JTAG register map is not deterministic

[sgherbst]

Running make.py multiple times with the same JTAG inputs (i.e., Markdown files and the constant package) produces different register maps, which can be verified by diffing the file build/all/jtag/reg_list.json from different runs of the script. I think we should get to the bottom of this before tapeout because it could make it quite difficult to know for sure what the register map is on the final chip. In particular, even though we could read the Git hash as part of the JTAG ID, that information would not be sufficient to verify the recreate the register map.

[sgherbst]

My guess is that this is related to the non-deterministic order of a set in Python3. For example, if you run this script multiple times, you will get different results:

# ref: https://stackoverflow.com/questions/60942487/non-deterministic-order-of-python-set?noredirect=1&lq=1
colors = ['blue', 'red', 'green', 'yellow']
print(set(colors))

I notice that a set is used in at least two places in JustTAG, so it could be that the non-deterministic ordering of Markdown files is changing the register address assignment. https://github.com/StanfordVLSI/JusTAG/blob/6153254f2d7fe466edd411bfb915fd8cfd6c57e5/justag/JusTAG.py#L45-L46

Since Python 3.7, dictionaries (but not sets) preserve insertion order. You can use this fact to create an ordered-set-like object from a dictionary:

colors = ['blue', 'red', 'green', 'yellow']
print({c: None for c in colors})

[sgherbst]

An even simpler option might be to have JusTAG depend on the ordered_set package, and switch the set instances to OrderedSet. (https://pypi.org/project/ordered-set/)