Micropython Build Environment for ESP32 in a Docker Container

This is an attempt to allow compiling and flashing of Micropython onto an ESP32 based system from any platform, that can run a docker container as a command line alias.

Creating the Cross Compiler Tool Chain

Cross compiling the Micropython Firmware requires the compiler tool chain to be installed and pointed to by Environment Variables. On top of that, Micropython itself requires very specific commit hashes of that tool chain to be checked out to compile different Micropython versions. In order to avoid the need to rebuild the Docker container any time those requirements change (which will be when you just checkout any release tag of Micropython) we will setup those dependencies in a directory $HOME/esp32-devel. The Docker container will use the tool chain there and you can checkout and adjust as needed, without rebuilding the container itself.

The components hosted there (for now) are the Espressif Xtensa ESP32 cross compiler and the Espressif ESP IDF. The script setup.sh will create and populate that directory. What it does is

mkdir $HOME/esp32-devel || exit 1
cd $HOME/esp32-devel || exit 1

wget https://dl.espressif.com/dl/xtensa-esp32-elf-linux64-1.22.0-80-g6c4433a-5.2.0.tar.gz
tar xzf xtensa-esp32-elf-linux64-1.22.0-80-g6c4433a-5.2.0.tar.gz

git clone --recursive https://github.com/espressif/esp-idf.git
cd esp-idf
git submodule update --init
cd ..

Do not forget to do the "git submodule update --init" part after you checked out another version of the esp-idf. You will get very cryptic and incomprehensible errors.

Installing Docker

Well, this is Linux-Distro dependent and all Linux-Distro-Managers are very opinionated people. So this all depends. It isn't too bad as it all starts with something like

sudo yum install docker

or

sudo apt-get install docker

The trouble starts after that. Somehow you will need to make $USER (that's you) a member of the Unix group, that is allowed to use docker. Since giving someone permission to use Docker is essentially giving them root access, do not give it to anyone who isn't already allowed to use sudo ALL. You have been warned.

On a CentOS system one creates a group "docker" and adds the group to the user's groups via usermod command.

sudo groupadd docker
sudo usermod -a -G docker myusername

Creating the Docker Image

Creating the docker image "esp32-devel" is done by running the build.sh script.

There will be intermediate delta images left behind (you can see them with "docker images --all"). Leave them there for now as they can significantly speed up the image build process in case there are any problems and you need to modify the Dockerfile. Once done and everything is working you probably want to issue a "docker system prune -f" command, to reclaim all those GBs of wasted space in /var.

The build.sh script also tries to communicate to the Dockerfile the GID of the group that is required to use /dev/ttyUSBx. This group is normally called "dialout". Since UIDs and GIDs between Docker container and host are only matched numerical, there can be problems here. I opted for just attempting to create a group with that GID and make the docker internal user a member of that. See above: If you already are allowed to use root, no harm done.

Adding the "esp32" alias

The alias.sh file contains a line that belongs into your .bashrc file. Assuming you use bash.

Check the line. Your ESP32 might not be on /dev/ttyUSB0.

After you do that and enabling it by logging in again or sourcing you .bashrc, you should be able to do stuff like

cd .../micropython/ports/esp32
esp32 make -j4
esp32 make erase
esp32 make deploy

And that's it for now.