[gblargg]

I wonder whether the power button really directly starts the CPU. I wouldn't be surprised if the Intel Management Engine (or AMD equivalent), a CPU that's running all the time, is what gets the power button signal and starts the CPU.

[panny]

I think that is the job of the embedded controller, which is before the bootloader bringing up CPU. On Chromebooks, that part is open source along with the coreboot bootloader.

https://chromium.googlesource.com/chromiumos/platform/ec/+/H...