bmegli
commented
5 years ago The packet structure
| Start Byte | Size | Type | Payload | End Byte | |
|---|---|---|---|---|---|
| bytes | 1 | 1 | 1 | type dependent | 1 |
| value | fixed 0xFB | 0-255 | defined set | type dependent | fixed 0xFC |
- CRC is already included in USB (not needed)
- Start Byte, Size, Type, End Byte can all be used for sync
- Size includes all the bytes ( payload bytes + 4)
- Payload starts with 4 bytes timestamp in microseconds
Types
Preliminary
| Type | Value | Payload bytes | Info |
|---|---|---|---|
| ODOMETRY | 0x01 | 28 | encoders and IMU quaternions |
| XV11LIDAR | 0x02 | 15 | lidar data |
| RPLIDARA3 | 0x03 | 138 | compressed ultra capsules, sequence |
ODOMETRY
| Timestamp | Left encoder | Right encoder | QW | QX | QY | QZ | |
|---|---|---|---|---|---|---|---|
| bytes | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
| type | uint32 | int32 | int32 | float | float | float | float |
| unit | us | counts | counts | quaternion | quaternion | quaternion | quaternion |
XV11LIDAR
| Timestamp | Angle quad | Speed64 | Distances x 4 [mm] | |
|---|---|---|---|---|
| bytes | 4 | 1 | 2 | 8 |
| type | uint32 | uint8_t | uint16_t | uint16_t x 4 (array) |
| unit | us | 0,89 for 0-3,356-359 | rpm = Speed/64 | flag, distances or error_code |
- the packet is raw XV11Lidar packet with timestamp, without signal strength, CRC
- Distances are 14 bits mm distances or error code, 1 bit strength warning, 1 bit invalid_data
- if invalid_data bit is set, the field carries error code
- otherwise it is distance in mm
- strength warning when power received is lower than expected for the distance
RPLIDARA3
| Timestamp | Device ID | Sequence | Data | |
|---|---|---|---|---|
| bytes | 4 | 1 | 1 | 132 |
| type | uint32 | uint8 | uint8 | ultra_capsules |
| unit | us | ID | counts | RPLidarA3 internal |
- device ID identifies lidar when using multiple lidars
- data is not decoded on MCU due to complexity
- sequence if for checking if data angles follow one another
- data corresponds to rplidar_response_ultra_capsule_measurement_nodes_t in rplidar_sdk
- decoding should do the same as _ultraCapsuleToNormal in rplidar_sdk
Design and implement communication protocol for handling serial/USB communication.
MCU <--> higher level controller
Requirements:
Document the protocol on wiki