FrSky SPort protocol specs

It's a master/slave protocol. The RX sends a poll packet every 12ms (4bytes)

2bytes	description
0x7E	poll header
ID	physical ID (1-28) computed with a CRC

The receiver will poll the IDs in sequence to find which one is present. If only one physical ID is found, the receiver will alternate the sensor polling and the search (present sensor, next ID to search, present sensor, next ID and so on). If more sensors are found, the poll sequence returns almost to a normal search pattern.

Sensor behavior

The sensor answers to every pool on its physical ID to announce its presence. If no data can be transmitted (no refresh), the sensor answers by an empty packet and a false CRC (type 0x00, ID 0x0000, value 0x00000000, CRC 0xFF).

byte(s)	descrption
1	type 0x10,0x30,0x31,0x32
2	sensor logical ID
4	value
1	CRC

byte[0] types (from betaflight for MSP over Frsky)

• FSSP_DATA_FRAME = 0x10 (Standard Frsky sensor Frame, OpenTX passes to LUA sensor_logical_ID:0x5000-0x50FF)
• FSSP_MSPC_FRAME_SMARTPORT = 0x30, // MSP client frame
• FSSP_MSPC_FRAME_FPORT = 0x31, // MSP client frame
• FSSP_MSPS_FRAME = 0x32, // MSP server frame (OpenTX passes to LUA sensor_logical_ID:0x0000-0xFFFF)

For full bandwidth 2 way communication with OpenTX, FC has to use sensor logical ID 0x32 because it's the only ID passed to LUA untouched. LUA can use all sensor IDs because the FC has full control on what to read or discard.

Phisycal Sensor ID List

Sensor Ids (from betaflight for MSP over Frsky)

1. FSSP_SENSOR_ID1 = 0x1B,
2. FSSP_SENSOR_ID2 = 0x0D,
3. FSSP_SENSOR_ID3 = 0x34,
4. FSSP_SENSOR_ID4 = 0x67

there are 32 ID's polled by smartport master, remaining 3 bits are crc (according to comments in openTx code)

ID	description
0x00	// Physical ID 0 - Vario2 (altimeter high precision)
0xA1	// Physical ID 1 - FLVSS Lipo sensor (can be sent with one or two cell voltages)
0x22	// Physical ID 2 - FAS-40S current sensor
0x83	// Physical ID 3 - GPS / altimeter (normal precision)
0xE4	// Physical ID 4 - RPM
0x45	// Physical ID 5 - SP2UART(Host)
0xC6	// Physical ID 6 - SPUART(Remote)
0x67	// Physical ID 7 -
0x48	// Physical ID 8 -
0xE9	// Physical ID 9 -
0x6A	// Physical ID 10 -
0xCB	// Physical ID 11 -
0xAC	// Physical ID 12 -
0x0D	// Physical ID 13 -
0x8E	// Physical ID 14 -
0x2F	// Physical ID 15 -
0xD0	// Physical ID 16 -
0x71	// Physical ID 17 -
0xF2	// Physical ID 18 -
0x53	// Physical ID 19 -
0x34	// Physical ID 20 -
0x95	// Physical ID 21 -
0x16	// Physical ID 22 -
0xB7	// Physical ID 23 - IMU ACC (x,y,z)
0x98	// Physical ID 24 -
0x39	// Physical ID 25 - Power Box
0xBA	// Physical ID 26 - Temp
0x1B	// Physical ID 27 - Fuel (ArduPilot/Betaflight)

From OpenTX frsky.h, line 189 - 17/5/2018

#define DATA_ID_VARIO             0x00 // 0
#define DATA_ID_FLVSS             0xA1 // 1
#define DATA_ID_FAS               0x22 // 2
#define DATA_ID_GPS               0x83 // 3
#define DATA_ID_RPM               0xE4 // 4
#define DATA_ID_SP2UH             0x45 // 5
#define DATA_ID_SP2UR             0xC6 // 6

From OpenTX frsky_sport.cpp, line 260 - 17/5/2018

#if defined(LUA)
  else if (primId == 0x32) {
    if (luaInputTelemetryFifo && luaInputTelemetryFifo->hasSpace(sizeof(SportTelemetryPacket))) {
      SportTelemetryPacket luaPacket;
      luaPacket.physicalId = physicalId;
      luaPacket.primId = primId;
      luaPacket.dataId = id;
      luaPacket.value = data;
      for (uint8_t i=0; i<sizeof(SportTelemetryPacket); i++) {
        luaInputTelemetryFifo->push(luaPacket.raw[i]);
      }
    }
  }
#endif

