Hector Martin

If there's a lesson I learned with Glasgow, it's that transparent bidirectional level shifters of any kind are evil. revA/B are broken for that reason (e.g. the I²C applet will never work), and revC0 pull-up support was broken because we used I²C-specific ones internally.

"Why is my I²C bus self-oscillating at 3MHz‽" (oh yeah and it's unrecoverable) Second lesson was that voltage regulators are 1-bit DRAM chips with ~1-2 minute data retention when powered off.

That was why I designed such a complex I/O cell for CLARKE (formerly STARSHIPRAIDER). I actually used two different unidirectional output buffers depending on VCCIO, and a comparator for the input. More expensive, but far more flexible than one magic chip.

I put the project on ice ~2 years ago because of my house renovation and not having a fast enough scope to adequately debug it. Maybe I can get back to it soonish.

Well, you went full crazy spec for yours :-) Glasgow is happy with bidirectional shifters *with direction input*. The reason revA/B didn't use those was to save FPGA pins to avoid having to use a BGA chip...