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Merge pull request #373 from embassy-rs/docs

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Time driver improvements, docs.
This commit is contained in:
Dario Nieuwenhuis 2021-08-26 23:37:37 +02:00 committed by GitHub
commit e56c6166dc
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GPG key ID: 4AEE18F83AFDEB23
21 changed files with 601 additions and 242 deletions
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1
Cargo.example.toml
View file

@ -45,7 +45,6 @@ members = [
#"examples/rp",
# std
#"embassy-std",
#"examples/std",
]

55
embassy-nrf/src/time_driver.rs
View file

@ -82,7 +82,7 @@ impl AlarmState {
const ALARM_COUNT: usize = 3;
struct State {
struct RtcDriver {
/// Number of 2^23 periods elapsed since boot.
period: AtomicU32,
alarm_count: AtomicU8,
@ -91,13 +91,13 @@ struct State {
}
const ALARM_STATE_NEW: AlarmState = AlarmState::new();
static STATE: State = State {
embassy::time_driver_impl!(static DRIVER: RtcDriver = RtcDriver {
period: AtomicU32::new(0),
alarm_count: AtomicU8::new(0),
alarms: Mutex::new([ALARM_STATE_NEW; ALARM_COUNT]),
};
});
impl State {
impl RtcDriver {
fn init(&'static self, irq_prio: crate::interrupt::Priority) {
let r = rtc();
r.cc[3].write(|w| unsafe { w.bits(0x800000) });
@ -159,14 +159,6 @@ impl State {
})
}
fn now(&self) -> u64 {
// `period` MUST be read before `counter`, see comment at the top for details.
let period = self.period.load(Ordering::Relaxed);
compiler_fence(Ordering::Acquire);
let counter = rtc().counter.read().bits();
calc_now(period, counter)
}
fn get_alarm<'a>(&'a self, cs: CriticalSection<'a>, alarm: AlarmHandle) -> &'a AlarmState {
// safety: we're allowed to assume the AlarmState is created by us, and
// we never create one that's out of bounds.
@ -188,8 +180,18 @@ impl State {
let f: fn(*mut ()) = unsafe { mem::transmute(alarm.callback.get()) };
f(alarm.ctx.get());
}
}
fn allocate_alarm(&self) -> Option<AlarmHandle> {
impl Driver for RtcDriver {
fn now(&self) -> u64 {
// `period` MUST be read before `counter`, see comment at the top for details.
let period = self.period.load(Ordering::Relaxed);
compiler_fence(Ordering::Acquire);
let counter = rtc().counter.read().bits();
calc_now(period, counter)
}
unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
let id = self
.alarm_count
.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
@ -201,7 +203,7 @@ impl State {
});
match id {
Ok(id) => Some(unsafe { AlarmHandle::new(id) }),
Ok(id) => Some(AlarmHandle::new(id)),
Err(_) => None,
}
}
@ -263,32 +265,11 @@ impl State {
}
}
struct RtcDriver;
embassy::time_driver_impl!(RtcDriver);
impl Driver for RtcDriver {
fn now() -> u64 {
STATE.now()
}
unsafe fn allocate_alarm() -> Option<AlarmHandle> {
STATE.allocate_alarm()
}
fn set_alarm_callback(alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
STATE.set_alarm_callback(alarm, callback, ctx)
}
fn set_alarm(alarm: AlarmHandle, timestamp: u64) {
STATE.set_alarm(alarm, timestamp)
}
}
#[interrupt]
fn RTC1() {
STATE.on_interrupt()
DRIVER.on_interrupt()
}
pub(crate) fn init(irq_prio: crate::interrupt::Priority) {
STATE.init(irq_prio)
DRIVER.init(irq_prio)
}

