STM32 利用systick 精确延时 nms

* File Name          : systick_delay.h
* Author             : shifu
* Version            : 
* Date               : 09/20/2008
* Description        : 
********************************************************************************/
/* Define to prevent recursive inclusion -------------------------------------*/
#ifndef __SYSTICK_DELAY_H
#define __SYSTICK_DELAY_H

/* Includes ------------------------------------------------------------------*/
#include "stm32f10x_systick.h"

/* SysTick clock countflag bit */
#define SysTick_CountFlag_Bit (u32)0x00010000

/* SysTick flag */
#define Count_Not_Arrived    (u32)0x0
#define Count_Arrived        (u32)0x00010000

/* CTRL TICKINT Mask */
#define CTRL_TICKINT_Enable   ((u32)0x00000002)
#define CTRL_TICKINT_Disable ((u32)0xFFFFFFFD)

/* Exported functions ------------------------------------------------------- */
void ST_Delay_Ms(u16 ms);

#endif

//***************************************************************************
// Function Name : systick_delay.c
// Description    : delay x ms 必须在AHB 设置以后使用
// Input           : ms
// Output         : None
// Return         : None
//***************************************************************************

#include"systick_delay.h"

void ST_Delay_Ms(u16 ms)
{
u32 statusreg = Count_Not_Arrived;

   //检查参数是否超过最大值0xffffff/9000＝1864，在AHB 72MHz时 最长时间0xffffff/9000
if(ms > 1864) ms = 1864;

//不产生异常中断请求
SysTick->CTRL &= CTRL_TICKINT_Disable;

//时钟选择 HCLK/8
SysTick->CTRL &= SysTick_CLKSource_HCLK_Div8;

//装入计数值
SysTick->LOAD = (u32)(ms * 9000);

//开始计数
SysTick->CTRL |= SysTick_Counter_Enable;

//检查标志位，等待延迟
while((statusreg & SysTick_CountFlag_Bit) == Count_Not_Arrived)
{
    statusreg = SysTick->CTRL;
}

//停止计数
SysTick->CTRL &= SysTick_Counter_Disable;

//清除计数
SysTick->VAL = SysTick_Counter_Clear; 
}//END