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Parser update for ELRS 4.0 #18

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sartstark wants to merge 2 commits into from
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Parser update for ELRS 4.0 #18

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8ab95d0
Update parser for ExpressLRS 4.0 compatibility
claude May 2, 2026
2dda465
Merge pull request #2
sartstark May 15, 2026
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13 changes: 10 additions & 3 deletions src/AlfredoCRSF.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -48,8 +48,9 @@ void AlfredoCRSF::handleByteReceived()
if (_rxBufPos > 1)
{
uint8_t len = _rxBuf[1];
// Sanity check the declared length, can't be shorter than Type, X, CRC
if (len < 3 || len > CRSF_MAX_PACKET_LEN)
// Length covers Type + payload + CRC. ELRS 4.0 (PR #3429) allows
// broadcast frames with zero payload, so the minimum value is 2.
if (len < 2 || len > (CRSF_MAX_PACKET_LEN - 2))
{
shiftRxBuffer(1);
reprocess = true;
Expand Down Expand Up @@ -94,6 +95,9 @@ void AlfredoCRSF::checkLinkDown()
void AlfredoCRSF::processPacketIn(uint8_t len)
{
const crsf_header_t *hdr = (crsf_header_t *)_rxBuf;
// ELRS 4.0 forces 0xC8 (CRSF_SYNC_BYTE / FLIGHT_CONTROLLER) on the serial
// wire for every frame, including ATTITUDE which used to be addressed to
// RADIO_TRANSMITTER. Handle ATTITUDE here so it parses on a 4.0 RX.
if (hdr->device_addr == CRSF_ADDRESS_FLIGHT_CONTROLLER) //Rx to FC
{
switch (hdr->type)
Expand All @@ -113,8 +117,11 @@ void AlfredoCRSF::processPacketIn(uint8_t len)
case CRSF_FRAMETYPE_VARIO:
packetVario(hdr);
break;
case CRSF_FRAMETYPE_ATTITUDE:
packetAttitude(hdr);
break;
}
}
}
else if (hdr->device_addr == CRSF_ADDRESS_CRSF_TRANSMITTER) //Headset to TX
{
if (hdr->type == CRSF_FRAMETYPE_RC_CHANNELS_PACKED)
Expand Down
52 changes: 25 additions & 27 deletions src/crsf_protocol.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,38 +33,30 @@ typedef enum
CRSF_FRAMETYPE_VARIO = 0x07,
CRSF_FRAMETYPE_BATTERY_SENSOR = 0x08,
CRSF_FRAMETYPE_BARO_ALTITUDE = 0x09,
//CRSF_FRAMETYPE_HEARTBEAT = 0x0B, //no need to support? (rev07)
//CRSF_FRAMETYPE_VIDEO_TRANSMITTER = 0x0F, //no need to support? (rev07)
CRSF_FRAMETYPE_AIRSPEED = 0x0A,
CRSF_FRAMETYPE_HEARTBEAT = 0x0B,
CRSF_FRAMETYPE_RPM = 0x0C,
CRSF_FRAMETYPE_TEMP = 0x0D,
CRSF_FRAMETYPE_CELLS = 0x0E,
CRSF_FRAMETYPE_LINK_STATISTICS = 0x14,
// CRSF_FRAMETYPE_OPENTX_SYNC = 0x10, //not in edgeTX
// CRSF_FRAMETYPE_RADIO_ID = 0x3A, //no need to support?
CRSF_FRAMETYPE_RC_CHANNELS_PACKED = 0x16,
// CRSF_FRAMETYPE_LINK_RX_ID = 0x1C, //no need to support?
// CRSF_FRAMETYPE_LINK_TX_ID = 0x1D, //no need to support?
CRSF_FRAMETYPE_ATTITUDE = 0x1E,
// CRSF_FRAMETYPE_FLIGHT_MODE = 0x21, //no need to support?
CRSF_FRAMETYPE_FLIGHT_MODE = 0x21,
// Extended Header Frames, range: 0x28 to 0x96
// CRSF_FRAMETYPE_DEVICE_PING = 0x28, //no "flight controller" needs to know about this
// CRSF_FRAMETYPE_DEVICE_INFO = 0x29, //no "flight controller" needs to know about this
// CRSF_FRAMETYPE_PARAMETER_SETTINGS_ENTRY = 0x2B, //no "flight controller" needs to know about this
// CRSF_FRAMETYPE_PARAMETER_READ = 0x2C, //no "flight controller" needs to know about this
// CRSF_FRAMETYPE_PARAMETER_WRITE = 0x2D, //no "flight controller" needs to know about this
// CRSF_FRAMETYPE_COMMAND = 0x32, //no "flight controller" needs to know about this
// KISS frames
// CRSF_FRAMETYPE_KISS_REQ = 0x78, //not in edgeTX
// CRSF_FRAMETYPE_KISS_RESP = 0x79, //not in edgeTX
// MSP commands
// CRSF_FRAMETYPE_MSP_REQ = 0x7A, //not in edgeTX
// CRSF_FRAMETYPE_MSP_RESP = 0x7B, //not in edgeTX
// CRSF_FRAMETYPE_MSP_WRITE = 0x7C, //not in edgeTX
// Ardupilot frames
// CRSF_FRAMETYPE_ARDUPILOT_RESP = 0x80,
CRSF_FRAMETYPE_DEVICE_PING = 0x28,
CRSF_FRAMETYPE_DEVICE_INFO = 0x29,
CRSF_FRAMETYPE_PARAMETER_SETTINGS_ENTRY = 0x2B,
CRSF_FRAMETYPE_PARAMETER_READ = 0x2C,
CRSF_FRAMETYPE_PARAMETER_WRITE = 0x2D,
CRSF_FRAMETYPE_ELRS_STATUS = 0x2E, // ELRS good/bad packet count and status flags
CRSF_FRAMETYPE_COMMAND = 0x32,
} crsf_frame_type_e;

