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This is FRC Team 971's main code repository. There are README* files throughout the source tree documenting specifics for their respective folders.


All development of AOS is done on our gerrit instance at with github being a read-only mirror. We are happy to add external contributors. If you are interested, reach out to Austin Schuh or Stephan Massalt and we will help you get access. In case of disputes over if a patch should be taken or not, Austin has final say.

Submissions must be made under the terms of the following Developer Certificate of Origin.

By making a contribution to this project, I certify that:

    (a) The contribution was created in whole or in part by me and I
        have the right to submit it under the open source license
        indicated in the file; or

    (b) The contribution is based upon previous work that, to the best
        of my knowledge, is covered under an appropriate open source
        license and I have the right under that license to submit that
        work with modifications, whether created in whole or in part
        by me, under the same open source license (unless I am
        permitted to submit under a different license), as indicated
        in the file; or

    (c) The contribution was provided directly to me by some other
        person who certified (a), (b) or (c) and I have not modified

    (d) I understand and agree that this project and the contribution
        are public and that a record of the contribution (including all
        personal information I submit with it, including my sign-off) is
        maintained indefinitely and may be redistributed consistent with
        this project or the open source license(s) involved.

To do this, add the following to your commit message. Gerrit will enforce that all commits have been signed off.

Signed-off-by: Random J Developer <>

Git has support for adding Signed-off-by lines by using git commit -s, or you can setup a git commit hook to automatically sign off your commits. Stack Overflow has instructions for how to do this if you are interested.

Access to the code

The main central location for our code is our Gerrit server at To download a copy of the 971 code on your computer, follow these steps:

  1. Fill out an SVN account request form to get an SVN account. 1. Mention that you are part of the software team and need Gerrit access 2. It is recommended to use your firstname in all lowercase for your username
  2. Go to our Gerrit server and create an account.
  3. Contact Brian Silverman or Stephan Massalt with your SVN username to get access to the code in Gerrit.
  4. When you log into Gerrit the first time, please add your Email Address
  5. Add your SSH key to Gerrit in order to be able to check out code 1. If you don't already have an ssh key, you can create one using ssh-keygen -t ed25519. This will create a public/private key pair-- the default location for your public key will be ~/.ssh/ 2. Log into Gerrit and go to Settings->SSH Keys and paste your public key into the New SSH Key text box and clicking on ADD NEW SSH KEY
  6. Install git: sudo apt install git
  7. Go to the 971-Robot-Code project in Gerrit and run the command to Download the 971-Robot-Code repository. 1. We recommend downloading the code via SSH using the clone with commit-msg hook command 2. NOTE: Running with the option to clone with commit-msg hook will save you trouble later.

To learn more about git, open a terminal and run man git, or see git(1) (especially the NOTES section).


The instructions below assume you have the following:

  1. A host computer with an appropriate OS or VM to compile the 971 code using Bazel 1. The currently supported operating system for building the code is amd64 Debian Buster. 2. It is likely to work on any x86\_64 GNU/Linux system (e.g., Ubuntu 20.04), but that's not at all well-tested.
  2. Your favorite text editor installed, e.g., vim, emacs
  3. Access to the 971-Robot-Code repository and have downloaded the source code
  4. The ability to ssh into target CPU's like the roborio and Raspberry Pi

Building the code

We use Bazel to build the code. Bazel has extensive docs, including a nice build encyclopedia reference, and does a great job with fast, correct incremental rebuilds.

There are a couple options for building code that are given here-- setting up either your own computer, or using the frc971 build server.

Steps to set up a computer to build the code:

  1. Install any Bazel version:

    1. Check to see if the version of Linux you're running has an apt package for Bazel: apt-cache search bazel or just try sudo apt install bazel
    2. More likely, you'll need to install manually-- see here. We recommend using apt-key instead of gnupg in setting up the key:
      1. Step 1: Add Bazel distribution URI as a package source
        sudo apt install curl
        curl -fsSL | sudo apt-key add -
        echo "deb [arch=amd64] stable jdk1.8" | sudo tee /etc/apt/sources.list.d/bazel.list
      2. Step 2: Install Bazel
        sudo apt update && sudo apt install bazel
  2. Install the required packages:

    sudo apt-get update
    sudo apt-get install python
  3. Change settings to allow Bazel's sandboxing to work-- follow the directions in doc/frc971.conf. For example, the commands to do this would be:

