/* p2_3.c Toggle LED0 on SAMD21 Xplained Pro at 1 Hz
 * In this program the system clock is increased from 1 MHz
 * to 8 MHz. The loop count in the function delayMs() needs 
 * to be adjusted.
 *
 * 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_SYSCTRL_OSC8M &= ~0x00000300;   /* OSC8M prescaler divided by 1 */

    REG_PORT_DIR1 = 0x40000000;         /* make PB30 output */

    /* toggle LED continuously at 1Hz */
    while(1) {
        REG_PORT_OUTCLR1 = 0x40000000;  /* turn on LED0 */
        delayMs(500);
        REG_PORT_OUTSET1 = 0x40000000;  /* turn off LED0 */
        delayMs(500);
    }
}

/* millisecond delay based on 8 MHz system clock */
void delayMs(int n) {
int i;
for (; n > 0; n--)
    for (i = 0; i < 1143; i++)  /* loop count 1143 for Keil MDK-ARM v5 */
                                /* loop count 1600 for Atmel Studio 7 */
        __asm("nop");
}