Because the chips are so simple, I actually found the datasheets for Padauks to be sufficient. In particular, I don't think it's any more confusing than say STM32 or even NRF52 datasheets, mostly because the chips are so much easier and thus the datasheets are sooooo much shorter. Granted, I have not worked with 8-bit MCUs other than Padauks.

Their compiler/macro-assembler also seems to be working just fine, once you get past the UI from early 2000s. The error messages that must have been auto-translated from Traditional Chinese, but you squint a little bit and get the idea.