bare0.rs

//! bare0.rs
//!
//! Simple bare metal application
//! What it covers:
//! - constants
//! - global (static) variables
//! - checked vs. wrapping arithmetics
//! - safe and unsafe code
//! - making a safe API
//! - assertions
//! - panic handling

// build without the Rust standard library
#![no_std]
// no standard main, we declare main using [entry]
#![no_main]

// Minimal runtime / startup for Cortex-M microcontrollers
//extern crate cortex_m_rt as rt;
// Panic handler, for textual output using semihosting
extern crate panic_semihosting;
// Panic handler, infinite loop on panic
// extern crate panic_halt;

// import entry point
use cortex_m_rt::entry;

// a constant (cannot be changed at run-time)
const X_INIT: u32 = 10;
//const X_INIT: u32 = core::u32::MAX;

// global mutable variables (changed using unsafe code)
static mut X: u32 = X_INIT;
static mut Y: u32 = 0;

#[entry]
fn main() -> ! {
    // local mutable variable (changed in safe code)
    let mut x = unsafe { X };

    loop {
        x += 1; // <- place breakpoint here (3)
        unsafe {
            X += 1;
            Y = X;
            assert!(x == X && X == Y);
        }
    }
}

// Here we assume you are using `vscode` with `cortex-debug`.
//
// 0. Compile/build the example in debug (dev) mode.
//
//    > cargo build --example bare0
//    (or use the vscode build task)
//
// 1. Run the program in the debugger, let the program run for a while and
//    then press pause.
//
//    Look under Variables/Local what do you find.
//
//    ** your answer here **
//
//    In the Expressions (WATCH -vscode) view add X and Y
//    what do you find
//
//    ** your answer here **
//
//    Step through one complete iteration of the loop