ardupilot/libraries/AP_CANManager/AP_SLCANIface.cpp

/*
 * This file is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This file is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Author: Siddharth Bharat Purohit
 * Referenced from implementation by Pavel Kirienko <pavel.kirienko@zubax.com>
 * for Zubax Babel
 */

#include "AP_SLCANIface.h"

#if HAL_MAX_CAN_PROTOCOL_DRIVERS
#include <AP_HAL/AP_HAL.h>
#include <AP_Common/AP_Common.h>

#include "AP_CANManager.h"

#include <AP_SerialManager/AP_SerialManager.h>
#include <stdio.h>
#include <AP_Vehicle/AP_Vehicle.h>

#define LOG_TAG "SLCAN"

extern const AP_HAL::HAL& hal;

const AP_Param::GroupInfo SLCAN::CANIface::var_info[] = {
    // @Param: CPORT
    // @DisplayName: SLCAN Route
    // @Description: CAN Interface ID to be routed to SLCAN, 0 means no routing
    // @Values: 0:Disabled,1:First interface,2:Second interface
    // @User: Standard
    // @RebootRequired: True
    AP_GROUPINFO("CPORT", 1, SLCAN::CANIface, _slcan_can_port, 0),

    // @Param: SERNUM
    // @DisplayName: SLCAN Serial Port
    // @Description: Serial Port ID to be used for temporary SLCAN iface, -1 means no temporary serial. This parameter is automatically reset on reboot or on timeout. See CAN_SLCAN_TIMOUT for timeout details
    // @Values: -1:Disabled,0:Serial0,1:Serial1,2:Serial2,3:Serial3,4:Serial4,5:Serial5,6:Serial6
    // @User: Standard
    AP_GROUPINFO("SERNUM", 2, SLCAN::CANIface, _slcan_ser_port, -1),

    // @Param: TIMOUT
    // @DisplayName: SLCAN Timeout
    // @Description: Duration of inactivity after which SLCAN is switched back to original driver in seconds.
    // @Range: 0 127
    // @User: Standard
    AP_GROUPINFO("TIMOUT", 3, SLCAN::CANIface, _slcan_timeout, 0),

    // @Param: SDELAY
    // @DisplayName: SLCAN Start Delay
    // @Description: Duration after which slcan starts after setting SERNUM in seconds.
    // @Range: 0 127
    // @User: Standard
    AP_GROUPINFO("SDELAY", 4, SLCAN::CANIface, _slcan_start_delay, 1),

    AP_GROUPEND
};

////////Helper Methods//////////

static bool hex2nibble_error;

static uint8_t nibble2hex(uint8_t x)
{
    // Allocating in RAM because it's faster
    static uint8_t ConversionTable[] = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
    };
    return ConversionTable[x & 0x0F];
}

static uint8_t hex2nibble(char c)
{
    // Must go into RAM, not flash, because flash is slow
    static uint8_t NumConversionTable[] = {
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9
    };

    static uint8_t AlphaConversionTable[] = {
        10, 11, 12, 13, 14, 15
    };

    uint8_t out = 255;

    if (c >= '0' && c <= '9') {
        out = NumConversionTable[int(c) - int('0')];
    } else if (c >= 'a' && c <= 'f') {
        out = AlphaConversionTable[int(c) - int('a')];
    } else if (c >= 'A' && c <= 'F') {
        out = AlphaConversionTable[int(c) - int('A')];
    }

    if (out == 255) {
        hex2nibble_error = true;
    }
    return out;
}

bool SLCAN::CANIface::push_Frame(AP_HAL::CANFrame &frame)
{
    AP_HAL::CANIface::CanRxItem frm;
    frm.frame = frame;
    frm.flags = 0;
    frm.timestamp_us = AP_HAL::native_micros64();
    return add_to_rx_queue(frm);
}

