From dc0ff5562c15cc2ef1637681df99abfbb1ec6620 Mon Sep 17 00:00:00 2001
From: Pavel 'LEdoian' Turinsky <ledoian@matfyz.cz>
Date: Mon, 13 Apr 2020 02:43:47 +0200
Subject: [PATCH] Implement IRQ handling of the button

---
 main.c | 56 ++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 38 insertions(+), 18 deletions(-)

diff --git a/main.c b/main.c
index 00aa67a..122b650 100644
--- a/main.c
+++ b/main.c
@@ -11,12 +11,17 @@
 
 #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 400000		// This is bad -- it's a value that was found to be OK
+#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
@@ -26,44 +31,59 @@ void setup (void) {			// All the blackbox code
 	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);
 }
 
-void initial_wait (void) {
-	gpio_clear(GPIOC, GPIO8 | GPIO9);
-	while (gpio_get(GPIOA, GPIO0) == 0);
-	return;
+// 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();
 
-	initial_wait();
-
 	// Array of what leds should be on
 	uint16_t states[4] = {0, GPIO9, GPIO8, GPIO9 | GPIO8};
-	enum {FORWARD, BACKWARD} direction = FORWARD;
-	bool pressed = true;
-	bool change = false;
 	char state = 0;
 	int i;
 
 	while (true) {
-		change = false;
 		for (i=0 ; i<DELAY ; i++) {
-			if (/*Button pressed, but was not*/ gpio_get(GPIOA, GPIO0) && (pressed == false) ) {
-				pressed = true;
-				change = true;
-			} else if (/*Button not pressed*/gpio_get(GPIOA, GPIO0) == 0)  {
-				pressed = false;
-			}
+			__asm ("nop");
 		}
 
-		if (change) direction = (direction == FORWARD ? BACKWARD : FORWARD);	// Switch direction
 		state = (direction == FORWARD ? (state + 1)%4 : (/*state+4-1*/ state+3)%4 ); // New state
 
 		gpio_set(GPIOC, states[state]);