Cepton Sensor Communication Specifications

1. Revision History

Current version:

Version	Date	Changes
0.9.5	05/13/2025	Update INFO and Point Data packet format
0.9.4	09/19/2024	Update Panic timestamp meaning
0.9.3	07/09/2024	Correct INFO V1 common header order
0.9.2	05/29/2024	Update to the PANIC packet offsets
0.9.1	01/19/2024	Update INFO and PANIC packet format
0.9	07/19/2023	Define frame aggregation behavior
0.8.3	08/27/2022	Define blooming and blocked bits
0.8.2	03/02/2022	Functional safety clarifications
0.8.1	01/27/2022	Add noise bit in point flag
0.8	01/11/2022	Clarify SDK reserved bits
0.7.1	01/10/2022	Draft document, add v2 point header
0.7	08/21/2021	Draft document, add v1 point data
0.6	07/14/2021	Draft document, not finalized

2. Overview

This document outlines the data communication protocol for Nova series of lidars produced by Cepton.

There are three general type of communications supported by Cepton's lidar sensors:

1. Data being sent out by sensor on a regular basis:
   • Point Data: UDP packet.
   • INFO data: UDP packet sent out twice per second.
2. Data being sent out by sensor under specific conditions:
   • Fault data: UDP packet sent out when a fault occurs.
   • ARP lookup: If configured with destination IP but no destination MAC, sensor will send ARP query to resolve destination MAC address.
3. Other protocols sensor supports:
   • ARP query: sensor will respond to ARP query to report its own MAC address to the local network.
   • PTP 802.1AS: Sensor supports Level 2 PTP protocol, aka gPTP.
   • PTP over UDP: Sensor supports PTP over UDP as defined in IEEE1588-2008
   • Configuration: UDP packet containing configuration request (this is not covered by this document)

3. Point Data Packet

Point data is accumulated as the lidar measurements happen. Once a full packet is filled the data will be sent out.

• Protocol: UDP packet on IPv4
• Destination IP: 255.255.255.255 (Configurable)
• Destination port: 8808 (Configurable)

Point data is a stream of measurements following strict order:

• All data follow the firing sequence.
• In the case of two lasers fired at the same time, the point data sequence between the two are predetermined. E.g. in Nova sensors channel 0 and channel 2 fire together, the point data will always be channel 0 first then channel 2, even if the laser return of 2 comes back first. The second laser that is fired at the same time always has relative timestamp value of 0.
• A no-return condition happens when laser shot out doesn't hit a valid target. No return points are not present in the point stream. (Note: This can be changed if desirable )
• A maximum time lapse value is defined based on minimum allowed data rate (20ms ). When time approaches maximum time lapse and the point data buffer is still not filled, the shorter packet will be sent out.
• When double return is enabled, the second return will only be present in the point data stream if it is valid. When present, it will be placed right after the first return and before any other laser channels. The SecondReturn flag will be set and relative timestamp is always 0.
• For double returns, first return is always the strongest. If the farthest return is not also the strongest, it will be the second return. Otherwise the second return will be second strongest signal.

3.1. Point Data Packet Structure

In the payload of the UDP packet, after the 24 bytes header, each point is contiguously placed based on the point size. There are up to 144 points of 10 bytes each.

Offset	Block	Size	Description
0	Header	24	Point Data Packet Header
24	Point0		Point #0
	Point1		Point #1
...	...	...	...
	PointN		Point #N

Offset	Field	Size	Value	Description
0	Signature	4	STDV	4 byte signature to identify packet type
4	HeaderVersion	1		Header type
5	HeaderSize	1		Header size
6	Flags	2	0	Flags
8	Timestamp	8		Reference timestamp
16	PointVersion	1	0/1	Point structure type
17	PointSize	1		Point structure size
18	PointCount	2	144	Number of points in this packet
20	SequenceId	4		Version 2+: Sequencing ID for packet stream

(*When there aren't enough points to fill all 144 possible points in the UDP Packet, this number can be smaller, and the remaining space is filled with empty points (all values equal to 0). )

Corresponding C structure:

struct CeptonPointDataHeader {
  uint32_t signature;
  uint8_t header_version;
  uint8_t header_size;
  uint16_t flags;
  int64_t reference_system_time_usec;;
  uint8_t point_version;
  uint8_t point_size;
  uint16_t point_count;
  uint32_t sequence_id;
};

Reference timestamp holds the reference time for the first point. This is the number of microseconds (us) since the sensor boot up time. To convert this timestamp to universal time, please reference INFO packet description.

