【ufun学习】定时器时钟的研究
<div class='showpostmsg'><p><br />对于定时器，勾引我要研究的只是一句话，而这句话老让我范合计。</p>
<p><br />
</p>
<p>有的看官觉得说的没有争议。但实践引来就不一样了。</p>
<p>下边的代码是初使化的通用代码:</p>
<pre>
<code>TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);
//???????
TIM_ClearITPendingBit(TIM2,TIM_IT_Update);//TIM_ClearFlag(TIM2,TIM_FLAG_Update);//??????
//????????0-0xffff,72M/36000=2000
TIM_TimeBaseStructure.TIM_Period = arr;
//????????0-oxffff,???36000??
TIM_TimeBaseStructure.TIM_Prescaler = psc;
////???????????
//????,???0,??????
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;</code></pre>
<p>TIM_CKD_DIV1 是预分频吗？？？？？</p>
<p>我查了下书：</p>
<p></p>
<p> </p>
<p> </p>
<p>显然，它不是预分频。那么只有prescaler是了。有的看官说了，这不费话么，写着预分频么？？？？</p>
<p>本人对英语不是十分精通。</p>
<p> </p>
<p>疑问又来了，谁没有事会把预分频设为1呢？？？？</p>
<p>我想这块之所以到现在没有范病，是因为大家都抄来抄去，哪家例程也不会设为1。那么，设为1果真是36MHZ么？？？？</p>
<p> </p>
<p>我用下边的证明：</p>
<pre>
<code>#include "stm32f10x.h"
#include "stdio.h"
#include "main.h"
#include "stdlib.h"
#define B_ON GPIO_ResetBits(GPIOA,GPIO_Pin_0)
#define B_OFF GPIO_SetBits(GPIOA,GPIO_Pin_0)
void GPIO_Config(void);
void TIM2_Config(u16 arr,u16 psc);
void NVIC_Config(void);
uint32_t count;
//???
int main(void)
{
GPIO_Config();
//((1+arr )/72M)*(1+psc )=((1+1999)/72M)*(1+35999)=1?
//TIM2_Config(1999,35999);
TIM2_Config(35999,1);
NVIC_Config();
while(1);
}
//???GPIO
void GPIO_Config(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);
//PC13?
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_Init(GPIOA,&GPIO_InitStructure);
GPIO_ResetBits(GPIOA,GPIO_Pin_0); //??LED
}
void TIM2_Config(u16 arr,u16 psc)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);
TIM_ClearITPendingBit(TIM2,TIM_IT_Update);//TIM_ClearFlag(TIM2,TIM_FLAG_Update);//??????
TIM_TimeBaseStructure.TIM_Period = arr;
TIM_TimeBaseStructure.TIM_Prescaler = psc;
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM2,&TIM_TimeBaseStructure);
TIM_ITConfig(TIM2,TIM_IT_Update,ENABLE);
TIM_Cmd(TIM2,ENABLE);
}
void NVIC_Config(void)
{
NVIC_InitTypeDef NVIC_InitStructure;
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);
NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 3;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
}
//--------------------stm32f10x_it.c------------------------
void TIM2_IRQHandler(void)
{
if(TIM_GetITStatus(TIM2,TIM_IT_Update)!=RESET)
{
count++;
TIM_ClearITPendingBit(TIM2,TIM_IT_Update);
if(count >= 1000)
{
GPIO_WriteBit(GPIOA,GPIO_Pin_0,(BitAction)(!GPIO_ReadOutputDataBit(GPIOA,GPIO_Pin_0)));
count = 0;
}
}
}
</code></pre>
<p>它和不用1时的时间是一样的。这就证明了，只要我们在预分频不用1，定时器的时钟就是APB时钟的两倍即72MHZ。</p>
<p>话又说回来了，谁平时有病才把第二个参数设为1。</p>
<p><br />
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