typedef enum
{
CRSF_ADDRESS_BROADCAST = 0x00,
CRSF_ADDRESS_USB = 0x10,
CRSF_ADDRESS_BLUETOOTH_WIFI = 0x12,
CRSF_ADDRESS_TBS_CORE_PNP_PRO = 0x80,
CRSF_ADDRESS_RESERVED1 = 0x8A,
CRSF_ADDRESS_CURRENT_SENSOR = 0xC0,
Expand All @@ -76,6 +68,7 @@ typedef enum
CRSF_ADDRESS_RADIO_TRANSMITTER = 0xEA,
CRSF_ADDRESS_CRSF_RECEIVER = 0xEC,
CRSF_ADDRESS_CRSF_TRANSMITTER = 0xEE,
CRSF_ADDRESS_ELRS_LUA = 0xEF,
} crsf_addr_e;

typedef struct crsf_header_s
Expand Down Expand Up @@ -106,6 +99,11 @@ typedef struct crsf_channels_s
uint16_t ch15 : 11;
} PACKED crsf_channels_t;

// ELRS appends an extra status byte after crsf_channels_t in the extended
// CHANNELS_PACKED frame; we ignore it but accept the larger payload size.
#define CRSF_CHANNELS_STATUS_ARMED (1 << 0)
#define CRSF_CHANNELS_STATUS_ARMING_MODE_CH5 (1 << 1)

typedef struct crsfPayloadLinkstatistics_s
{
uint8_t uplink_RSSI_1;
Expand All @@ -115,10 +113,10 @@ typedef struct crsfPayloadLinkstatistics_s
uint8_t active_antenna;
uint8_t rf_Mode;
uint8_t uplink_TX_Power;
uint8_t downlink_RSSI;
uint8_t downlink_RSSI; // ELRS 4.0 calls this downlink_RSSI_1
uint8_t downlink_Link_quality;
int8_t downlink_SNR;
} crsfLinkStatistics_t;
} PACKED crsfLinkStatistics_t;

typedef struct crsf_sensor_battery_s
{
Expand Down Expand Up @@ -152,9 +150,9 @@ typedef struct crsf_sensor_baro_altitude_s

typedef struct crsf_sensor_attitude_s
{
uint16_t pitch; // pitch in radians, BigEndian
uint16_t roll; // roll in radians, BigEndian
uint16_t yaw; // yaw in radians, BigEndian
int16_t pitch; // radians * 10000, BigEndian
int16_t roll; // radians * 10000, BigEndian
int16_t yaw; // radians * 10000, BigEndian
} PACKED crsf_sensor_attitude_t;

// Use standard byte order macros for better portability
Expand Down
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