三星2410用看門狗實現的定時 1us爲單位中文註釋-原創嘍

 

static int delayLoopCount = FCLK/10000/10;

void delay(int nTime)
{
    // time=0: adjust the Delay function by WatchDog timer.
    // time>0: the number of loop time
    // resolution of time is 100us.
    int i,adjust=0;
    if(nTime==0)
    {
        nTime   = 200;
        adjust = 1;
        delayLoopCount = 400;
  //PCLK/1M,Watch-dog disable,1/64,interrupt disable,reset disable
        WTCON = ((PCLK/1000000-1)<<8)|(2<<3); //看門狗定時器的預分頻值設置爲 PCLK/1000000 分頻值 爲64
        WTDAT = 0xffff;                              //for first update          
        WTCNT = 0xffff;                              //resolution=64us @any PCLK      所以一個週期的時間是     64/1000000  s    即爲64us
  //肯能誤解的是這裏conut值是遞減的但是減一次就是64us 即到0xfffe時候 所以dat來補充的時候過了  ffff×64us時間還是很長的
        WTCON = ((PCLK/1000000-1)<<8)|(2<<3)|(1<<5); //Watch-dog timer start           打開
    }
    for(;nTime>0;nTime--)
        for(i=0;i<delayLoopCount;i++);    //測量80000個時鐘週期內有幾個64us  ，但是貌似還是不是很精確，因爲最後一個在64us中間的情況好像沒有考慮
    if(adjust==1)
    {
        WTCON = ((PCLK/1000000-1)<<8)|(2<<3);   //Watch-dog timer stop
        i = 0xffff - WTCNT;                     //1count->64us, 200*400 cycle runtime = 64*i us  測試結果給i這裏僅僅只是第一次的效果，以後不會再有了
        delayLoopCount = 8000000/(i*64);         //200*400:64*i=1*x:100 -> x=80000*100/(64*i)    同上
    }
 /*           

 

 

                                                                                                                   1
 最終以後調用 每次使用的只有    ntime × delayloopcount × ------------- 
                                                                                                                PCLK

 

 

                                                     1
 可以有等式        80000  × -----------  =   i × 64 us
                                                    pclk

 

 

 所以你想要的是 ntime = 1 的時候 下面式子相等

                                                            1
   ntime × delayloopcount × -------------   = 1us
                                                          PCLK

 

 

                                                            8000000
 現在就開始假設了 delayloopcount = ------------------
                                                                                     1
                                                        80000 ×---------
                                                                                  pclk

 

 

                                                                 8000000
  帶入上面看你得到了什麼    1× -------------------------- = 1
                                                                 8000000
 
 
  */
}