108 lines
2.8 KiB
Rust
108 lines
2.8 KiB
Rust
use defmt::info;
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use embassy_stm32::exti::ExtiInput;
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use embassy_time::{Duration, Timer};
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const START: u8 = 0x7E;
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const STOP: u8 = 0x81;
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const MAX_PAYLOAD: usize = 64;
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fn crc8(crc: u8, byte: u8) -> u8 {
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let mut c = crc ^ byte;
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for _ in 0..8 {
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c = if c & 0x80 != 0 {
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(c << 1) ^ 0x07
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} else {
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c << 1
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};
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}
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c
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}
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async fn sample_byte(pin: &mut ExtiInput<'static>, bit_time: Duration) -> u8 {
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let mut byte = 0u8;
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for _ in 0..8 {
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let bit = if pin.is_high() { 1 } else { 0 };
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byte = (byte << 1) | bit;
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Timer::after(bit_time).await;
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}
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byte
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}
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#[embassy_executor::task]
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pub async fn bit_receive_and_decode(mut pin: ExtiInput<'static>) {
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loop {
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pin.wait_for_falling_edge().await;
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let t1 = embassy_time::Instant::now();
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pin.wait_for_rising_edge().await;
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let bit_time = embassy_time::Instant::now().duration_since(t1);
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Timer::after(bit_time / 2).await;
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let mut start_byte = 0u8;
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for _ in 0..7 {
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let bit = if pin.is_high() { 1 } else { 0 };
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start_byte = (start_byte << 1) | bit;
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Timer::after(bit_time).await;
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}
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if start_byte != START {
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info!("start fail: 0x{:02X}", start_byte);
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continue;
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}
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// len
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let len = sample_byte(&mut pin, bit_time).await;
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if len as usize > MAX_PAYLOAD {
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info!("bad len {}", len);
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continue;
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}
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// payload
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let mut payload = [0u8; MAX_PAYLOAD];
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for i in 0..(len as usize) {
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payload[i] = sample_byte(&mut pin, bit_time).await;
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}
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// crc
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let crc_recv = sample_byte(&mut pin, bit_time).await;
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// parita
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let parity_recv = if pin.is_high() { 1 } else { 0 };
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Timer::after(bit_time).await;
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// stop
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let stop = sample_byte(&mut pin, bit_time).await;
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if stop != STOP {
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info!("bad stop 0x{:02X}", stop);
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continue;
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}
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// verify CRC
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let mut crc_calc = crc8(0, len);
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for i in 0..(len as usize) {
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crc_calc = crc8(crc_calc, payload[i]);
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}
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if crc_calc != crc_recv {
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info!("crc nesedi 0x{:02X} ma byt 0x{:02X}", crc_recv, crc_calc);
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continue;
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}
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// verify parity
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let mut ones = len.count_ones() + crc_recv.count_ones();
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for i in 0..(len as usize) {
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ones += payload[i].count_ones();
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}
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if (ones as u8 & 1) != parity_recv {
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info!("nesedi parita");
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continue;
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}
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if let Ok(s) = core::str::from_utf8(&payload[..len as usize]) {
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info!("RX OK: \"{}\"", s);
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} else {
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info!("RX OK: {} bytes", len);
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}
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}
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}
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