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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。 Note
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 /** ****************************************************************************** * @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_BASE uint32_t dwt_init(void);
#ifdef __cplusplus extern "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 * @author Frederic 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 __cplusplus extern "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;
/* Enable clock 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 #endif uint32_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 }
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