esp_idf_svc/timer.rs
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//! High resolution hardware timer based task scheduling
//!
//! Although FreeRTOS provides software timers, these timers have a few
//! limitations:
//!
//! - Maximum resolution is equal to RTOS tick period
//! - Timer callbacks are dispatched from a low-priority task
//!
//! EspTimer is a set of APIs that provides one-shot and periodic timers,
//! microsecond time resolution, and 52-bit range.
use core::num::NonZeroU32;
use core::time::Duration;
use core::{ffi, ptr};
extern crate alloc;
use alloc::boxed::Box;
use alloc::sync::Arc;
use esp_idf_hal::task::asynch::Notification;
use crate::sys::*;
use ::log::debug;
#[cfg(esp_idf_esp_timer_supports_isr_dispatch_method)]
pub use isr::*;
use crate::handle::RawHandle;
struct UnsafeCallback<'a>(*mut Box<dyn FnMut() + Send + 'a>);
impl<'a> UnsafeCallback<'a> {
fn from(boxed: &mut Box<dyn FnMut() + Send + 'a>) -> Self {
Self(boxed)
}
unsafe fn from_ptr(ptr: *mut ffi::c_void) -> Self {
Self(ptr as *mut _)
}
fn as_ptr(&self) -> *mut ffi::c_void {
self.0 as *mut _
}
unsafe fn call(&self) {
let reference = self.0.as_mut().unwrap();
(reference)();
}
}
pub struct EspTimer<'a> {
handle: esp_timer_handle_t,
_callback: Box<dyn FnMut() + Send + 'a>,
}
impl EspTimer<'_> {
pub fn is_scheduled(&self) -> Result<bool, EspError> {
Ok(unsafe { esp_timer_is_active(self.handle) })
}
pub fn cancel(&self) -> Result<bool, EspError> {
let res = unsafe { esp_timer_stop(self.handle) };
Ok(res != ESP_OK)
}
pub fn after(&self, duration: Duration) -> Result<(), EspError> {
self.cancel()?;
esp!(unsafe { esp_timer_start_once(self.handle, duration.as_micros() as _) })?;
Ok(())
}
pub fn every(&self, duration: Duration) -> Result<(), EspError> {
self.cancel()?;
esp!(unsafe { esp_timer_start_periodic(self.handle, duration.as_micros() as _) })?;
Ok(())
}
extern "C" fn handle(arg: *mut ffi::c_void) {
if crate::hal::interrupt::active() {
#[cfg(esp_idf_esp_timer_supports_isr_dispatch_method)]
{
let signaled = crate::hal::interrupt::with_isr_yield_signal(move || unsafe {
UnsafeCallback::from_ptr(arg).call();
});
if signaled {
unsafe {
crate::sys::esp_timer_isr_dispatch_need_yield();
}
}
}
#[cfg(not(esp_idf_esp_timer_supports_isr_dispatch_method))]
{
unreachable!();
}
} else {
unsafe {
UnsafeCallback::from_ptr(arg).call();
}
}
}
}
unsafe impl Send for EspTimer<'_> {}
impl Drop for EspTimer<'_> {
fn drop(&mut self) {
self.cancel().unwrap();
while unsafe { esp_timer_delete(self.handle) } != ESP_OK {
// Timer is still running, busy-loop
}
debug!("Timer dropped");
}
}
impl RawHandle for EspTimer<'_> {
type Handle = esp_timer_handle_t;
fn handle(&self) -> Self::Handle {
self.handle
}
}
pub struct EspAsyncTimer {
timer: EspTimer<'static>,
notification: Arc<Notification>,
}
impl EspAsyncTimer {
pub async fn after(&mut self, duration: Duration) -> Result<(), EspError> {
self.timer.cancel()?;
self.notification.reset();
self.timer.after(duration)?;
self.notification.wait().await;
Ok(())
}
pub fn every(&mut self, duration: Duration) -> Result<&'_ mut Self, EspError> {
self.timer.cancel()?;
self.notification.reset();
self.timer.every(duration)?;
Ok(self)
}
pub async fn tick(&mut self) -> Result<(), EspError> {
self.notification.wait().await;
Ok(())
}
}
impl embedded_hal_async::delay::DelayNs for EspAsyncTimer {
async fn delay_ns(&mut self, ns: u32) {
EspAsyncTimer::after(self, Duration::from_micros(ns as _))
.await
.unwrap();
}
async fn delay_ms(&mut self, ms: u32) {
EspAsyncTimer::after(self, Duration::from_millis(ms as _))
.await
.unwrap();
}
}
pub trait EspTimerServiceType {
fn is_isr() -> bool;
}
#[derive(Clone, Debug)]
pub struct Task;
impl EspTimerServiceType for Task {
fn is_isr() -> bool {
false
}
}
pub struct EspTimerService<T>(T)
where
T: EspTimerServiceType;
impl<T> EspTimerService<T>
where
T: EspTimerServiceType,
{
pub fn now(&self) -> Duration {
Duration::from_micros(unsafe { esp_timer_get_time() as _ })
}
pub fn timer<F>(&self, callback: F) -> Result<EspTimer<'static>, EspError>
where
F: FnMut() + Send + 'static,
{
self.internal_timer(callback, false)
}
/// Same as `timer` but does not wake the device from light sleep.
