOTE - accessing the LED port should use a critical section
because it is accessed from multiple tasks, and the button interrupt
- in this trivial case, for simplicity, the critical section is
omitted. */
STM32vldiscovery_LEDToggle( LED3 );
static void prvSetupHardware( void )
/* Ensure that all 4 interrupt priority bits are used as the pre-emption
priority. */
NVIC_PriorityGroupConfig( NVIC_PriorityGroup_4 );
/* Set up the LED outputs and the button inputs. */
STM32vldiscovery_LEDInit( LED3 );
STM32vldiscovery_LEDInit( LED4 );
/* Start with the LEDs off. */
STM32vldiscovery_LEDOff( LED3 );
STM32vldiscovery_LEDOff( LED4 );
void vApplicationMallocFailedHook( void )
/* Called if a call to pvPortMalloc() fails because there is insufficient
free memory available in the FreeRTOS heap. pvPortMalloc() is called
internally by FreeRTOS API functions that create tasks, queues, software
timers, and semaphores. The size of the FreeRTOS heap is set by the
configTOTAL_HEAP_SIZE configuration constant in FreeRTOSConfig.h. */
for( ;; );
void vApplicationStackOverflowHook( TaskHandle_t pxTask, char *pcTaskName )
( void ) pcTaskName;
( void ) pxTask;
/* Run time stack overflow checking is performed if
configconfigCHECK_FOR_STACK_OVERFLOW is defined to 1 or 2. This hook
function is called if a stack overflow is detected. */
for( ;; );
void vApplicationIdleHook( void )
volatile size_t xFreeStackSpace;
/* This function is called on each cycle of the idle task. In this case it
does nothing useful, other than report the amout of FreeRTOS heap that
remains unallocated. */
xFreeStackSpace = xPortGetFreeHeapSize();
if( xFreeStackSpace > 100 )
/* By now, the kernel has allocated everything it is going to, so
if there is a lot of heap remaining unallocated then
the value of configTOTAL_HEAP_SIZE in FreeRTOSConfig.h can be
reduced accordingly. */