add stm32 dev template

templates/dev/stm32-blink/src/main.c

@@ -0,0 +1,50 @@
+#include <libopencm3/cm3/systick.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+
+/* Nucleo-G474RE: LD2 is on PA5 */
+#define BLINK_PORT GPIOA
+#define BLINK_PIN GPIO5
+#define BLINK_PERIOD_MS 1000
+
+static volatile uint32_t s_ticks = 0;
+
+void sys_tick_handler(void) { s_ticks++; }
+
+static void delay_ms(uint32_t ms) {
+  uint32_t until = s_ticks + ms;
+  while (s_ticks < until)
+    ;
+}
+
+static void clock_setup(void) {
+  rcc_clock_setup_pll(&rcc_hsi_configs[RCC_CLOCK_3V3_170MHZ]);
+}
+
+static void systick_setup(void) {
+  /* 1 ms tick at 170 MHz core clock */
+  systick_set_reload(rcc_ahb_frequency / 1000 - 1);
+  systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
+  systick_counter_enable();
+  systick_interrupt_enable();
+}
+
+static void gpio_setup(void) {
+  rcc_periph_clock_enable(RCC_GPIOA);
+  gpio_mode_setup(BLINK_PORT, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, BLINK_PIN);
+  gpio_set_output_options(BLINK_PORT, GPIO_OTYPE_PP, GPIO_OSPEED_LOW,
+                          BLINK_PIN);
+}
+
+int main(void) {
+  clock_setup();
+  systick_setup();
+  gpio_setup();
+
+  while (1) {
+    gpio_toggle(BLINK_PORT, BLINK_PIN);
+    delay_ms(BLINK_PERIOD_MS);
+  }
+
+  return 0;
+}