/* ################################################################################################################# * LightTelemetry protocol (LTM) * * Ghettostation one way telemetry protocol for really low bitrates (2400 bauds). * * Protocol details: 3 different frames, little endian. * G Frame (GPS position) (2 Hz): 18BYTES * 0x24 0x54 0x47 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xC0 * $ T G --------LAT-------- -------LON--------- SPD --------ALT-------- SAT/FIX CRC * A Frame (Attitude) (5 Hz): 10BYTES * 0x24 0x54 0x41 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xC0 * $ T A --PITCH-- --ROLL--- -HEADING- CRC * S Frame (Sensors) (2 Hz): 11BYTES * 0x24 0x54 0x53 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xC0 * $ T S VBAT(mV) Current(mA) RSSI AIRSPEED ARM/FS/FMOD CRC * ################################################################################################################# */ #include "AP_LTM_Telem.h" #include #include #include #include #include extern const AP_HAL::HAL& hal; // init - perform required initialisation void AP_LTM_Telem::init() { const AP_SerialManager &serial_manager = AP::serialmanager(); // check for LTM_Port if ((_port = serial_manager.find_serial( AP_SerialManager::SerialProtocol_LTM_Telem, 0))) { _port->set_flow_control(AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE); // initialise UART _port->begin(0, AP_SERIALMANAGER_LTM_BUFSIZE_RX, AP_SERIALMANAGER_LTM_BUFSIZE_TX); hal.scheduler->register_io_process( FUNCTOR_BIND_MEMBER(&AP_LTM_Telem::tick, void)); } } void AP_LTM_Telem::send_LTM(uint8_t lt_packet[], uint8_t lt_packet_size) { // check space before write if (_port->txspace() < lt_packet_size) { return; } // calculate checksum uint8_t lt_crc = 0x00; for (uint8_t i = 3; i < lt_packet_size - 1; i++) { lt_crc ^= lt_packet[i]; } lt_packet[lt_packet_size - 1] = lt_crc; _port->write(lt_packet, lt_packet_size); } // GPS frame void AP_LTM_Telem::send_Gframe(void) { const AP_GPS &gps = AP::gps(); const uint8_t sats_visible = gps.num_sats(); const uint8_t fix_type = (uint8_t)gps.status(); int32_t lat = 0; // latitude int32_t lon = 0; // longtitude uint8_t gndspeed = 0; // gps ground speed (m/s) int32_t alt = 0; { AP_AHRS &ahrs = AP::ahrs(); WITH_SEMAPHORE(ahrs.get_semaphore()); float alt_ahrs; ahrs.get_relative_position_D_home(alt_ahrs); alt = (int32_t) roundf(-alt_ahrs * 100.0); // altitude (cm) Location loc; if (ahrs.get_position(loc)) { lat = loc.lat; lon = loc.lng; gndspeed = (uint8_t) roundf(gps.ground_speed()); } } uint8_t lt_buff[LTM_GFRAME_SIZE]; // protocol: START(2 bytes)FRAMEID(1byte)LAT(cm,4 bytes)LON(cm,4bytes)SPEED(m/s,1bytes)ALT(cm,4bytes)SATS(6bits)FIX(2bits)CRC(xor,1byte) // START lt_buff[0] = 0x24; //$ lt_buff[1] = 0x54; //T // FRAMEID lt_buff[2] = 0x47; // G ( gps frame at 5hz ) // PAYLOAD lt_buff[3] = (lat >> 8 * 0) & 0xFF; lt_buff[4] = (lat >> 8 * 1) & 0xFF; lt_buff[5] = (lat >> 8 * 2) & 0xFF; lt_buff[6] = (lat >> 8 * 3) & 0xFF; lt_buff[7] = (lon >> 8 * 0) & 0xFF; lt_buff[8] = (lon >> 8 * 1) & 0xFF; lt_buff[9] = (lon >> 8 * 2) & 0xFF; lt_buff[10] = (lon >> 8 * 3) & 0xFF; lt_buff[11] = (gndspeed >> 8 * 0) & 0xFF; lt_buff[12] = (alt >> 8 * 0) & 0xFF; lt_buff[13] = (alt >> 8 * 1) & 0xFF; lt_buff[14] = (alt >> 8 * 2) & 0xFF; lt_buff[15] = (alt >> 8 * 3) & 0xFF; lt_buff[16] = ((sats_visible << 2) & 0xFF) | ((fix_type > 3 ? 