/* p5_2.c Toggle LED0 on SAMD21 Xplained Pro at 5 Hz using SysTick

 * This program uses SysTick to generate 200 ms delay to
 * toggle the LED0.
 * System clock is running at 1 MHz. SysTick is configure
 * to count down from 199999 to zero to give a 200 ms delay.
 * The LED0 is connected to PB30.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

int main (void)
{
    // make PB30 output for LED
    REG_PORT_DIRSET1 = 0x40000000;     /* make PB30 output for LED */
    
    /* Configure SysTick */
    SysTick->LOAD = 200000 - 1; /* reload with number of clocks per second */
    SysTick->VAL = 0;
    SysTick->CTRL = 5;     /* enable it, no interrupt, use system clock */

    while (1) {
        if (SysTick->CTRL & 0x10000) {   /* if COUNT flag is set */
            REG_PORT_OUTTGL1 = 0x40000000;  /* toggle red LED */
        }
    }
}