GC19038/STLib/hardware_delay.c

#include "st_sys.h"

/*
*********************************************************************************************************
*                                             寄存器
*********************************************************************************************************
*/
#define  DWT_CYCCNT  *(volatile unsigned int *)0xE0001004
#define  DWT_CR      *(volatile unsigned int *)0xE0001000
#define  DEM_CR      *(volatile unsigned int *)0xE000EDFC
#define  DBGMCU_CR   *(volatile unsigned int *)0xE0042004

#define  DEM_CR_TRCENA               (1 << 24)
#define  DWT_CR_CYCCNTENA            (1 <<  0)

static volatile int system_core_clock = 400; //系统时钟

/**
 * 初始化软件延时
 * 
 * @author lxz 
 * 
 * @param clk 设备硬件时钟
 */
void hw_delay_init(int clk)
{
    system_core_clock = clk * 1000000;
    DEM_CR         |= (unsigned int)DEM_CR_TRCENA;   /* Enable Cortex-M4's DWT CYCCNT reg.  */
    DWT_CYCCNT      = (unsigned int)0u;
    DWT_CR         |= (unsigned int)DWT_CR_CYCCNTENA;
}

/**
 * 微妙级延时
 * 
 * @author LXZ (2018/8/16)
 * 
 * @param usec 
 */
void hw_delay_us(int usec)
{

    uint32_t tCnt, tDelayCnt;
    uint32_t tStart;

    tStart = DWT_CYCCNT;                                     /* 刚进入时的计数器值 */
    tCnt = 0;
    tDelayCnt = usec * (system_core_clock / 1000000);  /* 需要的节拍数 */

    while (tCnt < tDelayCnt)
    {
        tCnt = DWT_CYCCNT - tStart; /* 求减过程中，如果发生第一次32位计数器重新计数，依然可以正确计算 */
    }
}

/**
 * 获取当前的微秒值,该值只是近似值，偏差一个us
 * 
 * @author lxz (2019/5/30/周四)
 * 
 * @param void 
 * 
 * @return int 
 */
int hw_read_us(void)
{
    uint32_t usec = system_core_clock / 1000000;
    return (DWT_CYCCNT + (usec >> 1)) / usec;
}