/**
 * General frame format:
 *  <type> <id> <dlc> <data>
 * The emitting functions below are highly optimized for speed.
 */
bool SLCAN::CANIface::handle_FrameDataExt(const char* cmd, bool canfd)
{
    AP_HAL::CANFrame f {};
    hex2nibble_error = false;
    f.canfd = canfd;
    f.id = f.FlagEFF |
           (hex2nibble(cmd[1]) << 28) |
           (hex2nibble(cmd[2]) << 24) |
           (hex2nibble(cmd[3]) << 20) |
           (hex2nibble(cmd[4]) << 16) |
           (hex2nibble(cmd[5]) << 12) |
           (hex2nibble(cmd[6]) <<  8) |
           (hex2nibble(cmd[7]) <<  4) |
           (hex2nibble(cmd[8]) <<  0);
    f.dlc = hex2nibble(cmd[9]);
    if (hex2nibble_error || f.dlc > (canfd?15:8)) {
        return false;
    }
    {
        const char* p = &cmd[10];
        const uint8_t dlen = AP_HAL::CANFrame::dlcToDataLength(f.dlc);
        for (unsigned i = 0; i < dlen; i++) {
            f.data[i] = (hex2nibble(*p) << 4) | hex2nibble(*(p + 1));
            p += 2;
        }
    }
    if (hex2nibble_error) {
        return false;
    }
    return push_Frame(f);
}

/**
 * General frame format:
 *  <type> <id> <dlc> <data>
 * The emitting functions below are highly optimized for speed.
 */
bool SLCAN::CANIface::handle_FDFrameDataExt(const char* cmd)
{
#if HAL_CANFD_SUPPORTED
    return false;
#else
    AP_HAL::CANFrame f {};
    hex2nibble_error = false;
    f.canfd = true;
    f.id = f.FlagEFF |
           (hex2nibble(cmd[1]) << 28) |
           (hex2nibble(cmd[2]) << 24) |
           (hex2nibble(cmd[3]) << 20) |
           (hex2nibble(cmd[4]) << 16) |
           (hex2nibble(cmd[5]) << 12) |
           (hex2nibble(cmd[6]) <<  8) |
           (hex2nibble(cmd[7]) <<  4) |
           (hex2nibble(cmd[8]) <<  0);
    f.dlc = hex2nibble(cmd[9]);
    if (f.dlc > AP_HAL::CANFrame::dataLengthToDlc(AP_HAL::CANFrame::MaxDataLen)) {
        return false;
    }
    {
        const char* p = &cmd[10];
        for (unsigned i = 0; i < AP_HAL::CANFrame::dlcToDataLength(f.dlc); i++) {
            f.data[i] = (hex2nibble(*p) << 4) | hex2nibble(*(p + 1));
            p += 2;
        }
    }
    if (hex2nibble_error) {
        return false;
    }
    return push_Frame(f);
#endif //#if HAL_CANFD_SUPPORTED
}

bool SLCAN::CANIface::handle_FrameDataStd(const char* cmd)
{
    AP_HAL::CANFrame f {};
    hex2nibble_error = false;
    f.id = (hex2nibble(cmd[1]) << 8) |
           (hex2nibble(cmd[2]) << 4) |
           (hex2nibble(cmd[3]) << 0);
    if (cmd[4] < '0' || cmd[4] > ('0' + AP_HAL::CANFrame::NonFDCANMaxDataLen)) {
        return false;
    }
    f.dlc = cmd[4] - '0';
    if (f.dlc > AP_HAL::CANFrame::NonFDCANMaxDataLen) {
        return false;
    }
    {
        const char* p = &cmd[5];
        for (unsigned i = 0; i < f.dlc; i++) {
            f.data[i] = (hex2nibble(*p) << 4) | hex2nibble(*(p + 1));
            p += 2;
        }
    }
    if (hex2nibble_error) {
        return false;
    }
    return push_Frame(f);
}

bool SLCAN::CANIface::handle_FrameRTRExt(const char* cmd)
{
    AP_HAL::CANFrame f {};
    hex2nibble_error = false;
    f.id = f.FlagEFF | f.FlagRTR |
           (hex2nibble(cmd[1]) << 28) |
           (hex2nibble(cmd[2]) << 24) |
           (hex2nibble(cmd[3]) << 20) |
           (hex2nibble(cmd[4]) << 16) |
           (hex2nibble(cmd[5]) << 12) |
           (hex2nibble(cmd[6]) <<  8) |
           (hex2nibble(cmd[7]) <<  4) |
           (hex2nibble(cmd[8]) <<  0);
    if (cmd[9] < '0' || cmd[9] > ('0' + AP_HAL::CANFrame::NonFDCANMaxDataLen)) {
        return false;
    }
    f.dlc = cmd[9] - '0';

