A loop was 360 .. decoding of cam would be a simple single-edge (to mimick eTPU as a baseline) where determining phase is cake. Could even be handled outside of the HET.
The HET works. SWAG works. But to reach 1/10 of a degree resolution on the angle clk is not possible. That was the requirement, and I don't think it's unreasonable at all (up to max 20k and 60 teeth). With HWAG and 60 teeth at 1/10 resolution resulted in about an 8k limit, if I remember right. Not bad. But that leaves no room for anything else and depending on undocumented hardware doesn't leave a good feeling when it comes to getting support. It'd be pulling teeth for a one-man show like myself. I had to contact the rep under my work email just to get the hwag doc.
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What if the N2HET was used only to decode trigger wheels and initiate ignition / injection events ...
My math was based on this bare-bones case of doing only decode (as you mention). There just wasn't enough time in a loop to even do that. There's also a clk divisor issue where you run the core clk at 300MHz, but you can't run the HET at full speed. It doesn't matter, because the HET couldn't run fast enough to handle the resolution requirement anyways.
I still love their setup, but it doesn't meet my requirement. I'd relax the requirement, but I don't think it's unreasonable. Probably back to the 56xx since I don't ever see having time to 'go for' the final solution and just use an FPGA.
With more thought around this, I bet there is a way. I just wish I had multiple people to bounce ideas off of and brainstorm. It's so easy to get stuck in old/non-original thinking when it's only yourself. Rusefi seems to avoid this ... maybe I go camp out at his house for a while and see things from another perspective.