Add optional echo-checking #3
Description
When a device echoes back the data sent to it, we should verify that what we sent is what came back.
Of course, without knowledge of the serial protocol involved it is difficult to be sure when, for example, we send a Q and subsequently receive a Q whether that is the echo or part of another message (and the echo still to follow). There's also the question of what to do if the echo does not come back.
We can still provide a general mechanism which...
- Keeps track of recently sent data
- Queries the higher-level protocol whether what we see is an echo
- Notifies the higher level if an echo is not received promptly
- Holds back further outgoing data if echoes are outstanding