132
embassy-rp/src/timer.rs
View file

@ -19,38 +19,40 @@ const DUMMY_ALARM: AlarmState = AlarmState {
callback: Cell::new(None),
};
static ALARMS: Mutex<[AlarmState; ALARM_COUNT]> = Mutex::new([DUMMY_ALARM; ALARM_COUNT]);
static NEXT_ALARM: AtomicU8 = AtomicU8::new(0);
struct TimerDriver {
alarms: Mutex<[AlarmState; ALARM_COUNT]>,
next_alarm: AtomicU8,
}
fn now() -> u64 {
loop {
unsafe {
let hi = pac::TIMER.timerawh().read();
let lo = pac::TIMER.timerawl().read();
let hi2 = pac::TIMER.timerawh().read();
if hi == hi2 {
return (hi as u64) << 32 | (lo as u64);
embassy::time_driver_impl!(static DRIVER: TimerDriver = TimerDriver{
alarms: Mutex::new([DUMMY_ALARM; ALARM_COUNT]),
next_alarm: AtomicU8::new(0),
});
impl Driver for TimerDriver {
fn now(&self) -> u64 {
loop {
unsafe {
let hi = pac::TIMER.timerawh().read();
let lo = pac::TIMER.timerawl().read();
let hi2 = pac::TIMER.timerawh().read();
if hi == hi2 {
return (hi as u64) << 32 | (lo as u64);
}
}
}
}
}
struct TimerDriver;
embassy::time_driver_impl!(TimerDriver);
impl Driver for TimerDriver {
fn now() -> u64 {
now()
}
unsafe fn allocate_alarm() -> Option<AlarmHandle> {
let id = NEXT_ALARM.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
if x < ALARM_COUNT as u8 {
Some(x + 1)
} else {
None
}
});
unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
let id = self
.next_alarm
.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
if x < ALARM_COUNT as u8 {
Some(x + 1)
} else {
None
}
});
match id {
Ok(id) => Some(AlarmHandle::new(id)),
@ -58,18 +60,18 @@ impl Driver for TimerDriver {
}
}
fn set_alarm_callback(alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
let n = alarm.id() as usize;
critical_section::with(|cs| {
let alarm = &ALARMS.borrow(cs)[n];
let alarm = &self.alarms.borrow(cs)[n];
alarm.callback.set(Some((callback, ctx)));
})
}
fn set_alarm(alarm: AlarmHandle, timestamp: u64) {
fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) {
let n = alarm.id() as usize;
critical_section::with(|cs| {
let alarm = &ALARMS.borrow(cs)[n];
let alarm = &self.alarms.borrow(cs)[n];
alarm.timestamp.set(timestamp);
// Arm it.
@ -78,44 +80,46 @@ impl Driver for TimerDriver {
// it is checked if the alarm time has passed.
unsafe { pac::TIMER.alarm(n).write_value(timestamp as u32) };
let now = now();
let now = self.now();
// If alarm timestamp has passed, trigger it instantly.
// This disarms it.
if timestamp <= now {
trigger_alarm(n, cs);
self.trigger_alarm(n, cs);
}
})
}
}
fn check_alarm(n: usize) {
critical_section::with(|cs| {
let alarm = &ALARMS.borrow(cs)[n];
let timestamp = alarm.timestamp.get();
if timestamp <= now() {
trigger_alarm(n, cs)
} else {
// Not elapsed, arm it again.
// This can happen if it was set more than 2^32 us in the future.
unsafe { pac::TIMER.alarm(n).write_value(timestamp as u32) };
impl TimerDriver {
fn check_alarm(&self, n: usize) {
critical_section::with(|cs| {
let alarm = &self.alarms.borrow(cs)[n];
let timestamp = alarm.timestamp.get();
if timestamp <= self.now() {
self.trigger_alarm(n, cs)
} else {
// Not elapsed, arm it again.
// This can happen if it was set more than 2^32 us in the future.
unsafe { pac::TIMER.alarm(n).write_value(timestamp as u32) };
}
});
// clear the irq
unsafe { pac::TIMER.intr().write(|w| w.set_alarm(n, true)) }
}
fn trigger_alarm(&self, n: usize, cs: CriticalSection) {
// disarm
unsafe { pac::TIMER.armed().write(|w| w.set_armed(1 << n)) }
let alarm = &self.alarms.borrow(cs)[n];
alarm.timestamp.set(u64::MAX);
// Call after clearing alarm, so the callback can set another alarm.
if let Some((f, ctx)) = alarm.callback.get() {
f(ctx);
}
});
// clear the irq
unsafe { pac::TIMER.intr().write(|w| w.set_alarm(n, true)) }
}
fn trigger_alarm(n: usize, cs: CriticalSection) {
// disarm
unsafe { pac::TIMER.armed().write(|w| w.set_armed(1 << n)) }
let alarm = &ALARMS.borrow(cs)[n];
alarm.timestamp.set(u64::MAX);
// Call after clearing alarm, so the callback can set another alarm.
if let Some((f, ctx)) = alarm.callback.get() {
f(ctx);
}
}
@ -123,7 +127,7 @@ fn trigger_alarm(n: usize, cs: CriticalSection) {
pub unsafe fn init() {
// init alarms
critical_section::with(|cs| {
let alarms = ALARMS.borrow(cs);
let alarms = DRIVER.alarms.borrow(cs);
for a in alarms {
a.timestamp.set(u64::MAX);
}
@ -144,20 +148,20 @@ pub unsafe fn init() {
#[interrupt]
unsafe fn TIMER_IRQ_0() {
check_alarm(0)
DRIVER.check_alarm(0)
}
#[interrupt]
unsafe fn TIMER_IRQ_1() {
check_alarm(1)
DRIVER.check_alarm(1)
}
#[interrupt]
unsafe fn TIMER_IRQ_2() {
check_alarm(2)
DRIVER.check_alarm(2)
}
#[interrupt]
unsafe fn TIMER_IRQ_3() {
check_alarm(3)
DRIVER.check_alarm(3)
}

