ardupilot/libraries/AP_MSP/AP_MSP_Telem_Backend.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/>.
*/

#include <AP_AHRS/AP_AHRS.h>
#include <AP_Baro/AP_Baro.h>
#include <AP_Airspeed/AP_Airspeed.h>
#include <AP_BattMonitor/AP_BattMonitor.h>
#include <AP_Compass/AP_Compass.h>
#include <AP_ESC_Telem/AP_ESC_Telem.h>
#include <RC_Channel/RC_Channel.h>
#include <AP_Common/AP_FWVersion.h>
#include <AP_GPS/AP_GPS.h>
#include <AP_Notify/AP_Notify.h>
#include <AP_OpticalFlow/AP_OpticalFlow.h>
#include <AP_RangeFinder/AP_RangeFinder.h>
#include <AP_RCMapper/AP_RCMapper.h>
#include <AP_RSSI/AP_RSSI.h>
#include <AP_RTC/AP_RTC.h>
#include <GCS_MAVLink/GCS.h>

#include "AP_MSP.h"
#include "AP_MSP_Telem_Backend.h"

#include <ctype.h>
#include <stdio.h>

#if HAL_MSP_ENABLED

extern const AP_HAL::HAL& hal;
constexpr uint8_t AP_MSP_Telem_Backend::arrows[8];

using namespace MSP;

AP_MSP_Telem_Backend::AP_MSP_Telem_Backend(AP_HAL::UARTDriver *uart) : AP_RCTelemetry(MSP_TIME_SLOT_MAX)
{
    _msp_port.uart = uart;
}

/*
  Scheduler helper
 */
void AP_MSP_Telem_Backend::setup_wfq_scheduler(void)
{
    // initialize packet weights for the WFQ scheduler
    // priority[i] = 1/_scheduler.packet_weight[i]
    // rate[i] = LinkRate * ( priority[i] / (sum(priority[1-n])) )

    set_scheduler_entry(EMPTY_SLOT, 50, 50);          // nothing to send
    set_scheduler_entry(NAME, 200, 200);              // 5Hz  12 chars string used for general purpose text messages
    set_scheduler_entry(STATUS, 500, 500);            // 2Hz  flightmode
    set_scheduler_entry(CONFIG, 200, 200);            // 5Hz  OSD item positions
    set_scheduler_entry(RAW_GPS, 250, 250);           // 4Hz  GPS lat/lon
    set_scheduler_entry(COMP_GPS, 250, 250);          // 4Hz  home direction and distance
    set_scheduler_entry(ATTITUDE, 200, 200);          // 5Hz  attitude
    set_scheduler_entry(ALTITUDE, 250, 250);          // 4Hz  altitude(cm) and velocity(cm/s)
    set_scheduler_entry(ANALOG, 250, 250);            // 4Hz  rssi + batt
#if AP_BATTERY_ENABLED
    set_scheduler_entry(BATTERY_STATE, 500, 500);     // 2Hz  battery
#endif
#if HAL_WITH_ESC_TELEM
    set_scheduler_entry(ESC_SENSOR_DATA, 500, 500);   // 2Hz  ESC telemetry
#endif
    set_scheduler_entry(RTC_DATETIME, 1000, 1000);    // 1Hz  RTC
}

/*
 * init - perform required initialisation
 */
bool AP_MSP_Telem_Backend::init()
{
    enable_warnings();
    return AP_RCTelemetry::init();
}

bool AP_MSP_Telem_Backend::init_uart()
{
    if (_msp_port.uart != nullptr)  {
        // re-init port here for use in this thread
        _msp_port.uart->begin(0);
        return true;
    }
    return false;
}

void AP_MSP_Telem_Backend::process_outgoing_data()
{
    if (is_scheduler_enabled()) {
        AP_RCTelemetry::run_wfq_scheduler();
    }
}

/*
  Scheduler helper
 */
bool AP_MSP_Telem_Backend::is_packet_ready(uint8_t idx, bool queue_empty)
{
    switch (idx) {
    case EMPTY_SLOT:        // empty slot
    case NAME:              // used for status_text messages
    case STATUS:            // flightmode
    case CONFIG:            // OSD config
    case RAW_GPS:           // lat,lon, speed
    case COMP_GPS:          // home dir,dist
    case ATTITUDE:          // Attitude
    case ALTITUDE:          // Altitude and Vario
    case ANALOG:            // Rssi, Battery, mAh, Current
#if AP_BATTERY_ENABLED
    case BATTERY_STATE:     // voltage, capacity, current, mAh
#endif
#if HAL_WITH_ESC_TELEM
    case ESC_SENSOR_DATA:   // esc temp + rpm
#endif
    case RTC_DATETIME:      // RTC
        return true;
    default:
        return false;
    }
}

/*
  Invoked at each scheduler step
 */
void AP_MSP_Telem_Backend::process_packet(uint8_t idx)
{
    if (idx == EMPTY_SLOT) {
        return;
    }

    uint8_t out_buf[MSP_PORT_OUTBUF_SIZE] {};

    msp_packet_t reply = {
        .buf = { .ptr = out_buf, .end = MSP_ARRAYEND(out_buf), },
        .cmd = (int16_t)msp_packet_type_map[idx],
        .flags = 0,
        .result = 0,
    };
    uint8_t *out_buf_head = reply.buf.ptr;

    msp_process_out_command(msp_packet_type_map[idx], &reply.buf);
    uint32_t len = reply.buf.ptr - &out_buf[0];
    sbuf_switch_to_reader(&reply.buf, out_buf_head); // change streambuf direction
    if (len > 0) {
        // don't send zero length packets
        msp_serial_encode(&_msp_port, &reply, _msp_port.msp_version);
    }

