This is working well enough that I thought it was worth getting a review started. There are a few small TODOs left, and a few other things I'll leave comments about. For now, this doesn't use the mcpwm subsystem, it just manually times the pulse based on digital interrupts. I'd suggest that if we want to move to a mcpwm based approach that we land this implementation first in order to unblock using this sensor with the micro-rdk.

Meanwhile, I'm getting a clippy error I don't totally understand:

error: unused `#[macro_use]` import
  --> src/lib.rs:12:13
   |
12 | #[macro_use(defer)]
   |             ^^^^^
   |
   = note: `-D unused-imports` implied by `-D warnings`

error: could not compile `micro-rdk` (lib) due to previous error
make: *** [Makefile:62: clippy-native] Error 101
Error: Process completed with exit code 2.

I really am using the defer macro though, so I'm not sure why it is complaining. However, if I try to move the

#[macro_use(defer)]
extern crate scopeguard;

block into hcsr04.rs it fails to compile:

error: could not compile `micro-rdk` (lib) due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
error[E0468]: an `extern crate` loading macros must be at the crate root
  --> /host/micro-rdk/src/esp32/hcsr04.rs:44:1
   |
44 | extern crate scopeguard;
   | ^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0468`.
make: *** [Makefile:11: build-esp32-bin] Error 101

So, I'm not sure where I should be doing this (or doing something else).

Meanwhile, I'm getting a clippy error I don't totally understand:

error: unused `#[macro_use]` import
  --> src/lib.rs:12:13
   |
12 | #[macro_use(defer)]
   |             ^^^^^
   |
   = note: `-D unused-imports` implied by `-D warnings`

error: could not compile `micro-rdk` (lib) due to previous error
make: *** [Makefile:62: clippy-native] Error 101
Error: Process completed with exit code 2.

I really am using the defer macro though, so I'm not sure why it is complaining. However, if I try to move the

#[macro_use(defer)]
extern crate scopeguard;

block into hcsr04.rs it fails to compile:

error: could not compile `micro-rdk` (lib) due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
error[E0468]: an `extern crate` loading macros must be at the crate root
  --> /host/micro-rdk/src/esp32/hcsr04.rs:44:1
   |
44 | extern crate scopeguard;
   | ^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0468`.
make: *** [Makefile:11: build-esp32-bin] Error 101

So, I'm not sure where I should be doing this (or doing something else).

@gvaradarajan pointed out to me on slack that I hadn't guarded the macro(use) with #[cfg(feature = "esp32")], so that's fixed now.

I filed two new tickets and added TODO's referencing them:

• https://viam.atlassian.net/browse/RSDK-6278, for not blocking the executor
• https://viam.atlassian.net/browse/RSDK-6279, for refactoring Esp32GPIOPin such that the ultrasonic sensor can use it instead of using PinDriver directly.