embassy-rp: Add Watchdog

embassy-rp/src/lib.rs

@@ -36,6 +36,7 @@ pub mod clocks;
 pub mod flash;
 pub mod multicore;
 mod reset;
+pub mod watchdog;
 
 // Reexports
 
@@ -119,6 +120,8 @@ embassy_hal_common::peripherals! {
 
     PIO0,
     PIO1,
+
+    WATCHDOG,
 }
 
 #[link_section = ".boot2"]

embassy-rp/src/watchdog.rs

@@ -0,0 +1,111 @@
+//! Watchdog
+//!
+//! The watchdog is a countdown timer that can restart parts of the chip if it reaches zero. This can be used to restart the
+//! processor if software gets stuck in an infinite loop. The programmer must periodically write a value to the watchdog to
+//! stop it from reaching zero.
+//!
+//! Credit: based on `rp-hal` implementation (also licensed Apache+MIT)
+
+use core::marker::PhantomData;
+
+use embassy_time::Duration;
+
+use crate::pac;
+use crate::peripherals::WATCHDOG;
+
+/// Watchdog peripheral
+pub struct Watchdog<'d> {
+    phantom: PhantomData<&'d WATCHDOG>,
+    load_value: u32, // decremented by 2 per tick (µs)
+}
+
+impl<'d> Watchdog<'d> {
+    /// Create a new `Watchdog`
+    pub fn new(_watchdog: WATCHDOG) -> Self {
+        Self {
+            phantom: PhantomData,
+            load_value: 0,
+        }
+    }
+
+    /// Start tick generation on clk_tick which is driven from clk_ref.
+    ///
+    /// # Arguments
+    ///
+    /// * `cycles` - Total number of tick cycles before the next tick is generated.
+    ///   It is expected to be the frequency in MHz of clk_ref.
+    pub fn enable_tick_generation(&mut self, cycles: u8) {
+        const WATCHDOG_TICK_ENABLE_BITS: u32 = 0x200;
+        unsafe {
+            let watchdog = pac::WATCHDOG;
+            watchdog
+                .tick()
+                .write_value(pac::watchdog::regs::Tick(WATCHDOG_TICK_ENABLE_BITS | cycles as u32))
+        }
+    }
+
+    /// Defines whether or not the watchdog timer should be paused when processor(s) are in debug mode
+    /// or when JTAG is accessing bus fabric
+    pub fn pause_on_debug(&mut self, pause: bool) {
+        unsafe {
+            let watchdog = pac::WATCHDOG;
+            watchdog.ctrl().write(|w| {
+                w.set_pause_dbg0(pause);
+                w.set_pause_dbg1(pause);
+                w.set_pause_jtag(pause);
+            })
+        }
+    }
+
+    fn load_counter(&self, counter: u32) {
+        unsafe {
+            let watchdog = pac::WATCHDOG;
+            watchdog.load().write_value(pac::watchdog::regs::Load(counter));
+        }
+    }
+
+    fn enable(&self, bit: bool) {
+        unsafe {
+            let watchdog = pac::WATCHDOG;
+            watchdog.ctrl().write(|w| w.set_enable(bit))
+        }
+    }
+
+    // Configure which hardware will be reset by the watchdog
+    // (everything except ROSC, XOSC)
+    unsafe fn configure_wdog_reset_triggers(&self) {
+        let psm = pac::PSM;
+        psm.wdsel().write_value(pac::psm::regs::Wdsel(
+            0x0001ffff & !(0x01 << 0usize) & !(0x01 << 1usize),
+        ));
+    }
+
+    /// Feed the watchdog timer
+    pub fn feed(&mut self) {
+        self.load_counter(self.load_value)
+    }
+
+    /// Start the watchdog timer
+    pub fn start(&mut self, period: Duration) {
+        const MAX_PERIOD: u32 = 0xFFFFFF;
+
+        let delay_us = period.as_micros() as u32;
+        if delay_us > MAX_PERIOD / 2 {
+            panic!(
+                "Period cannot exceed maximum load value of {} ({} microseconds))",
+                MAX_PERIOD,
+                MAX_PERIOD / 2
+            );
+        }
+        // Due to a logic error, the watchdog decrements by 2 and
+        // the load value must be compensated; see RP2040-E1
+        self.load_value = delay_us * 2;
+
+        self.enable(false);
+        unsafe {
+            self.configure_wdog_reset_triggers();
+        }
+        self.load_counter(self.load_value);
+        self.enable(true);
+    }
+}

examples/rp/src/bin/watchdog.rs

@@ -0,0 +1,48 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use defmt::info;
+use embassy_executor::Spawner;
+use embassy_rp::gpio;
+use embassy_rp::watchdog::*;
+use embassy_time::{Duration, Timer};
+use gpio::{Level, Output};
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_rp::init(Default::default());
+    info!("Hello world!");
+
+    let mut watchdog = Watchdog::new(p.WATCHDOG);
+    let mut led = Output::new(p.PIN_25, Level::Low);
+
+    // Set the LED high for 2 seconds so we know when we're about to start the watchdog
+    led.set_high();
+    Timer::after(Duration::from_secs(2)).await;
+
+    // Set to watchdog to reset if it's not reloaded within 1.05 seconds, and start it
+    watchdog.start(Duration::from_millis(1_050));
+    info!("Started the watchdog timer");
+
+    // Blink once a second for 5 seconds, refreshing the watchdog timer once a second to avoid a reset
+    for _ in 1..=5 {
+        led.set_low();
+        Timer::after(Duration::from_millis(500)).await;
+        led.set_high();
+        Timer::after(Duration::from_millis(500)).await;
+        info!("Feeding watchdog");
+        watchdog.feed();
+    }
+
+    info!("Stopped feeding, device will reset in 1.05 seconds");
+    // Blink 10 times per second, not feeding the watchdog.
+    // The processor should reset in 1.05 seconds, or 5 blinks time
+    loop {
+        led.set_low();
+        Timer::after(Duration::from_millis(100)).await;
+        led.set_high();
+        Timer::after(Duration::from_millis(100)).await;
+    }
+}