replace static muts with mutexes

hifive1/CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
+- Replace static muts with Mutexes
 - Apply clippy changes
 - Bump MSRV to 1.72
 - Adapt to new Cargo workspace

hifive1/Cargo.toml

@@ -11,6 +11,7 @@ edition = "2021"
 rust-version = "1.72"
 
 [dependencies]
+critical-section = { version = "1.1.3" }
 e310x-hal = { path = "../e310x-hal", version = "0.11.0" }
 embedded-hal = "0.2.7"
 riscv = "0.10.1"

hifive1/src/stdout.rs

@@ -1,6 +1,7 @@
 //! Stdout based on the UART hooked up to FTDI or J-Link
 
-use core::fmt;
+use core::{cell::RefCell, fmt};
+use critical_section::Mutex;
 use e310x_hal::{
     clock::Clocks,
     e310x::Uart0,
@@ -10,12 +11,11 @@ use e310x_hal::{
     time::Bps,
 };
 use nb::block;
-use riscv::interrupt;
-
-static mut STDOUT: Option<SerialWrapper> = None;
 
 struct SerialWrapper(Tx<Uart0>);
 
+static STDOUT: Mutex<RefCell<Option<SerialWrapper>>> = Mutex::new(RefCell::new(None));
+
 impl core::fmt::Write for SerialWrapper {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         for byte in s.as_bytes() {
@@ -50,28 +50,27 @@ pub fn configure<X, Y>(
     let serial = Serial::new(uart, (tx, rx), baud_rate, clocks);
     let (tx, rx) = serial.split();
 
-    interrupt::free(|| unsafe {
-        STDOUT.replace(SerialWrapper(tx));
-    });
+    critical_section::with(|cs| STDOUT.borrow(cs).replace(Some(SerialWrapper(tx))));
+
     rx
 }
 
 /// Writes string to stdout
 pub fn write_str(s: &str) {
-    interrupt::free(|| unsafe {
-        if let Some(stdout) = STDOUT.as_mut() {
+    critical_section::with(|cs| {
+        if let Some(stdout) = STDOUT.borrow(cs).borrow_mut().as_mut() {
             let _ = stdout.write_str(s);
         }
-    })
+    });
 }
 
 /// Writes formatted string to stdout
 pub fn write_fmt(args: fmt::Arguments) {
-    interrupt::free(|| unsafe {
-        if let Some(stdout) = STDOUT.as_mut() {
+    critical_section::with(|cs| {
+        if let Some(stdout) = STDOUT.borrow(cs).borrow_mut().as_mut() {
             let _ = stdout.write_fmt(args);
         }
-    })
+    });
 }
 
 /// Macro for printing to the serial standard output