CURIOSITY
http://youtu.be/_gZK0tW8EhQ http://ai.jpl.nasa.gov/public/home/cichy/ http://flightsoftware.jhuapl.edu/fsw10.html http://win-dms-ms1.caltech.edu/five/Viewer/?peid=476727664f1b4d8390d3ab37670ababd http://nodis3.gsfc.nasa.gov/displayDir.cfm?t=NPR&c=7150&s=2 http://www.flownet.com/gat/jpl-lisp.html http://compass.informatik.rwth-aachen.de/ws-slides/havelund.pdf http://www.cs.cmu.edu/~agroce/icse10.pdf
The code is based on that of MER (Spirit and Opportunity), which were based off of their first lander, MPF (Sojourner). It's 3.5 million lines of C (much of it autogenerated), running on a RA50 processor manufactured by BAE and the VxWorks Operating system. Over a million lines were hand coded.
The code is implemented as 150 separate modules, each performing a different function. Highly coupled modules are organized into Components that abstract the modules they contain, and "specify either a specific function, activity, or behavior." These components are futher organized into layers, and there are "no more than 10 top-level components."
Source: Keynote talk by Benjamin Cichy at 2010 Workshop on Spacecraft Flight Software (FSW-10), slides, audio, and video (starts with mission overview, architecture discussion at slide 80).
Edit: Someone on Hacker News asked "Not sure what means that most of the C code is auto generated. From what?"
I'm not 100% sure, although there probably is a separate presentation in that year or a different year that describes their auto-generation process. I know that it was a popular topic in general at the FSW-11 conference.
Simulink is a possibility. It's a MATLAB component popular among mechanical engineers, and therefore most navigation & control engineers, and allows them to 'code' and simulate things without thinking they're coding.
Model-based programming is definitely a thing that the industry is slowly becoming aware of, but I don't know how well it's catching on at JPL or if they would have chosen to use it when the project started.
The third and most likely possibility is for the communication code. With all space systems, you need to send commands to the flight software from the ground software, and receive telemetry from the flight software and process it with the ground software. Each command/telemetry packet is a heterogeneous data structure, and is is necessary that both sides are working from the exact same packet definition, and format the packet so it is correctly formatted on the one side, and parsed on the other side. This involves getting a whole lot of things right, including data type, size, and endianness (although the latter is usually a global thing, you could have multiple processors onboard with different endianness).
But that's just the surface. You need lots of repetitive code on both sides to handle things like logging, command/telemetry validation, limit checking, and error handling. And then you can do more sophisticated things. Say you have a command to set a hardware register value, and that value is sent back in telemetry in a particular packet. You could generate ground software that monitors that telemetry point to ensure that when this register value is set, eventually the telemetry changes to reflect the change. And of course, some telemetry points are more important than others (e.g. main bus current), and are designated to come down in multiple packets, which involves extra copying on the flight side and data de-duplication on the ground side.
With all that, it's much easier (in my opinion) to write one collection of static text files (in XML, csv, or some DSL/what-have-you), run them through a perl/python script, and presto! Code!
I do not work at JPL, so I cannot provide any detail that is not in the video, with one exception. I've heard that the autogenerated C code is written by Python scripts, and the amount of autocoding in a project varies greatly depending on who the FSW lead is.
NASA are extermely careful with their code. Everything (EVERYTHING) is done in the spec first and is repeatedly reviewed, checked and refined. When it is put into the life code stream it is almost a cut and paste of the spec's reference. The test scripts are given at least as much attention as the code is and no 'flashy' or clever code tricks are allowed unless they are critically needed.
No, not everything at NASA has the same set of code standards. But every project involving software engineering has the same set of process standards. See NPR7150. nodis3.gsfc.nasa.gov/displayDir.cfm?t=NPR&c=7150&s=2 and even then this depends on the class of the software. Class A software usually involved keeping Humans alive in space. But class H software is general purpose desktop software. Class H software does not require verification and validation, but class A does. – Sean McCauliff
This might shed some light on Wind River, the contractor who makes VxWorks: windriver.com/news/press/pr.html?ID=10901 I've read that NASA has a team of people whose job is to find as many bugs as they can in the control system code written by another team. The bug-finding team is rewarded for bugs they find and they are really quite good in finding arcane bugs. When a bug is found, a 5Y- type analysis is done to find out how the software dev process could be improved to eliminate the possibility of similar bugs in the future. A very painstaking and expensive process. – Jim Raden
What was the C auto-generated from? The keynote states that some of it are autogenerated protocol encoding/decoding routines (for communication with earth), generated by python programs from XML descriptions.
Back in the 90s there was a software engineering fad (unfair term but it was faddish at the time) called the process maturity index, and JPL was one of two software development sites that qualified for the highest rank (5) which involves continuous improvement, measuring everything, and going from rigorous spec to code via mathematical proof.
This process (which Ed Jourdan neatly eviscerated when applied to business software) produces software that is as reliable as the specification and underlying hardware.