Implement StdRegister readback

[kcaisley]

On my behavioral-modules branch, I've had this fix for a while, but actually Stella needs it too now. Can we merge this? Since my other branch is too big to review quickly

[kcaisley]

Hmm, I'm now uncertain if this is a good idea. Do we know the historical reason why this was not implemented? Back in 2019 Jens changed it:

I guess one thing to think about here, is that it will update the StdRegister object which might not be desirable? Just directly calling get_data would avoid this. But I'm not sure if that is a bug or feature.

[kcaisley]

To be more clear, .get_data() fetches raw bytes from the hardware; but this StdRegister.read() additionally copies those bytes into the named fields. If we request to read just one named field, then only that one will be refreshed in StdRegister. So what I mean is:

daq["gpio1"].read()  # Refresh every field
ready = daq["gpio1"]["COMP_IDELAY_RDY"]  # Access and refresh only one field

[cbespin]

It seems reasonable to me and well-worded that .read() reads all hardware values into the dictionary fields. Especially, if it is needed and useful, you have my blessings 😀

[cbespin]

Feel free to merge when ready

[kcaisley]

Sweet okay, let's try it!