esp-hal/esp-hal-embassy/src/time_driver.rs

use core::cell::{Cell, RefCell};

use critical_section::Mutex;
use embassy_time_driver::{AlarmHandle, Driver};
use esp_hal::{
    interrupt::{InterruptHandler, Priority},
    prelude::*,
    time::now,
    timer::{AnyTimer, OneShotTimer},
};

pub const MAX_SUPPORTED_ALARM_COUNT: usize = 7;

pub type Timer = OneShotTimer<'static, AnyTimer>;

static TIMERS: Mutex<RefCell<Option<&'static mut [Timer]>>> = Mutex::new(RefCell::new(None));

#[allow(clippy::type_complexity)]
struct AlarmState {
    pub callback: Cell<Option<(fn(*mut ()), *mut ())>>,
    pub allocated: Cell<bool>,
}

unsafe impl Send for AlarmState {}

impl AlarmState {
    pub const fn new() -> Self {
        Self {
            callback: Cell::new(None),
            allocated: Cell::new(false),
        }
    }
}

pub(super) struct EmbassyTimer {
    alarms: Mutex<[AlarmState; MAX_SUPPORTED_ALARM_COUNT]>,
}

embassy_time_driver::time_driver_impl!(static DRIVER: EmbassyTimer = EmbassyTimer {
    alarms: Mutex::new([const { AlarmState::new() }; MAX_SUPPORTED_ALARM_COUNT]),
});

impl EmbassyTimer {
    pub(super) fn init(timers: &'static mut [Timer]) {
        if timers.len() > MAX_SUPPORTED_ALARM_COUNT {
            panic!(
                "Maximum of {} timers can be used.",
                MAX_SUPPORTED_ALARM_COUNT
            );
        }

        critical_section::with(|cs| {
            timers.iter_mut().enumerate().for_each(|(n, timer)| {
                timer.enable_interrupt(false);
                timer.stop();

                if DRIVER.alarms.borrow(cs)[n].allocated.get() {
                    // FIXME: we should track which core allocated an alarm and bind the interrupt
                    // to that core.
                    timer.set_interrupt_handler(HANDLERS[n]);
                }
            });

            TIMERS.replace(cs, Some(timers));
        });
    }

    fn on_interrupt(&self, id: usize) {
        let cb = critical_section::with(|cs| {
            let mut timers = TIMERS.borrow_ref_mut(cs);
            let timers = unwrap!(timers.as_mut(), "Time driver not initialized");
            let timer = &mut timers[id];

            timer.clear_interrupt();

            let alarm = &self.alarms.borrow(cs)[id];
            alarm.callback.get()
        });

        if let Some((f, ctx)) = cb {
            f(ctx);
        }
    }

    fn arm(timer: &mut Timer, timestamp: u64) {
        let now = now().duration_since_epoch();
        let ts = timestamp.micros();
        // if the TS is already in the past make the timer fire immediately
        let timeout = if ts > now { ts - now } else { 0.micros() };
        unwrap!(timer.schedule(timeout));
        timer.enable_interrupt(true);
    }
}

impl Driver for EmbassyTimer {
    fn now(&self) -> u64 {
        now().ticks()
    }

    unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
        critical_section::with(|cs| {
            for (i, alarm) in self.alarms.borrow(cs).iter().enumerate() {
                if alarm.allocated.get() {
                    continue;
                }
                let mut timer = TIMERS.borrow_ref_mut(cs);
                // `allocate_alarm` may be called before `esp_hal_embassy::init()`, so
                // we need to check if we have timers.
                if let Some(timer) = &mut *timer {
                    // If we do, bind the interrupt handler to the timer.
                    // This ensures that alarms allocated after init are correctly bound to the
                    // core that created the executor.
                    let timer = unwrap!(
                        timer.get_mut(i),
                        "There are not enough timers to allocate a new alarm. Call `esp_hal_embassy::init()` with the correct number of timers."
                    );
                    timer.set_interrupt_handler(HANDLERS[i]);
                }

                // set alarm so it is not overwritten
                alarm.allocated.set(true);
                return Some(AlarmHandle::new(i as u8));
            }
            None
        })
    }

    fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
        let n = alarm.id() as usize;
        critical_section::with(|cs| {
            let alarm = &self.alarms.borrow(cs)[n];
            alarm.callback.set(Some((callback, ctx)));
        })
    }

    fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) -> bool {
        // If `embassy-executor/integrated-timers` is enabled and there are no pending
        // timers, embassy still calls `set_alarm` with `u64::MAX`. By returning
        // `true` we signal that no re-polling is necessary.
        if timestamp == u64::MAX {
            return true;
        }

        // The hardware fires the alarm even if timestamp is lower than the current
        // time. In this case the interrupt handler will pend a wake-up when we exit the
        // critical section.
        //
        // This is correct behavior. See https://docs.rs/embassy-time-driver/0.1.0/embassy_time_driver/trait.Driver.html#tymethod.set_alarm
        // (... the driver should return true and arrange to call the alarm callback as
        // soon as possible, but not synchronously.)
        critical_section::with(|cs| {
            let mut timers = TIMERS.borrow_ref_mut(cs);
            let timers = unwrap!(timers.as_mut(), "Time driver not initialized");
            let timer = &mut timers[alarm.id() as usize];

            Self::arm(timer, timestamp);
        });

        true
    }
}

static HANDLERS: [InterruptHandler; MAX_SUPPORTED_ALARM_COUNT] = [
    handler0, handler1, handler2, handler3, handler4, handler5, handler6,
];

#[handler(priority = Priority::max())]
fn handler0() {
    DRIVER.on_interrupt(0);
}
#[handler(priority = Priority::max())]
fn handler1() {
    DRIVER.on_interrupt(1);
}
#[handler(priority = Priority::max())]
fn handler2() {
    DRIVER.on_interrupt(2);
}
#[handler(priority = Priority::max())]
fn handler3() {
    DRIVER.on_interrupt(3);
}
#[handler(priority = Priority::max())]
fn handler4() {
    DRIVER.on_interrupt(4);
}
#[handler(priority = Priority::max())]
fn handler5() {
    DRIVER.on_interrupt(5);
}
#[handler(priority = Priority::max())]
fn handler6() {
    DRIVER.on_interrupt(6);
}