HardwareTimer inverterTimer(4);

#define SYSTICK_CTRL (uint32_t *)(0xe000e010)

void setup()
{
pinMode(PB0,OUTPUT);
pinMode(PB8,OUTPUT);

inverterTimer.setMode(TIMER_CH4, TIMER_OUTPUT_COMPARE);
inverterTimer.pause();
inverterTimer.setPrescaleFactor(1);
inverterTimer.setCount(0);
inverterTimer.setOverflow(3600);
inverterTimer.setCompare(TIMER_CH4, 1);
inverterTimer.attachCompare4Interrupt(timer_Handler);
inverterTimer.refresh();
inverterTimer.resume();

//SysTick->CTRL = 0; works for Due, stops systick ints
//*SYSTICK_CTRL = 0;
//systick_init(1000); // writes my own systick count value, much faster "seconds" now
}

void timer_Handler()
{
gpio_write_bit(GPIOB, 0, HIGH);
gpio_write_bit(GPIOB, 0, LOW);
}

void loop()
{
// this will show the latency of the interrupt. You will see about 1uS
// before anything is executed in the interrupt code, then the int code runs
// then another 1uS before this code here continues.
// calling an interrupt costs 2uS of time where nothing can be done.
gpio_write_bit(GPIOB, 8, HIGH);
gpio_write_bit(GPIOB, 8, LOW);

}