/* p2_1.c Toggle LED0 on SAMD21 Xplained Pro at 1 Hz
 * This program toggles LED0 for 0.5 second ON and 0.5 second OFF
 * by writing 0 or 1 to bit 30 of the OUT register.
 * The LED is connected to PB30.
 * The LED is low active (a '0' turns ON the LED).
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.20
 */

#include "samd21.h"
void delayMs(int n);

int main (void) {
    REG_PORT_DIR1 |= 0x40000000;       /* make PB30 output */

    /* toggle LED continuously at 1Hz */
    while(1) {
        REG_PORT_OUT1 &= ~0x40000000;  /* turn on LED0 */
        delayMs(500);
        REG_PORT_OUT1 |= 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");
}