Home » Protocols used to talk between an embedded CPU and a PC

Protocols used to talk between an embedded CPU and a PC

Solutons:


There’s a lot to be said for client-server architecture and synchronous protocols. Simplicity and robustness, to start. If speed isn’t an issue, you might consider a compact, human-readable protocol to help with debugging. I’m thinking along the lines of modem AT commands: a “wakeup” sequence followed by a set/get command, followed by a terminator.

Host -->  [V02?]      // Request voltage #2
AVR  -->  [V02=2.34]  // Reply with voltage #2
Host -->  [V06=3.12]  // Set voltage #6
AVR  -->  [V06=3.15]  // Reply with voltage #6

Each side might time out if it doesn’t see the closing bracket, and they’d re-synchronize on the next open bracket, which cannot appear within the message itself.

Depending on speed and reliability requirements, you might encode the commands into one or two bytes and add a checksum.

It’s always a good idea to reply with the actual voltage, rather than simply echoing the command, as it saves a subsequent read operation.

Also helpful to define error messages, in case you need to debug.

Modbus might be what you are looking for. It was designed for exactly the type of problem you have. There is lots of code/tools out there and adherence to a standard could mean easy reuse later. It also support human readable ASCII so it is still easy to understand/test.

See FreeModBus for windows and embedded source.

My vote is for the human readable.

But if you go binary, try to put a header byte at the beginning to mark the beginning of a packet. I’ve always had bad luck with serial protocols getting out of sync. The header byte allows the embedded system to re-sync with the PC. Also, add a checksum at the end.

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