Understanding Borrowing and Peripheral Access in Rust

The Rust programming language has unique ways of managing memory safety, especially when dealing with hardware peripherals in embedded systems. This section of the Rust Embedded Book focuses on borrowing concepts and how they apply to peripheral access.

Key Concepts

1. Borrowing in Rust

• Borrowing allows a function to use a variable without taking ownership of it.
• Rust enforces strict rules about how data can be accessed through borrowing, which prevents data races and ensures memory safety.

2. Mutable and Immutable Borrows

• Immutable Borrow (&T): Multiple parts of code can read data simultaneously.
• Mutable Borrow (&mut T): Only one part of code can modify data at a time, ensuring no other access occurs during modification.

3. Peripherals as Shared Resources

• In embedded systems, peripherals (like GPIO pins, timers, etc.) are shared resources that need careful access management.
• Rust’s borrowing rules help coordinate access to these peripherals, ensuring that only one piece of code can modify a peripheral at any time.

Common Scenarios

Example 1: Accessing a Peripheral

• When you borrow a peripheral (e.g., a timer), you must declare whether it will be borrowed mutably or immutably.
• If you mutably borrow a peripheral, you cannot immutably borrow it elsewhere until the mutable borrow goes out of scope.

Example 2: Borrowing Restrictions

• If a function takes a mutable reference to a peripheral, no other function can access that peripheral until the mutable reference is dropped.

fn use_timer(timer: &mut Timer) {
    timer.start(); // Mutable borrow
    // Cannot access timer here immutably
} // Mutable borrow ends here

Conclusion

Understanding borrowing in Rust is crucial for safely managing peripheral access in embedded systems. By adhering to Rust's borrowing rules, developers can ensure that their code is both safe and efficient, preventing potential issues that could arise from concurrent access to shared resources.