nullplan wrote:
Perhaps, if you don't know both the Intel SDM and the AMD APM tell you how to initialize an AP if you know its local APIC ID?
The Intel SDM is very large, so it's possible I missed it, but I was under the impression that it only explained how
firmware should bring APs online, and didn't cover how the OS should do so after firmware has initialized everything.
nullplan wrote:
And to this day it contains information considered relevant by historians, such as how to initialize secondary CPUs if those are 486s, which was that stuff with the INIT level de-assert, which I didn't fully absorb, either, since it is about as relevant today as a punch card.
Before the APIC was integrated into the CPU, those IPIs were used to turn the reset signal on and off. You had to leave the signal on for some minimum amount of time for the CPU to reset properly, and the APIC didn't know how long that should be.
rdos wrote:
AFAIK, 486 processors always came with PIC, and so would need some other initialization process.
The 486 didn't come with any interrupt controller. It was up to the motherboard to provide APICs if it wanted to support two or more 486 processors.