62
embassy-stm32/src/time_driver.rs
View file

@ -26,12 +26,12 @@ type T = peripherals::TIM3;
#[cfg(feature = "time-driver-tim2")]
#[interrupt]
fn TIM2() {
STATE.on_interrupt()
DRIVER.on_interrupt()
}
#[cfg(feature = "time-driver-tim3")]
#[interrupt]
fn TIM3() {
STATE.on_interrupt()
DRIVER.on_interrupt()
}
// Clock timekeeping works with something we call "periods", which are time intervals
@ -76,7 +76,7 @@ impl AlarmState {
}
}
struct State {
struct RtcDriver {
/// Number of 2^15 periods elapsed since boot.
period: AtomicU32,
alarm_count: AtomicU8,
@ -85,13 +85,14 @@ struct State {
}
const ALARM_STATE_NEW: AlarmState = AlarmState::new();
static STATE: State = State {
embassy::time_driver_impl!(static DRIVER: RtcDriver = RtcDriver {
period: AtomicU32::new(0),
alarm_count: AtomicU8::new(0),
alarms: Mutex::new([ALARM_STATE_NEW; ALARM_COUNT]),
};
});
impl State {
impl RtcDriver {
fn init(&'static self) {
let r = T::regs();
@ -185,16 +186,6 @@ impl State {
})
}
fn now(&self) -> u64 {
let r = T::regs();
let period = self.period.load(Ordering::Relaxed);
compiler_fence(Ordering::Acquire);
// NOTE(unsafe) Atomic read with no side-effects
let counter = unsafe { r.cnt().read().cnt() };
calc_now(period, counter)
}
fn get_alarm<'a>(&'a self, cs: CriticalSection<'a>, alarm: AlarmHandle) -> &'a AlarmState {
// safety: we're allowed to assume the AlarmState is created by us, and
// we never create one that's out of bounds.
@ -213,8 +204,20 @@ impl State {
let f: fn(*mut ()) = unsafe { mem::transmute(alarm.callback.get()) };
f(alarm.ctx.get());
}
}
fn allocate_alarm(&self) -> Option<AlarmHandle> {
impl Driver for RtcDriver {
fn now(&self) -> u64 {
let r = T::regs();
let period = self.period.load(Ordering::Relaxed);
compiler_fence(Ordering::Acquire);
// NOTE(unsafe) Atomic read with no side-effects
let counter = unsafe { r.cnt().read().cnt() };
calc_now(period, counter)
}
unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
let id = self
.alarm_count
.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
@ -226,7 +229,7 @@ impl State {
});
match id {
Ok(id) => Some(unsafe { AlarmHandle::new(id) }),
Ok(id) => Some(AlarmHandle::new(id)),
Err(_) => None,
}
}
@ -269,29 +272,8 @@ impl State {
}
}
struct RtcDriver;
embassy::time_driver_impl!(RtcDriver);
impl Driver for RtcDriver {
fn now() -> u64 {
STATE.now()
}
unsafe fn allocate_alarm() -> Option<AlarmHandle> {
STATE.allocate_alarm()
}
fn set_alarm_callback(alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
STATE.set_alarm_callback(alarm, callback, ctx)
}
fn set_alarm(alarm: AlarmHandle, timestamp: u64) {
STATE.set_alarm(alarm, timestamp)
}
}
pub(crate) fn init() {
STATE.init()
DRIVER.init()
}
// ------------------------------------------------------

10
embassy/Cargo.toml
View file

@ -7,9 +7,17 @@ resolver = "2"
[features]
default = []
std = ["futures/std", "embassy-traits/std"]
std = ["futures/std", "embassy-traits/std", "time", "time-tick-1mhz"]
# Enable `embassy::time` module.
# NOTE: This feature is only intended to be enabled by crates providing the time driver implementation.
# Enabling it directly without supplying a time driver will fail to link.
time = []
# Set the `embassy::time` tick rate.
# NOTE: This feature is only intended to be enabled by crates providing the time driver implementation.
# If you're not writing your own driver, check the driver documentation to customize the tick rate.
# If you're writing a driver and your tick rate is not listed here, please add it and send a PR!
time-tick-32768hz = ["time"]
time-tick-1000hz = ["time"]
time-tick-1mhz = ["time"]

67
embassy/src/executor/arch/std.rs Normal file
View file

@ -0,0 +1,67 @@
use std::marker::PhantomData;
use std::sync::{Condvar, Mutex};
use super::{raw, Spawner};
pub struct Executor {
inner: raw::Executor,
not_send: PhantomData<*mut ()>,
signaler: &'static Signaler,
}
impl Executor {
pub fn new() -> Self {
let signaler = &*Box::leak(Box::new(Signaler::new()));
Self {
inner: raw::Executor::new(
|p| unsafe {
let s = &*(p as *const () as *const Signaler);
s.signal()
},
signaler as *const _ as _,
),
not_send: PhantomData,
signaler,
}
}
/// Runs the executor.
///
/// This function never returns.
pub fn run(&'static mut self, init: impl FnOnce(Spawner)) -> ! {
init(unsafe { self.inner.spawner() });
loop {
unsafe { self.inner.run_queued() };
self.signaler.wait()
}
}
}
struct Signaler {
mutex: Mutex<bool>,
condvar: Condvar,
}
impl Signaler {
fn new() -> Self {
Self {
mutex: Mutex::new(false),
condvar: Condvar::new(),
}
}
fn wait(&self) {
let mut signaled = self.mutex.lock().unwrap();
while !*signaled {
signaled = self.condvar.wait(signaled).unwrap();
}
*signaled = false;
}
fn signal(&self) {
let mut signaled = self.mutex.lock().unwrap();
*signaled = true;
self.condvar.notify_one();
}
}

