soft-serial/src/lib.rs

#![no_std]

use core::marker::PhantomData;

use arduino_hal::{
    delay_us,
    port::{
        mode::{Input, PullUp},
        Pin, PinOps,
    },
};

use avr_device::asm::delay_cycles;

use static_pins::StaticPinOps;

pub type PollResult = Result<(), PollError>;
pub type ReadByteResult = Result<u8, CorruptedData>;
pub type CorruptedData = (u8, u8);

const SERIAL_DELAY: u32 = 4;
const FIRST_HALF_SERIAL_DELAY: u32 = SERIAL_DELAY / 2;
const SECOND_HALF_SERIAL_DELAY: u32 = SERIAL_DELAY - FIRST_HALF_SERIAL_DELAY;

const READING_ADJUST: u32 = 16;
const FIRST_ENTRY_READING: u32 = 30;
const LSB: u8 = 0x01;
const MSB: u8 = 0x80;

pub enum PollError {
    NotFound,
    NotReady,
}

pub struct HalfDuplexSerial<P> {
    _pin: PhantomData<Pin<Input<PullUp>, P>>,
}

impl<P> HalfDuplexSerial<P>
where
    P: PinOps + StaticPinOps,
{
    #[inline]
    pub fn new(_pin: Pin<Input<PullUp>, P>) -> Self {
        Self {
            _pin: PhantomData {},
        }
    }
}

pub trait SoftSerial<P>
where
    P: PinOps + StaticPinOps,
{
    fn poll(&self) -> PollResult;
    fn response(&self);

    fn sync_reciever(&self);
    fn sync_transmitter(&self);

    fn write_byte(&self, data: u8);
    fn read_byte(&self) -> ReadByteResult;

    #[inline]
    fn finish_write(&self) {
        P::into_pull_up_input();
        while P::is_low() {}
    }

    fn write_bytes(&self, transmit_data: &[u8]) {
        for byte in transmit_data {
            self.write_byte(*byte);
            self.sync_transmitter();
        }
    }

    fn read_bytes(&self, recieve_buffer: &mut [u8]) {
        for byte in recieve_buffer {
            if let Ok(data) = self.read_byte() {
                *byte = data;
            }
            self.sync_reciever();
        }
    }
}

impl<P> SoftSerial<P> for HalfDuplexSerial<P>
where
    P: PinOps + StaticPinOps,
{
    fn poll(&self) -> PollResult {
        P::into_output();
        delay_cycles(1);
        P::into_pull_up_input();

        delay_us(SERIAL_DELAY);

        if P::is_low() {
            return PollResult::Err(PollError::NotFound);
        }

        delay_us(SERIAL_DELAY);

        if P::is_high() {
            return PollResult::Err(PollError::NotReady);
        }

        while P::is_low() {}

        PollResult::Ok(())
    }

    fn response(&self) {
        P::into_output_high();

        delay_us(FIRST_HALF_SERIAL_DELAY);

        P::set_low();

        delay_us(SERIAL_DELAY);

        P::into_pull_up_input();
    }

    #[inline(never)]
    fn sync_transmitter(&self) {
        P::into_output();

        delay_us(SERIAL_DELAY);

        P::set_high();
    }

    #[inline(never)]
    fn sync_reciever(&self) {
        while P::is_high() {}

        while P::is_low() {}
    }

    #[inline(never)]
    fn write_byte(&self, data: u8) {
        let (mut data, mut parity_bit) = (data, 0);

        for _ in 0..8 {
            if data & MSB == 0 {
                P::set_high();
                parity_bit ^= 0;
            } else {
                P::set_low();
                parity_bit ^= 1;
            }

            delay_us(SERIAL_DELAY);

            data <<= 1;
        }

        // Hamming code and CRC are very weightful and slow, so I use simple parity check

        if parity_bit == 0 {
            P::set_high();
        } else {
            P::set_low();
        }

        delay_us(SERIAL_DELAY);
    }

    #[inline(never)]
    fn read_byte(&self) -> ReadByteResult {
        let (mut data, mut reciever_parity_bit) = (0, 0);

        delay_cycles(FIRST_ENTRY_READING);
        for _ in 0..8 {
            delay_us(FIRST_HALF_SERIAL_DELAY);

            if P::is_low() {
                data |= 1;
                reciever_parity_bit ^= 1;
            } else {
                data |= 0;
                reciever_parity_bit ^= 0;
            }

            delay_cycles(READING_ADJUST);
            delay_us(SECOND_HALF_SERIAL_DELAY);

            data <<= 1;
        }

        delay_us(FIRST_HALF_SERIAL_DELAY);

        let transmitter_parity_bit = (P::read() >> P::PIN_NUM) & LSB;

        delay_cycles(READING_ADJUST);
        delay_us(SECOND_HALF_SERIAL_DELAY);

        if reciever_parity_bit != transmitter_parity_bit {
            return Err((data, reciever_parity_bit));
        }

        Ok(data)
    }
}