AP_BLHeli.cpp

/*
   This program 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 program 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/>.
 */
/*
  implementation of MSP and BLHeli-4way protocols for pass-through ESC
  calibration and firmware update

  With thanks to betaflight for a great reference
  implementation. Several of the functions below are based on
  betaflight equivalent functions
 */

#include "AP_BLHeli.h"

#if HAVE_AP_BLHELI_SUPPORT

#if CONFIG_HAL_BOARD == HAL_BOARD_CHIBIOS
#include <hal.h>
#endif

#include <AP_Math/crc.h>
#include <AP_Vehicle/AP_Vehicle_Type.h>
#if APM_BUILD_TYPE(APM_BUILD_Rover)
#include <AR_Motors/AP_MotorsUGV.h>
#else
#include <AP_Motors/AP_Motors_Class.h>
#endif
#include <GCS_MAVLink/GCS_MAVLink.h>
#include <GCS_MAVLink/GCS.h>
#include <AP_SerialManager/AP_SerialManager.h>
#include <AP_BoardConfig/AP_BoardConfig.h>
#include <AP_ESC_Telem/AP_ESC_Telem.h>
#include <SRV_Channel/SRV_Channel.h>
#include <AP_BattMonitor/AP_BattMonitor.h>

extern const AP_HAL::HAL& hal;

#define debug(fmt, args ...) do { if (debug_level) { GCS_SEND_TEXT(MAV_SEVERITY_INFO, "ESC: " fmt, ## args); } } while (0)
#ifdef BLHELI_DEBUG
#define debug_console(fmt, args ...) do { hal.console->printf(fmt "\n", ## args); } while (0)
#else
#define debug_console(fmt, args ...) do {} while(0)
#endif

// key for locking UART for exclusive use. This prevents any other writes from corrupting
// the MSP protocol on hal.console
#define BLHELI_UART_LOCK_KEY 0x20180402

// if no packets are received for this time and motor control is active BLH will disconnect (stoping motors)
#define MOTOR_ACTIVE_TIMEOUT 1000

const AP_Param::GroupInfo AP_BLHeli::var_info[] = {
    // @Param: MASK
    // @DisplayName: BLHeli Channel Bitmask
    // @Description: Enable of BLHeli pass-thru servo protocol support to specific channels. This mask is in addition to motors enabled using SERVO_BLH_AUTO (if any)
    // @Bitmask: 0:Channel1,1:Channel2,2:Channel3,3:Channel4,4:Channel5,5:Channel6,6:Channel7,7:Channel8,8:Channel9,9:Channel10,10:Channel11,11:Channel12,12:Channel13,13:Channel14,14:Channel15,15:Channel16, 16:Channel 17, 17: Channel 18, 18: Channel 19, 19: Channel 20, 20: Channel 21, 21: Channel 22, 22: Channel 23, 23: Channel 24, 24: Channel 25, 25: Channel 26, 26: Channel 27, 27: Channel 28, 28: Channel 29, 29: Channel 30, 30: Channel 31, 31: Channel 32
    // @User: Advanced
    // @RebootRequired: True
    AP_GROUPINFO("MASK",  1, AP_BLHeli, channel_mask, 0),

#if APM_BUILD_COPTER_OR_HELI || APM_BUILD_TYPE(APM_BUILD_ArduPlane) || APM_BUILD_TYPE(APM_BUILD_Rover)
    // @Param: AUTO
    // @DisplayName: BLHeli pass-thru auto-enable for multicopter motors
    // @Description: If set to 1 this auto-enables BLHeli pass-thru support for all multicopter motors
    // @Values: 0:Disabled,1:Enabled
    // @User: Standard
    // @RebootRequired: True
    AP_GROUPINFO("AUTO",  2, AP_BLHeli, channel_auto, 0),
#endif

    // @Param: TEST
    // @DisplayName: BLHeli internal interface test
    // @Description: Setting SERVO_BLH_TEST to a motor number enables an internal test of the BLHeli ESC protocol to the corresponding ESC. The debug output is displayed on the USB console.
    // @Values: 0:Disabled,1:TestMotor1,2:TestMotor2,3:TestMotor3,4:TestMotor4,5:TestMotor5,6:TestMotor6,7:TestMotor7,8:TestMotor8
    // @User: Advanced
    AP_GROUPINFO("TEST",  3, AP_BLHeli, run_test, 0),

    // @Param: TMOUT
    // @DisplayName: BLHeli protocol timeout
    // @Description: This sets the inactivity timeout for the BLHeli protocol in seconds. If no packets are received in this time normal MAVLink operations are resumed. A value of 0 means no timeout
    // @Units: s
    // @Range: 0 300
    // @User: Standard
    AP_GROUPINFO("TMOUT",  4, AP_BLHeli, timeout_sec, 0),

    // @Param: TRATE
    // @DisplayName: BLHeli telemetry rate
    // @Description: This sets the rate in Hz for requesting telemetry from ESCs. It is the rate per ESC. Setting to zero disables telemetry requests
    // @Units: Hz
    // @Range: 0 500
    // @User: Standard
    AP_GROUPINFO("TRATE",  5, AP_BLHeli, telem_rate, 10),

    // @Param: DEBUG
    // @DisplayName: BLHeli debug level
    // @Description: When set to 1 this enabled verbose debugging output over MAVLink when the blheli protocol is active. This can be used to diagnose failures.
    // @Values: 0:Disabled,1:Enabled
    // @User: Standard
    AP_GROUPINFO("DEBUG",  6, AP_BLHeli, debug_level, 0),

    // @Param: OTYPE
    // @DisplayName: BLHeli output type override
    // @Description: When set to a non-zero value this overrides the output type for the output channels given by SERVO_BLH_MASK. This can be used to enable DShot on outputs that are not part of the multicopter motors group.
    // @Values: 0:None,1:OneShot,2:OneShot125,3:Brushed,4:DShot150,5:DShot300,6:DShot600,7:DShot1200
    // @User: Advanced
    // @RebootRequired: True
    AP_GROUPINFO("OTYPE",  7, AP_BLHeli, output_type, 0),

    // @Param: PORT
    // @DisplayName: Control port
    // @Description: This sets the mavlink channel to use for blheli pass-thru. The channel number is determined by the number of serial ports configured to use mavlink. So 0 is always the console, 1 is the next serial port using mavlink, 2 the next after that and so on.
    // @Values: 0:Console,1:Mavlink Serial Channel1,2:Mavlink Serial Channel2,3:Mavlink Serial Channel3,4:Mavlink Serial Channel4,5:Mavlink Serial Channel5
    // @User: Advanced
    AP_GROUPINFO("PORT",  8, AP_BLHeli, control_port, 0),

    // @Param: POLES
    // @DisplayName: BLHeli Motor Poles
    // @Description: This allows calculation of true RPM from ESC's eRPM. The default is 14.
    // @Range: 1 127
    // @User: Advanced
    // @RebootRequired: True
    AP_GROUPINFO("POLES",  9, AP_BLHeli, motor_poles, 14),

    // @Param: 3DMASK
    // @DisplayName: BLHeli bitmask of 3D channels
    // @Description: Mask of channels which are dynamically reversible. This is used to configure ESCs in '3D' mode, allowing for the motor to spin in either direction. Note that setting an ESC as reversible with this option on AM32 will result in the forward direction of the ESC changing. You can combine with parameter with the SERVO_BLH_RVMASK parameter to maintain the same direction when the ESC is in 3D mode as it has in unidirectional (non-3D) mode.
    // @Bitmask: 0:Channel1,1:Channel2,2:Channel3,3:Channel4,4:Channel5,5:Channel6,6:Channel7,7:Channel8,8:Channel9,9:Channel10,10:Channel11,11:Channel12,12:Channel13,13:Channel14,14:Channel15,15:Channel16, 16:Channel 17, 17: Channel 18, 18: Channel 19, 19: Channel 20, 20: Channel 21, 21: Channel 22, 22: Channel 23, 23: Channel 24, 24: Channel 25, 25: Channel 26, 26: Channel 27, 27: Channel 28, 28: Channel 29, 29: Channel 30, 30: Channel 31, 31: Channel 32
    // @User: Advanced
    // @RebootRequired: True
    AP_GROUPINFO("3DMASK",  10, AP_BLHeli, channel_reversible_mask, 0),

