Communication

For the communication, we need a bus that puzzles can connect to and be removed from.
RS485 is a robust technology for this.

There are a lot of protocols for RS485Address, strongly focused on factories. ModBUS is one of the most well-known. It is however limited to what can be communicated. We will therefor write a small protocol ourselves.

The controller has to be able to:

• address individual puzzles
• send commands
• send data (solutions for the puzzle)
• receive updates on the status

This results in this protocol.

  graph LR
    A0[Address]---C0[Command]---D0[Data]---R0[Response]

Bits will be sent Most-Significant-Bit first (also known als Little Endian).

The address is a block of 8 bits. This allows for addressing 256 individual puzzles. The following addresses have been assigned:

The command is a block of 8 bits. This allows for addressing 256 individual commands. The following command are defined:

The data is a blob of 32 bits, depending on the command being send.
If no data has to be send, it will be all zeros (0x00, 0x00, 0x00, 0x00).

The communication will be encrypted, since people should not be able to fake signals and get to the treasure that way. AES-128 is a standard algorythm that can be implemented in a very light way on the microcontrollers. It will contain mechanisms to prevent sniffing, replay attacks and command injection.