    1. sudo cp doc/frc971.conf /etc/sysctl.d/
    2. sudo sysctl --system
  4. In order to run certain tests, you need to give yourself permissions--follow the "Set up real-time niceties" section of aos/events/

Setting up access to a workspace on the build server

In order to use the build server, you'll first need to get ssh access set up. (NOTE: you don't need to do any of the other setup steps done for your own computer, since things like bazel, python, etc. are already installed on the build server)

  1. Use ssh-keygen to create a public and private key.
# In windows:
# Important use Powershell!
cd ~/.ssh
ssh-keygen -t ed25519 -f id_971_ed25519
chmod 600 id_971_ed25519
# In Linux and MacOS:
cd ~
ssh-keygen -t ed25519 -f ~/.ssh/id_971_ed25519
chmod 600 ./.ssh/id_971_ed25519
  1. Send the contents of to Stephan Massalt along with the password that you want to use. WAIT for feedback, as he needs to setup the account.
cat ~/.ssh/
# Then send the stuff that gets printed to Stephan via slack.
  1. Once you hear back from Stephan, test SSH.
ssh -p 2222 -i ~/.ssh/id_971_ed25519
  1. If that doesnt work, then send the error msg to #coding However, if it does then use the exit command and then SSH tunnel.
ssh -p 2222 -i ~/.ssh/id_971_ed25519 -L 9971:
  1. So at this point you run the Remote Desktop app in Windows. Once you get there, all you need to do is put for the computer name, and use your SVN username. Once you get connected, accept the server certificate and then enter your password that you gave Stephan. (It's either something unique or your SVN pwd) Then select the Default panel config. You can exit the Remote Desktop if you are good w/ the raw cmd line interface. And for future logins all you have to do is tunnel and then login using the app. Now if you have a graphical application that you are developing (e.g., spline UI), then you have to run the build command in the Remote Desktop application.
  2. Very important: In order for you to be able to commit, you need to configure your email address in git. To do this, run the following command, replacing <YOUR EMAIL> with the email that you are using for Gerrit:
git config --global "<YOUR EMAIL>"

If there are any questions, post to the #coding Slack channel so that other people who may reach the same issue can refer back to that.

Bazel commands for building, testing, and deploying the code:

  • Build and test everything (on the host system, for the roborio target-- note, this may take a while):
bazel test //...
bazel build --config=roborio -c opt //...
  • Build the code for a specific robot:
# For the roborio:
bazel build --config=roborio -c opt //y2020/...
# For the raspberry pi:
bazel build --config=armv7 -c opt //y2020/...
  • Configuring a roborio: Freshly imaged roboRIOs need to be configured to run the 971 code at startup. This is done by using the script.
bazel run -c opt //frc971/config:setup_roborio -- roboRIO-XXX-frc.local
  • Download code to a robot:
# For the roborio
bazel run --config=roborio -c opt //y2020:download_stripped -- roboRIO-971-frc.local

This assumes the roborio is reachable at roboRIO-971-frc.local. If that does not work, you can try with a static IP address like (see troubleshooting below)

# For the raspberry pi's
bazel run --config=armv7 -c opt //y2020:pi_download_stripped --


  1. The raspberry pi's require that you have your ssh key installed on them in order to copy code over
  2. They are configured to use the IP addresses 10.X.71.Y, where X is 9, 79, 89, or 99 depending on the robot number (971, 7971, 8971, or 9971, respectively), and Y is 101, 102, etc for pi #1, #2, etc.
  • Downloading specific targets to the robot
    1. Generally if you want to update what's running on the robot, you can use the download_stripped (or pi_download_stripped) targets. These will rsync only the changed files, and so are pretty efficient.
    2. If you have a need to compile a specific module, you can build stripped versions of the individual modules by adding "_stripped" to the module name. For example, to build the calibration code (//y2020/vision:calibration) for the pi (armv7), run:
    bazel run --config=armv7 -c opt //y2020/vision:calibration_stripped
    You will then need to manually copy the resulting file over to the robot.

Code reviews

We want all code to at least have a second person look it over before it gets merged into the master branch. Gerrit has extensive documentation on starting reviews. There is also a good intro User Guide and an intro to working with Gerrit and Gerrit workflows

TL;DR: Make and commit your changes, do git push origin HEAD:refs/for/master, and then click on the provided link to add reviewers. If you just upload a change without adding any reviewers, it might sit around for a long time before anybody else notices it.

git-review can make the upload process simpler.

Some other useful packages <TODO: Need to review these>

These aren't strictly necessary to build the code, but Michael found the additional tools provided by these packages useful to install when working with the code on May 13, 2018.

