First, thanks for helping me out.
Ok, well I am having trouble getting that running as well, so that might be part of it. When running greytest on the thumby, it just looks like it restarts and reloads the main menu. Same thing happens when using the sample code in the readme for ugrey .
Trying it in the emulator on
https://code.thumby.us/, doesn't seem to work either. After figuring out i needed to mark /lib/ugrey.mpy as emulatable, it seems to run without error (including not exiting), but nothing appears on the emulated screen. Also, adding print statements doesn't seem to work, even the simple program below doesn't print anything to the console and the program doesn't exit. Even if I put invalid code below 'import ugrey' it doesn't seem to be evaluated and give an error
import sys
import ugrey
print ('hello world')
sys.exit()
The version info I can find is MicroPython v1.19.1 on 2022-06-18
I did try
https://github.com/TinyCircuits/TinyCircuits-Thumby-Games/tree/master/Fireplace and could calibrate the greyscale in that program (but I know it is using a different driver).