Further thoughts on possibilities:
This design uses serial for it's connection so that needs to be kept in mind when considering connection options. Serial can do an awful lot - VT100 display for now, but see the Apple2Pi project as to how much two a way serial connection can provide.
I'd say for an 8bit computer that would be pretty much everything, and indeed as the ADAMs expansion bus is a serial protocol I expect not a great challenge for a talented coder, which I'm not.
For a fast bit-mapped display - I guess the TMS9918 with it's own RAM sort-of communicates with the rest of the computer via a serial interface and so could be reproduced with a Pi going through it's UART but I suspect not quick enough...
...that's not to say a Pi-based bit-mapped graphics / HDMI isn't possible, there is an HDMI board for the ZX Spectrum that does precisely that job:
-I imagine you'd connect enough of the PIs GPIO pins to the same lines on the ADAMs bus that the TMS9918 sits on, maybe a bit of buffering and certainly a bit of level logic required.
-A custom firmware on the Pi to emulate the 9918 and produce the video out.
In the former case I expect I could whip up an interface pretty easily, but in the coding would be waaay beyond me, I guess the software components would be something along the lines of:
-Someone who knows how to program the 'metal' of a Pi - maybe Hogglet over on the *. forum or the author of PiGFX
-A state machine to snoop the ADAMs bus for communication and handle transfers over the GPIO - maybe that could be lifted from the ZX Spectrum HDMI interface
-TMS9918 (or better) emulation - F18a core suitable?
-The Pi can act as local VRAM
-Some code to wrap it all together...
...that would indeed be an awesome project and you'd potentially have an F18a-like implementation using off-the-shelf components. Back to reality:
-All of that can be 'fudged' to a certain extent over serial as the A2Pi software does - The Pi acts as both a 'super multi-device expansion' and/or can use the host computer's I/O for it's own purposes and emulate any system within it's capability.
-Of course on the ADAM that would require porting / recreating the retro-side communications software...
,,,for now the best I can do is make the board and have it run PiGFX:
-MIB2 compatible serial
-A colour VT100 terminal for TDOS / CP/M
-Oh, and I happen to have my name down on the F18a waiting list.
Edited by CharlesMouse, Thu May 9, 2019 5:46 AM.