一.信号量的基本概念 

"give"给出资源，计数值加1；"take"获得资源，计数值减1 

二.创建信号量 

一开始的时候任务1计算，计算完之后信号量里面的计数值增加1，任务2获得信号量，但是任务2里面的计数值为0，就在里面阻塞，等任务1释放give信号量的时候，任务2被唤醒。

static int sum = 0;
static volatile int flagCalcEnd = 0;
static volatile int flagUARTused = 0;
static SemaphoreHandle_t xSemCalc;void Task1Function(void * param)
{volatile int i = 0;while (1){for (i = 0; i < 10000000; i++)sum++;//printf("1");xSemaphoreGive(xSemCalc);vTaskDelete(NULL);}
}void Task2Function(void * param)
{while (1){//if (flagCalcEnd)flagCalcEnd = 0;xSemaphoreTake(xSemCalc,portMAX_DELAY);flagCalcEnd = 1;printf("sum = %d\r\n", sum);}
}void TaskGenericFunction(void * param)
{while (1){if (!flagUARTused){flagCalcEnd = 1;printf("%s\r\n", (char *)param);flagCalcEnd = 0;vTaskDelay(1);}}
}/*-----------------------------------------------------------*/int main( void )
{TaskHandle_t xHandleTask1;#ifdef DEBUGdebug();
#endifprvSetupHardware();printf("Hello, world!\r\n");xSemCalc=xSemaphoreCreateCounting(10,0);xTaskCreate(Task1Function, "Task1", 100, NULL, 1, &xHandleTask1);xTaskCreate(Task2Function, "Task2", 100, NULL, 1, NULL);//xTaskCreate(TaskGenericFunction, "Task3", 100, "Task 3 is running", 1, NULL);//xTaskCreate(TaskGenericFunction, "Task4", 100, "Task 4 is running", 1, NULL);/* Start the scheduler. */vTaskStartScheduler();/* Will only get here if there was not enough heap space to create theidle task. */return 0;
}

void TaskGenericFunction(void * param)
{while (1){xSemaphoreTake(xSemUART,portMAX_DELAY);//获得信号量printf("%s\r\n", (char *)param);xSemaphoreGive(xSemUART);//释放信号量vTaskDelay(1);}
}/*-----------------------------------------------------------*/int main( void )
{TaskHandle_t xHandleTask1;#ifdef DEBUGdebug();
#endifprvSetupHardware();printf("Hello, world!\r\n");xSemCalc=xSemaphoreCreateCounting(10,0);xTaskCreate(Task1Function, "Task1", 100, NULL, 1, &xHandleTask1);xTaskCreate(Task2Function, "Task2", 100, NULL, 1, NULL);xSemUART=xSemaphoreCreateBinary();xSemaphoreGive(xSemUART);xTaskCreate(TaskGenericFunction, "Task3", 100, "Task 3 is running", 1, NULL);xTaskCreate(TaskGenericFunction, "Task4", 100, "Task 4 is running", 1, NULL);/* Start the scheduler. */vTaskStartScheduler();/* Will only get here if there was not enough heap space to create theidle task. */return 0;
}

三.give和take