Flags: There is no packet level flags defined. This byte has to be 0 at all time.

3.2. Point Data Structure

Offset	Field	Size	Unit	Range	Description
0	X	2	0.5cm	-163.840m to 163.835m	X coordinate
2	Y	2	0.5cm	0 to 327.68m	Y coordinate
4	Z	2	0.5cm	-163.840m to 163.835m	Z coordinate
6	Reflectivity	1	%	0 to 255	Reflectivity
7	Timestamp	1	us	0 to 255	Time difference from the point before
8	LaserId	1		0 to 63	Laser ID
9	Flags	1			Flags
10+	Internal				When PointSize > 10, these are internal data

Corresponding C structure:

struct CeptonPointData {
  int16_t x;
  uint16_t y;
  int16_t z;
  uint8_t reflectivity;
  uint8_t timestamp_offset_usec;
  uint8_t laser_id;
  uint8_t flags;
};

Coordinates: Looking from the sensor bore-sight,

• X represents left to right (negative to positive)
• Y represents near to far (0 and up)
• Z represents bottom to top (negative to positive)

Coordinates X and Z are signed short, while Y is unsigned. The reference point (0,0,0) is located at the geometric center of the sensor, which is at the mid-point of all 3 primary dimensions of the sensor enclosure.

Reflectivity: 0-100% reflectivity are measured by assuming Lambertian reflection model. Non-Lambertian materials, such as retro-reflective surfaces commonly found in road signs and warning cones, can produce higher than 100% reflectivity. For reflectivity less than 127%, intensity is equal to reflectivity. For reflectivity greater than or equal to 127%, we convert to intensity exponentially using quantize_table[reflectivity-127]:

private static float[] quantize_table = {
  127.0f,  130.7f,  134.5f,  138.4f,  142.4f,  146.6f,  150.9f,  155.3f,
  159.8f,  164.4f,  169.2f,  174.1f,  179.2f,  184.4f,  189.8f,  195.3f,
  201.0f,  206.9f,  212.9f,  219.1f,  225.4f,  232.0f,  238.8f,  245.7f,
  252.9f,  260.2f,  267.8f,  275.6f,  283.6f,  291.9f,  300.4f,  309.1f,
  318.1f,  327.4f,  336.9f,  346.7f,  356.8f,  367.2f,  377.9f,  388.9f,
  400.2f,  411.9f,  423.9f,  436.2f,  448.9f,  462.0f,  475.4f,  489.2f,
  503.5f,  518.1f,  533.2f,  548.8f,  564.7f,  581.2f,  598.1f,  615.5f,
  633.4f,  651.9f,  670.8f,  690.4f,  710.5f,  731.1f,  752.4f,  774.3f,
  796.9f,  820.1f,  843.9f,  868.5f,  893.8f,  919.8f,  946.6f,  974.1f,
  1002.5f, 1031.7f, 1061.7f, 1092.6f, 1124.4f, 1157.2f, 1190.9f, 1225.5f,
  1261.2f, 1297.9f, 1335.7f, 1374.6f, 1414.6f, 1455.8f, 1498.2f, 1541.8f,
  1586.6f, 1632.8f, 1680.4f, 1729.3f, 1779.6f, 1831.4f, 1884.8f, 1939.6f,
  1996.1f, 2054.2f, 2114.0f, 2175.5f, 2238.9f, 2304.0f, 2371.1f, 2440.1f,
  2511.2f, 2584.3f, 2659.5f, 2736.9f, 2816.6f, 2898.6f, 2983.0f, 3069.8f,
  3159.2f, 3251.1f, 3345.8f, 3443.2f, 3543.4f, 3646.6f, 3752.7f, 3862.0f,
  3974.4f, 4090.1f, 4209.2f, 4331.7f, 4457.8f, 4587.6f, 4721.1f, 4858.6f,
  5000.0f};

Timestamp: This value is the relative value from the time since last point in the packet. For the very first point, it is time since the packet header's reference time. Notice that 0 value is possible for dual firing mode or dual return's second return. The timestamp represents the time of firing, for the time accuracy afforded (> 1us, ~300m traveled), it is OK to use directly as target point time (time when target is hit by laser).

