FreeRTOS计数型信号量

API函数

//创建
#if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
    #define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount )
                                xQueueCreateCountingSemaphore( ( uxMaxCount ), ( uxInitialCount ) )
    QueueHandle_t xQueueCreateCountingSemaphore( const UBaseType_t uxMaxCount,
                                                const UBaseType_t uxInitialCount )
#endif

//释放
#define xSemaphoreGive( xSemaphore )
xQueueGenericSend( ( QueueHandle_t ) ( xSemaphore ), NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )
BaseType_t xQueueGenericSend( QueueHandle_t xQueue, const void * const pvItemToQueue,
                            TickType_t xTicksToWait, const BaseType_t xCopyPosition )

//获取信号量值
#define uxSemaphoreGetCount( xSemaphore ) uxQueueMessagesWaiting( ( QueueHandle_t ) ( xSemaphore ) )
UBaseType_t uxQueueMessagesWaiting( const QueueHandle_t xQueue )

//等待
#define xSemaphoreTake( xSemaphore, xBlockTime )
xQueueGenericReceive( ( QueueHandle_t ) ( xSemaphore ), NULL, ( xBlockTime ), pdFALSE )
BaseType_t xQueueGenericReceive( QueueHandle_t xQueue, void * const pvBuffer,
                                TickType_t xTicksToWait, const BaseType_t xJustPeeking )

使用举例

SemaphoreHandle_t semaphore;

void start_task(void *pvParameters)
{
    semaphore = xSemaphoreCreateCounting(10, 0);
}

void give_task(void *pvParameters)
{
    UBaseType_t count;

    while(1)
    {
        key = KEY_Scan(0);
        if(key == WKUP_PRES)
        {
            err = xSemaphoreGive(semaphore);

            count = uxSemaphoreGetCount(semaphore);

            printf("give_task uxSemaphoreGetCount %d\r\n", count);
        }

        vTaskDelay(10);
    }
}

void take_task(void *pvParameters)
{
    while(1)
    {
        xSemaphoreTake(semaphore, portMAX_DELAY);

        count = uxSemaphoreGetCount(semaphore);

        printf("take_task uxSemaphoreGetCount %d\r\n", count);

        vTaskDelay(1000);
    }
}

实验现象