i-k-bus-board/firmware/lib/KLine/KLineTransport.cpp

// Hardware transport for single-wire automotive buses (K-line family)
// Extracted from IbusEsp32 — all ISR/timer/ring-buffer logic lives here.
// Protocol handlers (IbusHandler, KLineObd2) read/write through this layer.

#include "KLineTransport.h"
#include "driver/uart.h"

KLineTransport::KLineTransport()
    : _serial(nullptr),
      _ledPin(-1),
      _txPin(-1),
      _uartNum(1),
      _rxRing(KLINE_RX_BUFFER_SIZE),
      _txRing(KLINE_TX_BUFFER_SIZE),
      _idleTimer(nullptr),
      _lastRxTransitionUs(0),
      _clearToSend(false),
      _isTransmitting(false),
      _lastTxMs(0) {}

KLineTransport::~KLineTransport() {
    if (_idleTimer) {
        esp_timer_stop(_idleTimer);
        esp_timer_delete(_idleTimer);
    }
}

void KLineTransport::begin(HardwareSerial& serial, int8_t rxPin, int8_t txPin,
                            int8_t ledPin, uint8_t uartNum,
                            const KLineConfig& config) {
    _serial = &serial;
    _ledPin = ledPin;
    _txPin = txPin;
    _uartNum = uartNum;
    _config = config;

    if (_ledPin >= 0) {
        pinMode(_ledPin, OUTPUT);
        digitalWrite(_ledPin, LOW);
    }

    _serial->begin(_config.baud, _config.framing, rxPin, txPin);

    if (_config.txInvert) {
        uart_set_line_inverse((uart_port_t)uartNum, UART_SIGNAL_TXD_INV);
    }

    if (_config.idleTimeoutUs > 0) {
        setupBusIdleDetection(rxPin);
    } else {
        // Master/slave mode — always clear to send (no contention)
        _clearToSend = true;
    }
}

// --- Bus idle detection ---
// On every RX pin transition (bus activity), record timestamp and clear CTS.
// Periodic timer checks whether bus has been quiet for >= idleTimeoutUs.

void KLineTransport::setupBusIdleDetection(int8_t rxPin) {
    _lastRxTransitionUs = (uint32_t)esp_timer_get_time();
    _clearToSend = false;

    pinMode(rxPin, INPUT);
    attachInterruptArg(digitalPinToInterrupt(rxPin), onRxPinChange, this, CHANGE);

    esp_timer_create_args_t args = {};
    args.callback = onIdleTimerCallback;
    args.arg = this;
    args.name = "kline_idle";
    esp_timer_create(&args, &_idleTimer);
    esp_timer_start_periodic(_idleTimer, _config.idleCheckUs);
}

void IRAM_ATTR KLineTransport::onRxPinChange(void* arg) {
    KLineTransport* self = static_cast<KLineTransport*>(arg);
    if (self->_isTransmitting) return;
    self->_lastRxTransitionUs = (uint32_t)esp_timer_get_time();
    self->_clearToSend = false;
}

void KLineTransport::onIdleTimerCallback(void* arg) {
    KLineTransport* self = static_cast<KLineTransport*>(arg);
    if (self->_clearToSend || self->_isTransmitting) return;
    uint32_t elapsed = (uint32_t)esp_timer_get_time() - self->_lastRxTransitionUs;
    if (elapsed >= self->_config.idleTimeoutUs) {
        self->_clearToSend = true;
    }
}

// --- UART drain + RX ring accessors ---

void KLineTransport::drainUart() {
    while (_serial->available()) {
        _rxRing.write(_serial->read());
    }
}

int KLineTransport::rxAvailable() {
    return _rxRing.available();
}

int KLineTransport::rxPeek(int n) {
    return _rxRing.peek(n);
}

void KLineTransport::rxRemove(int n) {
    _rxRing.remove(n);
}

int KLineTransport::rxRead() {
    return _rxRing.read();
}

void KLineTransport::flushRx() {
    uart_flush_input((uart_port_t)_uartNum);
    while (_rxRing.available() > 0) {
        _rxRing.read();
    }
}

