FreddyV wrote on 2022-07-17, 14:02:
@polpo is Back and progressing well 😀
Heh, I should give an update!
This project has bifurcated into two projects. Yeah, I'm well aware of the perils of scope creep...
The first is a cheap, accessible card, based on the Raspberry Pi Pico. The Pico is only $4 and available in unlimited quantities, unlike the "big" Raspberry Pis. The RP2040 microprocessor is definitely more limited than the 1+GHz SoCs on the big Pis, but it has a few hardware features such as PIO and interpolators that make sound card emulation potentially feasible. I currently have a Pico emulating Adlib on the ISA bus, still using my original prototype ISA card adapter. Video is here: https://twitter.com/ianpolpo/status/1548495373840240641. I'm currently porting the GUS emulation and playback code to the Pico. Time will tell how much optimization this will require. The RP2040 doesn't have enough onboard RAM to support the full 1MB sample ram of the GUS, so I am using SPI PSRAM, which some back-of-the-napkin math tells me will be fast enough.
@FreddyV has been helping me with ideas for the second: a fully-featured card based on the big Pis that can support almost anything that an 8-bit ISA card is capable of. There will be some tricks to bring full 20-bit addressing, memory support, and multiple IRQs and DMAs. Right now this only exists as some schematics in KiCAD but some of the ideas are already being used on the Pico project, such as multiplexing the address and data lines to conserve GPIO pins.