OSDev.org

Posted: **Thu Apr 15, 2010 12:33 pm**

Currently I am still using the PIC but the PIC only delivers interrupts to the BSP. I would like to ditch the PIC and go with the IO APIC instead since it can send interrupts to any available CPU Core in the system.

I have taken a look at the Intel manuals, OSDev articles, and some of the posts here but can't find a good step-by-step guide.

So far I have this:

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; Enable the system for Symmetric I/O Mode as per MPS 1.4
	mov al, 0x70			; Select the IMCR register
	out 0x22, al
	mov al, 0x01			; Instruct NMIs and 8259 INTs to go through APIC
	out 0x23, al

Not much there yet as I still need to figure out what to do with LINT0 and LINT1. Do I need to completely mask the PIC after this? Does the above code need to be run on each CPU Core (I would think not)? Does anyone have experience getting your own OS out of PIC Mode and into Symmetric I/O Mode?

Posted: **Mon Apr 19, 2010 8:29 am**

I did a bit more poking around an got the timer working at the very least:

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	xor eax, eax
	mov rdi, [os_LocalAPICAddress]
	add rdi, 0x03E0
	stosd				; Timer: Divisor Config

	mov eax, 10000			; countdown from 10000?
	mov rdi, [os_LocalAPICAddress]
	add rdi, 0x0380
	stosd				; Timer: Initial Count

	mov eax, 0x20			; Timer: interrupt-ID
	bts eax, 17			; do periodic interrupt 
	mov rdi, [os_LocalAPICAddress]
	add rdi, 0x0320	
	stosd				; set APIC Timer's LVT

which properly triggers the int 0x20 code:

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apic_test:
	push rdi
	push rax

	call timer_debug	; Display a counter onscreen

	mov rdi, [os_LocalAPICAddress]
	add rdi, 0xb0
	xor eax, eax
	stosd

	pop rax
	pop rdi
	iretq

This is just APIC stuff though and I'm not that interested in the Timer. What I want to get working over the IO-APIC is the Keyboard and RTC.

Posted: **Mon Apr 19, 2010 2:32 pm**

Haven't got much experience with the IO APIC, but I guess you have to set the redirection table entries. In an ACPI system, ISA IRQ numbers correspond directly to GSI numbers, while in non-ACPI systems, you have to parse the MP table, as I understand it.

This stosd thing you have in your code seems awkward, by the way, when you could just do this:

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mov rdi, [os_LocalAPICAddress]
and dword ptr [rdi+0x3e0],0
mov dword ptr [rdi+0x380],10000
mov dword ptr [rdi+0x320],0x20020

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