int main()
{
    выкл();
}

AT91C_BASE_TC0->TC_RC = AT91B_MASTER_CLOCK >> 12;  /* MCKR divided by 1024 * 4 */

void timer_handler(void)
{
  volatile unsigned long dummy;
  /* Clear status bit */
  dummy = AT91C_BASE_TC0->TC_SR;
  ....
}

static void configure_tc(void)
{
    volatile unsigned long dummy;

    /* Enable periph clock for the PIO controller */
    AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC0);

    /* Enable the periph */
    /* Disable the clock and the interrupts */
    AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS;
    AT91C_BASE_TC0->TC_IDR = 0xFFFFFFFF;

    /* Clear status bit */
    dummy = AT91C_BASE_TC0->TC_SR;

    /* Set the Mode of the Timer Counter */
    AT91C_BASE_TC0->TC_CMR = AT91C_TC_CLKS_TIMER_DIV5_CLOCK | AT91C_TC_CPCTRG;
    AT91C_BASE_TC0->TC_RC = AT91B_MASTER_CLOCK >> 12;  /* MCKR divided by 1024 * 4 */

    /* Enable interrupts */
    /* Disable the interrupt on the interrupt controller */
    AT91C_BASE_AIC->AIC_IDCR = (1 << AT91C_ID_TC0);
    /* Save the interrupt handler routine pointer and the interrupt priority */
    AT91C_BASE_AIC->AIC_SVR[AT91C_ID_TC0] = (unsigned long) timer_handler;
    /* Store the Source Mode Register */
    AT91C_BASE_AIC->AIC_SMR[AT91C_ID_TC0] = AT91C_AIC_SRCTYPE_INT_HIGH_LEVEL | AT91C_AIC_PRIOR_LOWEST;
    /* Clear the interrupt on the interrupt controller */
    AT91C_BASE_AIC->AIC_ICCR = (1 << AT91C_ID_TC0);

    AT91C_BASE_TC0->TC_IER = AT91C_TC_CPCS;

    /* Enable the interrupt on the interrupt controller */
    AT91C_BASE_AIC->AIC_IECR = (1 << AT91C_ID_TC0);
}

AT91C_BASE_TC0->TC_IER = AT91C_TC_CPCS;