#if defined(HAL_WITH_BIDIR_DSHOT) || HAL_WITH_IO_MCU_BIDIR_DSHOT
    // @Param: BDMASK
    // @DisplayName: BLHeli bitmask of bi-directional dshot channels
    // @Description: Mask of channels which support bi-directional dshot telemetry. This is used for ESCs which have firmware that supports bi-directional dshot allowing fast rpm telemetry values to be returned for the harmonic notch.
    // @Bitmask: 0:Channel1,1:Channel2,2:Channel3,3:Channel4,4:Channel5,5:Channel6,6:Channel7,7:Channel8,8:Channel9,9:Channel10,10:Channel11,11:Channel12,12:Channel13,13:Channel14,14:Channel15,15:Channel16, 16:Channel 17, 17: Channel 18, 18: Channel 19, 19: Channel 20, 20: Channel 21, 21: Channel 22, 22: Channel 23, 23: Channel 24, 24: Channel 25, 25: Channel 26, 26: Channel 27, 27: Channel 28, 28: Channel 29, 29: Channel 30, 30: Channel 31, 31: Channel 32
    // @User: Advanced
    // @RebootRequired: True
    AP_GROUPINFO("BDMASK",  11, AP_BLHeli, channel_bidir_dshot_mask, 0),
#endif

    // @Param: RVMASK
    // @DisplayName: BLHeli bitmask of reversed channels
    // @Description: Mask of channels which are reversed. This is used to configure ESCs to reverse motor direction. Note that when combined with SERVO_BLH_3DMASK this will change what direction is considered to be forward.
    // @Bitmask: 0:Channel1,1:Channel2,2:Channel3,3:Channel4,4:Channel5,5:Channel6,6:Channel7,7:Channel8,8:Channel9,9:Channel10,10:Channel11,11:Channel12,12:Channel13,13:Channel14,14:Channel15,15:Channel16, 16:Channel 17, 17: Channel 18, 18: Channel 19, 19: Channel 20, 20: Channel 21, 21: Channel 22, 22: Channel 23, 23: Channel 24, 24: Channel 25, 25: Channel 26, 26: Channel 27, 27: Channel 28, 28: Channel 29, 29: Channel 30, 30: Channel 31, 31: Channel 32
    // @User: Advanced
    // @RebootRequired: True
    AP_GROUPINFO("RVMASK",  12, AP_BLHeli, channel_reversed_mask, 0),

    AP_GROUPEND
};

#define RPM_SLEW_RATE 50

AP_BLHeli *AP_BLHeli::_singleton;

// constructor
AP_BLHeli::AP_BLHeli(void)
{
    // set defaults from the parameter table
    AP_Param::setup_object_defaults(this, var_info);
    _singleton = this;
    last_control_port = -1;
}

// map an incoming BLHeli motor request to the appropriate 
// output channel for use in serial output so that motor numbers
// are observed
uint8_t AP_BLHeli::blheli_chan_to_output_chan(uint8_t motor)
{
    // user has overidden the default output mask, we must use the motor map
    if (channel_mask.get() != 0) {
        return motor_map[motor];
    }
    // user is using motor mask and so we can use the servo channel options
    uint8_t chan = 0;   // 0 means motor 1 and is ok as a fallback
    SRV_Channels::find_channel(SRV_Channels::get_motor_function(motor), chan);
    return chan;
}

/*
  process one byte of serial input for MSP protocol
 */
bool AP_BLHeli::msp_process_byte(uint8_t c)
{
    if (msp.state == MSP_IDLE) {
        msp.escMode = PROTOCOL_NONE;
        if (c == '$') {
            msp.state = MSP_HEADER_START;
        } else {
            return false;
        }
    } else if (msp.state == MSP_HEADER_START) {
        msp.state = (c == 'M') ? MSP_HEADER_M : MSP_IDLE;
    } else if (msp.state == MSP_HEADER_M) {
        msp.state = MSP_IDLE;
        switch (c) {
            case '<': // COMMAND
                msp.packetType = MSP_PACKET_COMMAND;
                msp.state = MSP_HEADER_ARROW;
                break;
            case '>': // REPLY
                msp.packetType = MSP_PACKET_REPLY;
                msp.state = MSP_HEADER_ARROW;
                break;
            default:
                break;
        }
    } else if (msp.state == MSP_HEADER_ARROW) {
        if (c > sizeof(msp.buf)) {
            msp.state = MSP_IDLE;
        } else {
            msp.dataSize = c;
            msp.offset = 0;
            msp.checksum = 0;
            msp.checksum ^= c;
            msp.state = MSP_HEADER_SIZE;
        }
    } else if (msp.state == MSP_HEADER_SIZE) {
        msp.cmdMSP = c;
        msp.checksum ^= c;
        msp.state = MSP_HEADER_CMD;
    } else if (msp.state == MSP_HEADER_CMD && msp.offset < msp.dataSize) {
        msp.checksum ^= c;
        msp.buf[msp.offset++] = c;
    } else if (msp.state == MSP_HEADER_CMD && msp.offset >= msp.dataSize) {
        if (msp.checksum == c) {
            msp.state = MSP_COMMAND_RECEIVED;
        } else {
            msp.state = MSP_IDLE;
        }
    }
    return true;
}

/*
  update CRC state for blheli protocol
 */
void AP_BLHeli::blheli_crc_update(uint8_t c)
{
    blheli.crc = crc_xmodem_update(blheli.crc, c);
}

/*
  process one byte of serial input for blheli 4way protocol
 */
bool AP_BLHeli::blheli_4way_process_byte(uint8_t c)
{
    if (blheli.state == BLHELI_IDLE) {
        if (c == cmd_Local_Escape) {
            blheli.state = BLHELI_HEADER_START;
            blheli.crc = 0;
            blheli_crc_update(c);
        } else {
            return false;
        }
    } else if (blheli.state == BLHELI_HEADER_START) {
        blheli.command = c;
        blheli_crc_update(c);
        blheli.state = BLHELI_HEADER_CMD;
    } else if (blheli.state == BLHELI_HEADER_CMD) {
        blheli.address = c<<8;
        blheli.state = BLHELI_HEADER_ADDR_HIGH;
        blheli_crc_update(c);
    } else if (blheli.state == BLHELI_HEADER_ADDR_HIGH) {
        blheli.address |= c;
        blheli.state = BLHELI_HEADER_ADDR_LOW;
        blheli_crc_update(c);
    } else if (blheli.state == BLHELI_HEADER_ADDR_LOW) {
        blheli.state = BLHELI_HEADER_LEN;
        blheli.param_len = c?c:256;
        blheli.offset = 0;
        blheli_crc_update(c);
    } else if (blheli.state == BLHELI_HEADER_LEN) {
        blheli.buf[blheli.offset++] = c;
        blheli_crc_update(c);
        if (blheli.offset == blheli.param_len) {
            blheli.state = BLHELI_CRC1;
        }
    } else if (blheli.state == BLHELI_CRC1) {
        blheli.crc1 = c;
        blheli.state = BLHELI_CRC2;
    } else if (blheli.state == BLHELI_CRC2) {
        uint16_t crc = blheli.crc1<<8 | c;
        if (crc == blheli.crc) {
            blheli.state = BLHELI_COMMAND_RECEIVED;
        } else {
            blheli.state = BLHELI_IDLE;
        }
    }
    return true;
}


/*
  send a MSP protocol ack
 */
void AP_BLHeli::msp_send_ack(uint8_t cmd)
{
    msp_send_reply(cmd, 0, 0);
}

/*
  send a MSP protocol reply
 */
void AP_BLHeli::msp_send_reply(uint8_t cmd, const uint8_t *buf, uint8_t len)
{
    uint8_t *b = &msp.buf[0];
    *b++ = '$';
    *b++ = 'M';
    *b++ = '>';
    *b++ = len;
    *b++ = cmd;
    // acks do not have a payload
    if (len > 0) {
        memcpy(b, buf, len);
    }
    b += len;
    uint8_t c = 0;
    for (uint8_t i=0; i<len+2; i++) {
        c ^= msp.buf[i+3];
    }
    *b++ = c;
    uart->write_locked(&msp.buf[0], len+6, BLHELI_UART_LOCK_KEY);
}

void AP_BLHeli::putU16(uint8_t *b, uint16_t v)
{
    b[0] = v;
    b[1] = v >> 8;
}

uint16_t AP_BLHeli::getU16(const uint8_t *b)
{
    return b[0] | (b[1]<<8);
}

void AP_BLHeli::putU32(uint8_t *b, uint32_t v)
{
    b[0] = v;
    b[1] = v >> 8;
    b[2] = v >> 16;
    b[3] = v >> 24;
}

void AP_BLHeli::putU16_BE(uint8_t *b, uint16_t v)
{
    b[0] = v >> 8;
    b[1] = v;
}

