Compaq W4000 manual Apic Mode, Maskable Interrupt Priorities and Assignments, Slot

Technical Reference Guide

8259 Mode

The 8259 mode handles interrupts IRQ0-IRQ15 in the legacy (AT-system) method using 8259- equivalent logic. Table 4-8 lists the standard source configuration for maskable interrupts and their priorities in 8259 mode. If more than one interrupt is pending, the highest priority (lowest number) is processed first.

Table 4-8.Maskable Interrupt Priorities and Assignments

		Table 4-8.
	Maskable Interrupt Priorities and Assignments
Priority	Signal Label	Source (Typical)
1	IRQ0	Interval timer 1, counter 0
2	IRQ1	Keyboard
3	IRQ8-	Real-time clock
4	IRQ9	Unused
5	IRQ10	PCI devices/slots
6	IRQ11	Audio codec
7	IRQ12	Mouse
8	IRQ13	Coprocessor (math)
9	IRQ14	Primary IDE controller
10	IRQ15	Secondary IDE I/F controller
11	IRQ3	Serial port (COM2)
12	IRQ4	Serial port (COM1)
13	IRQ5	Network interface controller
14	IRQ6	Diskette drive controller
15	IRQ7	Parallel port (LPT1)
--	IRQ2	NOT AVAILABLE (Cascade from interrupt controller 2)

APIC Mode

The Advanced Programmable Interrupt Controller (APIC) mode provides enhanced interrupt processing with the following advantages:

♦Eliminates the processor’s interrupt acknowledge cycle by using a separate (APIC) bus

♦Programmable interrupt priority

♦Additional interrupts (total of 24)

The APIC mode accommodates eight PCI interrupt signals (INTA-..INTH-) for use by PCI devices. The PCI interrupts are evenly distributed to minimize latency and wired as follows:

ICH2		PCI	PCI	PCI			AGP	NIC	USB
Int. Cntlr.		Slot 1	Slot 2	Slot 3	Slot 4	Slot 5	Slot	I/F [1]	I/F #2
INTA-		INTA-	INTD-	INTC-	INTB-	INTD-	--	--	--
INTB-		--	--	--	--	--	--	--	--
INTC-	Wired	INTB-	INTA-	INTD-	INTC-	INTA-	INTA-	--	--
INTD-	to	--	--	--	--	--	INTB-	--	--
INTE-		--	--	--	--	---	--	INTA-	--
INTF-		INTC-	INTB-	INTA-	INTD-	INTB-	--	--	--
INTG-		INTD-	INTC-	INTB-	INTA-	INTC-	--	--	--
INTH-		--	--	--	--	--	--	--	INTC-
NOTES:

[1]Connection internal to the ICH2. Will be reported by BIOS as using INTA but is NOT shared with other functions using INTA.

Desktop and configurable minitower systems only.

Configurable minitower systems only.

Compaq Evo and Workstation Personal Computers4-17

Featuring the Intel Pentium 4 Processor

Second Edition - January 2003