freeRTOS的延时函数

1. vTaskDelay()
函数原型：void vTaskDelay(portTickType xTicksToDelay);
xTicksToDelay: 指定延时间，即指定心跳个数。调用该函数的任务将进入阻塞态，当延时结束时任务进入就绪态。
2. vTaskDelayUntil
函数原型：void vTaskDelayUntil(portTickType* pxPreviousWakeTime, portTickType xtimeIncrement);
pxPreviousWakeTime: 用来保存任务上一次离开阻塞态进入就绪态的时刻，每次执行完该函数，将结束时的时刻赋给pxPreviousWakeTime指向的变量，这个时刻做为参考点用来计算下一次离开阻塞态的时刻。
xtimeIncrement：用来指定延时的时间长度，以心跳为单位。
例程：

#include "includes.h"
#include <stdio.h>
#include "usart.h"


void xDelay(void);
void xtask(void *pvParameter);
const char *pcTask1Name = "Task1 is running\n";
const char *pcTask2Name = "Task2 is running\n";

int main()
{
   int ret = 0;
   uart_init(9600);     //????????????9600
   NVIC_Configuration();// ?è????????????·?×é

   /*
    *???¨??????????
    */
    xTaskCreate(xtask, //??????????
                "task1", //????????±???×??????????÷???±????
                512, //??????·????????????ó??
                (void*)pcTask1Name, //??????????????????
                1, //±?????????????
                NULL); //????????????±ú
    xTaskCreate(xtask, "task2", 512, (void*)pcTask2Name, 2, NULL);    //??????1?????¨????2
    /*
     *?????????÷???÷??????????????
     */

    vTaskStartScheduler();
    /*
     *??°????????á????????????·??????????ò??????????????×?????·¨??????????·???
     *????
     */
     while(1);
}
/***************************************
 * ?????ò???????±????
 **************************************/
void xDelay()
{
    int i;
    for(i = 200; i--; i >= 0);
}
/****************************************
 * ??????????????
 ***************************************/
 void xtask(void *pvParameter)
 {
     int i;


     //volatile unsigned long u1 = 0;
     portTickType xLastWakeTime;
     xLastWakeTime = xTaskGetTickCount();

     while(1)
     {
         printf("%s\n", (char*)pvParameter);
         vTaskDelayUntil(&xLastWakeTime, 10);
     }
 }

执行结果为：


例程2 
（1）创建两个任务，任务的有先级都为1，两个任务持续运行。
（2）创建第三个任务，任务的优先级为2，周期性的执行。

#include "includes.h"
#include <stdio.h>
#include "usart.h"


void xDelay(void);
void xtask(void *pvParameter);
void xtask3(void *pvParameter);
const char *pcTask1Name = "Task1 is running\n";
const char *pcTask2Name = "Task2 is running\n";
const char *pcTask3Name = "Task3 is running\n";


int main()
{
   int ret = 0;
   uart_init(9600);     //????????????9600
   NVIC_Configuration();// ?è????????????·?×é

   /*
    *???¨??????????
    */
    xTaskCreate(xtask, //??????????
                "task1", //????????±???×??????????÷???±????
                512, //??????·????????????ó??
                (void*)pcTask1Name, //??????????????????
                1, //±?????????????
                NULL); //????????????±ú
    xTaskCreate(xtask, "task2", 512, (void*)pcTask2Name, 1, NULL);    //??????1?????¨????2
    xTaskCreate(xtask3, "task3", 512, (void*)pcTask3Name, 2, NULL);    //??????1?????¨????2
    /*
     *?????????÷???÷??????????????
     */

    vTaskStartScheduler();
    /*
     *??°????????á????????????·??????????ò??????????????×?????·¨??????????·???
     *????
     */
     while(1);
}

/****************************************
 * ??????????????
 ***************************************/
void xtask(void *pvParameter)
{
     int i;


     //volatile unsigned long u1 = 0;

     while(1)
     {
         printf("%s", (char*)pvParameter);
     }
}
 /****************************************
 * ??????????????
 ***************************************/
void xtask3(void *pvParameter)
{
     int i;


     //volatile unsigned long u1 = 0;
     portTickType xLastWakeTime;
     xLastWakeTime = xTaskGetTickCount();

     while(1)
     {
         printf("%s", (char*)pvParameter);
         vTaskDelayUntil(&xLastWakeTime, 10);
     }
}