# Get some useful packages including git and subversion.
   apt-get update
   apt-get install git git-gui vim-gtk3
   apt-get install vim-doc git-doc exim4-doc-html yapf
   apt-get install bazel clang-format
   apt-get install python avahi-daemon
# Install apt-file so that packages can be searched
   apt-get install apt-file
   apt-file update
# Install sysstat so that you can tell how many resources are being used during
#   the compile.
   apt-get install sysstat
# iostat is used to observe how hard the disk is being worked and other
#   performance metrics.
   iostat -dx 1
# gitg is a graphical user interface for git.  I find it useful for
# understanding the revision history of the repository and viewing
# log messages and changes.
   apt-get install gitg
# Also may want to install `buildifier` for formatting BUILD files

Creating ssh aliases

It is also handy to alias logins to the raspberry pi's by adding lines like this to your ~/.ssh/config file:

Host pi-7971-2
    User pi
    ForwardAgent yes
    StrictHostKeyChecking no

or, for the roborio:

Host roborio-971
    User admin
    StrictHostKeyChecking no

This allows you to use the alias to ping, ssh, or run commands like:

# Download code to robot #7971's raspberry pi #2
bazel run --config=armv7 -c opt //y2020:download_stripped -- pi-7971-2

Roborio Kernel Traces

Currently (as of 2020.02.26), top tends to produce misleading statistics. As such, you can get more useful information about CPU usage by using kernel traces. Sample usage:

# Note that you will need to install the trace-cmd package on the roborio.
# This may be not be a trivial task.
# Start the trace
trace-cmd start -e sched_switch -e workqueue
# Stop the trace
trace-cmd stop
# Save the trace to trace.dat
trace-cmd extract

You can then scp the trace.dat file to your computer and run kernelshark trace.dat (may require installing the kernelshark apt package).

Notes on troubleshooting network setup

If the roboRIO has been configued to use a static IP address like, set the laptop to have an IP address on the 10.9.71.x subnet with a netmask of The ".x" is different than the .2 for the roboRIO or any other device on the network. The driver station uses .5 or .6 so avoid those. The radio uses .1 or .50 so avoid those too. A good choice might be in the 90-99 range. If you are at the school, disconnect from the student wireless network or try setting your netmask to if you want to be on both networks. The student wireless network is on a 10.?.?.? subnet which can cause problems with connecting to the robot.

If running Bazel on the download_stripped target does not work for the IP address you're using for the roborio or the raspberry pi, it probably means that the robot and laptop are on different subnets. They need to be on the same subnet for the laptop to connect to the robot. Connecting can be confirmed by using ping.

ping roboRIO-971-frc.local



If this does not work, perhaps the roboRIO has not been configured to have a static IP address. Use a USB cable to connect from a Windows laptop to the roboRIO and use a web browser (Chrome is preferred, IE/Edge is not-- see this technical note) to configure the roboRIO to have a static IP address of Browse to http://roborio-971-frc.local or Click on the "Ethernet" icon on the left, select "Static" for the "Configure IPv4 Address" option. Set the "IPv4 Address" to Set the "Subnet Mask" to "". Finally click on "Save" at the bottom of the screen. If you have trouble using an Ethernet cable, try using a USB cable (USB A->B).

Another option is to configure the laptop to have a link-local connection by using the "Network Settings" GUI. The laptop will then be on the same subnet in the address range of to James thinks this will only work over Ethernet (i.e., not USB; he is not sure what will happen if you attempt this over USB), and if the robot does not have a static IP address set and there is no DHCP server assigning an IP address to the roboRIO. James says to also note that this implies that the roboRIO will also have a 169.254.. IP addresss, and that the only simple way to figure it out is to use mDNS.

LSP Setup for Rust

You can run bazel run //tools:gen_rust_project to generate a rust-project.json file which rust-analyzer will pick up. You will need to execute this rule periodically as it will be outdated whenever the BUILD files change.

Note that there's currently no way to tell rust-analyzer how to compile the code, so while it will give you completion support, go to definition, and other niceties, it won't show compilation errors or warnings at this point.

Other resources

  1. Intro to AOS, our robot Operating System
  2. Introductory example: ping/pong
  3. Example of logging


  1. Add more on networking setup and troubleshooting
  2. Move Roborio Kernel Traces out of here, maybe into documentation/
  3. Currently requires apt install libsigsegv2, but this should be temporary