pub fn timer_nowake<F>(&self, callback: F) -> Result<EspTimer<'static>, EspError>
where
F: FnMut() + Send + 'static,
{
self.internal_timer(callback, true)
}
pub fn timer_async(&self) -> Result<EspAsyncTimer, EspError> {
self.internal_timer_async(false)
}
/// Same as `timer_async` but does not wake the device from light sleep.
pub fn timer_async_nowake(&self) -> Result<EspAsyncTimer, EspError> {
self.internal_timer_async(true)
}
/// # Safety
///
/// This method - in contrast to method `timer` - allows the user to pass
/// a non-static callback/closure. This enables users to borrow
/// - in the closure - variables that live on the stack - or more generally - in the same
/// scope where the service is created.
///
/// HOWEVER: care should be taken NOT to call `core::mem::forget()` on the service,
/// as that would immediately lead to an UB (crash).
/// Also note that forgetting the service might happen with `Rc` and `Arc`
/// when circular references are introduced: https://github.com/rust-lang/rust/issues/24456
///
/// The reason is that the closure is actually sent to a hidden ESP IDF thread.
/// This means that if the service is forgotten, Rust is free to e.g. unwind the stack
/// and the closure now owned by this other thread will end up with references to variables that no longer exist.
///
/// The destructor of the service takes care - prior to the service being dropped and e.g.
/// the stack being unwind - to remove the closure from the hidden thread and destroy it.
/// Unfortunately, when the service is forgotten, the un-subscription does not happen
/// and invalid references are left dangling.
///
/// This "local borrowing" will only be possible to express in a safe way once/if `!Leak` types
/// are introduced to Rust (i.e. the impossibility to "forget" a type and thus not call its destructor).
pub unsafe fn timer_nonstatic<'a, F>(&self, callback: F) -> Result<EspTimer<'a>, EspError>
where
F: FnMut() + Send + 'a,
{
self.internal_timer(callback, false)
}
/// # Safety
///
/// Same as `timer_nonstatic` but does not wake the device from light sleep.
pub unsafe fn timer_nonstatic_nowake<'a, F>(
&self,
callback: F,
) -> Result<EspTimer<'a>, EspError>
where
F: FnMut() + Send + 'a,
{
self.internal_timer(callback, true)
}
fn internal_timer<'a, F>(
&self,
callback: F,
skip_unhandled_events: bool,
) -> Result<EspTimer<'a>, EspError>
where
F: FnMut() + Send + 'a,
{
let mut handle: esp_timer_handle_t = ptr::null_mut();
let boxed_callback: Box<dyn FnMut() + Send + 'a> = Box::new(callback);
let mut callback = Box::new(boxed_callback);
let unsafe_callback = UnsafeCallback::from(&mut callback);
#[cfg(esp_idf_esp_timer_supports_isr_dispatch_method)]
let dispatch_method = if T::is_isr() {
esp_timer_dispatch_t_ESP_TIMER_ISR
} else {
esp_timer_dispatch_t_ESP_TIMER_TASK
};
#[cfg(not(esp_idf_esp_timer_supports_isr_dispatch_method))]
let dispatch_method = esp_timer_dispatch_t_ESP_TIMER_TASK;
esp!(unsafe {
esp_timer_create(
&esp_timer_create_args_t {
callback: Some(EspTimer::handle),
name: b"rust\0" as *const _ as *const _, // TODO
arg: unsafe_callback.as_ptr(),
dispatch_method,
skip_unhandled_events,
},
&mut handle as *mut _,
)
})?;
Ok(EspTimer {
handle,
_callback: callback,
})
}
fn internal_timer_async(&self, skip_unhandled_events: bool) -> Result<EspAsyncTimer, EspError> {
let notification = Arc::new(Notification::new());
let timer = {
let notification = Arc::downgrade(¬ification);
self.internal_timer(
move || {
if let Some(notification) = notification.upgrade() {
notification.notify(NonZeroU32::new(1).unwrap());
}
},
skip_unhandled_events,
)?
