Implement Timer Interrupt for Arduino Due

The code implement Timer Interrupt for Arduino Due, to toggle LED every second and send the duration in millisecond to PC via Serial port.

int led = 13;

volatile boolean ledon;
volatile unsigned long lasttime;
volatile unsigned long now;

int FREQ_1Hz = 1;

void TC3_Handler(){
    TC_GetStatus(TC1, 0);
    
    now = millis();
    
    digitalWrite(led, ledon = !ledon);
    
    Serial.println(now - lasttime);
    lasttime = now;
    
}

void startTimer(Tc *tc, uint32_t channel, IRQn_Type irq, uint32_t frequency){
  
    //Enable or disable write protect of PMC registers.
    pmc_set_writeprotect(false);
    //Enable the specified peripheral clock.
    pmc_enable_periph_clk((uint32_t)irq);  
    
    TC_Configure(tc, channel, TC_CMR_WAVE|TC_CMR_WAVSEL_UP_RC|TC_CMR_TCCLKS_TIMER_CLOCK4);
    uint32_t rc = VARIANT_MCK/128/frequency;
    
    TC_SetRA(tc, channel, rc/2);
    TC_SetRC(tc, channel, rc);
    TC_Start(tc, channel);
    
    tc->TC_CHANNEL[channel].TC_IER = TC_IER_CPCS;
    tc->TC_CHANNEL[channel].TC_IDR = ~TC_IER_CPCS;
    NVIC_EnableIRQ(irq);
}

void setup() {
    pinMode(led, OUTPUT);
    Serial.begin(9600);
    startTimer(TC1, 0, TC3_IRQn, FREQ_1Hz);
    lasttime = 0;
}

void loop() {

}

Implement Timer Interrupt for Arduino Due