/*
  process a MSP command from GCS
 */
void AP_BLHeli::msp_process_command(void)
{
    debug("MSP cmd %u len=%u", msp.cmdMSP, msp.dataSize);
    switch (msp.cmdMSP) {
    case MSP_API_VERSION: {
        debug("MSP_API_VERSION");
        uint8_t buf[3] = { MSP_PROTOCOL_VERSION, API_VERSION_MAJOR, API_VERSION_MINOR };
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_FC_VARIANT:
        debug("MSP_FC_VARIANT");
        msp_send_reply(msp.cmdMSP, (const uint8_t *)ARDUPILOT_IDENTIFIER, FLIGHT_CONTROLLER_IDENTIFIER_LENGTH);
        break;

    /*
      Notes:
        version 3.3.1 adds a reply to MSP_SET_MOTOR which was missing
        version 3.3.0 requires a workaround in blheli suite to handle MSP_SET_MOTOR without an ack
    */
    case MSP_FC_VERSION: {
        debug("MSP_FC_VERSION");
        uint8_t version[3] = { 3, 3, 1 };
        msp_send_reply(msp.cmdMSP, version, sizeof(version));
        break;
    }
    case MSP_BOARD_INFO: {
        debug("MSP_BOARD_INFO");
        // send a generic 'ArduPilot ChibiOS' board type
        uint8_t buf[7] = { 'A', 'R', 'C', 'H', 0, 0, 0 };
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_BUILD_INFO: {
        debug("MSP_BUILD_INFO");
         // build date, build time, git version
        uint8_t buf[26] {
                0x4d, 0x61, 0x72, 0x20, 0x31, 0x36, 0x20, 0x32, 0x30,
                0x31, 0x38, 0x30, 0x38, 0x3A, 0x34, 0x32, 0x3a, 0x32, 0x39,
                0x62, 0x30, 0x66, 0x66, 0x39, 0x32, 0x38};
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_REBOOT:
        debug("MSP: ignoring reboot command, end serial comms");
        serial_end();
        blheli.connected[blheli.chan] = false;
        break;

    case MSP_UID:
        // MCU identifier
        debug("MSP_UID");
        msp_send_reply(msp.cmdMSP, (const uint8_t *)UDID_START, 12);
        break;

        // a literal "4" is used for the PWMType here to allow Rover
        // to use the same number for the same protocol.  At time of
        // writing the AP_MotorsUGV::PWMType has not been unified with
        // AP_Motors::PWMType.
    case MSP_ADVANCED_CONFIG: {
        debug("MSP_ADVANCED_CONFIG");
        uint8_t buf[10];
        buf[0] = 1; // gyro sync denom
        buf[1] = 4; // pid process denom
        buf[2] = 0; // use unsynced pwm
        buf[3] = 4; // (uint8_t)AP_Motors::PWMType::DSHOT150;
        putU16(&buf[4], 480); // motor PWM Rate
        putU16(&buf[6], 450); // idle offset value
        buf[8] = 0; // use 32kHz
        buf[9] = 0; // motor PWM inversion
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_FEATURE_CONFIG: {
        debug("MSP_FEATURE_CONFIG");
        uint8_t buf[4];
        putU32(buf, (channel_reversible_mask.get() != 0) ? FEATURE_3D : 0); // from MSPFeatures enum
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_STATUS: {
        debug("MSP_STATUS");
        uint8_t buf[21];
        putU16(&buf[0], 1000); // loop time usec
        putU16(&buf[2], 0);    // i2c error count
        putU16(&buf[4], 0x27); // available sensors
        putU32(&buf[6], 0);    // flight modes
        buf[10] = 0;           // pid profile index
        putU16(&buf[11], 5);   // system load percent
        putU16(&buf[13], 0);   // gyro cycle time
        buf[15] = 0;           // flight mode flags length
        buf[16] = 18;          // arming disable flags count
        putU32(&buf[17], 0);   // arming disable flags
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_MOTOR_3D_CONFIG: {
        debug("MSP_MOTOR_3D_CONFIG");
        uint8_t buf[6];
        putU16(&buf[0], 1406); // 3D deadband low
        putU16(&buf[2], 1514); // 3D deadband high
        putU16(&buf[4], 1460); // 3D neutral
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_BATTERY_STATE: {
        debug("MSP_BATTERY_STATE");
        // ESC configurator seems to care a lot about the battery state,
        // try and at least provide something believable
        uint8_t buf[11] {};
#if AP_BATTERY_ENABLED
        AP_BattMonitor &battery = AP::battery();
        float v;
#if HAL_WITH_ESC_TELEM
        if (!AP::esc_telem().get_voltage(blheli_chan_to_output_chan(blheli.chan), v)) {
            v = battery.voltage();
        }        
#else
            v = battery.voltage();
#endif
        buf[0] = battery.healthy() ? uint8_t(roundf(v / 3.85)) : 0; // cell count, 0 means no battery
        putU16(&buf[1], uint16_t(battery.pack_capacity_mah())); // capacity in mAh
        buf[3] = uint8_t(roundf(v * 10.0)); // legacy V in 0.1V steps

        float cons = 0;
        UNUSED_RESULT(battery.consumed_mah(cons));
        putU16(&buf[4], uint16_t(roundf(cons))); // mAh used

        float amps = 0.0;
        UNUSED_RESULT(battery.current_amps(amps));
        putU16(&buf[6], uint16_t(roundf(amps * 100.0))); // A in 0.01A steps
        buf[8] = battery.healthy(); // alerts/state
        // We are advertising MSP v1.42 which means supporting the new voltage field
        putU16(&buf[9], uint16_t(roundf(v * 100.0))); // Voltage in 0.01V steps
#endif
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_MOTOR_CONFIG: {
        debug("MSP_MOTOR_CONFIG(n=%u, p=%u)", num_motors, motor_poles.get());
        uint8_t buf[10];
        SRV_Channel* channel = SRV_Channels::srv_channel(blheli_chan_to_output_chan(0));
        putU16(&buf[0], channel->get_output_min()); // min throttle
        putU16(&buf[2], channel->get_output_max()); // max throttle
        putU16(&buf[4], channel->get_output_min()); // min command
        // API 1.42
        buf[6] = num_motors; // motorCount
        buf[7] = motor_poles; // motorPoleCount
        buf[8] = 0; // useDshotTelemetry
        buf[9] = 0; // FEATURE_ESC_SENSOR
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_MOTOR: {
        debug("MSP_MOTOR");
        // get the output going to each motor
        uint8_t buf[16] {};
        for (uint8_t i = 0; i < num_motors; i++) {
            // if we have a mix of reversible and normal report a PWM of zero, this allows BLHeliSuite to conect
            uint8_t chan = blheli_chan_to_output_chan(i);
            uint16_t v = mixed_type ? 0 : hal.rcout->read(blheli_chan_to_output_chan(i));
            putU16(&buf[2*i], v);
            debug("MOTOR %u chan: %u val: %u",i,chan,v);
        }
        msp_send_reply(msp.cmdMSP, buf, sizeof(buf));
        break;
    }

    case MSP_SET_MOTOR: {
        debug("MSP_SET_MOTOR");
        if (!mixed_type) {
            // set the output to each motor
            uint8_t nmotors = msp.dataSize / 2;
            debug("MSP_SET_MOTOR %u", nmotors);
            motors_disabled_mask = SRV_Channels::get_disabled_channel_mask();
            SRV_Channels::set_disabled_channel_mask(0xFFFF);
            motors_disabled = true;
            EXPECT_DELAY_MS(1000);
            hal.rcout->cork();
            for (uint8_t i = 0; i < nmotors; i++) {
                if (i >= num_motors) {
                    break;
                }
                uint16_t v = getU16(&msp.buf[i*2]);
                debug("MSP_SET_MOTOR %u %u", i, v);
                // map from a MSP value to a value in the range 1000 to 2000
                uint16_t pwm = (v < 1000)?0:v;
                hal.rcout->write(blheli_chan_to_output_chan(i), pwm);
            }
            hal.rcout->push();
        } else {
            debug("mixed type, Motors Disabled");
        }
        msp_send_ack(msp.cmdMSP);
        break;
    }

    case MSP_SET_PASSTHROUGH: {
        debug("MSP_SET_PASSTHROUGH");
        if (msp.dataSize == 0) {
            msp.escMode = PROTOCOL_4WAY;
        } else if (msp.dataSize == 2) {
            msp.escMode = (enum escProtocol)msp.buf[0];
            msp.portIndex = msp.buf[1];
        }
        debug("escMode=%u portIndex=%u num_motors=%u", msp.escMode, msp.portIndex, num_motors);
        uint8_t n = num_motors;
        switch (msp.escMode) {
        case PROTOCOL_4WAY:
            break;
        default:
            n = 0;
            serial_end();
            break;
        }
        // doing the serial setup here avoids delays when doing it on demand and makes
        // BLHeliSuite considerably more reliable
        EXPECT_DELAY_MS(1000);
        if (!hal.rcout->serial_setup_output(blheli_chan_to_output_chan(0), 19200, motor_mask)) {
            msp_send_ack(ACK_D_GENERAL_ERROR);
            break;
        } else {
            msp_send_reply(msp.cmdMSP, &n, 1);
        }
        break;
    }
    default:
        debug("Unknown MSP command %u", msp.cmdMSP);
        break;
    }
}

