/* p5_2.c Toggling red LED at 5 Hz using SysTick

 * This program uses SysTick to generate 200 ms delay to
 * toggle the red LED.
 * System clock is running at 41.94 MHz. SysTick is configure
 * to count down from 8387999 to give a 200 ms delay.
 * The red LED is connected to PTB18.
 */

#include <MKL25Z4.H>

int main (void) {
    SIM->SCGC5 |= 0x0400;       /* enable clock to Port B */
    PORTB->PCR[18] = 0x100;     /* make PTB18 pin as GPIO */
    PTB->PDDR |= 0x040000;      /* make PTB18 as output pin */
    
    /* Configure SysTick */
    SysTick->LOAD = 8388000 - 1; /* reload with number of clocks per 200 ms */
    SysTick->CTRL = 5;     /* enable it, no interrupt, use system clock */

    while (1)
    {
        if (SysTick->CTRL & 0x10000)    /* if COUNT flag is set */
            PTB->PTOR = 0x040000;       /* toggle red LED */
    }
}