OpenTx DATA IDs from /radio/src/telemetry/frsky.h

// FrSky new DATA IDs (2 bytes)
#define ALT_FIRST_ID              0x0100
#define ALT_LAST_ID               0x010f
#define VARIO_FIRST_ID            0x0110
#define VARIO_LAST_ID             0x011f
#define CURR_FIRST_ID             0x0200
#define CURR_LAST_ID              0x020f
#define VFAS_FIRST_ID             0x0210
#define VFAS_LAST_ID              0x021f
#define CELLS_FIRST_ID            0x0300
#define CELLS_LAST_ID             0x030f
#define T1_FIRST_ID               0x0400
#define T1_LAST_ID                0x040f
#define T2_FIRST_ID               0x0410
#define T2_LAST_ID                0x041f
#define RPM_FIRST_ID              0x0500
#define RPM_LAST_ID               0x050f
#define FUEL_FIRST_ID             0x0600
#define FUEL_LAST_ID              0x060f
#define ACCX_FIRST_ID             0x0700
#define ACCX_LAST_ID              0x070f
#define ACCY_FIRST_ID             0x0710
#define ACCY_LAST_ID              0x071f
#define ACCZ_FIRST_ID             0x0720
#define ACCZ_LAST_ID              0x072f
#define GPS_LONG_LATI_FIRST_ID    0x0800
#define GPS_LONG_LATI_LAST_ID     0x080f
#define GPS_ALT_FIRST_ID          0x0820
#define GPS_ALT_LAST_ID           0x082f
#define GPS_SPEED_FIRST_ID        0x0830
#define GPS_SPEED_LAST_ID         0x083f
#define GPS_COURS_FIRST_ID        0x0840
#define GPS_COURS_LAST_ID         0x084f
#define GPS_TIME_DATE_FIRST_ID    0x0850
#define GPS_TIME_DATE_LAST_ID     0x085f
#define A3_FIRST_ID               0x0900
#define A3_LAST_ID                0x090f
#define A4_FIRST_ID               0x0910
#define A4_LAST_ID                0x091f
#define AIR_SPEED_FIRST_ID        0x0a00
#define AIR_SPEED_LAST_ID         0x0a0f
#define RBOX_BATT1_FIRST_ID       0x0b00
#define RBOX_BATT1_LAST_ID        0x0b0f
#define RBOX_BATT2_FIRST_ID       0x0b10
#define RBOX_BATT2_LAST_ID        0x0b1f
#define RBOX_STATE_FIRST_ID       0x0b20
#define RBOX_STATE_LAST_ID        0x0b2f
#define RBOX_CNSP_FIRST_ID        0x0b30
#define RBOX_CNSP_LAST_ID         0x0b3f
#define SD1_FIRST_ID              0x0b40
#define SD1_LAST_ID               0x0b4f
#define ESC_POWER_FIRST_ID        0x0b50
#define ESC_POWER_LAST_ID         0x0b5f
#define ESC_RPM_CONS_FIRST_ID     0x0b60
#define ESC_RPM_CONS_LAST_ID      0x0b6f
#define ESC_TEMPERATURE_FIRST_ID  0x0b70
#define ESC_TEMPERATURE_LAST_ID   0x0b7f
#define X8R_FIRST_ID              0x0c20
#define X8R_LAST_ID               0x0c2f
#define S6R_FIRST_ID              0x0c30
#define S6R_LAST_ID               0x0c3f
#define GASSUIT_TEMP_FIRST_ID     0x0d00
#define GASSUIT_TEMP_LAST_ID      0x0d0f
#define GASSUIT_SPEED_FIRST_ID    0x0d10
#define GASSUIT_SPEED_LAST_ID     0x0d1f
#define GASSUIT_FUEL_FIRST_ID     0x0d20
#define GASSUIT_FUEL_LAST_ID      0x0d2f
#define DIY_FIRST_ID              0x5000
#define DIY_LAST_ID               0x52ff
#define DIY_STREAM_FIRST_ID       0x5000
#define DIY_STREAM_LAST_ID        0x50ff
#define FACT_TEST_ID              0xf000
#define RSSI_ID                   0xf101
#define ADC1_ID                   0xf102
#define ADC2_ID                   0xf103
#define SP2UART_A_ID              0xfd00
#define SP2UART_B_ID              0xfd01
#define BATT_ID                   0xf104
#define RAS_ID                    0xf105
#define XJT_VERSION_ID            0xf106
#define FUEL_QTY_FIRST_ID         0x0a10
#define FUEL_QTY_LAST_ID          0x0a1f