I came across this schematic (well, my son dragged it into my attention):
This is for a universal keyboard controller. The thing that is really catching my eye, though, is that the thing appears to be set up to bit- bang the USB.
Has anyone ever heard of doing this? Tried it? Succeeded? USB slow is1.5MHz, so there's a remote possibility that one might possibly have enough time to do something if the processor isn't doing much else (the processor in the above schematic is clocking at 12MHz), but I'm pretty astonished that they're even managing that.