    _msp_port.c_state = MSP_IDLE;
}

#if AP_BATTERY_ENABLED
uint8_t AP_MSP_Telem_Backend::calc_cell_count(const float battery_voltage)
{
    return floorf((battery_voltage / CELLFULL) + 1);
}
#endif

float AP_MSP_Telem_Backend::get_vspeed_ms(void) const
{
    {
        // release semaphore as soon as possible
        AP_AHRS &_ahrs = AP::ahrs();
        Vector3f v {};
        WITH_SEMAPHORE(_ahrs.get_semaphore());
        if (_ahrs.get_velocity_NED(v)) {
            return -v.z;
        }
    }
    AP_Baro &_baro = AP::baro();
    WITH_SEMAPHORE(_baro.get_semaphore());
    return _baro.get_climb_rate();
}

void AP_MSP_Telem_Backend::update_home_pos(home_state_t &home_state)
{
    AP_AHRS &_ahrs = AP::ahrs();
    WITH_SEMAPHORE(_ahrs.get_semaphore());
    Location loc;
    float alt;
    if (_ahrs.get_location(loc) && _ahrs.home_is_set()) {
        const Location &home_loc = _ahrs.get_home();
        home_state.home_distance_m = home_loc.get_distance(loc);
        home_state.home_bearing_cd = loc.get_bearing_to(home_loc);
    } else {
        home_state.home_distance_m = 0;
        home_state.home_bearing_cd = 0;
    }
    _ahrs.get_relative_position_D_home(alt);
    home_state.rel_altitude_cm = -alt * 100;
    home_state.home_is_set = _ahrs.home_is_set();
}

#if AP_GPS_ENABLED
void AP_MSP_Telem_Backend::update_gps_state(gps_state_t &gps_state)
{
    AP_GPS& gps = AP::gps();

    memset(&gps_state, 0, sizeof(gps_state));

    WITH_SEMAPHORE(gps.get_semaphore());
    gps_state.fix_type = gps.status() >= AP_GPS::GPS_Status::GPS_OK_FIX_3D? 2:0;
    gps_state.num_sats = gps.num_sats();

    if (gps_state.fix_type > 0) {
        const Location &loc = AP::gps().location(); //get gps instance 0
        gps_state.lat = loc.lat;
        gps_state.lon = loc.lng;
        gps_state.alt_m = loc.alt/100; // 1m resolution
        gps_state.speed_cms = gps.ground_speed() * 100;
        gps_state.ground_course_cd = gps.ground_course_cd();
    }
}
#endif

#if AP_BATTERY_ENABLED
void AP_MSP_Telem_Backend::update_battery_state(battery_state_t &battery_state)
{
    memset(&battery_state, 0, sizeof(battery_state));

    const AP_BattMonitor &_battery = AP::battery();
    if (!_battery.current_amps(battery_state.batt_current_a)) {
        battery_state.batt_current_a = 0;
    }
    if (!_battery.consumed_mah(battery_state.batt_consumed_mah)) {
        battery_state.batt_consumed_mah = 0;
    }
    battery_state.batt_voltage_v =_battery.voltage();
    battery_state.batt_capacity_mah = _battery.pack_capacity_mah();

    const AP_Notify& notify = AP::notify();
    if (notify.flags.failsafe_battery) {
        battery_state.batt_state = MSP_BATTERY_CRITICAL;
    } else {
        battery_state.batt_state = MSP_BATTERY_OK;
    }
    // detect cellcount and update only if we get a higher values, we do not want to update it while discharging
    uint8_t cc = calc_cell_count(battery_state.batt_voltage_v);
    if (cc > battery_state.batt_cellcount) {
        battery_state.batt_cellcount = cc;
    }
}
#endif  // AP_BATTERY_ENABLED

void AP_MSP_Telem_Backend::update_airspeed(airspeed_state_t &airspeed_state)
{
    AP_AHRS &ahrs = AP::ahrs();
    WITH_SEMAPHORE(ahrs.get_semaphore());
    airspeed_state.airspeed_have_estimate = ahrs.airspeed_estimate(airspeed_state.airspeed_estimate_ms);
    if (!airspeed_state.airspeed_have_estimate) {
        airspeed_state.airspeed_estimate_ms = 0.0;
    }
}

/*
    MSP OSDs can display up to MSP_TXT_VISIBLE_CHARS chars (UTF8 characters are supported)
    We display the flight mode string either with or without wind state
*/
void AP_MSP_Telem_Backend::update_flight_mode_str(char *flight_mode_str, uint8_t size, bool wind_enabled)
{
#if OSD_ENABLED
    AP_OSD *osd = AP::osd();
    if (osd == nullptr) {
        return;
    }
#endif
    AP_Notify *notify = AP_Notify::get_singleton();
    if (notify == nullptr) {
        return;
    }
    // clear
    memset(flight_mode_str, 0, size);

    if (wind_enabled) {
        /*
          Wind is rendered next to the current flight mode, for the direction we use an UTF8 arrow (bytes 0xE286[nn])
          example: MANU 4m/s ↗
        */
        AP_AHRS &ahrs = AP::ahrs();
        Vector3f v;
        {
            WITH_SEMAPHORE(ahrs.get_semaphore());
            v = ahrs.wind_estimate();
        }
        bool invert_wind = false;
#if OSD_ENABLED
        AP_MSP *msp = AP::msp();
        if (msp == nullptr) {
            return;
        }

        invert_wind = osd->screen[msp->_msp_status.current_screen].check_option(AP_OSD::OPTION_INVERTED_WIND);
#endif
        if (invert_wind) {
            v = -v;
        }
        uint8_t units = OSD_UNIT_METRIC;
#if OSD_ENABLED
        units = osd->units == AP_OSD::UNITS_IMPERIAL ?  OSD_UNIT_IMPERIAL : OSD_UNIT_METRIC;
#endif
        // if needed convert m/s to ft/s
        const float v_length = (units == OSD_UNIT_METRIC) ? v.length() : v.length() * 3.28084;
        const char* unit = (units == OSD_UNIT_METRIC) ? "m/s" : "f/s";

        if (v_length > 1.0f) {
            const int32_t angle = wrap_360_cd(DEGX100 * atan2f(v.y, v.x) - ahrs.yaw_sensor);
            const int32_t interval = 36000 / ARRAY_SIZE(arrows);
            uint8_t arrow = arrows[((angle + interval / 2) / interval) % ARRAY_SIZE(arrows)];
            snprintf(flight_mode_str, size, "%s %d%s%c%c%c", notify->get_flight_mode_str(),  (uint8_t)roundf(v_length), unit, 0xE2, 0x86, arrow);
        } else {
            snprintf(flight_mode_str, size, "%s ---%s", notify->get_flight_mode_str(), unit);
        }
    } else {
        /*
            Flight mode is rendered with simple mode flags
            examples:
                MANU
                MANU [S]
                MANU [SS]
        */
#if HAL_GCS_ENABLED
        const char* simple_mode_str = gcs().simple_input_active() ? " [S]" : (gcs().supersimple_input_active() ? " [SS]" : "");
        snprintf(flight_mode_str, size, "%s%s", notify->get_flight_mode_str(), simple_mode_str);
#else
        snprintf(flight_mode_str, size, "%s", notify->get_flight_mode_str());
#endif
    }
}