    if (f.dlc > AP_HAL::CANFrame::NonFDCANMaxDataLen) {
        return false;
    }
    if (hex2nibble_error) {
        return false;
    }
    return push_Frame(f);
}

bool SLCAN::CANIface::handle_FrameRTRStd(const char* cmd)
{
    AP_HAL::CANFrame f {};
    hex2nibble_error = false;
    f.id = f.FlagRTR |
           (hex2nibble(cmd[1]) << 8) |
           (hex2nibble(cmd[2]) << 4) |
           (hex2nibble(cmd[3]) << 0);
    if (cmd[4] < '0' || cmd[4] > ('0' + AP_HAL::CANFrame::NonFDCANMaxDataLen)) {
        return false;
    }
    f.dlc = cmd[4] - '0';
    if (f.dlc <= AP_HAL::CANFrame::NonFDCANMaxDataLen) {
        return false;
    }
    if (hex2nibble_error) {
        return false;
    }
    return push_Frame(f);
}

static inline const char* getASCIIStatusCode(bool status)
{
    return status ? "\r" : "\a";
}

bool SLCAN::CANIface::init_passthrough(uint8_t i)
{
    // we setup undelying can iface here which we use for passthrough
    if (initialized_ ||
        _slcan_can_port <= 0 ||
        _slcan_can_port != i+1) {
        return false;
    }

    _can_iface = hal.can[i];
    _iface_num = _slcan_can_port - 1;
    _prev_ser_port = -1;
#if HAL_CANMANAGER_ENABLED
    AP::can().log_text(AP_CANManager::LOG_INFO, LOG_TAG, "Setting SLCAN Passthrough for CAN%d\n", _slcan_can_port - 1);
#endif
    return true;
}

/**
 * General frame format:
 *  <type> <id> <dlc> <data> [timestamp msec] [flags]
 * Types:
 *  R - RTR extended
 *  r - RTR standard
 *  T - Data extended
 *  t - Data standard
 * Flags:
 *  L - this frame is a loopback frame; timestamp field contains TX timestamp
 */
int16_t SLCAN::CANIface::reportFrame(const AP_HAL::CANFrame& frame, uint64_t timestamp_usec)
{
    if (_port == nullptr) {
        return -1;
    }
#if HAL_CANFD_SUPPORTED
    constexpr unsigned SLCANMaxFrameSize = 200;
#else
    constexpr unsigned SLCANMaxFrameSize = 40;
#endif
    uint8_t buffer[SLCANMaxFrameSize] = {'\0'};
    uint8_t* p = &buffer[0];
    /*
    * Frame type
    */
    if (frame.isRemoteTransmissionRequest()) {
        *p++ = frame.isExtended() ? 'R' : 'r';
    } else if (frame.isErrorFrame()) {
        return -1;     // Not supported
    }
#if HAL_CANFD_SUPPORTED
    else if (frame.canfd) {
        *p++ = frame.isExtended() ? 'D' : 'd';
    }
#endif 
    else {
        *p++ = frame.isExtended() ? 'T' : 't';
    }

    /*
    * ID
    */
    {
        const uint32_t id = frame.id & frame.MaskExtID;
        if (frame.isExtended()) {
            *p++ = nibble2hex(id >> 28);
            *p++ = nibble2hex(id >> 24);
            *p++ = nibble2hex(id >> 20);
            *p++ = nibble2hex(id >> 16);
            *p++ = nibble2hex(id >> 12);
        }
        *p++ = nibble2hex(id >> 8);
        *p++ = nibble2hex(id >> 4);
        *p++ = nibble2hex(id >> 0);
    }

    /*
    * DLC
    */
    *p++ = nibble2hex(frame.dlc);

    /*
    * Data
    */
    for (unsigned i = 0; i < AP_HAL::CANFrame::dlcToDataLength(frame.dlc); i++) {
        const uint8_t byte = frame.data[i];
        *p++ = nibble2hex(byte >> 4);
        *p++ = nibble2hex(byte);
    }

