# [−] [src] Module cortex_m_quickstart::examples::_0_minimal

Minimal Cortex-M program

When executed this program will hit the breakpoint set in `main`.

All Cortex-M programs need to:

- Contain the `#![no_main]` and `#![no_std]` attributes. Embedded programs don't use the standard Rust `main` interface or the Rust standard (`std`) library.

- Define their entry point using `entry!` macro.

- Define their panicking behavior, i.e. what happens when `panic!` is called. The easiest way to define a panicking behavior is to link to a panic handler crate

- Define the `HardFault` handler using the `exception!` macro. This handler (function) is called when a hard fault exception is raised by the hardware.

- Define a default handler using the `exception!` macro. This function will be used to handle all interrupts and exceptions which have not been assigned a specific handler.

    #![no_main] // <- IMPORTANT!
    #![no_std]

    extern crate cortex_m;

    #[macro_use(entry, exception)]
    extern crate cortex_m_rt as rt;

    // makes `panic!` print messages to the host stderr using semihosting
    extern crate panic_semihosting;

    use cortex_m::asm;
    use rt::ExceptionFrame;

    // the program entry point is ...
    entry!(main);

    // ... this never ending function
    fn main() -> ! {
        loop {
            asm::bkpt();
        }
    }

    // define the hard fault handler
    exception!(HardFault, hard_fault);

    fn hard_fault(ef: &ExceptionFrame) -> ! {
        panic!("HardFault at {:#?}", ef);
    }

    // define the default exception handler
    exception!(*, default_handler);

    fn default_handler(irqn: i16) {
        panic!("Unhandled exception (IRQn = {})", irqn);
    }

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