PSAS Flight Computer

Portland State Aerospace Society is an open source "space program" in Portland Oregon. We build and fly state-of-the-art rocket avionics systems. We've been testing ways to fly code on small-ish rockets for over 15 years.

This repo contains our current primary flight computer (an Intel Atom processor at the heart of a full stack of sensors, batteries, radios, and other electronics. This all fits in our 5.5 inch diameter, 12 foot tall, high power rocket that flies over straight up over 4 kilometers.

We've been refining the code to fly a roll control experiment in July 2014.

• More information about upcoming launch
• Watch a video from past launches
• Follow us on twitter @pdxaerospace

Documentation

The flight code is written in C, and features a generated main function and a callback-based event loop. The event loop code generator was written by a senior CS student group in 2013.

This abstraction lets us write small pieces of behavior with very little boilerplate. The goal is to be able to hand out well defined projects such as "write the parser for the GPS messages" to members without having to expect them to maintain the complicated interconnections to the rest of the system.

• PSAS Flight computer documentation (WIP).

This idea is very similar system to NASA's 'Core Flight Executive' system for spacecraft software abstraction.

Building the Flight Computer

Requirements

The code generator runs on python3 using the pyyaml package. It's recommended to use a python virtual environment like this:

$ sudo apt-get install python3 libyaml-0-2 python-pip virtualenvwrapper
# Close the tab and re-open it if virtualenvwrapper was installed.
$ mkvirtualenv -p `which python3` av3fc
$ 
(av3fc)$ pip install -r requirements.txt

Use deactivate to get out of the virtual environment. To get back into the virtual environment:

$ workon av3fc

Don't forget to initialize your submodules:

$ git submodule update --init

Building

Due to the need for user module abstraction, the build process for the framework is a little more complicated than that of a typical C application. Here is the general build process:

1. User module MIML files and the Main.miml file are passed into the code generator.
2. The code generator, upon successful parsing and validation, creates the fcfmain.c file that include the intermodular data handlers and a Miml.mk Makefile include file.
3. The Makefile imports the Miml.mk and should successfully compile, link and build the executable "fc."

To help uncomplicate this process, however, the Makefile has been created so that the user only needs to run:

$ make

BUT don't forget you need to be in your virtual environment for this to work (workon av3fc).

Using the Makefile

As discussed in the introduction to this section, the easiest way to use the Makefile is to just type make.

Here are some other possible uses: make miml generates Miml.mk. make builds the project. Then, every repeated use of make rebuilds the project. If one of the ".miml" files changes, make automatically runs the code generator to rebuild fcfmain.c and fcfmain.h. If the miml files change so that modules are added or removed, one would have to rebuild the Miml.mk manually by rerunning make miml.