void AP_MSP_Telem_Backend::enable_warnings()
{
    AP_MSP *msp = AP::msp();
    if (msp == nullptr) {
        return;
    }
    BIT_SET(msp->_osd_config.enabled_warnings, OSD_WARNING_FAIL_SAFE);
#if AP_BATTERY_ENABLED
    BIT_SET(msp->_osd_config.enabled_warnings, OSD_WARNING_BATTERY_CRITICAL);
#endif
}

void AP_MSP_Telem_Backend::process_incoming_data()
{
    if (_msp_port.uart == nullptr) {
        return;
    }

    uint32_t numc = MIN(_msp_port.uart->available(), 1024U);

    if (numc > 0) {
        // Process incoming bytes
        while (numc-- > 0) {
            const uint8_t c = _msp_port.uart->read();
            msp_parse_received_data(&_msp_port, c);

            if (_msp_port.c_state == MSP_COMMAND_RECEIVED) {
                msp_process_received_command();
            }
        }
    }
}

/*
  send an MSP packet
 */
void AP_MSP_Telem_Backend::msp_send_packet(uint16_t cmd, MSP::msp_version_e msp_version, const void *p, uint16_t size, bool is_request)
{
    uint8_t out_buf[MSP_PORT_OUTBUF_SIZE];

    msp_packet_t pkt = {
        .buf = { .ptr = out_buf, .end = MSP_ARRAYEND(out_buf), },
        .cmd = (int16_t)cmd,
        .flags = 0,
        .result = 0,
    };

    sbuf_write_data(&pkt.buf, p, size);
    sbuf_switch_to_reader(&pkt.buf, &out_buf[0]);
    msp_serial_encode(&_msp_port, &pkt, msp_version, is_request);
}

/*
  ported from betaflight/src/main/msp/msp_serial.c
 */
void AP_MSP_Telem_Backend::msp_process_received_command()
{
    uint8_t out_buf[MSP_PORT_OUTBUF_SIZE];

    msp_packet_t reply = {
        .buf = { .ptr = out_buf, .end = MSP_ARRAYEND(out_buf), },
        .cmd = -1,
        .flags = 0,
        .result = 0,
    };
    uint8_t *out_buf_head = reply.buf.ptr;

    msp_packet_t command = {
        .buf = { .ptr = _msp_port.in_buf, .end = _msp_port.in_buf + _msp_port.data_size, },
        .cmd = (int16_t)_msp_port.cmd_msp,
        .flags = _msp_port.cmd_flags,
        .result = 0,
    };

    const MSPCommandResult status = msp_process_command(&command, &reply);

    if (status != MSP_RESULT_NO_REPLY) {
        sbuf_switch_to_reader(&reply.buf, out_buf_head); // change streambuf direction
        msp_serial_encode(&_msp_port, &reply, _msp_port.msp_version);
    }

    _msp_port.c_state = MSP_IDLE;
}

/*
  ported from inav/src/main/fc/fc_msp.c
 */
MSPCommandResult AP_MSP_Telem_Backend::msp_process_command(msp_packet_t *cmd, msp_packet_t *reply)
{
    MSPCommandResult ret = MSP_RESULT_ACK;
    sbuf_t *dst = &reply->buf;
    sbuf_t *src = &cmd->buf;
    const uint16_t cmd_msp = cmd->cmd;
    // initialize reply by default
    reply->cmd = cmd->cmd;

    if (MSP2_IS_SENSOR_MESSAGE(cmd_msp)) {
        ret = msp_process_sensor_command(cmd_msp, src);
    } else {
        ret = msp_process_out_command(cmd_msp, dst);
    }

    // Process DONT_REPLY flag
    if (cmd->flags & MSP_FLAG_DONT_REPLY) {
        ret = MSP_RESULT_NO_REPLY;
    }

    reply->result = ret;
    return ret;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_command(uint16_t cmd_msp, sbuf_t *dst)
{
    switch (cmd_msp) {
    case MSP_API_VERSION:
        return msp_process_out_api_version(dst);
    case MSP_FC_VARIANT:
        return msp_process_out_fc_variant(dst);
    case MSP_FC_VERSION:
        return msp_process_out_fc_version(dst);
    case MSP_BOARD_INFO:
        return msp_process_out_board_info(dst);
    case MSP_BUILD_INFO:
        return msp_process_out_build_info(dst);
    case MSP_NAME:
        return msp_process_out_name(dst);
    case MSP_OSD_CONFIG:
        return msp_process_out_osd_config(dst);
    case MSP_STATUS:
    case MSP_STATUS_EX:
        return msp_process_out_status(dst);
    case MSP_RAW_GPS:
        return msp_process_out_raw_gps(dst);
    case MSP_COMP_GPS:
        return msp_process_out_comp_gps(dst);
    case MSP_ATTITUDE:
        return msp_process_out_attitude(dst);
    case MSP_ALTITUDE:
        return msp_process_out_altitude(dst);
    case MSP_ANALOG:
        return msp_process_out_analog(dst);
#if AP_BATTERY_ENABLED
    case MSP_BATTERY_STATE:
        return msp_process_out_battery_state(dst);
#endif
    case MSP_UID:
        return msp_process_out_uid(dst);
#if HAL_WITH_ESC_TELEM
    case MSP_ESC_SENSOR_DATA:
        return msp_process_out_esc_sensor_data(dst);
#endif
    case MSP_RTC:
        return msp_process_out_rtc(dst);
    case MSP_RC:
        return msp_process_out_rc(dst);
    default:
        // MSP always requires an ACK even for unsupported messages
        return MSP_RESULT_ACK;
    }
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_sensor_command(uint16_t cmd_msp, sbuf_t *src)
{
    MSP_UNUSED(src);