/*
  send a blheli 4way protocol reply
 */
void AP_BLHeli::blheli_send_reply(const uint8_t *buf, uint16_t len)
{
    uint8_t *b = &blheli.buf[0];
    *b++ = cmd_Remote_Escape;
    *b++ = blheli.command;
    putU16_BE(b, blheli.address); b += 2;
    *b++ = len==256?0:len;
    memcpy(b, buf, len);
    b += len;
    *b++ = blheli.ack;
    putU16_BE(b, crc_xmodem(&blheli.buf[0], len+6));
    uart->write_locked(&blheli.buf[0], len+8, BLHELI_UART_LOCK_KEY);
    debug("OutB(%u) 0x%02x ack=0x%02x", len+8, (unsigned)blheli.command, blheli.ack);
}

/*
  CRC used when talking to ESCs
 */
uint16_t AP_BLHeli::BL_CRC(const uint8_t *buf, uint16_t len)
{
    uint16_t crc = 0;
    while (len--) {
        uint8_t xb = *buf++;
        for (uint8_t i = 0; i < 8; i++) {
            if (((xb & 0x01) ^ (crc & 0x0001)) !=0 ) {
                crc = crc >> 1;
                crc = crc ^ 0xA001;
            } else {
                crc = crc >> 1;
            }
            xb = xb >> 1;
        }
    }
    return crc;
}

bool AP_BLHeli::isMcuConnected(void)
{
    return blheli.connected[blheli.chan];
}

void AP_BLHeli::setDisconnected(void)
{
    blheli.connected[blheli.chan] = false;
    blheli.deviceInfo[blheli.chan][0] = 0;
    blheli.deviceInfo[blheli.chan][1] = 0;
}

/*
  send a set of bytes to an RC output channel
 */
bool AP_BLHeli::BL_SendBuf(const uint8_t *buf, uint16_t len)
{
    bool send_crc = isMcuConnected();
    if (blheli.chan >= num_motors) {
        return false;
    }
    EXPECT_DELAY_MS(1000);
    hal.scheduler->delay_microseconds(100);
    if (!hal.rcout->serial_setup_output(blheli_chan_to_output_chan(blheli.chan), 19200, motor_mask)) {
        debug_console("serial_setup_output() failed\n");
        blheli.ack = ACK_D_GENERAL_ERROR;
        return false;
    }
    // ensure that the next write does not go out immediately in case the receiving side is not yet
    // ready
    hal.scheduler->delay_microseconds(100);

    if (serial_start_ms == 0) {
        serial_start_ms = AP_HAL::millis();
    }
    memcpy(blheli.buf, buf, len);
    uint16_t crc = BL_CRC(buf, len);
    blheli.buf[len] = uint8_t(crc & 0xFF);
    blheli.buf[len+1] = uint8_t(crc>>8);
    if (!hal.rcout->serial_write_bytes(blheli.buf, len+(send_crc?2:0))) {
        debug_console("serial_write_bytes() failed\n");
        blheli.ack = ACK_D_GENERAL_ERROR;
        return false;
    }
    // 19200 baud is 52us per bit - wait for half a bit between sending and receiving to avoid reading
    // the end of the last sent bit by accident
    hal.scheduler->delay_microseconds(26);
    return true;
}

/*
  read bytes from the ESC connection
 */
bool AP_BLHeli::BL_ReadBuf(uint8_t *buf, uint16_t len)
{
    bool check_crc = isMcuConnected();
    uint16_t req_bytes = len+(check_crc?3:1);
    EXPECT_DELAY_MS(1000);
    // byte time is 520us so 1000 per byte should be more than enough
    uint16_t n = hal.rcout->serial_read_bytes(blheli.buf, req_bytes, req_bytes * 1000);
    debug("BL_ReadBuf %u -> %u", len, n);
    if (req_bytes != n) {
        debug("short read");
        blheli.ack = ACK_D_GENERAL_ERROR;
        return false;
    }
    if (check_crc) {
        uint16_t crc = BL_CRC(blheli.buf, len);
        if ((crc & 0xff) != blheli.buf[len] ||
            (crc >> 8) != blheli.buf[len+1]) {
            debug("bad CRC");
            blheli.ack = ACK_D_GENERAL_ERROR;
            return false;
        }
        if (blheli.buf[len+2] != brSUCCESS) {
            debug("bad ACK 0x%02x", blheli.buf[len+2]);
            blheli.ack = ACK_D_GENERAL_ERROR;
            return false;
        }
    } else {
        if (blheli.buf[len] != brSUCCESS) {
            debug("bad ACK1 0x%02x", blheli.buf[len]);
            blheli.ack = ACK_D_GENERAL_ERROR;
            return false;
        }
    }
    if (len > 0) {
        memcpy(buf, blheli.buf, len);
    }
    return true;
}

uint8_t AP_BLHeli::BL_GetACK(uint16_t timeout_ms)
{
    uint8_t ack;
    EXPECT_DELAY_MS(timeout_ms);
    if (hal.rcout->serial_read_bytes(&ack, 1, timeout_ms * 1000) == 1) {
        return ack;
    }
    // return brNONE, meaning no ACK received in the timeout
    return brNONE;
}

bool AP_BLHeli::BL_SendCMDSetAddress()
{
    // skip if adr == 0xFFFF
    if (blheli.address == 0xFFFF) {
        return true;
    }
    debug("BL_SendCMDSetAddress 0x%04x", blheli.address);
    uint8_t sCMD[] = {CMD_SET_ADDRESS, 0, uint8_t(blheli.address>>8), uint8_t(blheli.address)};
    if (!BL_SendBuf(sCMD, 4)) {
        return false;
    }
    return BL_GetACK() == brSUCCESS;
}

bool AP_BLHeli::BL_ReadA(uint8_t cmd, uint8_t *buf, uint16_t n)
{
    if (BL_SendCMDSetAddress()) {
        uint8_t sCMD[] = {cmd, uint8_t(n==256?0:n)};
        if (!BL_SendBuf(sCMD, 2)) {
            return false;
        }
        bool ret = BL_ReadBuf(buf, n);
        if (ret && n == sizeof(esc_status) && blheli.address == esc_status_addr) {
            // display esc_status structure if we see it
            struct esc_status status;
            memcpy(&status, buf, n);
            debug("Prot %u Good %u Bad %u %x %x %x x%x\n",
                  (unsigned)status.protocol,
                  (unsigned)status.good_frames,
                  (unsigned)status.bad_frames,
                  (unsigned)status.unknown[0],
                  (unsigned)status.unknown[1],
                  (unsigned)status.unknown[2],
                  (unsigned)status.unknown2);
        }
        return ret;
    }
    return false;
}

/*
  connect to a blheli ESC
 */
bool AP_BLHeli::BL_ConnectEx(void)
{
    debug("BL_ConnectEx %u/%u at %u", blheli.chan, num_motors, blheli_chan_to_output_chan(blheli.chan));
    setDisconnected();
    const uint8_t BootInit[] = {0,0,0,0,0,0,0,0,0,0,0,0,0x0D,'B','L','H','e','l','i',0xF4,0x7D};
    if (!BL_SendBuf(BootInit, 21)) {
        return false;
    }

    uint8_t BootInfo[9];
    if (!BL_ReadBuf(BootInfo, 8)) {
        return false;
    }