Channel ID: Reports the channel ID, which usually indicate a distinct laser->APD pathway. Each channel correspond to a unique set of laser/APD pair.

Flags: per-point flags are defined in the table below

Bit	Value	Name	Description
0	1	Saturated	Set if the point is saturated
1	2	Reserved	Reserved
2	4	FrameParity	Frame parity bit
3	8	Reserved	Reserved
4	16	SecondReturn	Set for second return
5	32	NoReturn	Set if this point has no return
6	64	Noise	Set if this point is a noise
7	128	Blocked	Set if this point is blocked

(*The reserved bit#3 is defined in SDK as frame boundary. This is a software flag created by SDK and is not part of the communication protocol. Refer to Cepton SDK documentation for details)

Corresponding flags and enumerations

enum {
  CEPTON_POINT_SATURATED = 1 << 0,
  CEPTON_POINT_FRAME_PARITY = 1 << 2,
  CEPTON_POINT_SECOND_RETURN = 1 << 4,
  CEPTON_POINT_NO_RETURN = 1 << 5,
  CEPTON_POINT_NOISE = 1 << 6,
  CEPTON_POINT_BLOCKED = 1 << 7,
};

Saturated flag: Set if the signal received is too strong to be correctly measured. This usually happen when measuring retro-reflective targets. When this flag is set, the reflectivity is not trust worthy, and the distance accuracy is slightly reduced.

There are also some unspecified conditions that can be derived from the data stream itself:

FrameParity: Cleared for even frames and set for odd frames. This ensures the frame boundary as identified by the sensor is always communicated even when one of the data packet is lost.

Dual return case: If two consecutive points have same ChannelID and second point has Timestamp set to 0. The second point is the second return of the same laser firing. Second return signifies that the fired laser was somehow split up (e.g. hitting a corner of a near wall, then hitting a wall farther down). In this case, the strongest is always the first and farthest return can be determined by comparing Y value.

Blocked points: Some Cepton lidar products can detect blockage and report them. When blockage happens, there might still be a valid return. The distance of the return can be trusted but the reflectivity should be considered incorrect.

3.3. Point Data Configuration

Point data packets can be turned off completely.

For sensors that support turning on or off the second return feature, point data structure will not change. The second return, when present, will just be a repeat of the same laser channel, with time offset 0 and SecondReturn flag set.

4. INFO Packet

Offset	Block	Size	Description
0	Header	96	INFO packet header
96	DiagnosisApm	312	Application processing microcontroller diagnostic
408	DiagnosisKomodo	22	Komodo microcontroller diagnostic
430	DiagnosisFault	38	Fault diagnostic
468	DiagnosisGecko	12	Gecko diagnostic

4.1. INFO Packet Header Structure

INFO packet header is universal data for all Cepton sensors

Offset	Field	Size	Value	Description
0	Signature	4	INFZ	4 byte signature to identify packet type
4	HeaderMagic	2		2 bytes for future compatibility
6	Reserved	1		Reserved
7	SKU	1		SKU number
8	Model	2		Model number
10	ModelReserved	2		Reserved
12	SerialNumber	4		Sensor serial number
16	FirmwareVersion	4		Firmware release version number
20	ModelName	28		UTF-8 string for model name
48	PartNumber	4		Part Number
52	ApmVersion	4		Application Processor version
56	IoxVersion	4		IOX firmware version
60	IguanaVersion	4		Iguana firmware version
64	PowerUpTime	8		Microseconds since power up
72	TimeOffsetFromMaster	8		FSM-Master time offset in microseconds
80	TimeDriftCorrection	4		Clock drift correction
84	TimeSyncStatus	1		Time synchronization details
85	ReturnMode	1		Dual return mode
86	ThermalDerateState	1		Thermal derating
87	RangeEstimation	1		Single value range estimation for how far the sensor can see in meters
88	Temperature	2		Significant temperature
90	ChannelCount	2		Channel count number
92	FaultSummary	4		Fault cases summarization

HeaderMagic: The value of HeaderMagic is 0x0860. The total header size is 96 bytes, as indicated by the first 10 bits of the INFZ Magic Number. Bits 11 to 13 represent the INFZ version 1.

