blink.zig


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const std = @import("std");

const DDRB = @as(*volatile u8, @ptrFromInt(0x24));
const PORTB = @as(*volatile u8, @ptrFromInt(0x25));

const DELAY = 100;

pub export fn delay(n: u32) void {
    var i: u32 = 0;
    while (i < n) : (i += 1) {
        asm volatile ("nop" ::: "memory");
    }
}

pub export fn blink(n: u32) void {
    var i: u32 = 0;
    DDRB.* = DDRB.* | (1 << 5);

    while (i < n) : (i += 1) {
        // Toggle PB5
        PORTB.* ^= @as(u8, 1 << 5);
        delay(100_000);
        PORTB.* ^= @as(u8, 1 << 5);
        delay(200_000);
    }
}

pub export fn collatz(na: u32) u32 {
    var n: u32 = na;
    var c: u32 = 0;

    while (n > 1) : (c += 1) {
        if (n % 2 == 0) {
            n /= 2;
        } else {
            n = n + n + n + 1;
        }
    }

    return c;
}

pub export fn main() void {
    var i: u32 = 0;
    while (true) : (i += 1) {
        const c = collatz(i);
        blink(c);
        delay(500_000);
    }
}

pub export fn abort() void {
    // Set PB5 (pin 13) as output
    DDRB.* = DDRB.* | (1 << 5);

    while (true) {
        // Toggle PB5
        PORTB.* ^= @as(u8, 1 << 5);

        // Simple delay
        var i: usize = 0;
        while (i < DELAY) : (i += 1) {
            asm volatile ("nop" ::: "memory");
        }
    }
}