    // reply must start with 471
    if (strncmp((const char *)BootInfo, "471", 3) != 0) {
        blheli.ack = ACK_D_GENERAL_ERROR;        
        return false;
    }

    // extract device information
    blheli.deviceInfo[blheli.chan][2] = BootInfo[3];
    blheli.deviceInfo[blheli.chan][1] = BootInfo[4];
    blheli.deviceInfo[blheli.chan][0] = BootInfo[5];

    blheli.interface_mode[blheli.chan] = 0;

    uint16_t devword;
    memcpy(&devword, blheli.deviceInfo[blheli.chan], sizeof(devword));
    switch (devword) {
    case 0x9307:
    case 0x930A:
    case 0x930F:
    case 0x940B:
        blheli.interface_mode[blheli.chan] = imATM_BLB;
        debug("Interface type imATM_BLB");
        break;
    case 0xF310:
    case 0xF330:
    case 0xF410:
    case 0xF390:
    case 0xF850:
    case 0xE8B1:
    case 0xE8B2:
        blheli.interface_mode[blheli.chan] = imSIL_BLB;
        debug("Interface type imSIL_BLB");
        break;
    default:
        // BLHeli_32 MCU ID hi > 0x00 and < 0x90 / lo always = 0x06
        if ((blheli.deviceInfo[blheli.chan][1] > 0x00) && (blheli.deviceInfo[blheli.chan][1] < 0x90) && (blheli.deviceInfo[blheli.chan][0] == 0x06)) {
            blheli.interface_mode[blheli.chan] = imARM_BLB;
            debug("Interface type imARM_BLB");
        } else {
            blheli.ack = ACK_D_GENERAL_ERROR;
            debug("Unknown interface type 0x%04x", devword);
            break;
        }
    }
    blheli.deviceInfo[blheli.chan][3] = blheli.interface_mode[blheli.chan];
    if (blheli.interface_mode[blheli.chan] != 0) {
        blheli.connected[blheli.chan] = true;
    }
    return true;
}

bool AP_BLHeli::BL_SendCMDKeepAlive(void)
{
    uint8_t sCMD[] = {CMD_KEEP_ALIVE, 0};
    if (!BL_SendBuf(sCMD, 2)) {
        return false;
    }
    if (BL_GetACK() != brERRORCOMMAND) {
        return false;
    }
    return true;
}

bool AP_BLHeli::BL_PageErase(void)
{
    if (BL_SendCMDSetAddress()) {
        uint8_t sCMD[] = {CMD_ERASE_FLASH, 0x01};
        if (!BL_SendBuf(sCMD, 2)) {
            return false;
        }
        return BL_GetACK(3000) == brSUCCESS;
    }
    return false;
}

void AP_BLHeli::BL_SendCMDRunRestartBootloader(void)
{
    uint8_t sCMD[] = {RestartBootloader, 0};
    blheli.deviceInfo[blheli.chan][0] = 1;
    BL_SendBuf(sCMD, 2);
}

uint8_t AP_BLHeli::BL_SendCMDSetBuffer(const uint8_t *buf, uint16_t nbytes)
{
    uint8_t sCMD[] = {CMD_SET_BUFFER, 0, uint8_t(nbytes>>8), uint8_t(nbytes&0xff)};
    if (nbytes == 0) {
        // set high byte since 0 bytes == 256 bytes in this protocol
        sCMD[2] = 1;
    }
    if (!BL_SendBuf(sCMD, 4)) {
        debug_console("BL_SendCMDSetBuffer send cmd failed");
        return false;
    }
    uint8_t ack = BL_GetACK(5); // match betaflight timing
    // generally no ack returned for CMD_SET_BUFFER when flashing firmware
    if (ack != brNONE && ack != brSUCCESS) {
        debug("BL_SendCMDSetBuffer ack failed 0x%02x", ack);
        blheli.ack = ACK_D_GENERAL_ERROR;
        return false;
    }

    if (!BL_SendBuf(buf, nbytes)) {
        debug("BL_SendCMDSetBuffer send failed");
        blheli.ack = ACK_D_GENERAL_ERROR;
        return false;
    }
    return (BL_GetACK(40) == brSUCCESS);
}

bool AP_BLHeli::BL_WriteA(uint8_t cmd, const uint8_t *buf, uint16_t nbytes, uint32_t timeout_ms)
{
    if (BL_SendCMDSetAddress()) {
        if (!BL_SendCMDSetBuffer(buf, nbytes)) {
            debug_console("BL_SendCMDSetBuffer failed\n");
            blheli.ack = ACK_D_GENERAL_ERROR;
            return false;
        }
        uint8_t sCMD[] = {cmd, 0x01};
        if (!BL_SendBuf(sCMD, 2)) {
            debug_console("BL_SendBuf failed\n");
            return false;
        }
        uint8_t ack = BL_GetACK(timeout_ms);
        if (ack != brSUCCESS) {
            debug_console("BL_GetACK failed 0x%x\n", ack);
        }
        return (ack == brSUCCESS);
    }
    debug_console("BL_SendCMDSetAddress failed\n");
    blheli.ack = ACK_D_GENERAL_ERROR;
    return false;
}

bool AP_BLHeli::BL_WriteFlash(const uint8_t *buf, uint16_t n)
{
    return BL_WriteA(CMD_PROG_FLASH, buf, n, 500);
}

bool AP_BLHeli::BL_VerifyFlash(const uint8_t *buf, uint16_t n)
{
    if (BL_SendCMDSetAddress()) {
        if (!BL_SendCMDSetBuffer(buf, n)) {
            return false;
        }
        uint8_t sCMD[] = {CMD_VERIFY_FLASH_ARM, 0x01};
        if (!BL_SendBuf(sCMD, 2)) {
            return false;
        }
        uint8_t ack = BL_GetACK(40);
        switch (ack) {
        case brSUCCESS:
            blheli.ack = ACK_OK;
            break;
        case brERRORVERIFY:
            blheli.ack = ACK_I_VERIFY_ERROR;
            break;
        default:
            blheli.ack = ACK_D_GENERAL_ERROR;
            break;
        }
        return true;
    }
    return false;
}

/*
  process a blheli 4way command from GCS
 */
void AP_BLHeli::blheli_process_command(void)
{
    debug("BLHeli cmd 0x%02x len=%u", blheli.command, blheli.param_len);
    blheli.ack = ACK_OK;
    switch (blheli.command) {
    case cmd_InterfaceTestAlive: {
        debug("cmd_InterfaceTestAlive");
        if (!isMcuConnected()) {
            blheli.ack = ACK_D_GENERAL_ERROR;
        } else {
            BL_SendCMDKeepAlive();
            if (blheli.ack != ACK_OK) {
                setDisconnected();
            }
        }
        uint8_t b = 0;
        blheli_send_reply(&b, 1);
        break;
    }
    case cmd_ProtocolGetVersion: {
        debug("cmd_ProtocolGetVersion");
        uint8_t buf[1];
        buf[0] = SERIAL_4WAY_PROTOCOL_VER;
        blheli_send_reply(buf, sizeof(buf));
        break;
    }
    case cmd_InterfaceGetName: {
        debug("cmd_InterfaceGetName");
        uint8_t buf[5] = { 4, 'A', 'R', 'D', 'U' };
        blheli_send_reply(buf, sizeof(buf));
        break;
    }
    case cmd_InterfaceGetVersion: {
        debug("cmd_InterfaceGetVersion");
        uint8_t buf[2] = { SERIAL_4WAY_VERSION_HI, SERIAL_4WAY_VERSION_LO };
        blheli_send_reply(buf, sizeof(buf));
        break;
    }
    case cmd_InterfaceExit: {
        debug("cmd_InterfaceExit");
        msp.escMode = PROTOCOL_NONE;
        uint8_t b = 0;
        blheli_send_reply(&b, 1);
        serial_end();
        if (motors_disabled) {
            motors_disabled = false;
            SRV_Channels::set_disabled_channel_mask(motors_disabled_mask);
        }
        if (uart_locked) {
            debug("Unlocked UART");
            uart->lock_port(0, 0);
            uart_locked = false;
        }
        memset(blheli.connected, 0, sizeof(blheli.connected));
        break;
    }
    case cmd_DeviceReset: {
        debug("cmd_DeviceReset(%u)", unsigned(blheli.buf[0]));
        if (blheli.buf[0] >= num_motors) {
            debug("bad reset channel %u", blheli.buf[0]);
            blheli.ack = ACK_I_INVALID_CHANNEL;
            blheli_send_reply(&blheli.buf[0], 1);            
            break;
        }
        blheli.chan = blheli.buf[0];
        switch (blheli.interface_mode[blheli.chan]) {
        case imSIL_BLB:
        case imATM_BLB:
        case imARM_BLB:
            BL_SendCMDRunRestartBootloader();
            break;
        case imSK:
            break;
        }
        blheli_send_reply(&blheli.chan, 1);
        setDisconnected();
        break;
    }

