ST timer problems

void initialize_pit()
{
        unsigned int  flag, period, irq_id, mask, oldHandler, src_type, priority;
        volatile int status;
        void *newHandler;

        //period
    Timer0->ST_PIMR = period << 5;

        AT91F_ST_SetPeriodInterval(Timer0, period);
        //state
        //status = Timer0->ST_SR;

        //enable interrupt
        flag=1;
        Timer0->ST_IER = flag;

        AT91F_ST_EnableIt( Timer0, flag);

        //enable PMC
        AT91F_PMC_EnablePeriphClock(AT91C_BASE_PMC, 1 << AT91C_ID_IRQ0);

        //config AIC
        irq_id = 0;
        oldHandler = pAic->AIC_SVR[irq_id];
        mask = 0x1 << irq_id;
        pAic->AIC_IDCR = mask ;
        pAic->AIC_SVR[irq_id] = (unsigned int) newHandler ;

        //* Store the Source Mode Register
    pAic->AIC_SMR[irq_id] = src_type | priority  ;


        AT91F_AIC_ConfigureIt(pAic, irq_id, priority, src_type, newHandler);

        //enable AIC
        AT91F_AIC_EnableIt(pAic, 1);
}