From 91aaea761e5ab6117fb3613d5e0e20308ee65343 Mon Sep 17 00:00:00 2001
From: Dario Nieuwenhuis <dirbaio@dirbaio.net>
Date: Sat, 20 Feb 2021 01:43:10 +0100
Subject: [PATCH] Use Relaxed atomics with fence instead of SeqCst

---
 embassy-nrf/src/rtc.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/embassy-nrf/src/rtc.rs b/embassy-nrf/src/rtc.rs
index 079e9b32..1ddc460e 100644
--- a/embassy-nrf/src/rtc.rs
+++ b/embassy-nrf/src/rtc.rs
@@ -1,6 +1,6 @@
 use core::cell::Cell;
 use core::ops::Deref;
-use core::sync::atomic::{AtomicU32, Ordering};
+use core::sync::atomic::{compiler_fence, AtomicU32, Ordering};
 
 use embassy::time::Clock;
 
@@ -143,7 +143,7 @@ impl<T: Instance> RTC<T> {
 
     fn next_period(&self) {
         interrupt::free(|cs| {
-            let period = self.period.fetch_add(1, Ordering::SeqCst) + 1;
+            let period = self.period.fetch_add(1, Ordering::Relaxed) + 1;
             let t = (period as u64) << 23;
 
             for n in 0..ALARM_COUNT {
@@ -231,7 +231,8 @@ impl<T: Instance> RTC<T> {
 impl<T: Instance> embassy::time::Clock for RTC<T> {
     fn now(&self) -> u64 {
         // `period` MUST be read before `counter`, see comment at the top for details.
-        let period = self.period.load(Ordering::SeqCst);
+        let period = self.period.load(Ordering::Relaxed);
+        compiler_fence(Ordering::Acquire);
         let counter = self.rtc.counter.read().bits();
         calc_now(period, counter)
     }