timer interrupt - startup file - don't work

hello again,

now I'm able to turn on the leds on my AT91RM9200 board, but I'm not able to work with interrupts - I don't know if the problem is the code or the problem is still in the startup file? Is there a chance to get to know where the problem is?

I work with GNU compiler and that's my code for the interrupt... when I press the Halt button the yellow arrow stands at the position

0x00000018 EAFFFFFE B 0x00000018 (which is the irq-handler in the startup file)

the whole code in my main routine (timer interrupt) is

 void ST_interrupt (void)__attribute__ ((interrupt));


 void ST_interrupt(void)
{
        AT91C_BASE_PIOC->PIO_OER = AT91C_PIO_PC0 | AT91C_PIO_PC1;
        AT91C_BASE_PIOC->PIO_PER = AT91C_PIO_PC0 | AT91C_PIO_PC1;
        xyz->PIOD_PPUDR = AT91C_PIO_PC0 | AT91C_PIO_PC1;

        AT91C_BASE_AIC->AIC_EOICR = AT91C_BASE_ST->ST_SR;
}

int main(void)
{
        volatile int period;
        //config AIC
        AT91F_AIC_ConfigureIt(AT91C_BASE_AIC, AT91C_ID_SYS, AT91C_AIC_PRIOR_HIGHEST - 6, AT91C_AIC_SRCTYPE_INT_LEVEL_SENSITIVE, (void (*) ())ST_interrupt);

        period = 10000000; //delay in ms
        AT91F_ST_SetPeriodInterval(AT91C_BASE_ST, period);
        AT91F_AIC_EnableIt( AT91C_BASE_AIC, AT91C_ID_SYS);
        AT91F_ST_EnableIt(AT91C_BASE_ST, AT91C_ST_PITS);

         while(1);
}

I also tested the version with the following:

   AT91F_AIC_ConfigureIt(AT91C_BASE_AIC, AT91C_ID_SYS, AT91C_AIC_PRIOR_HIGHEST - 6, AT91C_AIC_SRCTYPE_INT_LEVEL_SENSITIVE, (&ST_interrupt);

But the result is always the same... In another thread I read that I must define the interrupt handler in the startup file, but when I take a look into the interupt example for the gnu compiler which comes with the keil enviroment - there are no changes...

I hope anybody could help me - if the problem could be in the startup file or if the startup file should be ok, when I'm able to turn on leds...

best regards
Johannes