Isn't it just a GPIO, like on older Macs?  Of course, we
cannot bring a CPU back online after doing that so it's
pretty useless I suppose.

We don't know for sure what the gpio does... wether it does a CPU soft
reset or tickles the SPU to make it do special things that cause us to
branch at 0x100. We do get the CPU back after that though. We use that
to bring them in after boot.

Ben.