panic.pio

.program panic

set pindirs, 1

pull block
out y, 32

.wrap_target
    mov x, y
    set pins, 1
loop_on:
    jmp x--, loop_on
    mov x, y
    set pins, 0
loop_off:
    jmp x--, loop_off
.wrap

panic_handler.rs

use core::panic::PanicInfo;
use pio_proc::pio_file;
use rp_pico::hal::{
    pac::Peripherals,
    pio::{PIOBuilder, PIOExt},
};

// Our panic handler LED lives on Gpio22
pub const PANIC_PIN: u8 = 22;

#[inline(never)]
#[panic_handler]
fn custom_panic(_info: &PanicInfo) -> ! {
    let program = pio_file!(
        "pio/panic.pio",
        select_program("panic")
    );

    let mut pac = unsafe { Peripherals::steal() };
    let (mut pio, sm0, _sm1, _sm2, _sm3) = pac.PIO0.split(&mut pac.RESETS);
    let installed = pio.install(&program.program).unwrap();
    let (sm, _rx, mut tx) = PIOBuilder::from_program(installed)
        .set_pins(PANIC_PIN, 1)
        .clock_divisor(0f32)
        .build(sm0);

    tx.write(1024);
    sm.start();

    loop {
        cortex_m::asm::nop();
    }
}