Add low power detector

README.org

@@ -48,10 +48,11 @@ the TB6612FNG motor driver.
 
 The led pattern is in Morse code.
 
-| Code | Meaning                      | Pattern |
-|------+------------------------------+---------|
-| I    | Regular reset                | ..      |
-| WW   | Reset due to window watchdog | .-- .-- |
+| Code | Meaning                                              | Pattern   |
+|------+------------------------------------------------------+-----------|
+| I    | Regular mode                                         | ..        |
+| LP   | Low power (Vdd is below 2.9V)                        | .-.. .--. |
+| WW   | Last reset was due to the window watchdog trigerring | .-- .--   |
 
 * Command set
 

controller/src/main.rs

@@ -17,6 +17,7 @@ use panic_probe as _;
 pub mod blinker;
 mod encoders;
 mod logic;
+mod power;
 mod tb6612fng;
 
 #[derive(Clone, Copy, Debug)]
@@ -90,6 +91,8 @@ async fn main(spawner: Spawner) {
         .spawn(blinker::blink(p.PB15, blink_pattern(reset_cause)))
         .unwrap();
 
+    spawner.spawn(power::watch_power_level()).unwrap();
+
     let motors = Tb6612fng::new(
         p.PA4,
         p.PA5,

controller/src/power.rs

+use crate::blinker;
+use embassy_stm32::pac;
+use embassy_time::Timer;
+
+#[embassy_executor::task]
+pub async fn watch_power_level() {
+    // Activate PWR clock
+    pac::RCC.apb1enr().modify(|w| w.set_pwren(true));
+    // Configure PVD for 2.9V
+    pac::PWR.cr().modify(|w| {
+        w.set_pls(0b111); // 2.9V
+        w.set_pvde(true);
+    });
+    // Check power level every second, switch blinker to
+    // LP (low power) if power goes beyond this value.
+    loop {
+        Timer::after_secs(1).await;
+        if pac::PWR.csr().read().pvdo() {
+            defmt::warn!("low power (< 2.9V) detected");
+            blinker::set_blink_pattern(".-.. .--.");
+            break;
+        }
+    }
+}