TivaCCriticalRegion

This repository demonstrates how to use cortex_m::interrupt::free to safely access shared data in a critical section on the TI TM4C123GXL LaunchPad using Rust. It is a minimal embedded example that toggles an onboard LED based on a shared flag, set inside a timer interrupt and cleared in the main loop.

Unlike platforms with native atomic support, this example uses Mutex<Cell<bool>> instead of AtomicBool to maintain compatibility with microcontrollers that do not fully support atomic operations in no_std environments.

Features

Runs on TI TM4C123GXL LaunchPad (Cortex-M4F)
Written in safe no_std Rust
Demonstrates safe shared-state access using cortex_m::interrupt::free
Uses a Mutex<Cell<bool>> flag shared between main and interrupt context
Blinks onboard LED when a timer-based flag is set

Requirements

Rust nightly toolchain with support for thumbv7em-none-eabihf
cortex-m and cortex-m-rt crates
Flashing tools like OpenOCD, probe-rs, or LM Flash Programmer
TivaWare and TivaCRustWare HAL

Setup

Add the target:
```
rustup target add thumbv7em-none-eabihf
```

Clone the repository:

git clone https://github.itap.purdue.edu/wang32/TivaCCriticalRegion.git
cd TivaCCriticalRegion

Build the project:
```
cargo build --release
```
Flash to the TM4C123GXL board using your preferred method.

Code Structure

SECONDS_FLAG is a Mutex<Cell<bool>> shared between main and an interrupt handler.
The interrupt handler sets SECONDS_FLAG to true.
The main loop checks and clears SECONDS_FLAG; if set, it toggles the LED.

Example Logic Snippet

interrupt::free(|cs| {
    let flag = SECONDS_FLAG.borrow(cs);
    if flag.get() {
        flag.set(false);
        GREEN_LED.toggle();
    }
});

License

This project is intended for educational and instructional use.

Acknowledgments

Inspired by the Rust embedded community and based on the cortex-m crate's safe interrupt handling patterns.

wang32/TivaCCriticalRegionMutex

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