Add readme

Makefile

@@ -13,6 +13,6 @@ CPU_FLAGS := -mthumb -mcpu=cortex-m3 -msoft-float -mfix-cortex-m3-ldrd
 	arm-none-eabi-objcopy -Obinary $*.elf $*.bin
 
 flash: main.bin
-	st-flash --reset write main.bin 0x08000000
+	st-flash write /dev/stlinkv1_4 main.bin 0x08000000
 
 .PHONY: flash

README.md

@@ -0,0 +1,35 @@
+Setup
+===
+
+1. Need the "newlib" arm library (else there is no stdint.h &co.)
+
+```sh
+pacman -S arm-none-eabi-newlib
+```
+
+2. Get Libopencm3
+
+```sh
+git submodule init
+git submodule update
+```
+
+3. Generate headers in Libopencm3
+
+```sh
+cd libopencm3
+make
+cd ..
+```
+
+Possibly there are also some udev rules & co, I think they can be acquired from
+the `stlink` package.
+
+Usage
+===
+
+```
+make
+```
+
+It does everything. At least for STM32VLDISCOVERY board at my computer.

main.c

@@ -13,27 +13,22 @@
 #include <libopencm3/stm32/gpio.h>
 #include <libopencm3/stm32/f1/exti.h>
 #include <libopencm3/stm32/f1/nvic.h>
-#include <libopencm3/stm32/f1/timer.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
 
-void setup_system (void) {
+volatile enum {FORWARD, BACKWARD} direction;
+volatile bool running = false;
+
+void setup (void) {			// All the blackbox code
+
 	// Set up clock
 	rcc_clock_setup_in_hse_8mhz_out_24mhz();
-}
 
-void setup_gpio_out (void) {
-	// Enable clock for GPIO C
+	// Enable the two GPIOs
 	rcc_periph_clock_enable(RCC_GPIOC);
-	// GPIO C8 amd C9 are the two LEDs
-	gpio_set_mode(GPIOC, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO8 | GPIO9);
-
-}
-
-void setup_exti0_in (void) {
-	// Enable clock for GPIO A
 	rcc_periph_clock_enable(RCC_GPIOA);
 
 	// Enable AFIO (we need that to map GPIO to EXTI)
@@ -44,6 +39,8 @@ void setup_exti0_in (void) {
 	// 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
@@ -58,32 +55,6 @@ void setup_exti0_in (void) {
 	exti_enable_request(EXTI0);
 }
 
-void setup_tim6_periodic_irq (void) {
-	// Enable clock
-	rcc_periph_clock_enable(RCC_TIM6);
-	
-	// Config:
-	// Set prescaler
-	timer_set_prescaler(TIM6, 65535);
-	// Set counter value
-	timer_set_period(TIM6, 183);
-
-	// Enable interrupts in NVIC
-	nvic_enable_irq(NVIC_TIM6_IRQ);
-	// Enable sending interrupts from the timer
-	timer_enable_irq(TIM6, TIM_DIER_UIE);
-
-	// Finally, enable the counter
-	timer_enable_counter(TIM6);
-}
-
-void setup (void) {
-	setup_system();
-	setup_gpio_out();
-	setup_exti0_in();
-	setup_tim6_periodic_irq();
-}
-
 // libopencm3 has a pre-declared interrupt handlers, so it needs to have this name
 void exti0_isr (void) {
 	// Clear the interrupt
@@ -91,27 +62,36 @@ void exti0_isr (void) {
 	// 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).
 	
-	// Toggle TIM6 in order to disable blinking
-	// Code inspired by libopencm3 source, since we cannot read the status otherwise…
-	TIM_CR1(TIM6) ^= TIM_CR1_CEN;
-}
-
-void tim6_isr (void) {
-	timer_clear_flag(TIM6, TIM_SR_UIF);
-	// Just change value of GPIO C9 (green LED)
-	uint16_t cur = gpio_get(GPIOC, GPIO9);
-	if (cur) {
-		gpio_clear(GPIOC, GPIO9);
+	if (!running) {
+		direction = FORWARD;
 	} else {
-		gpio_set(GPIOC, GPIO9);
+		direction = direction == FORWARD ? BACKWARD : FORWARD;
 	}
+	running = true;
 }
 
 
 int main (void) {
 	setup();
 
-	while (true) __asm ("wfi");
+	// Array of what leds should be on
+	uint16_t states[4] = {0, GPIO9, GPIO8, GPIO9 | GPIO8};
+	char state = 0;
+	int i;
+
+	// Initial wait
+	while (!running) ;
+
+	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;
 }