Your first program: Blinking an LED

In this tutorial, we look at what it takes to create the simplest program of all - one that blinks the onboard LED on the Raspberry Pi Pico.

The Program

The program itself is simple - about 15 lines of code.

// blink.go

package main

import (
"machine"
"time"
)

func main() {
    led := machine.LED
    led.Configure(machine.PinConfig{
    Mode: machine.PinOutput,
    })

    for {
        led.High()
        time.Sleep(500 * time.Millisecond)
        led.Low()
        time.Sleep(500 * time.Millisecond)
    }

}

Basic Steps to Interact with GPIO

The basic steps for interacting with a General Purpose Input-Output ( GPIO) pin on the Pico are the same:

1. Import the machine package.
2. Create a variable that is an instance of the GPIO pin.
3. Configure the instance.
4. Loop while doing something with the pin.

Let us examine each of these steps in detail.

Import the machine Package

import (
"machine"
... // other imports
)

The machine package provides an abstraction in Go to the underlying capabilities of the microcontroller target. It also defines some constants that make it easier when referring to the facilities of the microcontroller in Go. As an example, consider the machine.LED constant, which represents the onboard LED on the Pico.

Create an Instance of the Pin

led := machine.LED

Creating the variable and initializing it to an instance of Pin allows us to access the variable in other parts of the program.

Note that the pin is not configured yet. That needs to be done in the next step.

Configure the Pin Instance

led.Configure(machine.PinConfig{
Mode: machine.PinOutput,
})

The Configure function takes an instance of a type called PinConfig as its input.

The PinConfig type is defined as below:

type PinConfig struct {
Mode PinMode
}

The following Modes are accepted:

const (
    PinOutput PinMode = iota
    PinInput
    PinInputPulldown
    PinInputPullup
    PinAnalog
    PinUART
    PinPWM
    PinI2C
    PinSPI
)

Since we want the LED to blink, but are not concerned about its input, we configure the pin as a PinOutput.

Loop

Once the GPIO pins are initialized and configured, we loop while performing a set of tasks. This is typical of any microcontroller (or embedded) application.

In the case of this trivial "blink" program, we turn the LED on and off periodically inside the loop. For the purposes of this program, we use a time of 500 milliseconds between turning the LED on, and turning it off.

for {
    led.High()
    time.Sleep(500 * time.Millisecond)
    led.Low()
    time.Sleep(500 * time.Millisecond)
}

Outputing a High to the pin switches on the LED, while a Low turns it off. The time.sleep merely pauses the program so that the pin isn't toggled so frequently that the LED never appears to turn off.

Summary

In this tutorial, we learnt to:

1. Initialize and configure a single GPIO pin using TinyGo.
2. Output binary high or low values to the pin.
3. Run our program endlessly.

References

1. GitHub
2. machine package reference for Pico