Timing Improvements for PWM Demonstration

2 files changed, 13 insertions, 5 deletions

diff --git a/README.md b/README.md
index 36228fa..1ddab7f 100644
--- a/README.md
+++ b/README.md
@@ -44,4 +44,5 @@ call `load` and `run` again.
 
 - Nice [tutorial](https://jacobmossberg.se/posts/2018/08/11/run-c-program-bare-metal-on-arm-cortex-m3.html) about C programs on bare-metal ARM chips
 - Another useful [tutorial](https://www.rhye.org/post/stm32-with-opencm3-0-compiling-and-uploading/) about STM32 programming with libopencm3
+- A nice [PWM example](https://github.com/libopencm3/libopencm3-examples/blob/master/examples/stm32/f1/obldc/pwmleds/pwmleds.c) from the libopencm3 project
 
diff --git a/src/main.c b/src/main.c
index 18a6e4a..8e39278 100644
--- a/src/main.c
+++ b/src/main.c
@@ -80,7 +80,7 @@ static void timer_init(void)
 	// setup timer 2 for blinking
 	timer_set_counter(TIM2, 1);
 	timer_set_prescaler(TIM2, 1440);
-	timer_set_period(TIM2, 25000);
+	timer_set_period(TIM2, 50);
 
 	// enable timer / counter 2 and the corresponding interrupt for blinking
 	timer_enable_irq(TIM2, TIM_DIER_UIE);
@@ -122,14 +122,21 @@ void tim2_isr(void)
 {
 	// PWM handling
 	static uint32_t pwm_value;
-	pwm_value += 20000;
-	if (pwm_value > 60000) {
-		pwm_value = 0;
+	if (pwm_value == 0) {
+		pwm_value = 65535;
+	}
+	else {
+		pwm_value -= 20;
 	}
 	TIM3_CCR3 = pwm_value;
 
 	// toggle blink LED
-	gpio_toggle(GPIOC, GPIO13);
+	static uint32_t counter;
+	counter += 1;
+	if (counter > 500) {
+		gpio_toggle(GPIOC, GPIO13);
+		counter = 0;
+	}
 
 	// clear interrrupt flag
 	TIM_SR(TIM2) &= ~TIM_SR_UIF;