    switch (cmd_msp) {
    case MSP2_SENSOR_RANGEFINDER: {
        const MSP::msp_rangefinder_data_message_t *pkt = (const MSP::msp_rangefinder_data_message_t *)src->ptr;
        msp_handle_rangefinder(*pkt);
    }
    break;
    case MSP2_SENSOR_OPTIC_FLOW: {
        const MSP::msp_opflow_data_message_t *pkt = (const MSP::msp_opflow_data_message_t *)src->ptr;
        msp_handle_opflow(*pkt);
    }
    break;
    case MSP2_SENSOR_GPS: {
        const MSP::msp_gps_data_message_t *pkt = (const MSP::msp_gps_data_message_t *)src->ptr;
        msp_handle_gps(*pkt);
    }
    break;
    case MSP2_SENSOR_COMPASS: {
        const MSP::msp_compass_data_message_t *pkt = (const MSP::msp_compass_data_message_t *)src->ptr;
        msp_handle_compass(*pkt);
    }
    break;
    case MSP2_SENSOR_BAROMETER: {
        const MSP::msp_baro_data_message_t *pkt = (const MSP::msp_baro_data_message_t *)src->ptr;
        msp_handle_baro(*pkt);
    }
    break;
    case MSP2_SENSOR_AIRSPEED: {
        const MSP::msp_airspeed_data_message_t *pkt = (const MSP::msp_airspeed_data_message_t *)src->ptr;
        msp_handle_airspeed(*pkt);
    }
    break;
    }

    return MSP_RESULT_NO_REPLY;
}

void AP_MSP_Telem_Backend::msp_handle_opflow(const MSP::msp_opflow_data_message_t &pkt)
{
#if HAL_MSP_OPTICALFLOW_ENABLED
    AP_OpticalFlow *optflow = AP::opticalflow();
    if (optflow == nullptr) {
        return;
    }
    optflow->handle_msp(pkt);
#endif
}

void AP_MSP_Telem_Backend::msp_handle_rangefinder(const MSP::msp_rangefinder_data_message_t &pkt)
{
#if HAL_MSP_RANGEFINDER_ENABLED
    RangeFinder *rangefinder = AP::rangefinder();
    if (rangefinder == nullptr) {
        return;
    }
    rangefinder->handle_msp(pkt);
#endif
}

void AP_MSP_Telem_Backend::msp_handle_gps(const MSP::msp_gps_data_message_t &pkt)
{
#if HAL_MSP_GPS_ENABLED
    AP::gps().handle_msp(pkt);
#endif
}

void AP_MSP_Telem_Backend::msp_handle_compass(const MSP::msp_compass_data_message_t &pkt)
{
#if AP_COMPASS_MSP_ENABLED
    AP::compass().handle_msp(pkt);
#endif
}

void AP_MSP_Telem_Backend::msp_handle_baro(const MSP::msp_baro_data_message_t &pkt)
{
#if AP_BARO_MSP_ENABLED
    AP::baro().handle_msp(pkt);
#endif
}

void AP_MSP_Telem_Backend::msp_handle_airspeed(const MSP::msp_airspeed_data_message_t &pkt)
{
#if AP_AIRSPEED_MSP_ENABLED && AP_AIRSPEED_ENABLED
    auto *airspeed = AP::airspeed();
    if (airspeed) {
        airspeed->handle_msp(pkt);
    }
#endif
}

uint32_t AP_MSP_Telem_Backend::get_osd_flight_mode_bitmask(void)
{
    // Note: we only set the BOXARM bit (bit 0) which is the same for BF, INAV and DJI VTX
    // When armed we simply return 1 (1 == 1 << 0)
    if (hal.util->get_soft_armed()) {
        return 1U;
    }
    return 0U;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_api_version(sbuf_t *dst)
{
    const struct {
        uint8_t proto;
        uint8_t major;
        uint8_t minor;
    } api_version  {
        proto : MSP_PROTOCOL_VERSION,
        major : API_VERSION_MAJOR,
        minor : API_VERSION_MINOR
    };

    sbuf_write_data(dst, &api_version, sizeof(api_version));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_fc_version(sbuf_t *dst)
{
    const struct {
        uint8_t major;
        uint8_t minor;
        uint8_t patch;
    } fc_version {
        major : FC_VERSION_MAJOR,
        minor : FC_VERSION_MINOR,
        patch : FC_VERSION_PATCH_LEVEL
    };

    sbuf_write_data(dst, &fc_version, sizeof(fc_version));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_fc_variant(sbuf_t *dst)
{
    sbuf_write_data(dst, "ARDU", FLIGHT_CONTROLLER_IDENTIFIER_LENGTH);
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_raw_gps(sbuf_t *dst)
{
#if OSD_ENABLED
    AP_OSD *osd = AP::osd();
    if (osd == nullptr) {
        return MSP_RESULT_ERROR;
    }
#endif
    gps_state_t gps_state {};
#if AP_GPS_ENABLED
    update_gps_state(gps_state);
#endif

    // handle airspeed override
    bool airspeed_en = false;
#if OSD_ENABLED
    AP_MSP *msp = AP::msp();
    if (msp == nullptr) {
        return MSP_RESULT_ERROR;
    }

    airspeed_en = osd->screen[msp->_msp_status.current_screen].aspeed.enabled;
#endif
    if (airspeed_en) {
        airspeed_state_t airspeed_state;
        update_airspeed(airspeed_state);
        gps_state.speed_cms = airspeed_state.airspeed_estimate_ms * 100;           // airspeed in cm/s
    }

    sbuf_write_data(dst, &gps_state, sizeof(gps_state));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_comp_gps(sbuf_t *dst)
{
    home_state_t home_state;
    update_home_pos(home_state);

