I didn't do anything odd to cause the problem, as far as I can tell. I just plugged in my iPod, noticed it didn't show up in iTunes, and then quickly discovered that nothing at all that used FireWire was functional.
I tried shutting down and booting, restarting, logging in as another user, even resetting PRAM and NVRAM. Nothing worked; my devices were simply gone. I knew the ports were generally OK, though, as my iPod dock was charging the iPod, and my iSight's green light would flash when it was plugged in. It's just that the machine didn't want to admit that it knew anything at all about FireWire.
I then opened Console, in Applications -> Utilities, and opened to the system log. There I found tons and tons of these entries (line breaks added for narrower display):
Nov 29 05:17:21 gargantua5 kernel[0]: FireWire (OHCI) Apple ID 42 built-in:
no valid selfIDs for more than 2 minutes after bus reset.
Nov 29 05:20:33 gargantua5 kernel[0]: FireWire (OHCI) Apple ID 42 built-in:
no valid selfIDs for more than 2 minutes after bus reset.
Nov 29 05:23:45 gargantua5 kernel[0]: FireWire (OHCI) Apple ID 42 built-in:
no valid selfIDs for more than 2 minutes after bus reset.
etc...
These repeat about every three minutes for as long as the machine was powered up. Not encouraging, to say the least.
But this at least gave me something to Google on, which in turn led me to this Knowledge Base document. There they describe the standard FireWire troubleshooting tips (most of which I had already tried). Down at the bottom, though, they provided a solution that did work:
- Shut down the computer.
- Disconnect all FireWire devices and all other cables, except the keyboard and mouse cable(s).
- Disconnect the computer from the power outlet and wait for 3 to 5 minutes.
- Plug the computer back in and turn it on.
- Reconnect the FireWire device(s) (one at a time if there is more than one) and test. Test with each FireWire port if you have more than one.