3
embassy/src/executor/mod.rs
View file

@ -1,4 +1,5 @@
#[path = "arch/arm.rs"]
#[cfg_attr(feature = "std", path = "arch/std.rs")]
#[cfg_attr(not(feature = "std"), path = "arch/arm.rs")]
mod arch;
pub mod raw;
mod spawner;

4
embassy/src/io/mod.rs
View file

@ -1,7 +1,11 @@
mod error;
#[cfg(feature = "std")]
mod std;
mod traits;
mod util;
pub use self::error::*;
#[cfg(feature = "std")]
pub use self::std::*;
pub use self::traits::*;
pub use self::util::*;

35
embassy/src/io/std.rs Normal file
View file

@ -0,0 +1,35 @@
use core::pin::Pin;
use core::task::{Context, Poll};
use futures::io as std_io;
use super::{AsyncBufRead, AsyncWrite, Result};
pub struct FromStdIo<T>(T);
impl<T> FromStdIo<T> {
pub fn new(inner: T) -> Self {
Self(inner)
}
}
impl<T: std_io::AsyncBufRead> AsyncBufRead for FromStdIo<T> {
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>> {
let Self(inner) = unsafe { self.get_unchecked_mut() };
unsafe { Pin::new_unchecked(inner) }
.poll_fill_buf(cx)
.map_err(|e| e.into())
}
fn consume(self: Pin<&mut Self>, amt: usize) {
let Self(inner) = unsafe { self.get_unchecked_mut() };
unsafe { Pin::new_unchecked(inner) }.consume(amt)
}
}
impl<T: std_io::AsyncWrite> AsyncWrite for FromStdIo<T> {
fn poll_write(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8]) -> Poll<Result<usize>> {
let Self(inner) = unsafe { self.get_unchecked_mut() };
unsafe { Pin::new_unchecked(inner) }
.poll_write(cx, buf)
.map_err(|e| e.into())
}
}

37
embassy/src/io/traits.rs
View file

@ -5,9 +5,6 @@ use core::task::{Context, Poll};
#[cfg(feature = "alloc")]
use alloc::boxed::Box;
#[cfg(feature = "std")]
use futures::io as std_io;
use super::error::Result;
/// Read bytes asynchronously.
@ -159,37 +156,3 @@ where
self.get_mut().as_mut().poll_write(cx, buf)
}
}
#[cfg(feature = "std")]
pub struct FromStdIo<T>(T);
#[cfg(feature = "std")]
impl<T> FromStdIo<T> {
pub fn new(inner: T) -> Self {
Self(inner)
}
}
#[cfg(feature = "std")]
impl<T: std_io::AsyncBufRead> AsyncBufRead for FromStdIo<T> {
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>> {
let Self(inner) = unsafe { self.get_unchecked_mut() };
unsafe { Pin::new_unchecked(inner) }
.poll_fill_buf(cx)
.map_err(|e| e.into())
}
fn consume(self: Pin<&mut Self>, amt: usize) {
let Self(inner) = unsafe { self.get_unchecked_mut() };
unsafe { Pin::new_unchecked(inner) }.consume(amt)
}
}
#[cfg(feature = "std")]
impl<T: std_io::AsyncWrite> AsyncWrite for FromStdIo<T> {
fn poll_write(self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8]) -> Poll<Result<usize>> {
let Self(inner) = unsafe { self.get_unchecked_mut() };
unsafe { Pin::new_unchecked(inner) }
.poll_write(cx, buf)
.map_err(|e| e.into())
}
}

9
embassy/src/time/delay.rs
View file

@ -4,11 +4,10 @@ use super::{Duration, Instant, Timer};
/// Type implementing async delays and blocking `embedded-hal` delays.
///
/// For this interface to work, the Executor's clock must be correctly initialized before using it.
/// The delays are implemented in a "best-effort" way, meaning that the cpu will block for at least
/// the amount provided, but accuracy can be affected by many factors, including interrupt usage.
/// Make sure to use a suitable tick rate for your use case. The tick rate can be chosen through
/// features flags of this crate.
/// Make sure to use a suitable tick rate for your use case. The tick rate is defined by the currently
/// active driver.
pub struct Delay;
impl crate::traits::delay::Delay for Delay {
@ -58,9 +57,7 @@ impl embedded_hal::blocking::delay::DelayUs<u32> for Delay {
}
}
/// Blocks the cpu for at least `duration`.
///
/// For this interface to work, the Executor's clock must be correctly initialized before using it.
/// Blocks for at least `duration`.
pub fn block_for(duration: Duration) {
let expires_at = Instant::now() + duration;
while Instant::now() < expires_at {}

