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ESP32-S31 (very different from the S3)

That's literally and exactly what I said.

To be fair to GP, I too was confused by your use of brackets here.

I wasn't trying to be obtuse.

Formal grammar / technical documentation style guides consistently define:

[ ... ] = optional

{ ... } = repetition

| = alternatives

Hacker news isn't a formal grammar specification though. People use [1] for references here too (which you could easily have forgotten).

That's the SoC. The CPU is a small part of it. For example they could be using an open source design like the CVA6, or a commercial design from someone like Andes.

Espressif has a designed-in-house RISC-V CPU, so far as I know.

> Not sure I understand your question

I'm not sure why you are not sure - S3 was using Cadence's Xtensa 32-bit LX7 dual-core microprocessor, but the article on S31 only mentions "dual core" without too much detail.