Project Update 

Is this project dead? No! It just didn't work and I got distracted. I designed and built a full Motorola 68000 based single board computer, a TMS9118 video card, OPL3 sound card, and wrote a lot of retro software. But this project has still been percolating.

What's Changed?

I breadboarded the project as outlined so far but it didn't work. Rooting out bugs purely in hardware is tough tough work because you can't see the interactions inside the chips and specialized equipment to view and generate all the signals (logic analyzer, oscilloscopes, function generators, etc.) is cumbersome and expensive. So I took a step back and decided to try to simulate the circuit in software first, iron out the kinks, and then lay it down on the breadboard. 

I also looked at some other similar projects, namely Daryl Rictor's excellent 65SPI, a CPLD based SPI controller. His aims are/were very similar to mine: a clean interface to SPI for microcomputers. His working design includes the CPLD code which was an inspiration for some of the changes in my discrete design.

What's Next?

I have actively picked this project back up and hope to publish new logs outlining my progress. The current status is I have changed the design and simulated "working" hardware (this is actually tough to do even with current software tools). New logs will include both the original hardware design(s) for the pieces, failures with those designs, and changes meant to correct those failures. I think it's an important part of the learning process and will hopefully inspire others to maybe pick their project back up if they initially saw failure.