110
embassy/src/time/driver.rs
View file

@ -1,3 +1,60 @@
//! Time driver interface
//!
//! This module defines the interface a driver needs to implement to power the `embassy::time` module.
//!
//! # Implementing a driver
//!
//! - Define a struct `MyDriver`
//! - Implement [`Driver`] for it
//! - Register it as the global driver with [`time_driver_impl`].
//! - Enable the Cargo features `embassy/time` and one of `embassy/time-tick-*` corresponding to the
//! tick rate of your driver.
//!
//! If you wish to make the tick rate configurable by the end user, you should do so by exposing your own
//! Cargo features and having each enable the corresponding `embassy/time-tick-*`.
//!
//! # Linkage details
//!
//! Instead of the usual "trait + generic params" approach, calls from embassy to the driver are done via `extern` functions.
//!
//! `embassy` internally defines the driver functions as `extern "Rust" { fn _embassy_time_now() -> u64; }` and calls them.
//! The driver crate defines the functions as `#[no_mangle] fn _embassy_time_now() -> u64`. The linker will resolve the
//! calls from the `embassy` crate to call into the driver crate.
//!
//! If there is none or multiple drivers in the crate tree, linking will fail.
//!
//! This method has a few key advantages for something as foundational as timekeeping:
//!
//! - The time driver is available everywhere easily, without having to thread the implementation
//! through generic parameters. This is especially helpful for libraries.
//! - It means comparing `Instant`s will always make sense: if there were multiple drivers
//! active, one could compare an `Instant` from driver A to an `Instant` from driver B, which
//! would yield incorrect results.
//!
//! # Example
//!
//! ```
//! use embassy::time::driver::{Driver, AlarmHandle};
//!
//! struct MyDriver{}; // not public!
//! embassy::time_driver_impl!(static DRIVER: MyDriver = MyDriver{});
//!
//! impl Driver for MyDriver {
//! fn now(&self) -> u64 {
//! todo!()
//! }
//! unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
//! todo!()
//! }
//! fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
//! todo!()
//! }
//! fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) {
//! todo!()
//! }
//! }
//! ```
/// Alarm handle, assigned by the driver.
#[derive(Clone, Copy)]
pub struct AlarmHandle {
@ -21,22 +78,22 @@ impl AlarmHandle {
}
/// Time driver
pub trait Driver {
pub trait Driver: Send + Sync + 'static {
/// Return the current timestamp in ticks.
/// This is guaranteed to be monotonic, i.e. a call to now() will always return
/// a greater or equal value than earler calls.
fn now() -> u64;
fn now(&self) -> u64;
/// Try allocating an alarm handle. Returns None if no alarms left.
/// Initially the alarm has no callback set, and a null `ctx` pointer.
///
/// # Safety
/// It is UB to make the alarm fire before setting a callback.
unsafe fn allocate_alarm() -> Option<AlarmHandle>;
unsafe fn allocate_alarm(&self) -> Option<AlarmHandle>;
/// Sets the callback function to be called when the alarm triggers.
/// The callback may be called from any context (interrupt or thread mode).
fn set_alarm_callback(alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ());
fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ());
/// Sets an alarm at the given timestamp. When the current timestamp reaches that
/// timestamp, the provided callback funcion will be called.
@ -44,7 +101,7 @@ pub trait Driver {
/// When callback is called, it is guaranteed that now() will return a value greater or equal than timestamp.
///
/// Only one alarm can be active at a time. This overwrites any previously-set alarm if any.
fn set_alarm(alarm: AlarmHandle, timestamp: u64);
fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64);
}
extern "Rust" {
@ -70,49 +127,34 @@ pub(crate) fn set_alarm(alarm: AlarmHandle, timestamp: u64) {
/// Set the time Driver implementation.
///
/// # Example
///
/// ```
/// struct MyDriver;
/// embassy::time_driver_impl!(MyDriver);
///
/// unsafe impl embassy::time::driver::Driver for MyDriver {
/// fn now() -> u64 {
/// todo!()
/// }
/// unsafe fn allocate_alarm() -> Option<AlarmHandle> {
/// todo!()
/// }
/// fn set_alarm_callback(alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
/// todo!()
/// }
/// fn set_alarm(alarm: AlarmHandle, timestamp: u64) {
/// todo!()
/// }
/// }
///
/// See the module documentation for an example.
#[macro_export]
macro_rules! time_driver_impl {
($t: ty) => {
(static $name:ident: $t: ty = $val:expr) => {
static $name: $t = $val;
#[no_mangle]
fn _embassy_time_now() -> u64 {
<$t as $crate::time::driver::Driver>::now()
<$t as $crate::time::driver::Driver>::now(&$name)
}
#[no_mangle]
unsafe fn _embassy_time_allocate_alarm() -> Option<AlarmHandle> {
<$t as $crate::time::driver::Driver>::allocate_alarm()
unsafe fn _embassy_time_allocate_alarm() -> Option<$crate::time::driver::AlarmHandle> {
<$t as $crate::time::driver::Driver>::allocate_alarm(&$name)
}
#[no_mangle]
fn _embassy_time_set_alarm_callback(
alarm: AlarmHandle,
alarm: $crate::time::driver::AlarmHandle,
callback: fn(*mut ()),
ctx: *mut (),
) {
<$t as $crate::time::driver::Driver>::set_alarm_callback(alarm, callback, ctx)
<$t as $crate::time::driver::Driver>::set_alarm_callback(&$name, alarm, callback, ctx)
}
#[no_mangle]
fn _embassy_time_set_alarm(alarm: AlarmHandle, timestamp: u64) {
<$t as $crate::time::driver::Driver>::set_alarm(alarm, timestamp)
fn _embassy_time_set_alarm(alarm: $crate::time::driver::AlarmHandle, timestamp: u64) {
<$t as $crate::time::driver::Driver>::set_alarm(&$name, alarm, timestamp)
}
};
}