FirmwareVersion: The version fields for the sensor firmware, APM, IOX, and Iguana share the same structure defined in the table below:

Offset	Field	Size	Value	Description
0	Major	1		Major version number
1	Minor	1		Minor version number
2	Build	1		Build number
3	Revision	1		Revision number

FaultSummary: Per-point flags indicating various error conditions are defined as follows:

Bit	Value	Name	Description
0	1	Lidar data rationality check error	Any data rationality check error
1	2	Internal communication error	Any checksum mechanism failure
2	4	Temperature out of range	Any chip's temperature out of range
3	8	Voltage out of range	Any ADC measured voltage out of range
4	16	Boot failure	Any subsystem (iguana, gecko) boot failure
5	32	Ethernet communication	Any server/client or ethernet sync error
6	64	Lidar image irregularity	Partial/full laser blockage or distance
7	128	Micro-Motion Technology	Any mmt-related error
8	256	Security Error	Any unauthorized access or key provision
9	512	Session Error	Any incorrect session action
10-31		Reserved	Reserved

Corresponding c structure:

struct CeptonInfoHeader {
uint8_t padding0;
  uint8_t sku;
  uint16_t model_enum;
  uint8_t model_enum_reserved[2];
  uint32_t serial_number;
  typedef struct {
    uint8_t major;
    uint8_t minor;
    uint8_t build;
    uint8_t revision;
  } release_version, apm_version, iox_version, iguana_version;
  int64_t time_since_powerup;
  int64_t time_offset_from_master;
  int32_t time_drift_correction;
  uint8_t time_status;
  uint8_t return_mode;
  uint8_t thermal_derate_state;
  uint8_t range_estimation;  
  uint16_t temperature;
  uint16_t channel_count;
  uint32_t fault_summary;
};

4.2. INFO Diagnosis Data

The LiDAR diagnostic system includes four diagnostic payloads.

4.2.1 APM Diagnosis Payload 0

Offset	Field	Size	Value	Description
96	DiagType	2		Diagnostic structure type
98	DiagSize	2		Diagnostic structure size
100	SkuSoftware	2		SKU for software
102	MmtStatus	24		MMT status
126	TempApm	2		Komodo temperature
128	TempIOX	2		IOX temperature
130	TempOptic	2		Optic temperature
132	TempIguana	32		IGUANA temperature
164	ImuReadings	24		IMU rotation and acceleration reading
188	Reserved	2		Reserved
190	FaultApmLastError	2		Last APM error
192	FaultApmLastTs	8		Last APM error timestamp
200	Reserved	6		Reserved
206	FaultIoxLastError	2		Last IOX error
208	FaultIoxLastTsc	8		Last IOX error timestamp
216	IguanaRangeEstValues	16		Last IGUANA error enum
232	FaultIguanaLastError	16		Raw range estimation enum values from each IGUANA
248	FaultIguanaLastTs	128		Last IGUANA error timestamp
376	PtpPdelay	8		PTP link delay
384	PtpOffset	8		PTP master-slave offset
392	PtpStat	1		PTP status
393	Reserved	7		Reserved
400	LifeCount	8		Clock counter

MmtStatus: Describes the status of the MMT Monitor for both the X-axis (horizontal) and Z-axis (vertical). Each axis contains an identical set of fields as detailed in the table below.

Offset	Field	Size	Value	Description
0	Amplitude	2		Center-to-peak amplitude in encoder counts
2	DriveAmplitude	2		Driving Amplitude
4	Frequency	2		MMT frequency
6	PhaseError	2		MMT phase error
8	Reserved	4		Reserved

Corresponding c structure:

struct DiagnosticApm {
  uint16_t diag_type;
  uint16_t diag_size;
  uint16_t sku_software; 
  typedef struct {
   typedef struct {
      uint16_t amplitude;
      int16_t drive_amplitude;
      uint16_t frequency;
      int16_t phase_error;
      uint8_t reserved[4];
    } z, x;
  } mmt_status
  uint16_t temp_apm;
  uint16_t temp_iox;
  uint16_t temp_optic;
  uint16_t temp_iguana[16];
  int16_t imu_readings[2][6];  
  uint16_t padding0[1];
  uint16_t fault_apm_last_error;
  uint64_t fault_apm_last_ts_usec;  
  uint16_t padding1[3];
  uint16_t fault_iox_last_error;
  uint64_t fault_iox_last_ts_usec;
  uint8_t iguana_range_est_values[16];
  uint8_t fault_iguana_last_error[16];
  uint64_t fault_iguana_last_ts_usec[16];  
  uint64_t ptp_pdelay_nsec;
  uint64_t ptp_ms_offset_nsec;
  uint8_t ptp_stat;
  uint8_t reserved[7];
  uint64_t life_counter;
};