    // no need to apply yaw compensation, the DJI air unit will do it for us :-)
    uint16_t angle_deg = home_state.home_bearing_cd * 0.01;
    if (home_state.home_distance_m < 2) {
        //avoid fast rotating arrow at small distances
        angle_deg = 0;
    }

    const struct PACKED {
        uint16_t dist_home_m;
        uint16_t home_angle_deg;
        uint8_t toggle_gps;
    } gps {
        dist_home_m : uint16_t(constrain_int32(home_state.home_distance_m, 0, 0xFFFF)),
        home_angle_deg : angle_deg,
        toggle_gps : 1
    };

    sbuf_write_data(dst, &gps, sizeof(gps));
    return MSP_RESULT_ACK;
}

// Autoscroll message is the same as in minimosd-extra.
// Thanks to night-ghost for the approach.
MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_name(sbuf_t *dst)
{
#if OSD_ENABLED
    AP_OSD *osd = AP::osd();
    if (osd == nullptr) {
        return MSP_RESULT_ERROR;
    }
#endif
    AP_MSP *msp = AP::msp();
    if (msp == nullptr) {
        return MSP_RESULT_ERROR;
    }
    AP_Notify * notify = AP_Notify::get_singleton();
    if (notify) {
        uint16_t msgtime_ms = 10000; //default is 10 secs
#if OSD_ENABLED
        msgtime_ms = AP::osd()->msgtime_s * 1000;
#endif
        // text message is visible for _msp.msgtime_s but only if
        // a flight mode change did not steal focus
        const uint32_t visible_time_ms = AP_HAL::millis() - notify->get_text_updated_millis();
        if (visible_time_ms < msgtime_ms && !msp->_msp_status.flight_mode_focus) {
            char buffer[NOTIFY_TEXT_BUFFER_SIZE];
            strncpy(buffer, notify->get_text(), ARRAY_SIZE(buffer));
            const uint8_t len = strnlen(buffer, ARRAY_SIZE(buffer));

            for (uint8_t i=0; i<len; i++) {
                //normalize whitespace
                if (isspace(buffer[i])) {
                    buffer[i] = ' ';
                } else {
                    //converted to uppercase,
                    buffer[i] = toupper(buffer[i]);
                }
            }

            int8_t start_position = 0;
            //scroll if required
            //scroll pattern: wait, scroll to the left, wait, scroll to the right
            if (len > MSP_TXT_VISIBLE_CHARS) {
                const uint8_t chars_to_scroll = len - MSP_TXT_VISIBLE_CHARS;
                const uint8_t total_cycles = 2*message_scroll_delay + 2*chars_to_scroll;
                const uint8_t current_cycle = (visible_time_ms / message_scroll_time_ms) % total_cycles;

                //calculate scroll start_position
                if (current_cycle < total_cycles/2) {
                    //move to the left
                    start_position = current_cycle - message_scroll_delay;
                } else {
                    //move to the right
                    start_position = total_cycles - current_cycle;
                }
                start_position = constrain_int16(start_position, 0, chars_to_scroll);
                uint8_t end_position = start_position + MSP_TXT_VISIBLE_CHARS;

                //ensure array boundaries
                start_position = MIN(start_position, int8_t(ARRAY_SIZE(buffer)-1));
                end_position = MIN(end_position, int8_t(ARRAY_SIZE(buffer)-1));

                //trim invisible part
                buffer[end_position] = 0;
            }

            sbuf_write_data(dst, buffer + start_position, strlen(buffer + start_position));  // max MSP_TXT_VISIBLE_CHARS chars general text...
        } else {
            bool wind_en = false;
            char flight_mode_str[MSP_TXT_BUFFER_SIZE];
#if OSD_ENABLED
            wind_en = osd->screen[msp->_msp_status.current_screen].wind.enabled;
#endif
            update_flight_mode_str(flight_mode_str, ARRAY_SIZE(flight_mode_str), wind_en);
            sbuf_write_data(dst, flight_mode_str, ARRAY_SIZE(flight_mode_str));  // rendered as up to MSP_TXT_VISIBLE_CHARS chars with UTF8 support
        }
    }
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_status(sbuf_t *dst)
{

    struct PACKED {
        uint16_t task_delta_time;
        uint16_t i2c_error_count;
        uint16_t sensor_status;
        uint32_t flight_mode_flags;
        uint8_t pid_profile;
        uint16_t system_load;
        uint16_t gyro_cycle_time;
        uint8_t box_mode_flags;
        uint8_t arming_disable_flags_count;
        uint32_t arming_disable_flags;
        uint8_t extra_flags;
    } status {};

    status.flight_mode_flags = get_osd_flight_mode_bitmask();
    status.arming_disable_flags_count = 1;
    status.arming_disable_flags = !AP::notify().flags.armed;

    sbuf_write_data(dst, &status, sizeof(status));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_osd_config(sbuf_t *dst)
{
#if OSD_ENABLED
    AP_OSD *osd = AP::osd();
    if (osd == nullptr) {
        return MSP_RESULT_ERROR;
    }
#endif
    const AP_MSP *msp = AP::msp();
    if (msp == nullptr) {
        return MSP_RESULT_ERROR;
    }
    struct PACKED {
        uint8_t flags;
        uint8_t video_system;
        uint8_t units;
        uint8_t rssi_alarm;
        uint16_t capacity_alarm;
        uint8_t unused_0;
        uint8_t item_count;
        uint16_t alt_alarm;
        uint16_t items_position[OSD_ITEM_COUNT];
        uint8_t stats_items_count;
        uint16_t stats_items[OSD_STAT_COUNT] ;
        uint8_t timers_count;
        uint16_t timers[OSD_TIMER_COUNT];
        uint16_t enabled_warnings_old;
        uint8_t warnings_count_new;
        uint32_t enabled_warnings_new;
        uint8_t available_profiles;
        uint8_t selected_profile;
        uint8_t osd_stick_overlay;
    } osd_config {};

    // Configuration
    osd_config.units = OSD_UNIT_METRIC;
#if OSD_ENABLED
    osd_config.units = osd->units == AP_OSD::UNITS_METRIC ? OSD_UNIT_METRIC : OSD_UNIT_IMPERIAL;
#endif
    // Alarms
    osd_config.rssi_alarm = msp->_osd_config.rssi_alarm;
    osd_config.capacity_alarm = msp->_osd_config.cap_alarm;
    osd_config.alt_alarm = msp->_osd_config.alt_alarm;
    // Reuse old timer alarm (U16) as OSD_ITEM_COUNT
    osd_config.item_count = OSD_ITEM_COUNT;
    // Element position and visibility
    uint16_t pos = 0;   // default is hide this element
    for (uint8_t i = 0; i < OSD_ITEM_COUNT; i++) {
        pos = 0;    // 0 is hide this item
        if (msp->_osd_item_settings[i] != nullptr) {      // ok supported
            if (msp->_osd_item_settings[i]->enabled) {    // ok enabled
                // let's check if we need to hide this dynamically
                if (!BIT_IS_SET_64(osd_hidden_items_bitmask, i)) {
                    pos = MSP_OSD_POS(msp->_osd_item_settings[i]);
                }
            }
        }
        osd_config.items_position[i] = pos;
    }
    // Post flight statistics
    osd_config.stats_items_count = OSD_STAT_COUNT;             // stats items count
    // Timers
    osd_config.timers_count = OSD_TIMER_COUNT;                      // timers
    // Enabled warnings
    // API < 1.41
    // Send low word first for backwards compatibility
    osd_config.enabled_warnings_old = (uint16_t)(msp->_osd_config.enabled_warnings & 0xFFFF);
    // API >= 1.41
    // Send the warnings count and 32bit enabled warnings flags.
    // Add currently active OSD profile (0 indicates OSD profiles not available).
    // Add OSD stick overlay mode (0 indicates OSD stick overlay not available).
    osd_config.warnings_count_new = OSD_WARNING_COUNT;
    osd_config.enabled_warnings_new = msp->_osd_config.enabled_warnings;
    // If the feature is not available there is only 1 profile and it's always selected
    osd_config.available_profiles = 1;
    osd_config.selected_profile = 1;

