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Protocol Proposal (Chimpanzee)

Init

Code: 0xFF

Raspberry Pi -> Nucleo:

Must:

  • Specify Nucleo adress
  • Specify version, subversion
  • Specify frequency of heartbeat (in ms)

Packet Structure:

Byte Content Description
0xFF Init code
0x00 Address
0x01 Version
0x01 Sub-version
0x01 Interval entry See Interval table
0x97 CRC-8
0xEE End of packet Optional due init fixed dimension

Nucleo -> Raspberry Pi:

Must:

  • Specify adress
  • Specify version
  • Specify state

Packet Structure:

Byte Content Description
0xFF Init code
0x00 Address In case of multiple Nucleo
0x01 Version
0x01 Sub-version
0x?? Positive or negative response Based on the initialization
0x?? CRC-8
0xEE End of packet

0x00 is the only positive response

Init Faults:

  • 0x01 Serial not opened
  • 0x02 Old Version (Raspberry Pi)
  • 0x03 Old Version (Nucleo)
  • 0x04 Nucleo does not answer
  • 0x05 Invalid answer
  • 0x06 CRC failed
  • 0x07 Thrusters fail initialization
  • Others?

Communication

Code: 0xAA

Packet Structure:

Byte Content Description
0xAA Code Communication code
0x00 Address In case of multiple Nucleo
0x00 Command See list below
Arguments (dynamic) Arguments, variable based on command
CRC-8 See CRC-8 calculation rules
0xEE End of packet

In particular:

  • Command 0 (motor) has 8 arguments of uint16_t (Unidirectional)
  • Command 1 (arm) has 1 argument of uint16_t (Unidirectional)
  • Command 2 (sensor) see sensor polling command

Sensor polling command

Raspberry Pi -> Nucleo:
Payload Structure:
Byte Content Description
0x00 Sensor_ID ID for the sensor Nucleo must query
0x76 I2C address
0x00 Interval entry See Interval table
0x00 Type of sensor See type sensor list
Nucleo -> Raspberry Pi:
Payload Structure:
Byte Content Description
0x00 Sensor_ID ID of queried sensor
0x00 Type of sensor See type sensor list
Sensor data According to type sensor list

Heartbeat (Only from Nucleo to Raspberry)

Code: 0xBB

Packet Structure:

Byte Content Description
0xBB Code Heartbeat code
0x00 Address
0b1 Status 0 -> OK, 1 -> Not Working
0b0000000 Status code
0x?? Paylod According to Salvatore
0xEA CRC
0xEE End of packet

Status Codes:

OK Codes:

  • 000: Ready
  • 001: Processing PWM
  • ..

Not Working Codes:

  • 000: Not ready
  • 001: Thruster fail
  • ...

Byte stuffing

Behind each START_BYTES (0xAA, 0xBB and 0xFF), it is mandatory to prepend 0x7E as ESCAPE CHARACTER.

Behind each 0xEE byte, it is mandatory to prepend 0x7E as ESCAPE CHARACTER.

Behind each 0x7E byte, it is mandatory to prepend 0x7E as ESCAPE CHARACTER.

CRC-8 Calculation Rules

The CRC calculation must consider all the bytes in the packet, excluding:

  • ESCAPE CHARACTER(S)
  • END OF PACKET BYTE

Interval table

Interval table:

Byte (Hex) Interval (ms)
0x00 10 ms
0x01 20 ms
0x02 30 ms
0x03 40 ms
.. ..
0xFF 2550 ms

Sequence diagram

Diagram description