niosii 定时器究竟怎么工作

niosii, 定时器

一个看起来简单的timer,搞了一个下午,还没搞定!真的不知道是什么原因了,请高手指教:

#ifndef _TIMER1_H_
#define _TIMER1_H_

#include "system.h"
#include "altera_avalon_timer_regs.h"

#define PERIODL(DATA)     IOWR_ALTERA_AVALON_TIMER_PERIODL(TIMER_0_BASE,DATA)
#define PERIODH(DATA)     IOWR_ALTERA_AVALON_TIMER_PERIODH(TIMER_0_BASE,DATA)
#define CONTROL           IOWR_ALTERA_AVALON_TIMER_CONTROL(TIMER_0_BASE,0X0060)
#define STATUS            IORD_ALTERA_AVALON_TIMER_STATUS(TIMER_0_BASE)
#define STATUS_WR         IOWR_ALTERA_AVALON_TIMER_STATUS(TIMER_0_BASE,0X0000)
#define TO                ALTERA_AVALON_TIMER_STATUS_TO_MSK;

#endif

#include "alt_types.h"
#include "timer1.h"

void main()
{
alt_32 t=100000000;

alt_32 i=0;
alt_16 sta;

PERIODL(t&0x0000ffff);
PERIODH((t>>16)&0x0000ffff);

CONTROL;

while(1)
{
    sta=STATUS;
    if(sta&0x0001)
    {
      printf("a sencond passed! (%d)",i++);
      STATUS_WR;
    }
}

}