std_xdelay.c

个人曾经在工作上的源代码

/***
*void xdelay(unsigned int ms)
*
*Purpose:
*	Make an exactly millisecond delay
*
*Entry:
*	unsigned int ms  - The delay time (millisecond)
*
*Exit:
*   void
*
*Exceptions:
*	Note: 
*       .This function was created by Denny at Jun/26/2008
*       .Dongguan Siliten Electronics CO., LTD.
*       .The timer frequency is 1193180Hz
*       .The timer counter is 16bits, so only elapsed 55ms for\
*        counter a circle.
*
*******************************************************************************/
void xdelay(unsigned int ms)
{
    unsigned int base_counter;
    unsigned int circle;
    unsigned int counter;
    unsigned int last_counter;
    unsigned long end;
    unsigned long cur;

    _disable();
    //outportb(0x43, 0x30);
    base_counter = inportb(0x40);
    base_counter += inportb(0x40)<<8;
    _enable();
    circle = 0;
    last_counter = 0;
    end = (unsigned long)ms*1193;
    cur = 0;
    while (end > cur)
    {
        _disable();
        counter = inportb(0x40);
        counter += inportb(0x40)<<8;
        _enable();
        counter = base_counter - counter;
        if (counter-last_counter > 50)      // Illegal data
        {
            last_counter = counter;
            continue;
        }
        if ( (counter < last_counter) && (last_counter > 65000) && (counter < (65536-65000)) )
            circle++;
        cur = ((unsigned long)circle<<16) + counter;
        //printf("base:%u|cir:%u|cnt:%u|last:%u|end:%lu|cur:%lu\n", base_counter, circle, counter, last_counter, end, cur);
        last_counter = counter;
    }
}