    /*
    * Timestamp
    */
    {
        // SLCAN format - [0, 60000) milliseconds
        const auto slcan_timestamp = uint16_t(timestamp_usec / 1000U);
        *p++ = nibble2hex(slcan_timestamp >> 12);
        *p++ = nibble2hex(slcan_timestamp >> 8);
        *p++ = nibble2hex(slcan_timestamp >> 4);
        *p++ = nibble2hex(slcan_timestamp >> 0);
    }

    /*
    * Finalization
    */
    *p++ = '\r';
    const auto frame_size = unsigned(p - &buffer[0]);

    if (_port->txspace() < frame_size) {
        return 0;
    }
    //Write to Serial
    if (!_port->write_locked(&buffer[0], frame_size, _serial_lock_key)) {
        return 0;
    }
    return 1;
}

//Accepts command string, returns response string or nullptr if no response is needed.
const char* SLCAN::CANIface::processCommand(char* cmd)
{

    if (_port == nullptr) {
        return nullptr;
    }

    /*
    * High-traffic SLCAN commands go first
    */
    if (cmd[0] == 'T' || cmd[0] == 'D') {
        return handle_FrameDataExt(cmd, cmd[0]=='D') ? "Z\r" : "\a";
    } else if (cmd[0] == 't') {
        return handle_FrameDataStd(cmd) ? "z\r" : "\a";
    } else if (cmd[0] == 'R') {
        return handle_FrameRTRExt(cmd) ? "Z\r" : "\a";
    } else if (cmd[0] == 'r' && cmd[1] <= '9') { // The second condition is needed to avoid greedy matching
        // See long commands below
        return handle_FrameRTRStd(cmd) ? "z\r" : "\a";
    }
#if HAL_CANFD_SUPPORTED 
    else if (cmd[0] == 'D') {
        return handle_FDFrameDataExt(cmd) ? "Z\r" : "\a";
    }
#endif

    uint8_t resp_bytes[40];
    uint16_t resp_len;
    /*
    * Regular SLCAN commands
    */
    switch (cmd[0]) {
    case 'S':               // Set CAN bitrate
    case 'O':               // Open CAN in normal mode
    case 'L':               // Open CAN in listen-only mode
    case 'l':               // Open CAN with loopback enabled
    case 'C':               // Close CAN
    case 'M':               // Set CAN acceptance filter ID
    case 'm':               // Set CAN acceptance filter mask
    case 'U':               // Set UART baud rate, see http://www.can232.com/docs/can232_v3.pdf
    case 'Z': {             // Enable/disable RX and loopback timestamping
        return getASCIIStatusCode(true);    // Returning success for compatibility reasons
    }
    case 'F': {             // Get status flags
        resp_len = snprintf((char*)resp_bytes, sizeof(resp_bytes), "F%02X\r", unsigned(0));    // Returning success for compatibility reasons
        if (resp_len > 0) {
            _port->write_locked(resp_bytes, resp_len, _serial_lock_key);
        }
        return nullptr;
    }
    case 'V': {             // HW/SW version
        resp_len = snprintf((char*)resp_bytes, sizeof(resp_bytes),"V%x%x%x%x\r", 1, 0, 1, 0);
        if (resp_len > 0) {
            _port->write_locked(resp_bytes, resp_len, _serial_lock_key);
        }
        return nullptr;
    }
    case 'N': {             // Serial number
        const uint8_t uid_buf_len = 12;
        uint8_t uid_len = uid_buf_len;
        uint8_t unique_id[uid_buf_len];
        char buf[uid_buf_len * 2 + 1] = {'\0'};
        char* pos = &buf[0];
        if (hal.util->get_system_id_unformatted(unique_id, uid_len)) {
            for (uint8_t i = 0; i < uid_buf_len; i++) {
                *pos++ = nibble2hex(unique_id[i] >> 4);
                *pos++ = nibble2hex(unique_id[i]);
            }
        }
        *pos++ = '\0';
        resp_len = snprintf((char*)resp_bytes, sizeof(resp_bytes),"N%s\r", &buf[0]);
        if (resp_len > 0) {
            _port->write_locked(resp_bytes, resp_len, _serial_lock_key);
        }
        return nullptr;
    }
    default: {
        break;
    }
    }