    sbuf_write_data(dst, &osd_config, sizeof(osd_config));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_attitude(sbuf_t *dst)
{
    AP_AHRS &ahrs = AP::ahrs();
    WITH_SEMAPHORE(ahrs.get_semaphore());

    const struct PACKED {
        int16_t roll;
        int16_t pitch;
        int16_t yaw;
    } attitude {
        roll : int16_t(ahrs.roll_sensor * 0.1),     // centidegress to decidegrees
        pitch : int16_t(ahrs.pitch_sensor * 0.1),   // centidegress to decidegrees
        yaw : int16_t(ahrs.yaw_sensor * 0.01)       // centidegress to degrees
    };

    sbuf_write_data(dst, &attitude, sizeof(attitude));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_altitude(sbuf_t *dst)
{
    home_state_t home_state;
    update_home_pos(home_state);

    const struct PACKED {
        int32_t rel_altitude_cm;    // relative altitude cm
        int16_t vspeed_cms;         // climb rate cm/s
    } altitude {
        rel_altitude_cm : home_state.rel_altitude_cm,
        vspeed_cms : int16_t(get_vspeed_ms() * 100)
    };

    sbuf_write_data(dst, &altitude, sizeof(altitude));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_analog(sbuf_t *dst)
{
#if AP_BATTERY_ENABLED
    battery_state_t battery_state;
    update_battery_state(battery_state);

    float rssi;
    const struct PACKED {
        uint8_t voltage_dv;
        uint16_t mah;
        uint16_t rssi;
        int16_t current_ca;
        uint16_t voltage_cv;
    } analog {
        voltage_dv : (uint8_t)constrain_int16(battery_state.batt_voltage_v * 10, 0, 255),                   // battery voltage V to dV
        mah : (uint16_t)constrain_int32(battery_state.batt_consumed_mah, 0, 0xFFFF),                        // milliamp hours drawn from battery
        rssi : uint16_t(get_rssi(rssi) ? constrain_float(rssi,0,1) * 1023 : 0),                             // rssi 0-1 to 0-1023)
        current_ca : (int16_t)constrain_int32(battery_state.batt_current_a * 100, -0x8000, 0x7FFF),         // current A to cA (0.01 steps, range is -320A to 320A)
        voltage_cv : (uint16_t)constrain_int32(battery_state.batt_voltage_v * 100,0,0xFFFF)                 // battery voltage in 0.01V steps
    };
#else
    float rssi;
    const struct PACKED {
        uint8_t voltage_dv;
        uint16_t mah;
        uint16_t rssi;
        int16_t current_ca;
        uint16_t voltage_cv;
    } analog {
        voltage_dv : 0,
        mah : 0,
        rssi : uint16_t(get_rssi(rssi) ? constrain_float(rssi,0,1) * 1023 : 0),                             // rssi 0-1 to 0-1023)
        current_ca : 0,
        voltage_cv : 0
    };
#endif
    sbuf_write_data(dst, &analog, sizeof(analog));
    return MSP_RESULT_ACK;
}

#if AP_BATTERY_ENABLED
MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_battery_state(sbuf_t *dst)
{
    const AP_MSP *msp = AP::msp();
    if (msp == nullptr) {
        return MSP_RESULT_ERROR;
    }
    battery_state_t battery_state;
    update_battery_state(battery_state);

    const struct PACKED {
        uint8_t cellcount;
        uint16_t capacity_mah;
        uint8_t voltage_dv;
        uint16_t mah;
        int16_t current_ca;
        uint8_t state;
        uint16_t voltage_cv;
    } battery {
        cellcount : (uint8_t)constrain_int16((msp->_cellcount > 0 ? msp->_cellcount : battery_state.batt_cellcount), 0, 255),   // cell count 0 indicates battery not detected.
        capacity_mah : (uint16_t)battery_state.batt_capacity_mah,                                                               // in mAh
        voltage_dv : (uint8_t)constrain_int16(battery_state.batt_voltage_v * 10, 0, 255),                                       // battery voltage V to dV
        mah : (uint16_t)MIN(battery_state.batt_consumed_mah, 0xFFFF),                                                           // milliamp hours drawn from battery
        current_ca : (int16_t)constrain_int32(battery_state.batt_current_a * 100, -0x8000, 0x7FFF),                             // current A to cA (0.01 steps, range is -320A to 320A)
        state : (uint8_t)battery_state.batt_state,                                                                              // BATTERY: OK=0, CRITICAL=2
        voltage_cv : (uint16_t)constrain_int32(battery_state.batt_voltage_v * 100, 0, 0x7FFF)                                   // battery voltage in 0.01V steps
    };

    sbuf_write_data(dst, &battery, sizeof(battery));
    return MSP_RESULT_ACK;
}
#endif

