A developer known as doctormord has reverse engineered the Philips PM5139 function generator and shipped custom V2.0 firmware that adds six arbitrary waveforms and the ability to play music, including the DOOM E1M1 melody.
The PM5139 has no dedicated service manual. The only documentation available covers the PM5138A, a lesser sibling. Work began with two EPROM dumps from the original early-1990s Philips firmware. An 8051 emulator was used to run and interpret the code before any modifications were made, a methodical approach that kept the reverse engineering grounded in observed behavior rather than guesswork.
The full project, including firmware source and EPROM dumps, is on GitHub. What makes it worth reading is the process: how you navigate undocumented 8051 code, what the emulator revealed, and how those findings translated into stable new functionality on 35-year-old hardware.
[READ ORIGINAL →]