Getting the sound working turned out to be easier than expected and managed to get the YM2151 playing music fairly quickly.
To get some music playing I used a very basic player for the VGM music format and downloaded a few of the large collection of YM2151 format files they have.
The player reads the VGM file and passes any commands for the YM2151 directly to the chip. All other data such as PCM samples are ignored. Running the player for the first time resulted in some slightly distorted and unpleasant music but that was soon fixed after a few tweaks to the timing to get some lovely sounding arcade music.
Only downside of the player at the moment is there is no working disk so all the music data is compiled into the code. This does make the resulting executables rather large and slow to download over a serial link so until i manage to get the hard drive interface working there won’t be much more progress on the music front.
Next step is to get the V9990 up and running so there’s something to look at as well as listen to. In the meantime some music played on Y Ddraig.