I write embedded software - specifically a real-time OS - for a telecommunications chip. I should probably refrain from making a big point of the company name, since I gripe about my employer way too much on LJ. :-) I do love the technical part of my job.

The boot loader sits in an off-chip EEPROM, gets slurped into memory as soon as the board comes out of reset, turns on I/O, and waits for the real OS to arrive. When the real stuff shows up, it puts everything in the right place etc and jumps through a magic number. I just had to redesign the whole mess for a different chip. Took way too long. I'm proud of the fact that it essentially worked first try, though. Gnarly piece of crap to just work first try.