Moving on from COLE-2

Over the last few days I have been thinking a lot about COLE-2’s future, and I kept asking myself if it is worth taking this project all the way to a final build. After much debate I finally admitted to myself that it’s not.

This project is a stepping stone, part of a long-term plan to build my dream 65816 computer. Think of it as the Apple IIGS upgrade I wish Apple had produced 30 years ago. Each design iterates on the previous one until my goal is reached. Since COLE-2 is not the end goal, once I build it it will end up in the same drawer as COLE-1 when I start my next design. Thus I’ve decided not to pursue further work on this hardware design.

As a stepping stone I think this project has done very well for me. I learned how to design a 65816 system, how to program GALs and CPLDs, and even some FPGA skills. Now it’s time for me to take the next step towards my final goal.

The Joys of Programmable Logic

My next design will be built around the ULX3S, an FPGA development board based on the Lattice ECP5. Compared to the iCE40 I used for COLE-2’s video controller the ECP5 is a beast; it sports over 84,000 LUTs compared to the paltry 7,680 on the iCE40. With that level of resources available I can build the entire system inside the FPGA itself.

Nothing is 100% finalized yet, but my plan is to connect a 65816 directly to the FPGA. The FPGA will provide the CPU with all necessary resources, such as RAM, ROM, and I/O. Future iterations may even replace the CPU with a soft core inside the FPGA, which could let it reach speeds that a physical 65816 simply can’t achieve.

The beauty of this design is that I can iterate on it without changing the hardware at all. In theory this design can be anything once it’s built, even a IIGS-compatible build, just by changing the FPGA’s code. I think that level of freedom will keep me occupied for a very long time!

As a bonus this new design will be quite small. This will make it very easy for me to push it aside when I want to use my workbench for other projects for a while.

I don’t have a name for this project yet, other than “not COLE-3”. I’ll be thinking of names as I wait for my ULX3S to arrive, which should be before the end of the month. I’ll announce the name at that point.

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