Protocol¶
The protocol used for serial communication is implemented using POD's (Plain Old Datatypes) and serialised to little-endian binary before being sent back and forth over a serial interface.
Using a proper serial-connection rather than rely on the Serial-over-USB that comes standard with the Arduino Due is recommended to avoid the ≈ 4ms round-trip time in USB packet delivery.
Implementation - Commander¶
The protocol is best understood by reading through the protocol.py file on the
commander. It should be fairly easily understood by those familiar with Python.
It uses the standard library struct to pack and unpack data.
Implementation - Controller¶
The protocol must match the one implemented on the commander exactly, as any difference
in packet lengths will lead to future misalignment that cannot easily be corrected for.
A struct-like library is also used on the controller to allow for easy matching between the
controller and commander protocol implementations.
Packet overview¶
| ID (byte) | ID (ASCII) | Packet | Direction (Controller ↔ Commander) | Fields | Comment |
|---|---|---|---|---|---|
0x00 |
NUL |
NullPacket |
N/A | id |
Does nothing |
0x3F |
? |
UnknownPacket |
N/A | id |
An unknown packet was found |
0x23 |
# |
DebugPacket |
⟶ | id, msg |
Debug messages |
0x7E |
~ |
InfoPacket |
⟶ | id, msg |
Info messages |
0x21 |
! |
ErrorPacket |
⟶ | id, msg |
Error messages |
0x70 |
p |
PingPacket |
⟷ | id, timestamp |
Other end should respond with a pong |
0x50 |
P |
PongPacket |
⟷ | id, timestamp |
Response to ping |
0x24 |
$ |
RequestDebugInfoPacket |
⟵ | id |
Requests debug information from controller |
0x78 |
x |
SetPositionPacket |
⟵ | id, operation, cart_id, value |
Sets relative or absolute position |
0x58 |
X |
GetPositionPacket |
⟶ | id |
UNUSED. Gets position |
0x76 |
v |
SetVelocityPacket |
⟵ | id, operation, cart_id, value |
Sets relative or absolute maximum velocity |
0x56 |
V |
GetVelocityPacket |
⟶ | id |
UNUSED. Gets maximum velocity |
0x7C |
| |
FindLimitsPacket |
⟷ | id |
Instructs controller to perform limit finding routine |
0x2F |
/ |
CheckLimitPacket |
⟷ | id |
Instructs controller to perform limit checking routine |
0xA7 |
§ |
DoJigglePacket |
⟷ | id |
Instructs controller to perform a jiggle routine |
0x40 |
@ |
ObservationPacket |
⟶ | id, timestamp_micros, cart_id, position_steps, angle |
Observed state |
0x02 |
STX |
ExperimentStartPacket |
⟷ | id, timestamp_micros |
Observed state |
0x03 |
ETX |
ExperimentEndPacket |
⟷ | id |
Observed state |