208
embassy/src/time/driver_std.rs Normal file
View file

@ -0,0 +1,208 @@
use atomic_polyfill::{AtomicU8, Ordering};
use std::cell::UnsafeCell;
use std::mem;
use std::mem::MaybeUninit;
use std::sync::{Condvar, Mutex, Once};
use std::time::Duration as StdDuration;
use std::time::Instant as StdInstant;
use std::{ptr, thread};
use crate::time::driver::{AlarmHandle, Driver};
const ALARM_COUNT: usize = 4;
struct AlarmState {
timestamp: u64,
// This is really a Option<(fn(*mut ()), *mut ())>
// but fn pointers aren't allowed in const yet
callback: *const (),
ctx: *mut (),
}
unsafe impl Send for AlarmState {}
impl AlarmState {
const fn new() -> Self {
Self {
timestamp: u64::MAX,
callback: ptr::null(),
ctx: ptr::null_mut(),
}
}
}
struct TimeDriver {
alarm_count: AtomicU8,
once: Once,
alarms: UninitCell<Mutex<[AlarmState; ALARM_COUNT]>>,
zero_instant: UninitCell<StdInstant>,
signaler: UninitCell<Signaler>,
}
const ALARM_NEW: AlarmState = AlarmState::new();
crate::time_driver_impl!(static DRIVER: TimeDriver = TimeDriver {
alarm_count: AtomicU8::new(0),
once: Once::new(),
alarms: UninitCell::uninit(),
zero_instant: UninitCell::uninit(),
signaler: UninitCell::uninit(),
});
impl TimeDriver {
fn init(&self) {
self.once.call_once(|| unsafe {
self.alarms.write(Mutex::new([ALARM_NEW; ALARM_COUNT]));
self.zero_instant.write(StdInstant::now());
self.signaler.write(Signaler::new());
thread::spawn(Self::alarm_thread);
});
}
fn alarm_thread() {
loop {
let now = DRIVER.now();
let mut next_alarm = u64::MAX;
{
let alarms = &mut *unsafe { DRIVER.alarms.as_ref() }.lock().unwrap();
for alarm in alarms {
if alarm.timestamp <= now {
alarm.timestamp = u64::MAX;
// Call after clearing alarm, so the callback can set another alarm.
// safety:
// - we can ignore the possiblity of `f` being unset (null) because of the safety contract of `allocate_alarm`.
// - other than that we only store valid function pointers into alarm.callback
let f: fn(*mut ()) = unsafe { mem::transmute(alarm.callback) };
f(alarm.ctx);
} else {
next_alarm = next_alarm.min(alarm.timestamp);
}
}
}
let until =
unsafe { DRIVER.zero_instant.read() } + StdDuration::from_micros(next_alarm);
unsafe { DRIVER.signaler.as_ref() }.wait_until(until);
}
}
}
impl Driver for TimeDriver {
fn now(&self) -> u64 {
self.init();
let zero = unsafe { self.zero_instant.read() };
StdInstant::now().duration_since(zero).as_micros() as u64
}
unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
let id = self
.alarm_count
.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
if x < ALARM_COUNT as u8 {
Some(x + 1)
} else {
None
}
});
match id {
Ok(id) => Some(AlarmHandle::new(id)),
Err(_) => None,
}
}
fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
self.init();
let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
let alarm = &mut alarms[alarm.id() as usize];
alarm.callback = callback as *const ();
alarm.ctx = ctx;
}
fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) {
self.init();
let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
let alarm = &mut alarms[alarm.id() as usize];
alarm.timestamp = timestamp;
unsafe { self.signaler.as_ref() }.signal();
}
}
struct Signaler {
mutex: Mutex<bool>,
condvar: Condvar,
}
impl Signaler {
fn new() -> Self {
Self {
mutex: Mutex::new(false),
condvar: Condvar::new(),
}
}
fn wait_until(&self, until: StdInstant) {
let mut signaled = self.mutex.lock().unwrap();
while !*signaled {
let now = StdInstant::now();
if now >= until {
break;
}
let dur = until - now;
let (signaled2, timeout) = self.condvar.wait_timeout(signaled, dur).unwrap();
signaled = signaled2;
if timeout.timed_out() {
break;
}
}
*signaled = false;
}
fn signal(&self) {
let mut signaled = self.mutex.lock().unwrap();
*signaled = true;
self.condvar.notify_one();
}
}
pub(crate) struct UninitCell<T>(MaybeUninit<UnsafeCell<T>>);
unsafe impl<T> Send for UninitCell<T> {}
unsafe impl<T> Sync for UninitCell<T> {}
impl<T> UninitCell<T> {
pub const fn uninit() -> Self {
Self(MaybeUninit::uninit())
}
pub unsafe fn as_ptr(&self) -> *const T {
(*self.0.as_ptr()).get()
}
pub unsafe fn as_mut_ptr(&self) -> *mut T {
(*self.0.as_ptr()).get()
}
pub unsafe fn as_ref(&self) -> &T {
&*self.as_ptr()
}
pub unsafe fn write(&self, val: T) {
ptr::write(self.as_mut_ptr(), val)
}
}
impl<T: Copy> UninitCell<T> {
pub unsafe fn read(&self) -> T {
ptr::read(self.as_mut_ptr())
}
}

