Remove use of static mut.

1 files changed, 11 insertions, 8 deletions

diff --git a/examples/stm32f4/src/bin/usb_uac_speaker.rs b/examples/stm32f4/src/bin/usb_uac_speaker.rs
index 8d83afd1a..e22e07e63 100644
--- a/examples/stm32f4/src/bin/usb_uac_speaker.rs
+++ b/examples/stm32f4/src/bin/usb_uac_speaker.rs
@@ -1,7 +1,7 @@
 #![no_std]
 #![no_main]
 
-use core::cell::RefCell;
+use core::cell::{Cell, RefCell};
 
 use defmt::{panic, *};
 use embassy_executor::Spawner;
@@ -217,8 +217,8 @@ async fn usb_control_task(control_monitor: speaker::ControlMonitor<'static>) {
 /// This gives an (ideal) counter value of 336.000 for every update of the `FEEDBACK_SIGNAL`.
 #[interrupt]
 fn TIM2() {
-    static mut LAST_TICKS: u32 = 0;
-    static mut FRAME_COUNT: usize = 0;
+    static LAST_TICKS: Mutex<CriticalSectionRawMutex, Cell<u32>> = Mutex::new(Cell::new(0));
+    static FRAME_COUNT: Mutex<CriticalSectionRawMutex, Cell<usize>> = Mutex::new(Cell::new(0));
 
     critical_section::with(|cs| {
         // Read timer counter.
@@ -230,11 +230,14 @@ fn TIM2() {
         if status.ccif(CHANNEL_INDEX) {
             let ticks = timer.ccr(CHANNEL_INDEX).read();
 
-            *FRAME_COUNT += 1;
-            if *FRAME_COUNT >= FEEDBACK_REFRESH_PERIOD.frame_count() {
-                *FRAME_COUNT = 0;
-                FEEDBACK_SIGNAL.signal(ticks.wrapping_sub(*LAST_TICKS));
-                *LAST_TICKS = ticks;
+            let frame_count = FRAME_COUNT.borrow(cs);
+            let last_ticks = LAST_TICKS.borrow(cs);
+
+            frame_count.set(frame_count.get() + 1);
+            if frame_count.get() >= FEEDBACK_REFRESH_PERIOD.frame_count() {
+                frame_count.set(0);
+                FEEDBACK_SIGNAL.signal(ticks.wrapping_sub(last_ticks.get()));
+                last_ticks.set(ticks);
             }
         };