critical-section implementation for esp-lp-hal

[DivineGod]

Motivations

There's no critical-section implementation for esp-lp-hal besides the default implementation that comes from not specifying an implementation.

This currently causes an issue that a project with both esp-hal and esp-lp-hal cannot be in the same crate. And it might means that, since HP and LP memory is shared the LP core could access memory used by the HP core during a critical section of code.

Solution

Implement a multi-core safe critical-section for esp-lp-hal.

Alternatives

The alternative to not having a critical section is to somehow ensure that the cores won't ever have any resource conflicts, but we cannot rely on Rust to give us these guarantees.

[bugadani]

This currently causes an issue that a project with both esp-hal and esp-lp-hal cannot be in the same crate.

Defining a critical section may not be a solution anyway. The ESP32-S3 and the C6 use different restore state types (I don't really know why, but that's besides the point), and so if the lp-hal ends up matches one of them, the other one would have the same problem you have now.

Also note that esp-lp-hal does have a critical-section implementation via the riscv crate.