On a detected current spike, the hardware stops the motor without any CPU involvement. Pressing
button SW0 on the AVR128DB48 Curiosity Nano will trigger the Interrupt
Service Routine (ISR) ISR(PORTB_PORT_vect), which will
invoke the fan_start() routine to restart the fan
motor.
ISR(PORTB_PORT_vect)
{
fan_start();
PORTB.INTFLAGS=0xff;
}