光盘里的程序看不懂simple_test,帮忙解释一下

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SkyEye\ucosii4skyeye\ucosii4skyeye\samples\simple_test

在void my_test_isr(void)中
{
register volatile struct at91_timers* tt = (struct at91_timers*) (AT91_TC_BASE);
register volatile struct at91_timer_channel* tc = &tt->chans[KERNEL_TIMER].ch;

......................
}
上面的函数在做什么?