C6 PMU startup configuration

[bugadani]

This PR implements PMU setup based on esp-idf v5.1.2.

I implemented PMU setup because I wasn't sure if this was the cause of my MCU not waking up. Well it isn't, but why not add the code to esp-hal :)

I wonder if much of this code should just be ran before main(), these are pre-main in esp-idf, too.

Must

• The code compiles without errors or warnings.
• All examples work.
• cargo fmt was run.
• Your changes were added to the CHANGELOG.md in the proper section.
• You updated existing examples or added examples (if applicable).
• Added examples are checked in CI

Nice to have

• You add a description of your work to this PR.
• You added proper docs for your newly added features and code.

[bugadani]

I'm sorry for these macros. esp-idf just indexes into a register group with 3 (HP) or 2 (LP) groups. Unfortunately, in the PAC, the register field names are different for each power state(?) (they contain a bunch of the register's name for each field) and transmuting them would just be super confusing.

[bjoernQ]

From skimming over the code everything looks nice and tidy - probably not useful to compare it line by line with the C code.
Probably we "just" need to check if things still work with this and it should be fine - ideally also esp-wifi should still work when calling Rtc::new (I think there is at least a problem with the original ESP32 currently - reminds me I need to double check and create an issue for that)

[bugadani]

probably not useful to compare it line by line with the C code

Honestly, I've gone through this enough times and I still think there might be mistakes somewhere. But each register modification is hidden behind 2 levels of indirection and it's extremely annoying to compare.

Also, it is somewhat interesting that this PR tries to set the same values as esp-idf, but registers still end up with slightly different values in them, so there may be unintended differences.

I think it might be useful for someone to familiarize themselves with the basic flow, that way they can tell if the config values at least correspond to the values in esp-idf.

[bugadani]

So now that a new release cycle is going on, can we try and get this merged, or should I consider the PR in a permanent limbo until documentation becomes available?

@jessebraham @MabezDev @bjoernQ

[jessebraham]

So now that a new release cycle is going on, can we try and get this merged, or should I consider the PR in a permanent limbo until documentation becomes available?

I have no problem merging this, just haven't had the time to review it.

@SergioGasquez @JurajSadel can one or both of you please make some time to look over this? The draft chapter for the C6's PMU is available in our internal chat in the Documentation channel.

[SergioGasquez]

I tested a few examples and esp-wifi examples, and they were all working fine! Gone through the changes quickly, and they look good to me, probably tomorrow morning I'll take a deeper look at the changes!

[JurajSadel]

I went line-by-line with ESP-IDF so, hopefully, we haven't missed anything important here, haha
I left a comment where I'm not sure what we want to achieve, otherwise LGTM!

[JurajSadel]

LGTM, thank you!

[jessebraham]

Thanks for all your work on this!

Also thank you for reviewing @bjoernQ and @JurajSadel, and thanks for testing @SergioGasquez!