This is the code in the Apollo Guidance Computer for Apollo 11.
It's part of the LUMINARY sofware, which ran on the AGC on the Lunar Module. It's meant to check if the landing radar is pointed toward the lunar surface - because the LM went through several orientations, the landing radar could be pointed to the front or the side or down. You're landing on the Moon. Point it down.
Point is, you have to verify user input. Even if your users are the most meticulous and highly trained individuals in history. You have to see if they're lying. So you get to the BURNBABY.
Browse the code in GitHub - this code is in THE_LUNAR_LANDING.agc
There's a 2001 rewrite of the documentation. There's lots of funny instructions aside from P00 meaning root process of the computer, like an OS kernel which also includes the P00D00 abort routine. There is also
SEXTMARK(sextant mark) andENEMA(software restart).