Big Vim Button #2

Many years ago, I mounted a giant industrial stop button in a wooden box, hooked it up to an Arduino, and used it as a single-key keyboard. The idea was that you could then hit the "Escape" key with considerable gusto (it being a mainstay of your typical vim session).

This seems like a good candidate for learning some embedded rust, so I'm going to re-implement it wirelessly (Bluetooth Low Energy) using an ESP32.

Hardware

Board is an Adafruit Huzzah32 Feather V2, with 8MB flash and 2MB RAM, It's got LiPoly battery management onboard and an RGB LED.

We've got a red LED on GPIO13, an RGB LED (NeoPixel, WS2712B compatible) on GPIO0 (power from GPIO2).

We've got a button on GPIO38.

Project setup

Scaffolded the project using steps in The Rust on ESP Book.

Remember to source ~/.export-esp.sh

Board set to ESP32 (the original, as that's what I had plugged in).

Generated project with cargo generate and the template esp-idf-template (i.e. we're going to use std).

References

ESP32 Embeeded Rust at the HAL: GPIO Button controlled blinking has some useful background, although it targets the esp32c3 device and is no_std !!

ESP32 Standard Library Embedded Rust: GPIO Control would have been a much better starting point, in retrospect.

esp-idf-hal NeoPixel example using RMT peripheral

Things we have learned

Peripherals

The whole Peripherals business seems to be device-dependent. Peripherals::take() seems fairly uniquitous, as does Peripherals::steal(), but some PACs have a split() method to get at the structures within the Peripherals object, whereas ESP32 favours a constructor-based approach (e.g. IO::new).

Oh wait, this Peripherals is from pac::Peripherals in the esp32_hal (i.e. device specific) crate. And we want to use the esp-idf-hal multi-platform crate. Which seems to have something different:

use esp_idf_hal::peripherals::Peripherals;

let peripherals = Peripherals::take().unwrap(); // as before
let mut led = peripherals.pins.gpio2.into_output()?;  // NB 'pins' not 'GPIO'

led.set_high()?;
led.set_low()?;

no-std vs std, hal-esp32 vs esp-idf-hal

BUT GPIO access in esp-idf-hal has recently changed: Completely revamped GPIO metaphor

Now we convert a concrete pin like Gpio0 into a more generic pin Any*Pin using downgrade_*, e.g.:

use esp_idf_hal::peripherals::Peripherals;
use esp_idf_hal::gpio::OutputPin;  // marker trait
use esp_idf_hal::gpio::PinDriver; // pin driver sets pin modes

let peripherals = Peripherals::take().unwrap();

let mut led = PinDriver::output(peripherals.pins.gpio2.downgrade_output())?;

led.set_high()?;
led.setlow()?;

Individual pins are represented by TYPES

For example, GPIO0 is represented by Gpio0 which is a type, not an instance. This means that you can't put them in arrays. But handily, you can use those downgrade_* methods mentioned above to get an Any*Pin type that you can put in an array.

blowback/big-vim-button2