    case cmd_DeviceInitFlash: {
        uint8_t chan = blheli.buf[0];

        debug("cmd_DeviceInitFlash(%u)", unsigned(blheli.buf[0]));
        if (blheli.buf[0] >= num_motors) {
            debug("bad channel %u", blheli.buf[0]);
            blheli.ack = ACK_I_INVALID_CHANNEL;
            blheli_send_reply(&chan, 1);
            break;
        }
        // betaflight tries three times to connect, this avoids the need to wait some arbitrary
        // period for the interface to be up.
        bool failed = true;
        for (uint8_t i = 0; i<3; i++) {
            blheli.chan = chan;
            blheli.ack = ACK_OK;
            if (BL_ConnectEx()) {
                uint8_t buf[4] = {blheli.deviceInfo[blheli.chan][0],
                                blheli.deviceInfo[blheli.chan][1],
                                blheli.deviceInfo[blheli.chan][2],
                                blheli.deviceInfo[blheli.chan][3]};  // device ID
                blheli_send_reply(buf, sizeof(buf));
                failed = false;
                break;
            }
        }

        if (failed) {
            blheli.ack = ACK_D_GENERAL_ERROR;
            blheli_send_reply(&chan, 1);
            setDisconnected();
        }
        break;
    }

    case cmd_InterfaceSetMode: {
        debug("cmd_InterfaceSetMode(%u)", unsigned(blheli.buf[0]));
        blheli.interface_mode[blheli.chan] = blheli.buf[0];
        blheli_send_reply(&blheli.interface_mode[blheli.chan], 1);
        break;
    }

    case cmd_DeviceRead: {
        uint16_t nbytes = blheli.buf[0]?blheli.buf[0]:256;
        debug("cmd_DeviceRead(%u) n=%u", blheli.chan, nbytes);
        uint8_t buf[nbytes];
        uint8_t cmd = blheli.interface_mode[blheli.chan]==imATM_BLB?CMD_READ_FLASH_ATM:CMD_READ_FLASH_SIL;
        if (!BL_ReadA(cmd, buf, nbytes)) {
            nbytes = 1;
        }
        blheli_send_reply(buf, nbytes);
        break;
    }

    case cmd_DevicePageErase: {
        uint8_t page = blheli.buf[0];
        debug("cmd_DevicePageErase(%u) im=%u", page, blheli.interface_mode[blheli.chan]);
        switch (blheli.interface_mode[blheli.chan]) {
        case imSIL_BLB:
        case imARM_BLB: {
            if  (blheli.interface_mode[blheli.chan] == imARM_BLB) {
                // Address =Page * 1024
                blheli.address = page << 10;
            } else {
                // Address =Page * 512
                blheli.address = page << 9;
            }
            debug("ARM PageErase 0x%04x", blheli.address);
            BL_PageErase();
            blheli.address = 0;
            blheli_send_reply(&page, 1);
            break;
        }
        default:
            blheli.ack = ACK_I_INVALID_CMD;
            blheli_send_reply(&page, 1);
            break;
        }
        break;
    }

    case cmd_DeviceWrite: {
        uint16_t nbytes = blheli.param_len;
        debug("cmd_DeviceWrite n=%u im=%u", nbytes, blheli.interface_mode[blheli.chan]);
        uint8_t buf[nbytes];
        memcpy(buf, blheli.buf, nbytes);
        switch (blheli.interface_mode[blheli.chan]) {
        case imSIL_BLB:
        case imATM_BLB:
        case imARM_BLB: {
            if (!BL_WriteFlash(buf, nbytes)) {
                // For reasons unknown BL_WriteFlash can bork the DMA engine, make some attempt to get
                // back to a sane state if this happens. We can't call serial_end() as that will 
                // restart dshot output
                debug_console("cmd_DeviceWrite failed 0x%x: %u bytes", blheli.address, nbytes);
                hal.rcout->serial_reset(motor_mask);
            }
            break;
        }
        case imSK: {
            debug("Unsupported flash mode imSK");
            break;
        }
        }
        uint8_t b=0;
        blheli_send_reply(&b, 1);        
        break;
    }

    case cmd_DeviceVerify: {
        uint16_t nbytes = blheli.param_len;
        debug("cmd_DeviceWrite n=%u im=%u", nbytes, blheli.interface_mode[blheli.chan]);
        switch (blheli.interface_mode[blheli.chan]) {
        case imARM_BLB: {
            uint8_t buf[nbytes];
            memcpy(buf, blheli.buf, nbytes);            
            BL_VerifyFlash(buf, nbytes);
            break;
        }
        default:
            blheli.ack = ACK_I_INVALID_CMD;
            break;
        }
        uint8_t b=0;
        blheli_send_reply(&b, 1);        
        break;
    }

    case cmd_DeviceReadEEprom: {
        uint16_t nbytes = blheli.buf[0]?blheli.buf[0]:256;
        uint8_t buf[nbytes];
        debug("cmd_DeviceReadEEprom n=%u im=%u", nbytes, blheli.interface_mode[blheli.chan]);
        switch (blheli.interface_mode[blheli.chan]) {
        case imATM_BLB: {
            if (!BL_ReadA(CMD_READ_EEPROM, buf, nbytes)) {
                blheli.ack = ACK_D_GENERAL_ERROR;
            }
            break;
        }
        default:
            blheli.ack = ACK_I_INVALID_CMD;
            break;
        }
        if (blheli.ack != ACK_OK) {
            nbytes = 1;
            buf[0] = 0;
        }
        blheli_send_reply(buf, nbytes);
        break;
    }

    case cmd_DeviceWriteEEprom: {
        uint16_t nbytes = blheli.param_len;
        uint8_t buf[nbytes];
        memcpy(buf, blheli.buf, nbytes);
        debug("cmd_DeviceWriteEEprom n=%u im=%u", nbytes, blheli.interface_mode[blheli.chan]);
        switch (blheli.interface_mode[blheli.chan]) {
        case imATM_BLB:
            BL_WriteA(CMD_PROG_EEPROM, buf, nbytes, 3000);
            break;
        default:
            blheli.ack = ACK_D_GENERAL_ERROR;
            break;
        }
        uint8_t b = 0;
        blheli_send_reply(&b, 1);
        break;
    }

    case cmd_DeviceEraseAll:
    case cmd_DeviceC2CK_LOW:
    default:
        // ack=unknown command
        blheli.ack = ACK_I_INVALID_CMD;
        debug("Unknown BLHeli protocol 0x%02x", blheli.command);
        uint8_t b = 0;
        blheli_send_reply(&b, 1);
        break;
    }
}

/*
  process an input byte, return true if we have received a whole
  packet with correct CRC
 */
bool AP_BLHeli::process_input(uint8_t b)
{
    bool valid_packet = false;

    if (msp.escMode == PROTOCOL_4WAY && blheli.state == BLHELI_IDLE && b == '$') {
        debug("Change to MSP mode");
        msp.escMode = PROTOCOL_NONE;
        serial_end();
    }
    if (msp.escMode != PROTOCOL_4WAY && msp.state == MSP_IDLE && b == '/') {
        debug("Change to BLHeli mode");
        memset(blheli.connected, 0, sizeof(blheli.connected));
        msp.escMode = PROTOCOL_4WAY;
    }
    if (msp.escMode == PROTOCOL_4WAY) {
        blheli_4way_process_byte(b);
    } else {
        msp_process_byte(b);
    }
    if (msp.escMode == PROTOCOL_4WAY) {
        if (blheli.state == BLHELI_COMMAND_RECEIVED) {
            valid_packet = true;
            last_valid_ms = AP_HAL::millis();
            if (uart->lock_port(BLHELI_UART_LOCK_KEY, 0)) {
                uart_locked = true;
            }
            blheli_process_command();
            blheli.state = BLHELI_IDLE;
            msp.state = MSP_IDLE;
        }
    } else if (msp.state == MSP_COMMAND_RECEIVED) {
        if (msp.packetType == MSP_PACKET_COMMAND) {
            valid_packet = true;
            if (uart->lock_port(BLHELI_UART_LOCK_KEY, 0)) {
                uart_locked = true;
            }
            last_valid_ms = AP_HAL::millis();
            msp_process_command();
        }
        msp.state = MSP_IDLE;
        blheli.state = BLHELI_IDLE;
    }

    return valid_packet;
}

/*
  protocol handler for detecting BLHeli input
 */
bool AP_BLHeli::protocol_handler(uint8_t b, AP_HAL::UARTDriver *_uart)
{
    uart = _uart;
    if (hal.util->get_soft_armed()) {
        // don't allow MSP control when armed
        return false;
    }
    return process_input(b);
}