4.2.2 Komodo Diagnosis Payload 1

Offset	Field	Size	Value	Description
408	DiagType	2		Diagnostic structure type
410	DiagSize	2		Diagnostic structure size
412	SkuSoftware	2		SKU for Software
414	VoltageAdcOut	16		Komodo ADC Voltage

VoltageAdcOut

Offset	Field	Size	Value	Description
414	VoltageAdcOut	2		Komodo 0.8V
416	VoltageAdcOut	2		Komodo 1.0V
418	VoltageAdcOut	2		Komodo 1.8V
420	VoltageAdcOut	2		Komodo 3.3V
422	VoltageAdcOut	2		Komodo 5.3V
424	VoltageAdcOut	2		Optical Module 5.3V
426	VoltageAdcOut	2		Laser 32V
428	Reserved	2		Reserved

Corresponding c structure:

struct DiagnosticKomodo {
  uint16_t diag_type;
  uint16_t diag_size;
  uint16_t sku_software;
  uint16_t voltage_adc_out[8];
};

4.2.3 Fault Diagnosis Payload 2

Offset	Field	Size	Value	Description
430	DiagType	2		Diagnostic structure type
432	DiagSize	2		Diagnostic structure size
434	SkuSoftware	2		SKU for Software
436	FaultEntries	32		Fault entries

FaultEntries: In the FaultEntried structure, each field corresponds to a specific diagnostic fault condition detected by the system:

Offset	Field	Size	Value	Description
436	VoltageOutOfRange	8		Volate out of range
444	TemperatureOutRangeKomodo	1		Komodo temperature error
445	TemperatureOutRangeIox	1		IOX temperature error
446	TemperatureOutRangeIguana	1		Iguana temperature error
447	TemperatureOutRangeGecko	1		Gecko temperature error
448	IguanaIoxCommError	1		Iguana and IOX communication error
449	IoxGeckoCommError	1		IOX and Gecko communication error
450	GeckoKomodoCommError	1		Gecko and Komodo communication error
451	IguanaBootFailure	1		Iguana boot failure
452	ChipFailure	1		Chip failure
453	EthLnkDown	1		Ethernet link down
454	PtpExpiration	1		PTP expiration
455	ThermalShutDown	1		Thermal shut down
456	LasersPartialBlock	1		Lasers partial blockage
457	LasersFullBlock	1		Lasers full blockage
458	MmtInterlock	1		MMT interlock failure
459	IguanaFailure	1		Iguana bootup failure
460	FpgaRuntimeFail	1		FPGA runtime failure
461	MmtTimeout	1		MMT encoder timeout
462	GeckoBootFailure	1		Gecko boot failure
463	InvalidChannels	1		Missing or invalid channels
464	Reserved	4		Reserved

VoltageOutOfRange:

Offset	Field	Size	Value	Description
436	VoltageOutOfRange	1		Komodo 0.8V
437	VoltageOutOfRange	1		Komodo 1.0V
438	VoltageOutOfRange	1		Komodo 1.8V
439	VoltageOutOfRange	1		Komodo 3.3V
440	VoltageOutOfRange	1		Motor 5.3V
441	VoltageOutOfRange	1		OM 5.3V
442	VoltageOutOfRange	1		Laser 32V
443	VoltageOutOfRange	1		Reserved

