I always took it to mean fixed purpose control signals rather than sitting on a common bus.

It takes only one buffer overflow within a fixed purpose control signal handler to convert any bus into a general purpose bus.

No buses, only fixed purpose control signals.

It's pretty hard to buffer overflow

  if (read_gpio(Ignition_Enable_Pin)) {

But if that GPIO triggers an interrupt, you might be able to get the processor to do interesting things by oscillating the signal faster than the processor can disable interrupts and run the ISR.

That's almost always explicitly handled for line glitch reasons.

Haven't there been mod chips for consoles that worked by glitching the lines at just the right time?

The one I know of that glitched lines at the right time (the xbox 360 reset glitch hack modchips) worked by glitching the reset line at the right time via a CPLD that had been attached in such a way as to bypass the analog filtering.

I agree that this scheme doesn't protect against hardware implants modifying lines, but the threat model discussed thus far was around propagation of software implants throughout a system.

They're talking about a TV show[1], where one early episode revolved around the fact that they had avoided connecting the computers to keep the bad guys out. (Sorry if I'm telling you something you already knew; the question you started with made it unclear.)

The show created an aesthetic like an old submarine, even using set pieces salvaged from other submarine movies. That was an aesthetic choice, making everything look cluttered and cramped and slow, increasing tension in exactly the way old submarine movies used to. In those movies, the computers weren't connected because they didn't exist. Actions were coordinated by phone.

It's a bit contrived that they had computers but not networks. It was just a conceit of the show, and actually it was really mostly just in that one episode. But the aesthetic carried through and made for great atmosphere.

[1] https://en.wikipedia.org/wiki/Battlestar_Galactica_(2004_TV_...

I think the various ship subsystems were isolated and they used analog voice telephones to request various ship operations from crew in those sub areas.