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_esc_sensor_data(sbuf_t *dst)
{
#if HAL_WITH_ESC_TELEM
    AP_ESC_Telem& telem = AP::esc_telem();
    if (telem.get_last_telem_data_ms(0)) {
        struct PACKED {
            uint8_t num_motors;
            struct PACKED {
                uint8_t temp;
                uint16_t rpm;
            } data[ESC_TELEM_MAX_ESCS];
        } esc_sensor {};

        esc_sensor.num_motors = telem.get_num_active_escs();
        for (uint8_t i = 0; i < esc_sensor.num_motors; i++) {
            int16_t temp = 0;
            float rpm = 0.0f;
            IGNORE_RETURN(telem.get_rpm(i, rpm));
            IGNORE_RETURN(telem.get_temperature(i, temp));
            esc_sensor.data[i].temp = uint8_t(temp * 0.01f);
            esc_sensor.data[i].rpm = uint16_t(rpm * 0.1f);
        }
        sbuf_write_data(dst, &esc_sensor, 1 + 3*esc_sensor.num_motors);
    }
#endif
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_rtc(sbuf_t *dst)
{
    tm localtime_tm {}; // year is relative to 1900
    uint64_t time_usec = 0;
#if AP_RTC_ENABLED
    if (AP::rtc().get_utc_usec(time_usec)) { // may fail, leaving time_unix at 0
        const time_t time_sec = time_usec / 1000000;
        struct tm tmd {};
        localtime_tm = *gmtime_r(&time_sec, &tmd);
    }
#endif
    const struct PACKED {
        uint16_t year;
        uint8_t mon;
        uint8_t mday;
        uint8_t hour;
        uint8_t min;
        uint8_t sec;
        uint16_t millis;
    } rtc {
        year : uint16_t(localtime_tm.tm_year + 1900),   // tm_year is relative to year 1900
        mon : uint8_t(localtime_tm.tm_mon + 1),        // MSP requires [1-12] months
        mday : uint8_t(localtime_tm.tm_mday),
        hour : uint8_t(localtime_tm.tm_hour),
        min : uint8_t(localtime_tm.tm_min),
        sec : uint8_t(localtime_tm.tm_sec),
        millis : uint16_t((time_usec / 1000U) % 1000U)
    };

    sbuf_write_data(dst, &rtc, sizeof(rtc));
    return MSP_RESULT_ACK;
}

#if AP_RC_CHANNEL_ENABLED
MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_rc(sbuf_t *dst)
{
#if AP_RCMAPPER_ENABLED
    const RCMapper* rcmap = AP::rcmap();
    if (rcmap == nullptr) {
        return MSP_RESULT_ERROR;
    }

    // note: rcmap channels start at 1
    float roll = rc().rc_channel(rcmap->roll()-1)->norm_input_dz();
    float pitch = -rc().rc_channel(rcmap->pitch()-1)->norm_input_dz();
    float yaw = rc().rc_channel(rcmap->yaw()-1)->norm_input_dz();
    float throttle = rc().rc_channel(rcmap->throttle()-1)->norm_input_dz();

    const struct PACKED {
        uint16_t a;
        uint16_t e;
        uint16_t r;
        uint16_t t;
    } rc {
        // send only 4 channels, MSP order is AERT
        a : uint16_t(roll*500+1500),       // A
        e : uint16_t(pitch*500+1500),      // E
        r : uint16_t(yaw*500+1500),        // R
        t : uint16_t(throttle*1000+1000)    // T
    };

    sbuf_write_data(dst, &rc, sizeof(rc));
    return MSP_RESULT_ACK;
#else
    return MSP_RESULT_ERROR;
#endif
}
#endif  // AP_RC_CHANNEL_ENABLED

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_board_info(sbuf_t *dst)
{
    const AP_FWVersion &fwver = AP::fwversion();

    struct PACKED {
        uint16_t hw_revision;
        uint8_t aio_flags;
        uint8_t capabilities;
        uint8_t fw_string_len;
    } fw_info {};

#if HAL_WITH_OSD_BITMAP
    fw_info.aio_flags = 2; // 2 == FC with MAX7456
#else
    fw_info.aio_flags = 0; // 0 == FC without MAX7456
#endif
    fw_info.fw_string_len = strlen(fwver.fw_string);

    sbuf_write_data(dst, "ARDU", BOARD_IDENTIFIER_LENGTH);
    sbuf_write_data(dst, &fw_info, sizeof(fw_info));
    sbuf_write_data(dst, fwver.fw_string, strlen(fwver.fw_string));
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_build_info(sbuf_t *dst)
{
    const AP_FWVersion &fwver = AP::fwversion();

    // we don't use real dates here as that would mean we don't get
    // consistent builds. Being able to reproduce the exact build at a
    // later date is a valuable property of the code
    sbuf_write_data(dst, "Jan 01 1980", BUILD_DATE_LENGTH);
    sbuf_write_data(dst, "00:00:00", BUILD_TIME_LENGTH);
    sbuf_write_data(dst, fwver.fw_hash_str, GIT_SHORT_REVISION_LENGTH);
    return MSP_RESULT_ACK;
}

MSPCommandResult AP_MSP_Telem_Backend::msp_process_out_uid(sbuf_t *dst)
{
    uint8_t id[12] {};
    uint8_t len = sizeof(id);
    hal.util->get_system_id_unformatted(id, len);
    sbuf_write_data(dst, id, sizeof(id));
    return MSP_RESULT_ACK;
}

void AP_MSP_Telem_Backend::hide_osd_items(void)
{
#if OSD_ENABLED
    AP_OSD *osd = AP::osd();
    if (osd == nullptr) {
        return;
    }
#endif
    AP_MSP *msp = AP::msp();
    if (msp == nullptr) {
        return;
    }
#if AP_BATTERY_ENABLED
    const AP_Notify &notify = AP::notify();
#endif
    // clear all and only set the flashing ones
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_GPS_SATS);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_HOME_DIR);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_HOME_DIST);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_GPS_SPEED);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_CRAFT_NAME);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_AVG_CELL_VOLTAGE);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_MAIN_BATT_VOLTAGE);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_RTC_DATETIME);
    BIT_CLEAR(osd_hidden_items_bitmask, OSD_RSSI_VALUE);