    return getASCIIStatusCode(false);
}

// add bytes to parse the received SLCAN Data stream
inline void SLCAN::CANIface::addByte(const uint8_t byte)
{
    if (_port == nullptr) {
        return;
    }
    if ((byte >= 32 && byte <= 126)) {  // Normal printable ASCII character
        if (pos_ < SLCAN_BUFFER_SIZE) {
            buf_[pos_] = char(byte);
            pos_ += 1;
        } else {
            pos_ = 0;   // Buffer overrun; silently drop the data
        }
    } else if (byte == '\r') {  // End of command (SLCAN)

        // Processing the command
        buf_[pos_] = '\0';
        const char* const response = processCommand(reinterpret_cast<char*>(&buf_[0]));
        pos_ = 0;

        // Sending the response if provided
        if (response != nullptr) {

            _port->write_locked(reinterpret_cast<const uint8_t*>(response),
                                strlen(response), _serial_lock_key);
        }
    } else if (byte == 8 || byte == 127) {  // DEL or BS (backspace)
        if (pos_ > 0) {
            pos_ -= 1;
        }
    } else {    // This also includes Ctrl+C, Ctrl+D
        pos_ = 0;   // Invalid byte - drop the current command
    }
}

void SLCAN::CANIface::update_slcan_port()
{
    if (_set_by_sermgr) {
        // Once we pick SerialManager path we hold on 
        // to that until reboot
        return;
    }
    if (_port == nullptr) {
         _port = AP::serialmanager().find_serial(AP_SerialManager::SerialProtocol_SLCAN, 0);
        if (_port != nullptr) {
            _port->lock_port(_serial_lock_key, _serial_lock_key);
            _set_by_sermgr = true;
            return;
        }
    }
    if (_prev_ser_port != _slcan_ser_port) {
        if (!_slcan_start_req) {
            _slcan_start_req_time = AP_HAL::native_millis();
            _slcan_start_req = true;
        }
        if (((AP_HAL::native_millis() - _slcan_start_req_time) < ((uint32_t)_slcan_start_delay*1000))) {
            return;
        }
        _port = AP::serialmanager().get_serial_by_id(_slcan_ser_port);
        if (_port == nullptr) {
            _slcan_ser_port.set_and_save(-1);
            return;
        }
        _port->lock_port(_serial_lock_key, _serial_lock_key);
        _prev_ser_port = _slcan_ser_port;
        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "CANManager: Starting SLCAN Passthrough on Serial %d with CAN%d", _slcan_ser_port.get(), _iface_num);
        _last_had_activity = AP_HAL::native_millis();
    }
    if (_port == nullptr) {
        return;
    }
    if (((AP_HAL::native_millis() - _last_had_activity) > ((uint32_t)_slcan_timeout*1000)) &&
        (uint32_t)_slcan_timeout != 0) {
        _port->lock_port(0, 0);
        _port = nullptr;
        _slcan_ser_port.set_and_save(-1);
        _prev_ser_port = -1;
        _slcan_start_req = false;
    }
}

bool SLCAN::CANIface::set_event_handle(AP_HAL::EventHandle* evt_handle)
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        return _can_iface->set_event_handle(evt_handle);
    }
    return false;
}

uint16_t SLCAN::CANIface::getNumFilters() const
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        return _can_iface->getNumFilters();
    }
    return 0;
}

uint32_t SLCAN::CANIface::getErrorCount() const
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        return _can_iface->getErrorCount();
    }
    return 0;
}

void SLCAN::CANIface::get_stats(ExpandingString &str)
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        _can_iface->get_stats(str);
    }
}

bool SLCAN::CANIface::is_busoff() const
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        return _can_iface->is_busoff();
    }
    return false;
}

bool SLCAN::CANIface::configureFilters(const CanFilterConfig* filter_configs, uint16_t num_configs)
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        return _can_iface->configureFilters(filter_configs, num_configs);
    }
    return true;
}

void SLCAN::CANIface::flush_tx()
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        _can_iface->flush_tx();
    }

