From b41240dc6326464403b73351cb8ff24abedee59a Mon Sep 17 00:00:00 2001
From: xengineering <me@xengineering.eu>
Date: Mon, 27 Sep 2021 11:49:00 +0200
Subject: Switch from Delays to Timer / Counter

---
 src/main.c | 54 +++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 35 insertions(+), 19 deletions(-)

diff --git a/src/main.c b/src/main.c
index 50d7fdc..1027d18 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2,31 +2,27 @@
 
 
 #include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/flash.h>
 #include <libopencm3/stm32/gpio.h>
-
-
-/*
-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
+#include <libopencm3/stm32/timer.h>
+#include <libopencm3/cm3/nvic.h>
 
 
 static void clock_init(void);
 static void gpio_init(void);
-static void delay(uint32_t delay);
+void tim2_isr(void);
+static void nvic_init(void);
+static void timer_init(void);
 
 
 void main(void)
 {
 	clock_init();
 	gpio_init();
+	nvic_init();
+	timer_init();
 
-	while(1){
-		gpio_toggle(GPIOC, GPIO13);
-		delay(250 * DELAY_MS);
-	}
+	while(1);  // wait forever
 }
 
 
@@ -34,19 +30,39 @@ 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
+	rcc_periph_clock_enable(RCC_TIM2);   // for timer / counter 2
 }
 
 
 static void gpio_init(void)
 {
-	gpio_set_mode(GPIOC, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO13);
-	gpio_set(GPIOC, GPIO13);
+	gpio_set_mode(GPIOC,
+				  GPIO_MODE_OUTPUT_50_MHZ,
+				  GPIO_CNF_OUTPUT_PUSHPULL,
+				  GPIO13);
+}
+
+
+void tim2_isr(void)
+{
+	gpio_toggle(GPIOC, GPIO13);
+	TIM_SR(TIM2) &= ~TIM_SR_UIF;  // clear interrrupt flag
+}
+
+
+static void nvic_init(void)
+{
+	nvic_enable_irq(NVIC_TIM2_IRQ);
+	nvic_set_priority(NVIC_TIM2_IRQ, 1);
 }
 
 
-static void delay(uint32_t delay)
+static void timer_init(void)
 {
-	for (uint32_t i = 0; i < delay; i++) {
-		__asm__("nop");
-	}
+	gpio_set(GPIOC, GPIO13);
+	TIM_CNT(TIM2) = 1;               // set start value
+	TIM_PSC(TIM2) = 1440;            // set prescaler
+	TIM_ARR(TIM2) = 50000;           // interrupt value
+	TIM_DIER(TIM2) |= TIM_DIER_UIE;  // update interrupt enable
+	TIM_CR1(TIM2) |= TIM_CR1_CEN;    // enable timer
 }
-- 
cgit v1.2.3-70-g09d2