9
embassy/src/time/duration.rs
View file

@ -11,18 +11,27 @@ pub struct Duration {
}
impl Duration {
/// The smallest value that can be represented by the `Duration` type.
pub const MIN: Duration = Duration { ticks: u64::MIN };
/// The largest value that can be represented by the `Duration` type.
pub const MAX: Duration = Duration { ticks: u64::MAX };
/// Tick count of the `Duration`.
pub const fn as_ticks(&self) -> u64 {
self.ticks
}
/// Convert the `Duration` to seconds, rounding down.
pub const fn as_secs(&self) -> u64 {
self.ticks / TICKS_PER_SECOND
}
/// Convert the `Duration` to milliseconds, rounding down.
pub const fn as_millis(&self) -> u64 {
self.ticks * 1000 / TICKS_PER_SECOND
}
/// Convert the `Duration` to microseconds, rounding down.
pub const fn as_micros(&self) -> u64 {
self.ticks * 1_000_000 / TICKS_PER_SECOND
}

26
embassy/src/time/instant.rs
View file

@ -11,7 +11,9 @@ pub struct Instant {
}
impl Instant {
/// The smallest (earliest) value that can be represented by the `Instant` type.
pub const MIN: Instant = Instant { ticks: u64::MIN };
/// The largest (latest) value that can be represented by the `Instant` type.
pub const MAX: Instant = Instant { ticks: u64::MAX };
/// Returns an Instant representing the current time.
@ -21,39 +23,38 @@ impl Instant {
}
}
/// Instant as clock ticks since MCU start.
/// Create an Instant from a tick count since system boot.
pub const fn from_ticks(ticks: u64) -> Self {
Self { ticks }
}
/// Instant as milliseconds since MCU start.
/// Create an Instant from a millisecond count since system boot.
pub const fn from_millis(millis: u64) -> Self {
Self {
ticks: millis * TICKS_PER_SECOND as u64 / 1000,
ticks: millis * TICKS_PER_SECOND / 1000,
}
}
/// Instant representing seconds since MCU start.
/// Create an Instant from a second count since system boot.
pub const fn from_secs(seconds: u64) -> Self {
Self {
ticks: seconds * TICKS_PER_SECOND as u64,
ticks: seconds * TICKS_PER_SECOND,
}
}
/// Instant as ticks since MCU start.
/// Tick count since system boot.
pub const fn as_ticks(&self) -> u64 {
self.ticks
}
/// Instant as seconds since MCU start.
/// Seconds since system boot.
pub const fn as_secs(&self) -> u64 {
self.ticks / TICKS_PER_SECOND as u64
self.ticks / TICKS_PER_SECOND
}
/// Instant as miliseconds since MCU start.
/// Milliseconds since system boot.
pub const fn as_millis(&self) -> u64 {
self.ticks * 1000 / TICKS_PER_SECOND as u64
self.ticks * 1000 / TICKS_PER_SECOND
}
/// Duration between this Instant and another Instant
@ -92,11 +93,14 @@ impl Instant {
Instant::now() - *self
}
/// Adds one Duration to self, returning a new `Instant` or None in the event of an overflow.
pub fn checked_add(&self, duration: Duration) -> Option<Instant> {
self.ticks
.checked_add(duration.ticks)
.map(|ticks| Instant { ticks })
}
/// Subtracts one Duration to self, returning a new `Instant` or None in the event of an overflow.
pub fn checked_sub(&self, duration: Duration) -> Option<Instant> {
self.ticks
.checked_sub(duration.ticks)

