Blink LED with timer

src/main.c

@@ -1,8 +1,11 @@
 #include <inttypes.h>
+#include <stdbool.h>
+
 #include "rcc.h"
 #include "gpio.h"
 #include "flash.h"
 #include "pwr.h"
+#include "timer.h"
 
 #define exit 42
 
@@ -70,21 +73,25 @@ static void system_clock_init(void) {
   RCC->CR &= ~RCC_CR_HSION_ON;
 }
 
-static inline void spin(volatile uint32_t count) {
-  while (count--) (void) 0;
-}
-
 int main(void) {
   (void) system_clock_init();
+  (void) tim4_init();
+
+  (void) tim4_start();
 
   uint16_t led = PIN('C', 13);           // Blue LED
   RCC->AHB1ENR |= BIT(PINPORT(led));     // Enable GPIO clock for LED
   gpio_set_mode(led, GPIO_MODE_OUTPUT);  // Set blue LED to output mode
-  for (;;) {
-    gpio_write(led, true);
-    spin(999999);
-    gpio_write(led, false);
-    spin(999999);
+
+  uint16_t counter = TIM4->CNT;
+  bool led_on = false;
+  while(1) {
+	if ((TIM4->CNT - counter) >= 250) {
+	 led_on = !led_on;
+	 gpio_write(led, led_on);
+
+	 counter = TIM4->CNT;
+	}
   };
 
   return exit;

src/rcc.h

@@ -118,4 +118,7 @@ struct rcc {
 #define RCC_APB1ENR_PWREN_BIT 28
 #define RCC_APB1ENR_PWREN_CLOCK_ENABLE (1 << RCC_APB1ENR_PWREN_BIT)
 
+#define RCC_APB1ENR_TIM4_BIT 2
+#define RCC_APB1ENR_TIM4_ENABLE (1 << RCC_APB1ENR_TIM4_BIT)
+
 #endif