Monday, 1 August 2022

Simple, repeatable deployments in a MicroPython environment

Have you ever suffered from "It works on my machine"?

Most of us have, as users (well, it doesn't work on mine!") or as developers ("what have I done wrong this time?". 

The cause is almost always down to something that's on the developer's machine that they have forgotten about, but make use of. That something doesn't get included in the installation process, so users may not have it installed.

There's a great way to avoid that.

Testing an installation process if you have an OS

If the software you're developing runs under an Operating System, run the installation in a freshly-created virtual machine. That will ensure that you start without somethings installed. You'll only have the software that's specified in your installation process.

If that works, you're in good shape.

What about installing MicroPython software on devices like the Raspberry Pi Pico?

Testing an installation process for MicroPython projects

A comparable deployment process has three stages. You need to

  1. Wipe the MicroPython file system completely
  2. Install a known version of MicroPython
  3. Install the application code
You can find software to do stages 1 and 2 on GitHub
It's called mp-installer.

The README file has instructions for installation and use.

At present it only works on Linux, including Raspberry Pi OS on the Pi or other hardware.
I'll get it working on Windows and/or Mac/OS if I can find a helpful collaborator!

Installing the application code

If your application consists of one or two files you can install the code manually using Thonny.

If you want an automated process, or have many files to install, there's a great alternative.

Use mpremote to install MicroPython files

mpremote is a really useful utility written by the MicroPython team.

You call it from the command line. You can use it to move files to and from the Pico, run files, execute MicroPython commands. You can even force the Pico into boot-loader mode if you need to update the MicroPython interpreter.

You'll find instructions for installing and using mpremote here.

Here's a script that installs a complete application:

#!/usr/bin/env bash
cd ../src
mpremote cp
mpremote cp
mpremote cp -r mp/ :
mpremote cp -r pi_finder/ :

A repeatable, reliable process

You'll find that running mpremote in a script is a great way to install all the files your application needs.

If you first run with the nuke option, you'll have a repeatable automated installation process.

That way you'll be confident that your users will get all the software they need to run your application.

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