为什么这个程序中断嵌套不成功，特别简单，求指导

#include <avrdef.h>
#include"iom32v.h"
#pragma interrupt_handler int0:2
#pragma interrupt_handler int1:3
void int0(void)
{
    PORTC=1;
    SEI();
    while(1);
}
void int1(void)
{
    PORTC=0x80;
    SEI();
    while(1);
}
void main(void)
{
    PORTC = 0x00; //m103 output only
    DDRC  = 0xff;
    PORTD=0xff;
    DDRD=0X00;
    CLI(); //disable all interrupts
    MCUCR = 0x00;
    GICR  = 0xC0;
    TIMSK = 0x00; //timer interrupt sources
    SEI(); //re-enable interrupts
    while(1);
}

你确定timsk是这么设置的吗?