/*
  run a connection test to the ESCs. This is used to test the
  operation of the BLHeli ESC protocol
*/
void AP_BLHeli::run_connection_test(uint8_t chan)
{
    run_test.set_and_notify(0);
    debug_uart = hal.console;
    uint8_t saved_chan = blheli.chan;
    if (chan >= num_motors) {
        GCS_SEND_TEXT(MAV_SEVERITY_INFO, "ESC: bad channel %u", chan);
        return;
    }
    blheli.chan = chan;
    GCS_SEND_TEXT(MAV_SEVERITY_INFO, "ESC: Running test on channel %u",  blheli.chan);
    bool passed = false;
    for (uint8_t tries=0; tries<5; tries++) {
        EXPECT_DELAY_MS(3000);
        blheli.ack = ACK_OK;
        setDisconnected();
        if (BL_ConnectEx()) {
            uint8_t buf[256];
            uint8_t cmd = blheli.interface_mode[blheli.chan]==imATM_BLB?CMD_READ_FLASH_ATM:CMD_READ_FLASH_SIL;
            passed = true;
            blheli.address = blheli.interface_mode[blheli.chan]==imATM_BLB?0:0x7c00;
            passed &= BL_ReadA(cmd, buf, sizeof(buf));
            if (blheli.interface_mode[blheli.chan]==imARM_BLB) {
                if (passed) {
                    // read status structure
                    blheli.address = esc_status_addr;
                    passed &= BL_SendCMDSetAddress();
                }
                if (passed) {
                    struct esc_status status;
                    passed &= BL_ReadA(CMD_READ_FLASH_SIL, (uint8_t *)&status, sizeof(status));
                }
            }
            BL_SendCMDRunRestartBootloader();
            break;
        }
    }
    serial_end();
    SRV_Channels::set_disabled_channel_mask(motors_disabled_mask);
    motors_disabled = false;
    blheli.chan = saved_chan;
    GCS_SEND_TEXT(MAV_SEVERITY_INFO, "ESC: Test %s", passed?"PASSED":"FAILED");
    debug_uart = nullptr;
}

/*
  update BLHeli
 */
void AP_BLHeli::update(void)
{
    bool motor_control_active = false;
    for (uint8_t i = 0; i < num_motors; i++) {
        bool reversed = ((1U<< motor_map[i]) & channel_reversible_mask.get()) != 0;
        if (hal.rcout->read( motor_map[i]) != (reversed ? 1500 : 1000)) {
            motor_control_active = true;
        }
    }

    uint32_t now = AP_HAL::millis();
    if (initialised && uart_locked &&
        ((timeout_sec && now - last_valid_ms > uint32_t(timeout_sec.get())*1000U) || 
        (motor_control_active && now - last_valid_ms > MOTOR_ACTIVE_TIMEOUT))) {
        // we're not processing requests any more, shutdown serial
        // output
        if (serial_start_ms) {
            serial_end();
        }
        if (motors_disabled) {
            motors_disabled = false;
            SRV_Channels::set_disabled_channel_mask(motors_disabled_mask);
        }
        if (uart != nullptr) {
            debug("Unlocked UART");
            uart->lock_port(0, 0);
            uart_locked = false;
        }
        if (motor_control_active) {
            for (uint8_t i = 0; i < num_motors; i++) {
                bool reversed = ((1U<<motor_map[i]) & channel_reversible_mask.get()) != 0;
                hal.rcout->write(motor_map[i], reversed ? 1500 : 1000);
            }
        }
    }

    if (initialised || (channel_mask.get() == 0 && channel_auto.get() == 0)) {
        if (initialised && run_test.get() > 0) {
            run_connection_test(run_test.get() - 1);
        }
    }
}

void AP_BLHeli::serial_end()
{
    hal.rcout->serial_end(motor_mask);
    serial_start_ms = 0;
}

/*
  Initialize BLHeli, called by SRV_Channels::init()
  Used to install protocol handler
  The motor mask of enabled motors can be passed in
 */
void AP_BLHeli::init(uint32_t mask, AP_HAL::RCOutput::output_mode otype)
{
    initialised = true;

    run_test.set_and_notify(0);

#if HAL_GCS_ENABLED
    // only install pass-thru protocol handler if either auto or the motor mask are set
    if (channel_mask.get() != 0 || channel_auto.get() != 0) {
        if (last_control_port > 0 && last_control_port != control_port) {
            gcs().install_alternative_protocol((mavlink_channel_t)(MAVLINK_COMM_0+last_control_port), nullptr);
            last_control_port = -1;
        }
        if (gcs().install_alternative_protocol((mavlink_channel_t)(MAVLINK_COMM_0+control_port),
                                            FUNCTOR_BIND_MEMBER(&AP_BLHeli::protocol_handler,
                                                                bool, uint8_t, AP_HAL::UARTDriver *))) {
            debug("BLHeli installed on port %u", (unsigned)control_port);
            last_control_port = control_port;
        }
    }
#endif // HAL_GCS_ENABLED

#if HAL_WITH_IO_MCU
    if (AP_BoardConfig::io_enabled()) {
        // with IOMCU the local (FMU) channels start at 8
        chan_offset = 8;
    }
#endif

    mask |= uint32_t(channel_mask.get());

    /*
      allow mode override - this makes it possible to use DShot for
      rovers and subs, plus for quadplane fwd motors
     */
    // +1 converts from AP_Motors::pwm_type to AP_HAL::RCOutput::output_mode and saves doing a param conversion
    // this is the only use of the param, but this is still a bit of a hack
    const int16_t type = output_type.get() + 1;
    if (otype == AP_HAL::RCOutput::MODE_PWM_NONE) {
        otype = ((type > AP_HAL::RCOutput::MODE_PWM_NONE) && (type < AP_HAL::RCOutput::MODE_NEOPIXEL)) ? AP_HAL::RCOutput::output_mode(type) : AP_HAL::RCOutput::MODE_PWM_NONE;
    }
    switch (otype) {
    case AP_HAL::RCOutput::MODE_PWM_ONESHOT:
    case AP_HAL::RCOutput::MODE_PWM_ONESHOT125:
    case AP_HAL::RCOutput::MODE_PWM_BRUSHED:
    case AP_HAL::RCOutput::MODE_PWM_DSHOT150:
    case AP_HAL::RCOutput::MODE_PWM_DSHOT300:
    case AP_HAL::RCOutput::MODE_PWM_DSHOT600:
    case AP_HAL::RCOutput::MODE_PWM_DSHOT1200:
        if (mask) {
            hal.rcout->set_output_mode(mask, otype);
        }
        break;
    default:
        break;
    }

    uint32_t digital_mask = 0;
    // setting the digital mask changes the min/max PWM values
    // it's important that this is NOT done for non-digital channels as otherwise
    // PWM min can result in motors turning. set for individual overrides first
    if (mask && hal.rcout->is_dshot_protocol(otype)) {
        digital_mask = mask;
    }

