Windsurf helps me navigate the Apollo 11 code base and the 1202 alarm

Things sometimes nicely come together.

Apollo mission control — trying to deal with the 1202 alarm

While trying out Gemini’s capability to find YouTube Videos for me:

Me asking Gemini in Dutch for videos on the 1202 alarm triggered during the LM trip the moon surface

I watched a nice little movie by David Nunez: https://www.youtube.com/watch?v=YSwexZRLtU4 that provided a link to the Apollo 11 Source Code on GitHub — the original code used in the computer on board both the Lunar Module and the Command Module.

The Apollo 11 source code on GitHub

This code is written in AGC — assembly language, which was specifically designed for the Apollo Guidance Computer. Not a language I am familiar with obviously. However, I am curious to learn at least to some degree how it is organized and especially where that infamous 1202 alarm is triggered.

Fortunately I am currently trying out Windsurf. And one of the capabilities of this Agentic AI powered IDE is to explore a new code base. So can it help me surf this ancient code base and help me understand at least a little of it?

I clone the GitHub repo, opened the root folder in Windsurf IDE and started the exploration.

The opening move — have Cascade explain the code base

In some 25 seconds it came back with the following summary:

Initial summary of the Apollo 11 AGC code base

As an obvious next step: look at 1202. Where is it raised, why, how is it handled?

I need to do very little prompting to send Cascade on its mission. It easily recognized the 1202 reference

Another brief wait and Cascade has an answer for me — with code references and a little unprompted but nice historical context:

Where and how the 1202 in the AGC code base

By simply clicking on the reference in Cascade’s answer I can quickly look up the associated code:

Inspecting the code where the bailout exception is thrown (though these are anachronistic terms I guess)

To get a little more feel for how AGC code works, I ask Cascade for an example — one involving altitude calculations:

Prompting Cascade for code that works on calculations regarding altitude

It has to do a little digging around, then comes back with a nice example. Note that Cascade is helped tremendously by the ample documentation in this code base.

example of how the Apollo Guidance Computer (AGC) calculated and processed altitude data during the lunar landing

Using the Cascade agent in Windsurf proves a great way to get some hold on this very special code base. Even though AGC is far beyond me, I at least get a sense for how it is organized, at what level it operates and how some things are done.

The speed with which I gained this insight is almost insane. In less than 15 minutes I went from: “wow, the Apollo 11 code base is on line” to this last example of a clarified calculation in that same code base. Next I can start refactoring it ;-) .