120 lines
3.4 KiB
Rust
120 lines
3.4 KiB
Rust
use core::marker::PhantomData;
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use embassy_hal_common::{into_ref, Peripheral};
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use stm32_metapac::iwdg::vals::{Key, Pr};
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use crate::rcc::LSI_FREQ;
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pub struct IndependentWatchdog<'d, T: Instance> {
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wdg: PhantomData<&'d mut T>,
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}
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// 12-bit counter
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const MAX_RL: u16 = 0xFFF;
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/// Calculates maximum watchdog timeout in us (RL = 0xFFF) for a given prescaler
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const fn get_timeout_us(prescaler: u16, reload_value: u16) -> u32 {
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1_000_000 * (reload_value + 1) as u32 / (LSI_FREQ.0 / prescaler as u32)
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}
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/// Calculates watchdog reload value for the given prescaler and desired timeout
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const fn reload_value(prescaler: u16, timeout_us: u32) -> u16 {
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(timeout_us / prescaler as u32 * LSI_FREQ.0 / 1_000_000) as u16 - 1
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}
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impl<'d, T: Instance> IndependentWatchdog<'d, T> {
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/// Creates an IWDG (Independent Watchdog) instance with a given timeout value in microseconds.
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///
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/// [Self] has to be started with [Self::unleash()].
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/// Once timer expires, MCU will be reset. To prevent this, timer must be reloaded by repeatedly calling [Self::pet()] within timeout interval.
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pub fn new(_instance: impl Peripheral<P = T> + 'd, timeout_us: u32) -> Self {
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into_ref!(_instance);
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// Find lowest prescaler value, which makes watchdog period longer or equal to timeout.
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// This iterates from 4 (2^2) to 256 (2^8).
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let psc_power = unwrap!((2..=8).find(|psc_power| {
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let psc = 2u16.pow(*psc_power);
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timeout_us <= get_timeout_us(psc, MAX_RL)
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}));
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// Prescaler value
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let psc = 2u16.pow(psc_power);
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// Convert prescaler power to PR register value
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let pr = psc_power as u8 - 2;
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assert!(pr <= 0b110);
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// Reload value
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let rl = reload_value(psc, timeout_us);
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let wdg = T::regs();
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wdg.kr().write(|w| w.set_key(Key::ENABLE));
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wdg.pr().write(|w| w.set_pr(Pr::from_bits(pr)));
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wdg.rlr().write(|w| w.set_rl(rl));
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trace!(
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"Watchdog configured with {}us timeout, desired was {}us (PR={}, RL={})",
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get_timeout_us(psc, rl),
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timeout_us,
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pr,
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rl
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);
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IndependentWatchdog {
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wdg: PhantomData::default(),
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}
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}
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pub fn unleash(&mut self) {
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T::regs().kr().write(|w| w.set_key(Key::START));
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}
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pub fn pet(&mut self) {
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T::regs().kr().write(|w| w.set_key(Key::RESET));
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}
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}
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mod sealed {
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pub trait Instance {
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fn regs() -> crate::pac::iwdg::Iwdg;
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}
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}
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pub trait Instance: sealed::Instance {}
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foreach_peripheral!(
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(iwdg, $inst:ident) => {
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impl sealed::Instance for crate::peripherals::$inst {
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fn regs() -> crate::pac::iwdg::Iwdg {
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crate::pac::$inst
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}
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}
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impl Instance for crate::peripherals::$inst {}
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};
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);
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn can_compute_timeout_us() {
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assert_eq!(125, get_timeout_us(4, 0));
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assert_eq!(512_000, get_timeout_us(4, MAX_RL));
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assert_eq!(8_000, get_timeout_us(256, 0));
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assert_eq!(32768_000, get_timeout_us(256, MAX_RL));
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assert_eq!(8000_000, get_timeout_us(64, 3999));
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}
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#[test]
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fn can_compute_reload_value() {
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assert_eq!(0xFFF, reload_value(4, 512_000));
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assert_eq!(0xFFF, reload_value(256, 32768_000));
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assert_eq!(3999, reload_value(64, 8000_000));
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}
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}
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