#if APM_BUILD_COPTER_OR_HELI || APM_BUILD_TYPE(APM_BUILD_ArduPlane) || APM_BUILD_TYPE(APM_BUILD_Rover)
    /*
      plane and copter can use AP_Motors to get an automatic mask
     */
#if APM_BUILD_TYPE(APM_BUILD_Rover)
    AP_MotorsUGV *motors = AP::motors_ugv();
#else
    AP_Motors *motors = AP::motors();
#endif
    if (motors) {
        uint32_t motormask = motors->get_motor_mask();
        // set the rest of the digital channels
        if (motors->is_digital_pwm_type()) {
            digital_mask |= motormask;
        }
        mask |= motormask;
    }
#endif
    // tell SRV_Channels about ESC capabilities
    SRV_Channels::set_digital_outputs(digital_mask, uint32_t(channel_reversible_mask.get()) & digital_mask);
    // the dshot ESC type is required in order to send the reversed/reversible dshot command correctly
    hal.rcout->set_dshot_esc_type(SRV_Channels::get_dshot_esc_type());
    hal.rcout->set_reversible_mask(uint32_t(channel_reversible_mask.get()) & digital_mask);
    hal.rcout->set_reversed_mask(uint32_t(channel_reversed_mask.get()) & digital_mask);
#ifdef HAL_WITH_BIDIR_DSHOT
    // possibly enable bi-directional dshot
    hal.rcout->set_motor_poles(motor_poles);
#endif
#if defined(HAL_WITH_BIDIR_DSHOT) || HAL_WITH_IO_MCU_BIDIR_DSHOT
    hal.rcout->set_bidir_dshot_mask(uint32_t(channel_bidir_dshot_mask.get()) & digital_mask);
#endif
    // add motors from channel mask
    for (uint8_t i=0; i<16 && num_motors < max_motors; i++) {
        if (digital_mask & (1U<<i)) {
            motor_map[num_motors] = i;
            num_motors++;
        }
    }
    motor_mask = mask;
    debug("ESC: %u motors mask=0x%08lx", num_motors, digital_mask);

    // check if we have a combination of reversible and normal
    mixed_type = (mask != (mask & channel_reversible_mask.get())) && (channel_reversible_mask.get() != 0);

    if (num_motors != 0 && telem_rate > 0) {
        AP_SerialManager *serial_manager = AP_SerialManager::get_singleton();
        if (serial_manager) {
            telem_uart = serial_manager->find_serial(AP_SerialManager::SerialProtocol_ESCTelemetry,0);
        }
    }
}

/*
  read an ESC telemetry packet
 */
void AP_BLHeli::read_telemetry_packet(void)
{
#if HAL_WITH_ESC_TELEM
    uint8_t buf[telem_packet_size];
    if (telem_uart->read(buf, telem_packet_size) < telem_packet_size) {
        // short read, we should have 10 bytes ready when this function is called
        return;
    }

    // calculate crc
    uint8_t crc = 0;
    for (uint8_t i=0; i<telem_packet_size-1; i++) {    
        crc = crc8_dvb(buf[i], crc, 0x07);
    }

    if (buf[telem_packet_size-1] != crc) {
        // bad crc
        debug("Bad CRC on %u", last_telem_esc);
        return;
    }
    // record the previous rpm so that we can slew to the new one
    uint16_t new_rpm = ((buf[7]<<8) | buf[8]) * 200 / motor_poles;
    const uint8_t motor_idx = motor_map[last_telem_esc];
    // we have received valid data, mark the ESC as now active
    hal.rcout->set_active_escs_mask(1<<motor_idx);
    update_rpm(motor_idx, new_rpm);

    TelemetryData t {
        .temperature_cdeg = int16_t(buf[0] * 100),
        .voltage = float(uint16_t((buf[1]<<8) | buf[2])) * 0.01,
        .current = float(uint16_t((buf[3]<<8) | buf[4])) * 0.01,
        .consumption_mah = float(uint16_t((buf[5]<<8) | buf[6])),
    };

    update_telem_data(motor_idx, t,
        AP_ESC_Telem_Backend::TelemetryType::CURRENT
            | AP_ESC_Telem_Backend::TelemetryType::VOLTAGE
            | AP_ESC_Telem_Backend::TelemetryType::CONSUMPTION
            | AP_ESC_Telem_Backend::TelemetryType::TEMPERATURE);

    if (debug_level >= 2) {
        uint16_t trpm = new_rpm;
        if (has_bidir_dshot(last_telem_esc)) {
            trpm = hal.rcout->get_erpm(motor_idx);
            if (trpm != 0xFFFF) {
                trpm = trpm * 200 / motor_poles;
            }
        }
        DEV_PRINTF("ESC[%u] T=%u V=%f C=%f con=%f RPM=%u e=%.1f t=%u\n",
                            last_telem_esc,
                            t.temperature_cdeg,
                            t.voltage,
                            t.current,
                            t.consumption_mah,
                            trpm, hal.rcout->get_erpm_error_rate(motor_idx), (unsigned)AP_HAL::millis());
    }
#endif // HAL_WITH_ESC_TELEM
}

/*
  log bidir telemetry - only called if BLH telemetry is not active
 */
void AP_BLHeli::log_bidir_telemetry(void)
{
    uint32_t now = AP_HAL::millis();

    if (debug_level >= 2 && now - last_log_ms[last_telem_esc] > 100) {
        if (has_bidir_dshot(last_telem_esc)) {
            const uint8_t motor_idx = motor_map[last_telem_esc];
            uint16_t trpm = hal.rcout->get_erpm(motor_idx);
            if (trpm != 0xFFFF) {    // don't log invalid values as they are never used
                trpm = trpm * 200 / motor_poles;
            }

            if (trpm > 0) {
                last_log_ms[last_telem_esc] = now;
                DEV_PRINTF("ESC[%u] RPM=%u e=%.1f t=%u\n", last_telem_esc, trpm, hal.rcout->get_erpm_error_rate(motor_idx), (unsigned)AP_HAL::millis());
            }
        }
    }

    if (!SRV_Channels::have_digital_outputs()) {
        return;
    }

    // ask the next ESC for telemetry
    uint8_t idx_pos = last_telem_esc;
    uint8_t idx = (idx_pos + 1) % num_motors;
    for (; idx != idx_pos; idx = (idx + 1) % num_motors) {
        if (SRV_Channels::have_digital_outputs(1U << motor_map[idx])) {
            break;
        }
    }
    if (SRV_Channels::have_digital_outputs(1U << motor_map[idx])) {
        last_telem_esc = idx;
    }
}

/*
  update BLHeli telemetry handling
  This is called on push() in SRV_Channels
 */
void AP_BLHeli::update_telemetry(void)
{
#ifdef HAL_WITH_BIDIR_DSHOT
    // we might only have bi-dir dshot
    if (channel_bidir_dshot_mask.get() != 0 && !telem_uart) {
        log_bidir_telemetry();
    }
#endif
    if (!telem_uart || !SRV_Channels::have_digital_outputs()) {
        return;
    }
    uint32_t now = AP_HAL::micros();
    uint32_t telem_rate_us = 1000000U / uint32_t(telem_rate.get() * num_motors);
    if (telem_rate_us < 2000) {
        // make sure we have a gap between frames
        telem_rate_us = 2000;
    }
    if (!telem_uart_started || !telem_uart->is_owned_by_current_thread()) {
        // we need to use begin() here to ensure the correct thread owns the uart
        telem_uart->begin(115200);
        telem_uart_started = true;
    }

    uint32_t nbytes = telem_uart->available();

    if (nbytes > telem_packet_size) {
        // if we have more than 10 bytes then we don't know which ESC
        // they are from. Throw them all away
        telem_uart->discard_input();
        return;
    }
    if (nbytes > 0 &&
        nbytes < telem_packet_size &&
        (last_telem_byte_read_us == 0 ||
         now - last_telem_byte_read_us < 1000)) {
        // wait a bit longer, we don't have enough bytes yet
        if (last_telem_byte_read_us == 0) {
            last_telem_byte_read_us = now;
        }
        return;
    }
    if (nbytes > 0 && nbytes < telem_packet_size) {
        // we've waited long enough, discard bytes if we don't have 10 yet
        telem_uart->discard_input();
        return;
    }
    if (nbytes == telem_packet_size) {
        // we have a full packet ready to parse
        read_telemetry_packet();
        last_telem_byte_read_us = 0;
    }
    // we need to keep requesting telemetry even if we don't receive anything
    // as the request mask will be reset next cycle.
    if (now - last_telem_request_us >= telem_rate_us) {
        // ask the next ESC for telemetry
        uint8_t idx_pos = last_telem_esc;
        uint8_t idx = (idx_pos + 1) % num_motors;
        for (; idx != idx_pos; idx = (idx + 1) % num_motors) {
            if (SRV_Channels::have_digital_outputs(1U << motor_map[idx])) {
                break;
            }
        }
        uint32_t mask = 1U << motor_map[idx];
        if (SRV_Channels::have_digital_outputs(mask)) {
            hal.rcout->set_telem_request_mask(mask);
            last_telem_esc = idx;
            last_telem_request_us = now;
        }
    }
}

#endif // HAVE_AP_BLHELI_SUPPORT