Calibrate Delays

1 files changed, 17 insertions, 12 deletions

diff --git a/src/main.c b/src/main.c
index 74efae2..50d7fdc 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,47 +1,52 @@
+// vim: shiftwidth=4 tabstop=4 noexpandtab
 
 
 #include <libopencm3/stm32/rcc.h>
 #include <libopencm3/stm32/gpio.h>
 
 
-#define DELAY 100000
+/*
+SYSCLK should be at 72.000.000 Hz
+--> 18.000.000 __asm__("nop") per second (one instruction --> 4 clock cycles)
+--> 18.000 __asm__("nop") per millisecond
+*/
+#define DELAY_MS 18000  // FIXME seems to be too slow by factor of 4
 
 
-void clock_init(void);
-void gpio_init(void);
-void delay(void);
+static void clock_init(void);
+static void gpio_init(void);
+static void delay(uint32_t delay);
 
 
-int main(void)
+void main(void)
 {
 	clock_init();
 	gpio_init();
 
 	while(1){
 		gpio_toggle(GPIOC, GPIO13);
-		delay();
+		delay(250 * DELAY_MS);
 	}
-
-	return 0;
 }
 
 
-void clock_init(void)
+static void clock_init(void)
 {
+	rcc_clock_setup_pll(&rcc_hse_configs[RCC_CLOCK_HSE8_72MHZ]);
 	rcc_periph_clock_enable(RCC_GPIOC);  // for PC13 blinking
 }
 
 
-void gpio_init(void)
+static void gpio_init(void)
 {
 	gpio_set_mode(GPIOC, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO13);
 	gpio_set(GPIOC, GPIO13);
 }
 
 
-void delay(void)
+static void delay(uint32_t delay)
 {
-	for (int i = 0; i < DELAY; i++) {
+	for (uint32_t i = 0; i < delay; i++) {
 		__asm__("nop");
 	}
 }