3 : fix_type) & 0b00000011); // last 6 bits: sats number, first 2:fix type (0, 1, 2, 3) send_LTM(lt_buff, LTM_GFRAME_SIZE); _ltm_scheduler++; } // Sensors frame void AP_LTM_Telem::send_Sframe(void) { const AP_BattMonitor &battery = AP::battery(); const uint16_t volt = (uint16_t) roundf(battery.voltage() * 1000.0f); // battery voltage (expects value in mV) float current; if (!battery.current_amps(current)) { current = 0; } // note: max. current value we can send is 65.536 A const uint16_t amp = (uint16_t) roundf(current * 100.0f); // current sensor (expects value in hundredth of A) // airspeed in m/s if available and enabled - even if not used - otherwise send 0 const AP_Airspeed *aspeed = AP::airspeed(); uint8_t airspeed = 0; // airspeed sensor (m/s) if (aspeed && aspeed->enabled()) { airspeed = (uint8_t) roundf(aspeed->get_airspeed()); } const uint8_t flightmode = AP_Notify::flags.flight_mode; // flight mode uint8_t rssi = 0; // radio RSSI (%a) AP_RSSI *ap_rssi = AP_RSSI::get_singleton(); if (ap_rssi) { rssi = ap_rssi->read_receiver_rssi_uint8(); } const uint8_t armstat = AP_Notify::flags.armed; // 0: disarmed, 1: armed const uint8_t failsafe = AP_Notify::flags.failsafe_radio; // 0: normal, 1: failsafe uint8_t lt_buff[LTM_SFRAME_SIZE]; // START lt_buff[0] = 0x24; //$ lt_buff[1] = 0x54; //T // FRAMEID lt_buff[2] = 0x53; //S // PAYLOAD lt_buff[3] = (volt >> 8 * 0) & 0xFF; // VBAT converted to mV lt_buff[4] = (volt >> 8 * 1) & 0xFF; lt_buff[5] = (amp >> 8 * 0) & 0xFF; // actual current instead of consumed mAh in regular LTM lt_buff[6] = (amp >> 8 * 1) & 0xFF; lt_buff[7] = (rssi >> 8 * 0) & 0xFF; lt_buff[8] = (airspeed >> 8 * 0) & 0xFF; lt_buff[9] = ((flightmode << 2) & 0xFF) | ((failsafe << 1) & 0b00000010) | (armstat & 0b00000001); // last 6 bits: flight mode, 2nd bit: failsafe, 1st bit: arm status. send_LTM(lt_buff, LTM_SFRAME_SIZE); _ltm_scheduler++; } // Attitude frame void AP_LTM_Telem::send_Aframe(void) { int16_t pitch; int16_t roll; int16_t heading; { AP_AHRS &ahrs = AP::ahrs(); WITH_SEMAPHORE(ahrs.get_semaphore()); pitch = roundf(ahrs.pitch_sensor / 100.0); // attitude pitch in degrees roll = roundf(ahrs.roll_sensor / 100.0); // attitude roll in degrees heading = roundf(ahrs.yaw_sensor / 100.0); // heading in degrees } uint8_t lt_buff[LTM_AFRAME_SIZE]; // A Frame: $T(2 bytes)A(1byte)PITCH(2 bytes)ROLL(2bytes)HEADING(2bytes)CRC(xor,1byte) // START lt_buff[0] = 0x24; //$ lt_buff[1] = 0x54; //T // FRAMEID lt_buff[2] = 0x41; //A // PAYLOAD lt_buff[3] = (pitch >> 8 * 0) & 0xFF; lt_buff[4] = (pitch >> 8 * 1) & 0xFF; lt_buff[5] = (roll >> 8 * 0) & 0xFF; lt_buff[6] = (roll >> 8 * 1) & 0xFF; lt_buff[7] = (heading >> 8 * 0) & 0xFF; lt_buff[8] = (heading >> 8 * 1) & 0xFF; send_LTM(lt_buff, LTM_AFRAME_SIZE); _ltm_scheduler++; } // send LTM void AP_LTM_Telem::generate_LTM(void) { if (_ltm_scheduler & 1) { // is odd send_Aframe(); } else { // is even if (_ltm_scheduler % 4 == 0) { send_Sframe(); } else { send_Gframe(); } } if (_ltm_scheduler > 9) { _ltm_scheduler = 1; } } void AP_LTM_Telem::tick(void) { uint32_t now = AP_HAL::millis(); if (now - _last_frame_ms >= 100) { _last_frame_ms = now; generate_LTM(); } }