/* p10_1.c Relay control
 *
 * This program turns the relay connected to PA5 on and off every second.
 *
 * This program was tested with Keil uVision v5.23 with DFP v2.11.0.
 */

#include "stm32f4xx.h"

void delayMs(int n);

int main(void) {
    RCC->AHB1ENR |=  1;	            /* enable GPIOA clock */
    GPIOA->MODER &= ~0x00000C00;    /* clear pin mode */
    GPIOA->MODER |=  0x00000400;    /* set pin to output mode */

    while(1) {
        GPIOA->BSRR = 0x00000020;   /* turn on output */
        delayMs(500);
        GPIOA->BSRR = 0x00200000;   /* turn off output */
        delayMs(500);
    }
}

/* 16 MHz SYSCLK */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 3195; i++) ;
}