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IoT with Rust on ESP: Connecting WiFi

Omar Hiari on September 29, 2023

Introduction This post is the first in a new IoT series for using Rust on the ESP32. This new series will focus on several IoT hardware ...
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AJ •

Thanks for your helpful articles! I'm experimenting with porting my ESP-IDF project to Rust. In C API, I use esp_event_handler_instance_register to perform an action on WiFi connect event and would like to achieve the same in Rust.

Can the connection checking loop (while !wifi.is_connected()) be replaced with an event callback in Rust? I would appreciate an example!

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Omar Hiari • • Edited

Absolutely!
I hadn't done WiFi interrupts with Rust, but from the documentation, I realized there aren't any abstractions within EspWifi enabling interrupts with callbacks in the traditional sense. Though from what I've seen there are two alternative options:

  1. Going the non-blocking async path. There exists an AsyncWifi abstraction within the esp-idf-svc that achieves non-blocking operations (link to documentation). There are some usage examples in the esp-idf-svc repo. Note that its all the examples with the _async suffix.
  2. Leverage the lower level raw Rust bindings in the esp-idf-sys (link). Warning: not fun! :D. The older version of the Ferrous/Espressif ESP Rust training has an example of button interrupts using low-level bindings here and the associated explanations here and here. Additionally, I wrote a blog post about using the bindings for creating a multithreaded application here. I can tell you that as simple as it may look, it was quite a pain to get it to work. If you are not familiar with how the ESP Rust abstractions work you can check this post out as well.

I apologize if it seems that I overwhelmed you with information. However, I figure until more stability is brought to the project, workarounds need to be found to apply things in a certain manner.

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AJ •

Thanks! After going through esp-idf-svc sources I found some examples using sys_loop and was able to write the following function:

pub fn on_connect<F: Fn() + Send + 'static>(
    sys_loop: EspSystemEventLoop,
    cb: F,
) -> Result<EspSubscription<'static, System>, EspError> {
    sys_loop.subscribe::<WifiEvent, _>(move |event| {
        if let WifiEvent::ApStaConnected = event {
            cb()
        }
    })
}
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Omar Hiari • • Edited

Ah interesting, I wasn't aware of those abstractions :D This sparks the potential start of a whole new series for event handling with svc abstractions. Though where did you find the examples? I tried looking again but couldn't locate anything. Could you probably share a link please?

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AJ • • Edited

It was not in examples, that's why it took me quite some effort. Here is the link: github.com/esp-rs/esp-idf-svc/blob...

There is also this, but not as useful for my application.

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Omar Hiari • • Edited

Thanks for the insight! This also came in handy. Believe it or not, my exposure to the ESP-IDF came through Rust :D In std context, I often find myself referring back to the C documentation for insight. The Rust documentation still has a ways to go.

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AJ •

Indeed. I found it quite useful to refer to my C code and also look at how the Rust wrappers use the C API.