Hey there, I recently faced the challenge of how to send and receive data in a structured way (with efficient encoding, backwards compatibility, ...) between various tiny microcontrollers, where the amount of available RAM is measured in kilobytes.
So, I sat down and created femtopb, the smallest footprint protobuf library that I know of. It is of course #[no_std] and also doesn't require alloc; hence, all messages can be encoded and decoded using static or stack allocated memory. Checks are also made to ensure that the generated code can't possibly panic.
Feel free to check out the crate page, repo and docs (once the docs build completes)!