分享一个不完善的基于tim3的延时函数，顺便请大家帮忙完善

来俩不甜的 · 发表于 2016-4-7 14:14:13

用上ucos后，发现systick被占用了，所以写了这个基于TIM3采用时钟摘取法做的延时函数，用示波器测的时候发现每十几个准确的延时之间必然夹杂一个非常不准确的波形，不知道为什么。话不多说一些，上函数。
[mw_shl_code=applescript,true]#include "tim3delay.h"

vu8 overfull = 0;//溢出标志

void tim3delay_init(void)
{
      TIM_TimeBaseInitTypeDef       TIM_BaseInitStructure;
      NVIC_InitTypeDef                               NVIC_InitStructure;
      RCC_ClocksTypeDef                               rccclk;
      u8                                                                                     i;
      u8                                                                                     psc;//预分频系数

      RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);

      RCC_GetClocksFreq(&rccclk);
      if(rccclk.HCLK_Frequency == rccclk.PCLK1_Frequency)
            i = 1;
      else i = 2;

      psc = (u8)(rccclk.PCLK1_Frequency / 1000000) * i - 1;//此预分频下频率为1MHz

      TIM_BaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
      TIM_BaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
      TIM_BaseInitStructure.TIM_Period = 0xffff;
      TIM_BaseInitStructure.TIM_Prescaler = psc;
      TIM_TimeBaseInit(TIM3,&TIM_BaseInitStructure);

      TIM_ITConfig(TIM3,TIM_IT_Update,ENABLE);

      NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
      NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
      NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
      NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
      NVIC_Init(&NVIC_InitStructure);

      TIM_Cmd(TIM3,ENABLE);
}

void delay_us(u16 xus)
{
      u16 thecount;
      u32 nextcount;
      u8  overnum = 0;//当前超长延时下需要定时器溢出的次数

      thecount = TIM_GetCounter(TIM3);
      nextcount = (u32)thecount + (u32)xus;
      if(nextcount <= 65535)
            while(TIM3->CNT < nextcount);
      else
      {
            do{
                     nextcount -= 65535;
                     overnum++;
            }while(nextcount > 65535);
            overfull = 0;
            while((TIM3->CNT < nextcount) || (overnum > overfull));
      }
}

void delay_ms(u16 xms)//最大取值65
{
      delay_us(xms * 1000);
}

void TIM3_IRQHandler(void)
{
      if(TIM_GetITStatus(TIM3,TIM_IT_Update) != RESET)
      {
            TIM_ClearITPendingBit(TIM3,TIM_IT_Update);
            overfull++;
      }
}[/mw_shl_code]

来俩不甜的 · 发表于 2016-4-7 14:16:16

这是最主要的地方，也是出错的地方，别的初始化就不用看了[mw_shl_code=applescript,true]void delay_us(u16 xus)
{
      u16 thecount;
      u32 nextcount;
      u8  overnum = 0;//当前超长延时下需要定时器溢出的次数

      thecount = TIM_GetCounter(TIM3);
      nextcount = (u32)thecount + (u32)xus;
      if(nextcount <= 65535)
            while(TIM3->CNT < nextcount);
      else
      {
            do{
                     nextcount -= 65535;
                     overnum++;
            }while(nextcount > 65535);
            overfull = 0;
            while((TIM3->CNT < nextcount) || (overnum > overfull));
      }
}[/mw_shl_code]