zerorobert 发表于 2023-3-30 22:00

STM32HAL库微秒延时函数的实现---DWT和SysTick

以下两种延时方式来源：Arduino_Core_STM32源码delayMicroseconds(uint32_t us)函数的实现。
利用SysTick再实现微秒延时函数虽然SysTick已经被配置为1ms中断一次的模式，但每个1ms之间SysTick的当前值寄存器是一直在计数的（每计一个数的时间是1/SytemCoreClock）我们便可以利用该机制实现微秒延时函数。
void delayMicroseconds(uint32_t us){    __IO uint32_t currentTicks = SysTick->VAL;/* Number of ticks per millisecond */const uint32_t tickPerMs = SysTick->LOAD + 1;/* Number of ticks to count */const uint32_t nbTicks = ((us - ((us > 0) ? 1 : 0)) * tickPerMs) / 1000;/* Number of elapsed ticks */uint32_t elapsedTicks = 0;__IO uint32_t oldTicks = currentTicks;do {    currentTicks = SysTick->VAL;    elapsedTicks += (oldTicks < currentTicks) ? tickPerMs + oldTicks - currentTicks :                  oldTicks - currentTicks;    oldTicks = currentTicks;} while (nbTicks > elapsedTicks);}
以上函数可以直接复制到工程中使用，不需要额外的任何配置。http://6.eewimg.cn/news/uploadfile/2022/0809/20220809090806513.pngNote
虽然函数参数us为uint32_t类型，但是延时数不能过大，原因自己分析。建议超过1ms的延时时间使用HAL_Delay()。
利用DWT（数据观测点）实现微秒延时函数对于DWT大家可以搜索具体了解，这里我也不是很了解，就直说实现方法好了。
dwt.h文件/********************************************************************************* @file    dwt.h* @authorFrederic Pillon* @brief   Header for dwt.c module******************************************************************************* @attention** Copyright (c) 2019, STMicroelectronics* All rights reserved.** This software component is licensed by ST under BSD 3-Clause license,* the "License"; You may not use this file except in compliance with the* License. You may obtain a copy of the License at:*                        opensource.org/licenses/BSD-3-Clause********************************************************************************/
/* Define to prevent recursive inclusion -------------------------------------*/#ifndef _DWT_H_#define _DWT_H_
#include "stm32f4xx.h"#include
#ifndef UNUSED#define UNUSED(x) (void)x#endif
#ifdef DWT_BASEuint32_t dwt_init(void);
#ifdef __cplusplusextern "C" {#endif
//uint32_t dwt_init(void);void dwt_access(bool ena);
static inline uint32_t dwt_max_sec(void){return (UINT32_MAX / SystemCoreClock);};
static inline uint32_t dwt_max_msec(void){return (UINT32_MAX / (SystemCoreClock / 1000));};
static inline uint32_t dwt_max_usec(void){return (UINT32_MAX / (SystemCoreClock / 1000000));};
static inline uint32_t dwt_getCycles(void){return (DWT->CYCCNT);};
#ifdef __cplusplus}#endif
#endif /* DWT_BASE */#endif /* _DWT_H_ */
dwt.c文件/********************************************************************************* @file    dwt.c* @authorFrederic Pillon* @brief   Provide Data Watchpoint and Trace services******************************************************************************* @attention** Copyright (c) 2019, STMicroelectronics* All rights reserved.** This software component is licensed by ST under BSD 3-Clause license,* the "License"; You may not use this file except in compliance with the* License. You may obtain a copy of the License at:*                        opensource.org/licenses/BSD-3-Clause********************************************************************************/
#include "dwt.h"
#ifdef DWT_BASE#ifdef __cplusplusextern "C" {#endif

uint32_t dwt_init(void){
/* Enable use of DWT */if (!(CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA_Msk)) {    CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;}
/* Unlock */dwt_access(true);
/* Reset the clock cycle counter value */DWT->CYCCNT = 0;
/* Enableclock cycle counter */DWT->CTRL |=DWT_CTRL_CYCCNTENA_Msk;
/* 3 NO OPERATION instructions */__asm volatile(" nop      nt"               " nop      nt"               " nop      nt");
/* Check if clock cycle counter has started */return (DWT->CYCCNT) ? 0 : 1;}
void dwt_access(bool ena){#if (__CORTEX_M == 0x07U)/*   * Define DWT LSR mask which is (currentuly) not defined by the CMSIS.   * Same as ITM LSR one.   */#if !defined DWT_LSR_Present_Msk#define DWT_LSR_Present_Msk ITM_LSR_Present_Msk#endif#if !defined DWT_LSR_Access_Msk#define DWT_LSR_Access_Msk ITM_LSR_Access_Msk#endifuint32_t lsr = DWT->LSR;
if ((lsr & DWT_LSR_Present_Msk) != 0) {    if (ena) {      if ((lsr & DWT_LSR_Access_Msk) != 0) { //locked      DWT->LAR = 0xC5ACCE55;      }    } else {      if ((lsr & DWT_LSR_Access_Msk) == 0) { //unlocked      DWT->LAR = 0;      }    }}#else /* __CORTEX_M */UNUSED(ena);#endif /* __CORTEX_M */}
#ifdef __cplusplus}#endif
#endif
delayMicroseconds()函数void delayMicroseconds(uint32_t us){#if defined(DWT_BASE) && !defined(DWT_DELAY_DISABLED)int32_t start= dwt_getCycles();int32_t cycles = us * (SystemCoreClock / 1000000);
while ((int32_t)dwt_getCycles() - start < cycles);#endif}

qbwww 发表于 2023-3-31 12:40

void delayMicroseconds(uint32_t us)
{
    __IO uint32_t currentTicks = SysTick->VAL;
/* Number of ticks per millisecond */
const uint32_t tickPerMs = SysTick->LOAD + 1;
/* Number of ticks to count */
const uint32_t nbTicks = ((us - ((us > 0) ? 1 : 0)) * tickPerMs) / 1000;
/* Number of elapsed ticks */
uint32_t elapsedTicks = 0;
__IO uint32_t oldTicks = currentTicks;
do {
    currentTicks = SysTick->VAL;
    elapsedTicks += (oldTicks < currentTicks) ? tickPerMs + oldTicks - currentTicks :
                  oldTicks - currentTicks;
    oldTicks = currentTicks;
} while (nbTicks > elapsedTicks);
}

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