modern-embedded-programming-course/lesson-07/stm32c031-keil/main.c

// NOTE:
// Lesson #7 (arrays) cannot be really demonstrated on a STM32 board
// because the STM32 GPIO has completely different structure than TivaC.
// Therefore, this project simply repeats lesson #6.

#include "stm32c031.h"

// LED marked "LD4" on the NUCLEO-C031C6 board
#define LD4_PIN  5U

// external LED to be inserted between GND (short leg) and
// D12 (longer leg) on the CN9 connector
#define LD5_PIN  6U

int main(void) {
    // enable GPIOA clock port for the LEDs
    RCC_IOPENR_R |= (1U << 0U);

    // NUCLEO-C031C6 board has LED LD4 on GPIOA pin LD4_PIN
    // and external LED LD5 on GPIO LD5_PIN
    // set the LED pins as push-pull output, no pull-up, pull-down
    GPIOA_MODER_R   &= ~((3U << 2U*LD4_PIN) | (3U << 2U*LD5_PIN));
    GPIOA_MODER_R   |=  ((1U << 2U*LD4_PIN) | (1U << 2U*LD5_PIN));
    GPIOA_OTYPER_R  &= ~((1U <<    LD4_PIN) | (1U <<    LD5_PIN));
    GPIOA_OSPEEDR_R &= ~((3U << 2U*LD4_PIN) | (3U << 2U*LD5_PIN));
    GPIOA_OSPEEDR_R |=  ((1U << 2U*LD4_PIN) | (1U << 2U*LD5_PIN));
    GPIOA_PUPDR_R   &= ~((3U << 2U*LD4_PIN) | (3U << 2U*LD5_PIN));

    GPIOA_BSRR_R = (1U << LD5_PIN); // turn LD5 on

    while (1) { // endless loop
        GPIOA_BSRR_R = (1U << LD4_PIN); // turn LD4 on

        int volatile counter = 0;
        while (counter < 500000) {  // delay loop
            ++counter;
        }

        GPIOA_BSRR_R = (1U << (LD4_PIN + 16U)); // turn LD4 off
        counter = 0;
        while (counter < 500000) {  // delay loop
            ++counter;
        }

    }
    //return 0; // unreachable code
}