    if (_port) {
        _port->flush();
    }
}

void SLCAN::CANIface::clear_rx()
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        _can_iface->clear_rx();
    }
    rx_queue_.clear();
}

bool SLCAN::CANIface::is_initialized() const
{
    // When in passthrough mode methods is handled through can iface
    if (_can_iface) {
        return _can_iface->is_initialized();
    }
    return false;
}

bool SLCAN::CANIface::select(bool &read, bool &write, const AP_HAL::CANFrame* const pending_tx,
                             uint64_t blocking_deadline)
{
    update_slcan_port();
    bool ret = false;
    // When in passthrough mode select is handled through can iface
    if (_can_iface) {
        ret = _can_iface->select(read, write, pending_tx, blocking_deadline);
    }

    if (_port == nullptr) {
        return ret;
    }

    // if under passthrough, we only do send when can_iface also allows it
    if (_port->available_locked(_serial_lock_key) || rx_queue_.available()) {
        // allow for receiving messages over slcan
        read = true;
        ret = true;
    }

    return ret;
}


// send method to transmit the frame through SLCAN interface
int16_t SLCAN::CANIface::send(const AP_HAL::CANFrame& frame, uint64_t tx_deadline, AP_HAL::CANIface::CanIOFlags flags)
{
    update_slcan_port();
    int16_t ret = 0;
    // When in passthrough mode select is handled through can iface
    if (_can_iface) {
        ret = _can_iface->send(frame, tx_deadline, flags);
    }

    if (_port == nullptr) {
        return ret;
    }

    if (frame.isErrorFrame()
#if !HAL_CANFD_SUPPORTED
        || frame.dlc > 8
#endif
        ) {
        return ret;
    }
    reportFrame(frame, AP_HAL::native_micros64());
    return ret;
}

// receive method to read the frame recorded in the buffer
int16_t SLCAN::CANIface::receive(AP_HAL::CANFrame& out_frame, uint64_t& rx_time,
                                 AP_HAL::CANIface::CanIOFlags& out_flags)
{
    update_slcan_port();
    // When in passthrough mode select is handled through can iface
    if (_can_iface) {
        int16_t ret = _can_iface->receive(out_frame, rx_time, out_flags);
        if (ret > 0) {
            // we also pass this frame through to slcan iface,
            // and immediately return
            reportFrame(out_frame, AP_HAL::native_micros64());
            return ret;
        } else if (ret < 0) {
            return ret;
        }
    }

    // We found nothing in HAL's CANIface recieve, so look in SLCANIface
    if (_port == nullptr) {
        return 0;
    }

    if (_port->available_locked(_serial_lock_key)) {
        uint32_t num_bytes = _port->available_locked(_serial_lock_key);
        // flush bytes from port
        while (num_bytes--) {
            int16_t ret = _port->read_locked(_serial_lock_key);
            if (ret < 0) {
                break;
            }
            addByte(ret);
            if (!rx_queue_.space()) {
                break;
            }
        }
    }
    if (rx_queue_.available()) {
        // if we already have something in buffer transmit it
        CanRxItem frm;
        if (!rx_queue_.peek(frm)) {
            return 0;
        }
        out_frame = frm.frame;
        rx_time = frm.timestamp_us;
        out_flags = frm.flags;
        _last_had_activity = AP_HAL::millis();
        // Also send this frame over can_iface when in passthrough mode,
        // We just push this frame without caring for priority etc
        if (_can_iface) {
            bool read = false;
            bool write = true;
            _can_iface->select(read, write, &out_frame, 0); // select without blocking
            if (write && _can_iface->send(out_frame, AP_HAL::native_micros64() + 100000, out_flags) == 1) {
                    rx_queue_.pop();
                    num_tries = 0;
            } else if (num_tries > 8) {
                rx_queue_.pop();
                num_tries = 0;
            } else {
                num_tries++;
            }
        } else {
            // we just throw away frames if we don't
            // have any can iface to pass through to
            rx_queue_.pop();
        }
        return 1;
    }
    return 0;
}

void SLCAN::CANIface::reset_params()
{
    _slcan_ser_port.set_and_save(-1);
}
#endif