/* p2_6.c Toggle LED0 on SAMD21 Xplained Pro at 1 Hz
 * This program defines the registers without using the Atmel header files.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.20
 */

#define PORTBDIR        (*((volatile unsigned int*)0x41004480))
#define PORTBOUTCLR     (*((volatile unsigned int*)0x41004484))
#define PORTBOUTSET     (*((volatile unsigned int*)0x41004488))
    
void delayMs(int n);

int main (void) {
    PORTBDIR = 0x40000000;         /* make PB30 output */

    /* toggle LED continuously at 1Hz */
    while(1) {
        PORTBOUTCLR = 0x40000000;  /* turn on LED0 */
        delayMs(500);
        PORTBOUTSET = 0x40000000;  /* turn off LED0 */
        delayMs(500);
    }
}

/* millisecond delay based on 1 MHz system clock */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 199; i++)
            __asm("nop");
}