/*
 * Sound the speaker at 440Hz
 *
 * The speaker is connected to PB2.
 * Default clock 16 MHz is used.
 * Delay loop is used for time interval. The number
 * of delay cycles is determined empirically.
 */

#include "stm32f4xx.h"

void delay(void);

int main(void) {
    RCC->AHB1ENR |=  2;             /* enable GPIOB clock */

    GPIOB->MODER &= ~0x00000030;    /* clear pin mode */
    GPIOB->MODER |=  0x00000010;    /* set pins to output mode */

    while (1) {
        GPIOB->BSRR = 0x00000004;  /* turn on */
        delay();
        GPIOB->BSRR = 0x00040000;  /* turn off */
        delay();
    }
}

/* 16 MHz SYSCLK */
void delay(void) {
    int i;
    for (i = 0; i < 3630; i++) ;
}