pub fn twodigit(v: u8) -> [u8; 2] {
    let tens = v / 10;
    let ones = v % 10;
    let tens_c = tens + b'0';
    let ones_c = ones + b'0';
    [tens_c, ones_c]
}

pub fn u32_hex(mut v: u32) -> [u8; 8] {
    let mut buf = [0u8; 8];
    for i in (0..8).rev() {
        let num = v & 0b1111;
        v >>= 4;
        if num < 10 {
            buf[i] = b'0' + num as u8;
        } else {
            buf[i] = b'A' + (num as u8 - 10);
        }
    }
    buf
}