This is a project is born to build a secondary sound card expansion for my PC 128 OLIVETTI PRODEST HOME COMPUTER.
I have designed and built two different sound cards based on two different sound chip.
One sound card is based on PSG SN76489AN sound chip, the second is based on OPLL YM2413 sound chip.
Also i have coded the ASM 6809 routines to play sound demos.

Thomson computers have sound generator simply based on 6bit dac that fully commits the cpu countinuosly updating the sound samples. During sound streaming the computer can't do anything else.
Beucause of that there was the need to develop a secondary sound card based on specific sound chip that generates sound by itself, only programming your own registers.

Thomson computers have an expansion port with the main computer signals, data bus, address bus, chip select, master clock, and analog sound input that is mixed with the main sound generator.

The SN76489AN first chip selection is based on its simple architecture, 8 bit bus, four channels, up to two write sequences to generates sound or noise.
The YM2413 second chip selection is also based on its simple architecture, 8 bit bus, nine channels, two write addresses to generates sound with hardware instruments and rythems.
Single board develepments are better described to the links below or wiki section
SN76489AN SOUND CARD DEVELOPMENT
YM2413 SOUND CARD DEVELOPMENT

By properly setting card jumpers it changes the address. In this way you can mount two sound cards working simultaneously.
The interconnection card is a third-party project.
The assembly of the cards in this photo is the precious contribution of Benoit Rousseau. He help me to debug the cards on Thomson TO target.

Kicad and Freerounting to develop schematics and pcb.
DCMOTO emulator fully emulates both sound cards (http://dcmoto.free.fr/emulateur/index.html)

https://en.wikipedia.org/wiki/Texas_Instruments_SN76489
https://en.wikipedia.org/wiki/Yamaha_YM2413
http://dcmoto.free.fr/
https://vgmrips.net/packs/
https://www.smspower.org/Music/VGMs
http://atjs.mbnet.fi/mc6809/
http://map.grauw.nl/resources/sound/texas_instruments_sn76489an.pdf
http://map.grauw.nl/resources/sound/yamaha_ym2413_ds.pdf