ARM SAM3U Backup Mode

void WaitLoop(int loops)

{

  int i;

  for(i=0;i<loops;i++){}

};

int main (void) 

{

  unsigned int *SystemControlRegister = NULL;

  const int cloops=100000;

  unsigned int ledmask = 3;

  //stop watchdog

  WDT->WDT_MR = (1<<15);

  //System Control Register  

  SystemControlRegister = (unsigned int *)0xE000ED10;

  //set deep sleep bit

  *SystemControlRegister |= (0x1<<2);

  //enable wakeup events

  REG_SUPC_WUMR |= (0xF<<0);

  //wait for events

  __WFE();

  //Setup Pins PB0..PB1 for LEDs

    PIOB->PIO_PER    =  0x03;  //pio enable register            

    PIOB->PIO_OER    =  0x03;  //output enable register 

    PIOB->PIO_PUDR   =  0x03;  //pull up disable register

    PIOB->PIO_OWER   =  0x03;  //output write enable register

    PIOB->PIO_ABSR  &= ~0x03;  //ab select register

  while(1)

  {

    PIOB->PIO_CODR = ledmask;

    WaitLoop(cloops);

    PIOB->PIO_SODR = ledmask;

    WaitLoop(cloops);

  };

}