I'm having to deconstruct the code to get at the architecture of the system. The problem is that the code was written by clever guys that have long since gone away, and nobody really understands how it works except at a really surface level.
The biggest piece is called the sequencer. And it's clever. It does some really cool things. It's also written entirely in assembly, and has comments like "add one" and "quit now". And nowhere is there a description of what the higher-level structures are, like the "slot".
In really rough terms, it behaves like a synchronous multi-threaded interpreter for a very high-level language.
And it's really clever.
Oh, my, clever.
Note that there is a difference between clever and elegant.
Elegant code is clean and streamlined without losing understandability.
Clever code is brief and tricky, and may be optimized to next tuesday, but it's a right bitch to reverse-engineer. Clever code brings you things like this.