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This tutorial shows how to set up a nice working environment for developing Python on Ev3dev. The platform used is a BrickPi, but most of it is usable for regular LEGO EV3 bricks. {:.lead}

Ev3dev is a lean and modern system to run on the Raspberry Pi that powers the BrickPi. It's got multiple languages that work in a pretty similar way and make switching easy. Moreover, if you code in ev3dev on the BrickPi, people with a regular EV3 and Ev3dev will be able to run your code! Alas, it doesn't work the other way around as the BrickPi has a more limited set of motor commands.

For this tutorial, I will suppose you have burned an SD disk, connected your RPi and BrickPi to an ethernet cable and booted it. If you have an EV3 brick without ethernet, set up another networking connection first.

Now you can either attach a screen and keyboard to it for the setup, or connect to it via ssh. I prefer the latter. My router has a DNS that registers hostnames. It allows me to start a Terminal (on Mac) or Putty (on Windows) and simply do:

ssh robot@ev3dev

If you don't have a DNS try: robot@ev3dev.local or connect to it's IP address directly. eg. robot@192.168.0.2

The password is maker by default. If you used screen and keyboard, you're automatically logged in.

##Configure the right BrickPi##

You're logged in to the command line. Cool! This step will activate the BrickPi. Skip it if you have a normal EV3. Now several Mindstorms shields are available for the RPi, we have to setup the right one first. That is, if you haven't done so already after burning the image. For this go:

sudo nano /boot/flash/config.txt (the password is still maker) Scroll down and uncomment the appropriate lines for your hardware.

{% include icon.html type="info" %} I have multiple Raspberry Pis and Mindstorms brains. I like to keep them apart on the network by giving them separate names. I renamed mine like this:
sudo hostnamectl set-hostname ev3dev-rpi {:.alert .alert-info}

Finally do sudo reboot.

I prefer to have a passwordless ssh to the robot. For this I add a user with the same login name as on my development computer. Remember to give yourself sudo rights as explained on that same page. After adding that user, you can set up passwordless ssh.

{% include icon.html type="danger" %} This doesn't matter on BrickPi, but on robots with a screen, you will not be able to launch programs using the Brickman interface. For this, you must use the robot user! Only set up your own user account if you really know what you are doing. {:.alert .alert-danger}

With passwordless ssh and the same username on the ev3dev machine, you can go ssh ev3dev and you're in!

Next we need a versioning system. That's a tool for tracking changes you made to your code. Coincidentally the same tool is also very handy for transferring code between computers or sharing it on the web. There are several, but I prefer git. It's not installed by default so you have to do:

sudo apt-get update
sudo apt-get install git
git config --global user.email "you@example.com"
git config --global user.name "Your Name"

Now let's make a new project using our versioning system. Just type:

mkdir myproject.git
git init --bare myproject.git

Yay! Git is initialised in the new folder we created. We have a new project repository. Now we can clone this repository on our development machine, but first we need to do a little more configuring, to automatically deploy our code when we push it back to the ev3dev brick.

nano myproject.git/hooks/post-receive

add these lines. If you created a user with your own name, replace robot with that name:

#!/bin/sh
git --work-tree=/home/robot/myproject --git-dir=/home/robot/myproject.git checkout -f

and finally do:

chmod +x myproject.git/hooks/post-receive

Now typing code in nano is fine, but it's much nicer to do it inside a real IDE (Integrated Development Environment). There are many, like Visual Studio, Eclipse and PyCharm. My favourite is PyCharm Community Edition. So go grab a copy of that one and start it on your development machine.

{% include screenshot.html source="/images/osx/PyCharm/welcome.png" %}

What we are going to do now is make a clone of our project on the ev3dev machine to start working on it on the development machine. In the Welcome dialog choose: 'Checkout from version control' > 'Git' Now type the hostname of the ev3dev machine, followed by a semicolon the projectname. In the other fields choose a nice parent and project directory. (You might have to add .local after ev3dev depending on your DNS setup.)

{% include screenshot.html source="/images/osx/PyCharm/clone-repo.png" %}

When all goes wel you get a new window with your fresh empty project. If the 'testing' dialog stays on screen for a long time, it might be that your PyCharm master password is needed for your PyCharm password storage. Cancel the checkout, type the master password and try again.

So let's add some code. Right click on the 'myproject' folder in the left column and choose new > python file. Name it run-motor. PyCharm will ask if you want to add it to Git. That's nice! Of course we want that.

Now add the following code:

{% highlight python %} from ev3dev.auto import OUTPUT_A, Motor import time

m = Motor(OUTPUT_A) m.run_forever(duty_cycle_sp = 100) time.sleep(1) m.stop() {% endhighlight %}

When you're done press cmd-k or choose VCS > Commit Changes...

The commit message is box describing the changes you made to your code. That's handy later on when you do a lot of changes. For now type: first commit. Then go over the commit button and choose "commit and push" from the dropdown. In the next dialog click make sure to select the "alternative branch checkbox" and click "Push". Voila! Our code has arrived on the ev3dev brick. Let's take a look.

It's time to let the first motor run. Plug it into port A on your brick and ssh to your ev3dev brick. Maybe you have the terminal still open.

Now go

cd myproject
python run_motor.py

Tataaa! The motor is running full power for a second.

Back to the development machine. Maybe you noticed a problem: PyCharm puts red curly lines under the ev3dev library.

{% include screenshot.html source="/images/osx/PyCharm/missing-lib.png" %}

And that's logical, because the ev3dev library is missing on the development machine. If we install it we won't be able to run motors, but the documentation and autocomplete will be active. So on your development machine start a terminal and do:

git clone https://github.com/rhempel/ev3dev-lang-python.git
python ev3dev-lang-python/setup.py install
rm -r ev3dev-lang-python/ # Optional to remove the downloaded files. It's installed now anyway.

With the IDE (PyCharm) set up and the library installed you can code much faster. PyCharm will highlight most coding errors and typos. It will also suggest to autocomplete your code and show documentation. You can start typing m. and pycharm will suggest all possible methods and properties. Choose one. Now you can put your cursor inside the property and press F1 to see the docs. Or press cmd-down arrow to look inside the library where this property is defined. Neat huh? Happy coding.