For a while now I've been looking at OPL emulators. There's a few good ones around, used by MAME and DOSBox for example. But there are gaps in them. Some of them use samples for the percussion sounds for example.
Last year I came across this piece of work.https://docs.google.com/Doc?docid=0Aeywjj51RsmGZGQ4a3FuOWZfMTNjcWprZjRncA&hl=en
Then while figuring out how to build myself a logic analyser, I found this further piece of work by the same Olli Niemitalo. http://yehar.com/blog/?p=665
So I have started to investigate the digital behaviour of the OPL3, with a view to uncovering exactly what an emulator should be doing.