Corresponding c structure:

struct DiagnosticFault {
  uint16_t diag_type;
  uint16_t diag_size;
  uint16_t sku_software;

  union {
    struct {
      uint8_t voltage_out_range[8];
      uint8_t temperature_out_range_komodo;
      uint8_t temperature_out_range_iox;
      uint8_t temperature_out_range_iguana;
      uint8_t temperature_out_range_gecko;
      uint8_t iguana_iox_comm_crc_error;
      uint8_t iox_gecko_comm_crc_error;
      uint8_t gecko_komodo_comm_crc_error;
      uint8_t iguana_boot_failure;
      uint8_t phy_sync_failure;
      uint8_t eth_link_down;
      uint8_t ptp_expiration;
      uint8_t thermal_shut_down;
      uint8_t lasers_partial_block;
      uint8_t lasers_full_block;
      uint8_t mmt_interlock;
      uint8_t iguana_failure;
      uint8_t fpga_runtime_fail;
      uint8_t mmt_timeout;
      uint8_t gecko_boot_failure;
      uint8_t invalid_channels;
      uint8_t rsv[4];
    };
    uint8_t fault_entries[32];
  };
};

4.2.4 Gecko Diagnosis Payload 3

Offset	Field	Size	Value	Description
468	DiagType	2		Diagnostic structure type
470	DiagSize	2		Diagnostic structure size
472	GeckoStatus	8		Gecko Status

Corresponding c structure:

struct DiagnosticGecko {
  uint16_t diag_type;
  uint16_t diag_size;
  uint8_t gecko_status[8];
};

5. Frame Aggregation Logic

SDK provides a few methods to aggregate points such that the point cloud creates a frame. Two types of aggregation are available:

5.1 Natural Frame Aggretation

The lidar has a built-in notion of when a frame starts and ends. This is signified by the parity on points (shown in the CEPTON_POINT_FRAME_PARITY bit from the point flag). When the parity changes, the frame aggregator would then note to finish off the frame and start a new one. Frame aggregation utilizes this mode as the default.

When point packets are dropped, this mode will robustly still detect a frame change. In the unlikely event that a whole frame of the opposite parity is dropped, the aggregator will produce two frames of the same parity with variable results on what the frame looks like visually, but then resume normal operation.

5.2 Fixed Frame Aggregation

Users of the SDK can specify the period of time a frame should last before switching to a new frame by specifying it in microseconds (minimum 1000). This should be passed when listening to frames via the CeptonListenFrames function call.

At a given start timestamp, the internal frame aggregator would increment its time by adding on each point's relative timestamp value. When the starting timestamp reaches the fixed frame duration (or reach an internal buffer limit), it then takes the most recent point cloud packet's start time, adds on the aggregate time elapsed from the points taken in the packet, and restarts the time and frame aggregation from that point.

Note that based on this implementation, if any point packets get lost, the next incoming points will assume a timestamp earlier compared to its presumed ground truth timestamp until the current frame finishes. When the frame is complete, then the next frame will adjust accordingly to the current timestamp again.

6. Functional Safety Considerations

There are several built-in mechanisms to ensure the data sanity of the point cloud stream coming out of the lidar:

1. Both the ethernet MAC layer and UDP header has checksum that is populated and enforced. This guarantees there is no bit flip in the data arriving at the host PC.
2. Starting in header version 2, we have introduced a "sequence id" which can be used to detect any missing UDP packet.
3. Starting in header version 2, when the sequence IDs are contiguous, the timestamp starting point in header will match exactly the timestamp of last measurement in the previous point data packet. This ensures no gap in measurement occurs.

In addition, when any faults happen inside the sensor, the sensor will send out a "panic message" to inform the host as soon as possible.

Panic packet format:

Offset	Field	Size	Description
0	Header	12	PANIC packet header
12	Active Fault	24	Active fault detailed information

Panic packet header format:

Offset	Field	Size	Value	Description
0	Magic	4	PANC	8 bytes header magic signature
4	Serial Number	4		Sensor serial number
8	Sequence Id	2		Continuous increasing sequence id
10	Reserved	2		Reserve for future use

Panic packet active fault format:

Offset	Field	Size	Value	Description
0	Fault Identity	4		4 bytes field for unique fault case identification
8	Life Counter	4		Count of how many of this panic have been sent
12	Lidar Timestamp	8		Microseconds since power on. Matches point data header
14	Reserved	8		Reserve for future use

packet structure:

struct panic_packet {
  uint32_t signature;
  uint32_t serial_number;
  uint16_t sequence_id;
  uint16_t reserved;
  struct {
    uint32_t fault_identity;
    uint32_t life_counter;
    uint64_t ptp_timestamp;
    uint64_t reserved;
  } active_fault;
};