Rewrite time driver (#2559)

* Rewrite time driver

* Don't store priority

* Changelog

* Fix doc example

* Use separate locks for Alarms

* Mention generic queues

* Cache the next wakeup timestamp

* Immediately repoll if timestamp is in the past

* Add benchmark

* Remove equality check for now

* Enable interrupts when allocating the alarm

* Clean up

* Use relaxed ordering

* wut

* Typo

* Move benchmar

* fmt

.cargo/config.toml

@@ -1,3 +1,4 @@
 [alias]
 xtask = "run --package xtask --"
 xfmt = "xtask fmt-packages"
+qa = "xtask run-example qa-test"

esp-hal-embassy/CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - Reduce memory footprint by 4 bytes on multi-core MCUs.
+- The time driver no longer uses cross-core critical sections. (#2559)
 
 ### Fixed
 

esp-hal-embassy/src/executor/thread.rs

@@ -30,7 +30,7 @@ pub(crate) fn pend_thread_mode(_core: usize) {
     #[cfg(low_power_wait)]
     {
         // Signal that there is work to be done.
-        SIGNAL_WORK_THREAD_MODE[_core].store(true, Ordering::SeqCst);
+        SIGNAL_WORK_THREAD_MODE[_core].store(true, Ordering::Relaxed);
 
         // If we are pending a task on the current core, we're done. Otherwise, we
         // need to make sure the other core wakes up.
@@ -123,7 +123,8 @@ This will use software-interrupt 3 which isn't available for anything else to wa
 
         // we do not care about race conditions between the load and store operations,
         // interrupts will only set this value to true.
-        if SIGNAL_WORK_THREAD_MODE[cpu].load(Ordering::SeqCst) {
+        // Acquire makes no sense but at this time it's slightly faster than Relaxed.
+        if SIGNAL_WORK_THREAD_MODE[cpu].load(Ordering::Acquire) {
             // if there is work to do, exit critical section and loop back to polling
             unsafe {
                 core::arch::asm!(
@@ -140,7 +141,7 @@ This will use software-interrupt 3 which isn't available for anything else to wa
             unsafe { core::arch::asm!("waiti 0") };
         }
         // If this races and some waker sets the signal, we'll reset it, but still poll.
-        SIGNAL_WORK_THREAD_MODE[cpu].store(false, Ordering::SeqCst);
+        SIGNAL_WORK_THREAD_MODE[cpu].store(false, Ordering::Relaxed);
     }
 
     #[cfg(all(riscv, low_power_wait))]
@@ -149,14 +150,14 @@ This will use software-interrupt 3 which isn't available for anything else to wa
         // interrupts will only set this value to true.
         critical_section::with(|_| {
             // if there is work to do, loop back to polling
-            if !SIGNAL_WORK_THREAD_MODE[cpu].load(Ordering::SeqCst) {
+            if !SIGNAL_WORK_THREAD_MODE[cpu].load(Ordering::Relaxed) {
                 // if not, wait for interrupt
                 unsafe { core::arch::asm!("wfi") };
             }
         });
         // if an interrupt occurred while waiting, it will be serviced here
         // If this races and some waker sets the signal, we'll reset it, but still poll.
-        SIGNAL_WORK_THREAD_MODE[cpu].store(false, Ordering::SeqCst);
+        SIGNAL_WORK_THREAD_MODE[cpu].store(false, Ordering::Relaxed);
     }
 }
 

esp-hal-embassy/src/lib.rs

@@ -146,7 +146,7 @@ impl_array!(4);
 ///
 /// ```rust, no_run
 #[doc = esp_hal::before_snippet!()]
-/// use esp_hal::timg::TimerGroup;
+/// use esp_hal::timer::timg::TimerGroup;
 ///
 /// let timg0 = TimerGroup::new(peripherals.TIMG0);
 /// esp_hal_embassy::init(timg0.timer0);