    if (msp->_msp_status.flashing_on) {
        // flash satcount when no 3D Fix
        gps_state_t gps_state;
        update_gps_state(gps_state);
        if (gps_state.fix_type == 0) {
            BIT_SET(osd_hidden_items_bitmask, OSD_GPS_SATS);
        }
        // flash home dir and distance if home is not set
        home_state_t home_state;
        update_home_pos(home_state);
        if (!home_state.home_is_set) {
            BIT_SET(osd_hidden_items_bitmask, OSD_HOME_DIR);
            BIT_SET(osd_hidden_items_bitmask, OSD_HOME_DIST);
        }
        // flash airspeed if there's no estimate
        bool airspeed_en = false;
#if OSD_ENABLED
        airspeed_en = osd->screen[msp->_msp_status.current_screen].aspeed.enabled;
#endif
        if (airspeed_en) {
            airspeed_state_t airspeed_state;
            update_airspeed(airspeed_state);
            if (!airspeed_state.airspeed_have_estimate) {
                BIT_SET(osd_hidden_items_bitmask, OSD_GPS_SPEED);
            }
        }
        // flash text flightmode for 3secs after each change
        if (msp->_msp_status.flight_mode_focus) {
            BIT_SET(osd_hidden_items_bitmask, OSD_CRAFT_NAME);
        }
#if AP_BATTERY_ENABLED
        // flash battery on failsafe
        if (notify.flags.failsafe_battery) {
            BIT_SET(osd_hidden_items_bitmask, OSD_AVG_CELL_VOLTAGE);
            BIT_SET(osd_hidden_items_bitmask, OSD_MAIN_BATT_VOLTAGE);
        }
#endif
        // flash rtc if no time available
#if AP_RTC_ENABLED
        uint64_t time_usec;
        if (!AP::rtc().get_utc_usec(time_usec)) {
            BIT_SET(osd_hidden_items_bitmask, OSD_RTC_DATETIME);
        }
#else
            BIT_SET(osd_hidden_items_bitmask, OSD_RTC_DATETIME);
#endif
        // flash rssi if disabled
        float rssi;
        if (!get_rssi(rssi)) {
            BIT_SET(osd_hidden_items_bitmask, OSD_RSSI_VALUE);
        }
    }
    // disable flashing for min/max items
    if (displaying_stats_screen()) {
        BIT_CLEAR(osd_hidden_items_bitmask, OSD_HOME_DIST);
        BIT_CLEAR(osd_hidden_items_bitmask, OSD_GPS_SPEED);
        BIT_CLEAR(osd_hidden_items_bitmask, OSD_CRAFT_NAME);
        BIT_CLEAR(osd_hidden_items_bitmask, OSD_MAIN_BATT_VOLTAGE);
        BIT_CLEAR(osd_hidden_items_bitmask, OSD_RSSI_VALUE);
    }
}

#if HAL_WITH_MSP_DISPLAYPORT
// ported from betaflight/src/main/io/displayport_msp.c
void AP_MSP_Telem_Backend::msp_displayport_heartbeat()
{
    const uint8_t subcmd[] = { msp_displayport_subcmd_e::MSP_DISPLAYPORT_HEARTBEAT };

    // heartbeat is used to:
    // a) ensure display is not released by remote OSD software
    // b) prevent OSD Slave boards from displaying a 'disconnected' status.
    msp_send_packet(MSP_DISPLAYPORT, MSP::MSP_V1, subcmd, sizeof(subcmd), false);
}

void AP_MSP_Telem_Backend::msp_displayport_grab()
{
    msp_displayport_heartbeat();
}

void AP_MSP_Telem_Backend::msp_displayport_release()
{
    const uint8_t subcmd[] = { msp_displayport_subcmd_e::MSP_DISPLAYPORT_RELEASE };

    msp_send_packet(MSP_DISPLAYPORT, MSP::MSP_V1, subcmd, sizeof(subcmd), false);
}

void AP_MSP_Telem_Backend::msp_displayport_clear_screen()
{
    const uint8_t subcmd[] = { msp_displayport_subcmd_e::MSP_DISPLAYPORT_CLEAR_SCREEN };

    msp_send_packet(MSP_DISPLAYPORT, MSP::MSP_V1, subcmd, sizeof(subcmd), false);
}

void AP_MSP_Telem_Backend::msp_displayport_draw_screen()
{
    const uint8_t subcmd[] = { msp_displayport_subcmd_e::MSP_DISPLAYPORT_DRAW_SCREEN };
    msp_send_packet(MSP_DISPLAYPORT, MSP::MSP_V1, subcmd, sizeof(subcmd), false);
}

void AP_MSP_Telem_Backend::msp_displayport_write_string(uint8_t col, uint8_t row, bool blink, const char *string)
{
    const uint8_t len = strnlen(string, OSD_MSP_DISPLAYPORT_MAX_STRING_LENGTH);

    struct PACKED {
        uint8_t sub_cmd;
        uint8_t row;
        uint8_t col;
        uint8_t attr;
        uint8_t text[OSD_MSP_DISPLAYPORT_MAX_STRING_LENGTH];
    } packet {};

    packet.sub_cmd = msp_displayport_subcmd_e::MSP_DISPLAYPORT_WRITE_STRING;
    packet.row = row;
    packet.col = col;
    if (blink) {
        packet.attr |= DISPLAYPORT_MSP_ATTR_BLINK;
    }
    memcpy(packet.text, string, len);

    msp_send_packet(MSP_DISPLAYPORT, MSP::MSP_V1, &packet, 4 + len, false);
}

void AP_MSP_Telem_Backend::msp_displayport_set_options(const uint8_t font_index, const uint8_t screen_resolution)
{
    const uint8_t subcmd[] = { msp_displayport_subcmd_e::MSP_DISPLAYPORT_SET_OPTIONS, font_index, screen_resolution };
    msp_send_packet(MSP_DISPLAYPORT, MSP::MSP_V1, subcmd, sizeof(subcmd), false);
}
#endif //HAL_WITH_MSP_DISPLAYPORT
bool AP_MSP_Telem_Backend::displaying_stats_screen() const
{
#if OSD_ENABLED
    AP_OSD *osd = AP::osd();
    if (osd == nullptr) {
        return false;
    }
    AP_MSP *msp = AP::msp();
    if (msp == nullptr) {
        return false;
    }
    return osd->screen[msp->_msp_status.current_screen].stat.enabled;
#else
    return false;
#endif
}

bool AP_MSP_Telem_Backend::get_rssi(float &rssi) const
{
#if AP_RSSI_ENABLED
    AP_RSSI* ap_rssi = AP::rssi();
    if (ap_rssi == nullptr) {
        return false;
    }
    if (!ap_rssi->enabled()) {
        return false;
    }
    rssi =  ap_rssi->read_receiver_rssi(); // range is [0-1]
    return true;
#else
    return false;
#endif
}

#endif //HAL_MSP_ENABLED