stm32-better-blink/main.c

/*
 * My first project
 *
 * It blinks LEDs like counting in binary, when the button is pressed, it reverses the order
 *
 * Build on top of libopenocm3, blackbox parts of code (setup()) copied from
 * libopencm3-examples/examples/stm32/f1/stm32vl-discovery/button project
 *
 * Open source licence, let's say Artistic Licence, although it doesn't matter, as it is local only
 */

#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/stm32/f1/exti.h>
#include <libopencm3/stm32/f1/nvic.h>
#include <stdbool.h>

//#define DELAY 8000000		// Should be a second, or maybe not (second iff 8MHz clk, 1/3second if 24MHz clk)			// Too long!!
#define DELAY 4000000		// This is bad -- it's a value that was found to be OK
#define STM32F1 1			// Needed for libopencm3

enum {FORWARD, BACKWARD} direction;
bool running = false;

void setup (void) {			// All the blackbox code

	// Set up clock
	rcc_clock_setup_in_hse_8mhz_out_24mhz();

	// Enable the two GPIOs
	rcc_periph_clock_enable(RCC_GPIOC);
	rcc_periph_clock_enable(RCC_GPIOA);

	// Enable AFIO (we need that to map GPIO to EXTI)
	rcc_periph_clock_enable(RCC_AFIO);

	// Enable EXTI0 interrupt.
	// The interrupts are a bit magic, as the Internet says (the datasheet for F100RBT6B does not mention the EXTI/NVIC interface)
	// This one is for EXTI0 ~~ GPIOx0 pins
	nvic_enable_irq(NVIC_EXTI0_IRQ);

	// GPIO C8 amd C9 are the two LEDs
	gpio_set_mode(GPIOC, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO8 | GPIO9);

	// GPIO A0 is the push button
	// And we set it as a regular button and enable its interrupts in the next block
	gpio_set_mode(GPIOA, GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, GPIO0);
	
	// Configure the EXTI0 interrupts
	// 1. Which pin
	exti_select_source(EXTI0, GPIOA);
	// 2. Which edge
	exti_set_trigger(EXTI0, EXTI_TRIGGER_RISING);
	// 3. Enable the interrupts
	exti_enable_request(EXTI0);
}

// libopencm3 has a pre-declared interrupt handlers, so it needs to have this name
void exti0_isr (void) {
	// Clear the interrupt
	exti_reset_request(EXTI0);
	// NB: For some reason it is at the begining in the examples
	// It needs to be here (possibly because of reordering, when this was at the end, I usually got the interrupt twice).
	
	if (!running) {
		direction = FORWARD;
	} else {
		direction = direction == FORWARD ? BACKWARD : FORWARD;
	}
	running = true;
}


int main (void) {
	setup();

	// Array of what leds should be on
	uint16_t states[4] = {0, GPIO9, GPIO8, GPIO9 | GPIO8};
	char state = 0;
	int i;

	while (true) {
		for (i=0 ; i<DELAY ; i++) {
			__asm ("nop");
		}

		state = (direction == FORWARD ? (state + 1)%4 : (/*state+4-1*/ state+3)%4 ); // New state

		gpio_set(GPIOC, states[state]);
		gpio_clear(GPIOC, (GPIO8 | GPIO9) ^ states[state]);
	}
	return 0;
}