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Protocol.md

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Protocol (Transport, Layer 1)

The Raspberry Compute Module 3+ communicates with the on-board display/flap-controller using a simple byte-based serial protocol using the on-board serial bus.

Serial Bus

The serial bus itself is accessible via the /dev/ttyAMA0 device.

Setting Value
Baudrate 38400 Baud In/out
Parity Disabled
Stopbit 1 Stop bit
Character Size(bits) 8
RTS/CTS Hardware flow control Disabled

Protocol (Data, Layer 2)

Packets always start with a magic byte (0xFF), contain an address, some flags (so far unknown), a payload and its length, and end with a CRC32 of the packet itself.

Structure

Packet Structure

Offset Length Field
0 1 Magic Byte (0xFF)
1 2 Address (For most packets the Column ID, 1-22)
3 1 Flags
4 2 Payload Length
6 variable <Payload>
6 + len(payload) 4 Checksum(CRC32)

Payload Structure

Offset Length Field
0 1 Packet ID
1 variable <Payload data>

Checksum (CRC32)

Before a packet gets sent, the last 4 bytes are set to 0xFF and the whole packet gets checksummed using CRC32, the result is then stored in the last 4 bytes.

Packets

Packet IDs

Packet ID Name
0x00 Unknown/Not used
0x01 Set Target
0x02 Arm Column
0x03 Go
0x04 Ping
0x05 Write Register
0x06 Read Register

0x00 - Unknown

This type is currently not used, or not referenced anywhere

0x01 - Set Target

Offset Length Field
0 1 Packet ID(0x01)
1 7 Column data as bytes

Notes

For some reason there are not 6 but 7 characters in each column, comments in the original firmware might indicate a not-released version of Vestaboard with 7x22 (or even 7x23) flaps.

0x02 - Arm Column

Offset Length Field
0 1 Packet ID(0x02)

0x03 - Go

Offset Length Field
0 1 Packet ID(0x03)

0x04 - Ping

Offset Length Field
0 1 Packet ID(0x04)
1 2 Null bytes(0x00 0x00)

0x05 - Write Register

Offset Length Field
0 1 Packet ID(0x05)
1 1 Register ID
2 2 Register Value

0x06 - Read Register

Offset Length Field
0 1 Packet ID(0x06)
1 1 Register ID

Registers

Coming soon

Flap Characters

Colors

Value Color
0x00 Black
0x01 White
0x02 Red
0x03 Orange
0x04 Yellow
0x05 Green
0x06 Blue
0x07 Purple

How to set flaps

The process is simple, after opening a connection to the flap-controller, simply send 1-22 SetTarget packets, followed by 1-22 Arm packets, and commit using a Go packet.

sequenceDiagram
Pi ->> Board: SetTarget[ColId(Address): 1, Data: ('AAAAAA ')
Board ->> Pi: ACK
Pi ->> Board: Arm[ColId(Address): 1]
Board ->> Pi: ACK
Pi ->> Board: SetTarget[ColId(Address): 2, Data: ('BBBBBB ')
Board ->> Pi: ACK
Pi ->> Board: Arm[ColId(Address): 2]
Board ->> Pi: ACK
Pi ->> Board: SetTarget[ColId(Address): 3, Data: ('CCCCCC ')
Board ->> Pi: ACK
Pi ->> Board: Arm[ColId(Address): 3]
Board ->> Pi: ACK
Pi ->> Board: Go[Address: 1]
Board ->> Pi: ACK
Loading

Note

There has to be a small delay of about 40000μs between each packet, otherwise the board seems to go out-of-sync and sometimes lock up.

Result