WonderMCA part 4 – From silence to TADA – making Sound Blaster DMA work on an MCA PS/2
Why this was hard
When I started WonderMCA — a PicoMEM-style RP2350-based card for the IBM PS/2 MCA bus — the obvious “killer app” was Sound Blaster emulation. FreddyV has worked hard to bring the PicoMEM a working SBDSP emulator for ISA Bus; on MCA we get the same software base.
Except for one little detail: the DMA.
The whole point of a Sound Blaster emulation is that it streams 8-bit PCM sample data from RAM to the DAC without the CPU babysitting every sample. That stream goes through DMA (Direct Memory Acces). On an ISA Sound Blaster the DMA is pretty simple — there’s a single 8237 DMA controller on the chassis, you wire the card’s DREQ/DACK pins to one of its channels, and the controller’s hardware does the rest. Total mental load: 30 seconds.
MCA is not ISA. MCA has no 8237. MCA has CACP.
