What is the best way to get a receiver in sync with clock? Manchester encoding

Question

This is my first post here, first off let me know how I go.

I am going to be taking on a new project soon, to design a protocol for communication between two microcontrollers (I understand there is stuff out there but I would like to learn how low level stuff works). At the moment, I am doing some research of encodings and came across Manchester encoding, I understand how the data is sent.

But my current question is how would you get the clocks in sync, there would be a preamble in front of every message, which would give the receiver some time to detect the clock, but how would I calculate the amount of time between each read. For clarification, there would be no set transfer rate. Maybe I would have to sample the preamble every so often and see if there is a change, but maybe that could fail, if I read in the centre of a high or low.

If it is possible, I would like a detailed explanation on how I could do this, no something vague, but any information would help.

Thank you in advance.

If my question is too vague, please let me know.

EDIT: A solution through software, not hardware

Answer 1

if you wanted to create an answer, I would be happy to mark it as correct.

If you want a software solution then you can ascertain what the embedded clock rate is by 16x oversampling the data and looking for clock edges. This is precisely what a UART does because it has to find the optimum position to sample the data to get best reliability.

For Manchester encoding (see picture below), the clock is embedded into the data stream hence there are edges that define the clock every data symbol but, you would still need to detect those edges so you can remain in sync and decode the data correctly. You could of course use a hardware interrupt scheme but that is, strictly speaking a hardware/software solution.

You should also continue to perform clock recovery throughout the whole packet of data in case of small drifts but it's less of a problem with Manchester decoding compared to UART asynchronous data or scrambled synchronous data. But, the bottom line is; use a continual method to detect clock edges and not some initial calculation based on the preamble and hope that you stay in sync for the payload data. I mean, you might get away with that but, it's not ideal.