how would such a GPIO <-> PCMCIA interface work? the author said the CPLD handles the voltage conversion and “address decoding”, but what I don’t understand is how does the data end up on the Pi?
According to the article, the author is using the RP2040's PIO peripheral, which has access to both the GPIO pins and FIFO buffers for communication with the main CPU.
The PIO is magic adjacent given the unit cost. A relative of mine is using it to bit-bang a proprietary ethernet-like protocol to fix some expensive-to-replace surveillance camera networks. He's a 10x (at least) engineer and he's impressed by the capabilities. "And then it's just some C-code, which is of course trivial."