};
Ok(EspAsyncTimer {
timer,
notification,
})
}
}
pub type EspTaskTimerService = EspTimerService<Task>;
impl EspTimerService<Task> {
pub fn new() -> Result<Self, EspError> {
Ok(Self(Task))
}
}
impl<T> Clone for EspTimerService<T>
where
T: EspTimerServiceType + Clone,
{
fn clone(&self) -> Self {
Self(self.0.clone())
}
}
#[cfg(esp_idf_esp_timer_supports_isr_dispatch_method)]
mod isr {
use crate::sys::EspError;
#[derive(Clone, Debug)]
pub struct ISR;
impl super::EspTimerServiceType for ISR {
fn is_isr() -> bool {
true
}
}
pub type EspISRTimerService = super::EspTimerService<ISR>;
impl EspISRTimerService {
/// # Safety
/// TODO
pub unsafe fn new() -> Result<Self, EspError> {
Ok(Self(ISR))
}
}
}
/// This module is used to provide a time driver for the `embassy-time` crate.
///
/// The minimum provided resolution is ~ 20-30us when the CPU is at top speed of 240MHz
/// (https://docs.espressif.com/projects/esp-idf/en/v5.4/esp32/api-reference/system/esp_timer.html#timeout-value-limits)
///
/// The tick-rate is 1MHz (i.e. 1 tick is 1us).
#[cfg(feature = "embassy-time-driver")]
pub mod embassy_time_driver {
use core::cell::RefCell;
use core::task::Waker;
use ::embassy_time_driver::Driver;
use embassy_time_queue_utils::Queue;
use crate::private::mutex::Mutex;
use crate::timer::*;
struct EspDriverInner {
queue: embassy_time_queue_utils::Queue,
timer: Option<EspTimer<'static>>,
}
impl EspDriverInner {
fn now() -> u64 {
unsafe { esp_timer_get_time() as _ }
}
fn schedule_next_expiration(&mut self) {
/// End of epoch minus one day
const MAX_SAFE_TIMEOUT_US: u64 = u64::MAX - 24 * 60 * 60 * 1000 * 1000;
let timer = self.timer.as_mut().unwrap();
loop {
let now = Self::now();
let next_at = self.queue.next_expiration(now);
if now < next_at {
let after = next_at - now;
if after <= MAX_SAFE_TIMEOUT_US {
// Why?
// The ESP-IDF Timer API does not have a `Timer::at` method so we have to call it with
// `Timer::after(next_at - now)` instead. The problem is - even though the ESP IDF
// Timer API does not have a `Timer::at` method - _internally_ it takes our `next_at - now`,
// adds to it a **newer** "now" and sets this as the moment in time when the timer should trigger.
//
// Consider what would happen if we call `Timer::after(u64::MAX - now)`:
// The result would be something like `u64::MAX - now + (now + 1)` which would silently overflow and
// trigger the timer after 1us:
// https://github.com/espressif/esp-idf/blob/b5ac4fbdf9e9fb320bb0a98ee4fbaa18f8566f37/components/esp_timer/src/esp_timer.c#L188
//
// To workaround this problem, we make sure to never call `Timer::after(ms)` with `ms` greater than `MAX_SAFE_TIMEOUT_US`
// (i.e. the end of epoch - one day).
//
// Thus, even if we are un-scheduled between the calculation of our own `now` and the driver's newer `now`,
// there is one extra **day** of millis to accomodate for the potential overflow. If the overflow does happen still
// (which is kinda unthinkable given the time scales we are working with), the timer will re-trigger immediately,
// but hopefully on the next (or next after next and so on) re-trigger, we won't have the overflow anymore.
timer.after(Duration::from_micros(after)).unwrap();
}
break;
}
}
}
}
struct EspDriver {
inner: Mutex<RefCell<EspDriverInner>>,
}
impl EspDriver {
const fn new() -> Self {
Self {
inner: Mutex::new(RefCell::new(EspDriverInner {
queue: Queue::new(),
timer: None,
})),
}
}
}
unsafe impl Send for EspDriver {}
unsafe impl Sync for EspDriver {}
impl Driver for EspDriver {
fn now(&self) -> u64 {
EspDriverInner::now()
}
fn schedule_wake(&self, at: u64, waker: &Waker) {
let service = EspTimerService::<Task>::new().unwrap();
let guard = self.inner.lock();
let mut inner = guard.borrow_mut();
if inner.timer.is_none() {
// Driver is always statically allocated, so this is safe
let static_self: &'static Self = unsafe { core::mem::transmute(self) };
inner.timer = Some(
service
.timer(move || {
static_self
.inner
.lock()
.borrow_mut()
.schedule_next_expiration()
})
.unwrap(),
);
}
if inner.queue.schedule_wake(at, waker) {
inner.schedule_next_expiration();
}
}
}
pub type LinkWorkaround = [*mut (); 2];
#[used]
static mut __INTERNAL_REFERENCE: LinkWorkaround = [
_embassy_time_now as *mut _,
_embassy_time_schedule_wake as *mut _,
];
pub fn link() -> LinkWorkaround {
unsafe { __INTERNAL_REFERENCE }
}
::embassy_time_driver::time_driver_impl!(static DRIVER: EspDriver = EspDriver::new());
}