APIC(4)

💖 APIC(4) 💖

okay bestie, gather round, because this is the Kernel Interfaces Manual entry for apic and it is lowkey foundational. no cap.

✨ NAME ✨

apic — Advanced Programmable Interrupt Controller (APIC) driver

🎀 SYNOPSIS 🎀

This driver is a mandatory part of amd64 kernel. like, you don't get to opt out, it's just there, living its truth. 💅

To compile this driver into an i386 kernel, place the following line in your kernel configuration file:

device apic

The following tunable is settable from the loader(8):

• hint.apic.X.clock — controls event timers functionality support. Setting it to 0 disables it. Default value is 1. so like, if you set it to zero you're literally turning the vibe off, and the default is "yes bestie, we're doing this." ✨
• hint.apic.X.disabled — set this to 1 to disable APIC support, falling back to the legacy PIC. it's giving "i'm leaving the group chat and going back to the old one." 🫶

🌸 DESCRIPTION 🌸

There are two components in the Intel APIC system, and you need to know both of them:

1. the local APIC (LAPIC)
2. the I/O APIC

There is one local APIC in each CPU in the system. There is typically one I/O APIC for each peripheral bus in the system.

Local APICs manage all external interrupts for a specific processor. and on top of that, they are able to accept and generate inter-processor interrupts (IPIs). multitasking icon behavior, honestly. 👑

I/O APICs contain a redirection table, which is used to route the interrupts they receive from peripheral buses to one or more local APICs. it's the little matchmaker of the interrupt world, connecting buses to CPUs. 💌

Each local APIC includes one 32-bit programmable timer. This driver uses them to supply the kernel with one event timer named "LAPIC". The event timer provided by the driver supports both one-shot and periodic modes. Because of local APIC nature, it is per-CPU. The timer frequency is not reported by the platform, and so it is automatically measured by the driver on the first use. (not it figuring out its own tempo on the fly, we love a self-aware queen. 🎵)

Depending on CPU model, this timer may stop in C3 and deeper CPU sleep states. Driver automatically adjusts event timer priority and reports it to prevent entering dangerous sleep states when it is used. so like, it's out here protecting you from itself, which is honestly very mature of it. ⭐

ngl, that last part matters — the driver is actively managing priority so you don't slide into a sleep state it can't wake up from. respect the hustle. 💀

🌈 SEE ALSO 🌈

• atrtc(4)
• attimer(4)
• eventtimers(4)
• hpet(4)

and that's the whole page, bestie — no notes, no skips, every single detail preserved because we do not gatekeep kernel docs. 🦋

this has been the Debian rendition of the APIC(4) page, dated June 19, 2020. mwah. 💖✨