I've been telling a little fib for a while here. Or, more accurately, I've been letting you continue to believe something that isn't true.

This emulator isn't running on a Teensy 4.0.

Yes, it started that way; the hacked-together prototype used for debugging, which was useful through the proof of concept that I was, indeed, emulating a ProFile. But it had some timing issues and rather than pushing the brute-force "my CPU can out-CPU your CPU" race, I decided to take the more robust path.

It's on an FPGA, carried on a commercially made PCB, built so that anyone can build their own.

My first pass was on an Alchitry Cu dev board - which I quickly outgrew, and moved up to the Alchitry Au. Overkill, but functional.

Then I rebuilt it on the ULX3S-12F, which meant building another adapter in the middle to keep the wiring I'd built for the Au. Not pretty, but functional just the same (shown here with my bus sniffer in the middle of the wiring, and the original Teensy ProFile reader on the left).

The '12F is a better choice. The Au is based on the Artix-7, which is somewhere shy of $100 per part; the LFE5U-12F is a much more sane $20. To make my life easier I also built it around the only non-BGA version of the 12F.

This was challenging to route - the TQFP-144 is really dense. But I'd rather have the difficult routing than have to deal with ensuring a ball grid array device gets properly soldered to pads I can't even see.

The verdict? Still pending! The boards have arrived, they're waiting for me to build one and test it out.