optimize watchdog

Author: burrbull

CHANGELOG.md

@@ -9,12 +9,15 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
-  - enable `defmt` feature for VSCode
-  - `set_alarm` takes `Into<AlarmDay>`
+ - enable `defmt` feature for VSCode, `set_alarm` takes `Into<AlarmDay>` [#660]
+ - Optimize watchdog setup calculation [#657]
 
 ### Fixed
 
-  - Compilation with `defmt` feature enabled
+ - Compilation with `defmt` feature enabled
+
+[#657]: https://github.com/stm32-rs/stm32f4xx-hal/pull/657
+[#660]: https://github.com/stm32-rs/stm32f4xx-hal/pull/660
 
 ## [v0.16.1] - 2023-06-24
 

src/watchdog.rs

@@ -23,14 +23,16 @@ impl fmt::Debug for IndependentWatchdog {
     }
 }
 
-const MAX_PR: u8 = 0b110;
+const LSI_KHZ: u32 = 32;
+const MAX_PR: u32 = 0b110;
 const MAX_RL: u16 = 0xFFF;
 const KR_ACCESS: u16 = 0x5555;
 const KR_RELOAD: u16 = 0xAAAA;
 const KR_START: u16 = 0xCCCC;
 
 impl IndependentWatchdog {
-    /// Wrap and start the watchdog
+    /// Creates a new `IndependentWatchDog` without starting it. Call `start` to start the watchdog.
+    /// See `WatchdogEnable` and `Watchdog` for more info.
     pub fn new(iwdg: IWDG) -> Self {
         IndependentWatchdog { iwdg }
     }
@@ -40,15 +42,22 @@ impl IndependentWatchdog {
         dbgmcu.apb1_fz.modify(|_, w| w.dbg_iwdg_stop().bit(stop));
     }
 
-    fn setup(&self, timeout_ms: u32) {
-        let mut pr = 0;
-        while pr < MAX_PR && Self::timeout_period(pr, MAX_RL) < timeout_ms {
-            pr += 1;
-        }
+    /// Sets the watchdog timer timout period. Max: 32768 ms
+    fn setup(&self, timeout_ms: MilliSeconds) {
+        assert!(timeout_ms.ticks() < (1 << 15), "Watchdog timeout to high");
+        let pr = match timeout_ms.ticks() {
+            t if t == 0 => 0b000, // <= (MAX_PR + 1) * 4 / LSI_KHZ => 0b000,
+            t if t <= (MAX_PR + 1) * 8 / LSI_KHZ => 0b001,
+            t if t <= (MAX_PR + 1) * 16 / LSI_KHZ => 0b010,
+            t if t <= (MAX_PR + 1) * 32 / LSI_KHZ => 0b011,
+            t if t <= (MAX_PR + 1) * 64 / LSI_KHZ => 0b100,
+            t if t <= (MAX_PR + 1) * 128 / LSI_KHZ => 0b101,
+            _ => 0b110,
+        };
 
         let max_period = Self::timeout_period(pr, MAX_RL);
         let max_rl = u32::from(MAX_RL);
-        let rl = (timeout_ms * max_rl / max_period).min(max_rl) as u16;
+        let rl = (timeout_ms.ticks() * max_rl / max_period).min(max_rl) as u16;
 
         self.access_registers(|iwdg| {
             iwdg.pr.modify(|_, w| w.pr().bits(pr));
@@ -72,7 +81,7 @@ impl IndependentWatchdog {
 
     /// pr: Prescaler divider bits, rl: reload value
     ///
-    /// Returns ms
+    /// Returns timeout period in ms
     fn timeout_period(pr: u8, rl: u16) -> u32 {
         let divider: u32 = match pr {
             0b000 => 4,
@@ -85,7 +94,7 @@ impl IndependentWatchdog {
             0b111 => 256,
             _ => unreachable!(),
         };
-        (u32::from(rl) + 1) * divider / 32
+        (u32::from(rl) + 1) * divider / LSI_KHZ
     }
 
     fn access_registers<A, F: FnMut(&IWDG) -> A>(&self, mut f: F) -> A {
@@ -99,7 +108,7 @@ impl IndependentWatchdog {
     }
 
     pub fn start(&mut self, period: MilliSeconds) {
-        self.setup(period.ticks());
+        self.setup(period);
 
         self.iwdg.kr.write(|w| unsafe { w.key().bits(KR_START) });
     }