59
embassy/src/time/mod.rs
View file

@ -1,4 +1,44 @@
//! Time abstractions
//! Timekeeping, delays and timeouts.
//!
//! Timekeeping is done with elapsed time since system boot. Time is represented in
//! ticks, where the tick rate is defined by the current driver, usually to match
//! the tick rate of the hardware.
//!
//! Tick counts are 64 bits. At the highest supported tick rate of 1Mhz this supports
//! representing time spans of up to ~584558 years, which is big enough for all practical
//! purposes and allows not having to worry about overflows.
//!
//! [`Instant`] represents a given instant of time (relative to system boot), and [`Duration`]
//! represents the duration of a span of time. They implement the math operations you'd expect,
//! like addition and substraction.
//!
//! # Delays and timeouts
//!
//! [`Timer`] allows performing async delays. [`Ticker`] allows periodic delays without drifting over time.
//!
//! An implementation of the `embedded-hal` delay traits is provided by [`Delay`], for compatibility
//! with libraries from the ecosystem.
//!
//! # Wall-clock time
//!
//! The `time` module deals exclusively with a monotonically increasing tick count.
//! Therefore it has no direct support for wall-clock time ("real life" datetimes
//! like `2021-08-24 13:33:21`).
//!
//! If persistence across reboots is not needed, support can be built on top of
//! `embassy::time` by storing the offset between "seconds elapsed since boot"
//! and "seconds since unix epoch".
//!
//! # Time driver
//!
//! The `time` module is backed by a global "time driver" specified at build time.
//! Only one driver can be active in a program.
//!
//! All methods and structs transparently call into the active driver. This makes it
//! possible for libraries to use `embassy::time` in a driver-agnostic way without
//! requiring generic parameters.
//!
//! For more details, check the [`driver`] module.
mod delay;
pub mod driver;
@ -6,16 +46,27 @@ mod duration;
mod instant;
mod timer;
#[cfg(feature = "std")]
mod driver_std;
pub use delay::{block_for, Delay};
pub use duration::Duration;
pub use instant::Instant;
pub use timer::{with_timeout, Ticker, TimeoutError, Timer};
#[cfg(feature = "time-tick-1000hz")]
pub const TICKS_PER_SECOND: u64 = 1_000;
const TPS: u64 = 1_000;
#[cfg(feature = "time-tick-32768hz")]
pub const TICKS_PER_SECOND: u64 = 32_768;
const TPS: u64 = 32_768;
#[cfg(feature = "time-tick-1mhz")]
pub const TICKS_PER_SECOND: u64 = 1_000_000;
const TPS: u64 = 1_000_000;
/// Ticks per second of the global timebase.
///
/// This value is specified by the `time-tick-*` Cargo features, which
/// should be set by the time driver. Some drivers support a fixed tick rate, others
/// allow you to choose a tick rate with Cargo features of their own. You should not
/// set the `time-tick-*` features for embassy yourself as an end user.
pub const TICKS_PER_SECOND: u64 = TPS;

6
embassy/src/time/timer.rs
View file

@ -6,7 +6,13 @@ use futures::{future::select, future::Either, pin_mut, Stream};
use crate::executor::raw;
use crate::time::{Duration, Instant};
/// Error returned by [`with_timeout`] on timeout.
pub struct TimeoutError;
/// Runs a given future with a timeout.
///
/// If the future completes before the timeout, its output is returned. Otherwise, on timeout,
/// work on the future is stopped (`poll` is no longer called), the future is dropped and `Err(TimeoutError)` is returned.
pub async fn with_timeout<F: Future>(timeout: Duration, fut: F) -> Result<F::Output, TimeoutError> {
let timeout_fut = Timer::after(timeout);
pin_mut!(fut);

3
examples/std/Cargo.toml
View file

@ -5,8 +5,7 @@ name = "embassy-std-examples"
version = "0.1.0"
[dependencies]
embassy = { version = "0.1.0", path = "../../embassy", features = ["log"] }
embassy-std = { version = "0.1.0", path = "../../embassy-std" }
embassy = { version = "0.1.0", path = "../../embassy", features = ["log", "std", "time"] }
embassy-net = { version = "0.1.0", path = "../../embassy-net", features=["std", "log", "medium-ethernet", "tcp", "dhcpv4"] }
smoltcp = { git = "https://github.com/smoltcp-rs/smoltcp", rev="e4241510337e095b9d21136c5f58b2eaa1b78479", default-features = false }

3
examples/std/src/bin/net.rs
View file

@ -2,11 +2,10 @@
#![allow(incomplete_features)]
use clap::{AppSettings, Clap};
use embassy::executor::Spawner;
use embassy::executor::{Executor, Spawner};
use embassy::io::AsyncWriteExt;
use embassy::util::Forever;
use embassy_net::*;
use embassy_std::Executor;
use heapless::Vec;
use log::*;

2
examples/std/src/bin/serial.rs
View file

@ -5,9 +5,9 @@
mod serial_port;
use async_io::Async;
use embassy::executor::Executor;
use embassy::io::AsyncBufReadExt;
use embassy::util::Forever;
use embassy_std::Executor;
use log::*;
use nix::sys::termios;

2
examples/std/src/bin/tick.rs
View file

@ -1,9 +1,9 @@
#![feature(type_alias_impl_trait)]
#![allow(incomplete_features)]
use embassy::executor::Executor;
use embassy::time::{Duration, Timer};
use embassy::util::Forever;
use embassy_std::Executor;
use log::*;
#[embassy::task]