WhyCan Forum(哇酷开发者社区)

原版：
void delay_us(u32 nus)
{
    u32 ticks;
    u32 told, tnow, tcnt = 0;
    GET_CORE_CNT(told);                             //读取内核定时器数值
    ticks = nus * SYS_CORE_CLK_MHZ/4;                                   //目标延时节拍数=需要延时时间(us)*CORE_CLK(MHz)/4
    while (1)
    {
        GET_CORE_CNT(tnow);
        if (tnow != told)
        {
            if (tnow < told)tcnt = 0xFFFFFFFF - told + tnow; //CORE_CNT递增32位，计算已延时节拍数
            else tcnt = tnow - told;
            if (tcnt >= ticks)break;                   //延时完成
        }
    };
}

优化版：
void delay_us(u32 nus)
{
    u32 start,stop,ticks;
    start=CORE_CNT;
    ticks = nus * SYS_CORE_CLK_MHZ/4; 
    if(0xFFFFFFFF-start>=ticks){
        stop=start+ticks;
        while(CORE_CNT<stop && CORE_CNT>start){}
    }
    else{
        stop=ticks-(0xFFFFFFFF-start);
        while(CORE_CNT>start){}
        while(CORE_CNT<stop){}
    }
}

版本3
void delay_us(u32 nus)
{
    u32 start,stop,ticks;
    start=CORE_CNT;
    ticks = nus * SYS_CORE_CLK_MHZ/4; 
    while(CORE_CNT-start<ticks){}
}