Blinky

We have created a typical "hello world" application, but in embedded systems, the equivalent of "hello world" is blinky: simply blinking an LED.

We will continue working in the hello_world project.

Change the program

In order to blink an LED, we need to define an output pin and make a couple of other changes.

Firstly, let's rename the _peripherals variable to peripherals.

💡 In Rust, a variable can be prefixed with an underscore (_) to indicate that it is unused. Since we'll be using it, let's remove the leading underscore.

Next, we will define our LED:

#![allow(unused)]
fn main() {
let mut led = Output::new(
    peripherals.GPIO19,
    Level::Low,
    OutputConfig::default().with_drive_mode(DriveMode::OpenDrain),
);
}

The code above will not compile as is, since the compiler won't know where Output and other types are coming from. To fix that, import the required types like so:

#![allow(unused)]
fn main() {
use esp_hal::gpio::{DriveMode, Level, Output, OutputConfig};
}

💡 Whenever a you have a missing declaration error, you can use rust-analyzer to help you fix it.

Place the cursor on the missing type name and press Ctrl + . on the keyboard. In the context menu, select Import <Type> or Qualify <Type>.

"Import" will add the required use declaration, while "Qualify" will prefix the module path in-place.

Finally, add the following line to the body of the loop to toggle the LED every cycle:

#![allow(unused)]
fn main() {
led.toggle();
}

Experiment

Output has other methods than toggle. Try using set_high and set_low methods to change the LED blinking pattern.