// --- LED control ---

void KLineTransport::ledOn() {
    if (_ledPin >= 0) digitalWrite(_ledPin, HIGH);
}

void KLineTransport::ledOff() {
    if (_ledPin >= 0) digitalWrite(_ledPin, LOW);
}

// --- Transmit ---

void KLineTransport::write(const uint8_t* message, uint8_t size) {
    uint8_t totalNeeded = size + 2;  // length prefix + message + checksum
    int freeSpace = _txRing.capacity() - _txRing.available();
    if (freeSpace < totalNeeded) {
#ifdef KLINE_DEBUG
        Serial.println("TX DROP: buffer full");
#endif
        return;
    }

    uint8_t checksum = calculateChecksum(message, size);
    _txRing.write(size + 1);  // total bytes: message + checksum
    for (uint8_t i = 0; i < size; i++) {
        _txRing.write(message[i]);
    }
    _txRing.write(checksum);
}

void KLineTransport::sendRaw(const uint8_t* data, uint8_t len) {
    _isTransmitting = true;
    for (uint8_t i = 0; i < len; i++) {
        _serial->write(data[i]);
    }
    _serial->flush();
    delayMicroseconds(200);

    if (_config.idleTimeoutUs > 0) {
        _lastRxTransitionUs = (uint32_t)esp_timer_get_time();
        _clearToSend = false;
    }
    __asm__ __volatile__("" ::: "memory");
    _isTransmitting = false;
}

void KLineTransport::run() {
    trySend();
}

void KLineTransport::trySend() {
    if (!_clearToSend) return;
    if (_txRing.available() <= 0) return;
    if (millis() - _lastTxMs < _config.packetGapMs) return;
    sendNextPacket();
    _lastTxMs = millis();
}

void KLineTransport::sendNextPacket() {
    if (_txRing.available() <= 0) return;

    int packetLen = _txRing.read();
    if (packetLen <= 0 || packetLen > KLINE_MAX_MSG) {
#ifdef KLINE_DEBUG
        Serial.print("TX CORRUPT len=");
        Serial.println(packetLen);
#endif
        while (_txRing.available() > 0) _txRing.read();
        return;
    }

    if (_txRing.available() < packetLen) {
#ifdef KLINE_DEBUG
        Serial.println("TX UNDERRUN");
#endif
        while (_txRing.available() > 0) _txRing.read();
        return;
    }

    _isTransmitting = true;

    for (int i = 0; i < packetLen; i++) {
        int raw = _txRing.read();
        if (raw < 0) {
#ifdef KLINE_DEBUG
            Serial.println("TX ABORT: underrun");
#endif
            if (_config.idleTimeoutUs > 0) {
                _lastRxTransitionUs = (uint32_t)esp_timer_get_time();
                _clearToSend = false;
            }
            __asm__ __volatile__("" ::: "memory");
            _isTransmitting = false;
            return;
        }
        _serial->write((uint8_t)raw);
    }

    _serial->flush();
    delayMicroseconds(200);

    if (_config.idleTimeoutUs > 0) {
        _lastRxTransitionUs = (uint32_t)esp_timer_get_time();
        _clearToSend = false;
    }
    __asm__ __volatile__("" ::: "memory");
    _isTransmitting = false;
}

// --- Checksum utilities ---

uint8_t KLineTransport::checksumXor(const uint8_t* data, uint8_t length) {
    uint8_t checksum = 0;
    for (uint8_t i = 0; i < length; i++) {
        checksum ^= data[i];
    }
    return checksum;
}

uint8_t KLineTransport::checksumMod256(const uint8_t* data, uint8_t length) {
    uint8_t checksum = 0;
    for (uint8_t i = 0; i < length; i++) {
        checksum += data[i];
    }
    return checksum;
}

uint8_t KLineTransport::calculateChecksum(const uint8_t* data, uint8_t length) const {
    switch (_config.checksumType) {
    case CHECKSUM_MOD256:
        return checksumMod256(data, length);
    case CHECKSUM_XOR:
    default:
        return checksumXor(data, length);
    }
}