Module cortex_m_quickstart::examples::_5_exception

Overriding an exception handler

You can override an exception handler using the exception! macro.

---

#![deny(unsafe_code)]
#![no_main]
#![no_std]

extern crate cortex_m;
#[macro_use]
extern crate cortex_m_rt as rt;
extern crate cortex_m_semihosting as sh;
extern crate panic_semihosting;

use core::fmt::Write;

use cortex_m::peripheral::syst::SystClkSource;
use cortex_m::Peripherals;
use rt::ExceptionFrame;
use sh::hio::{self, HStdout};

entry!(main);

fn main() -> ! {
    let p = Peripherals::take().unwrap();
    let mut syst = p.SYST;

    // configures the system timer to trigger a SysTick exception every second
    syst.set_clock_source(SystClkSource::Core);
    syst.set_reload(8_000_000); // period = 1s
    syst.enable_counter();
    syst.enable_interrupt();

    loop {}
}

// try commenting out this line: you'll end in `default_handler` instead of in `sys_tick`
exception!(SysTick, sys_tick, state: Option<HStdout> = None);

fn sys_tick(state: &mut Option<HStdout>) {
    if state.is_none() {
        *state = Some(hio::hstdout().unwrap());
    }

    if let Some(hstdout) = state.as_mut() {
        hstdout.write_str(".").unwrap();
    }
}

exception!(HardFault, hard_fault);

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

exception!(*, default_handler);

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