4 Summary of the HP/Phoenix BIOS

BIOS Addresses

The PCI interrupt lines A, B, C and D are spread across the four inputs of the interrupt router (which is part of the PCI/ISA bridge, in the PIIX3 chip). Since most PCI devices are single-function, this allows for an even distribution of the lines. The distribution is shown in the following diagram. In this, Slot 4 is present only on minitower models (and is omitted on desktop models); Slot R refers to the PCI proprietary slot on the rear side of the double sided backplane of desktop models (and is omitted on minitower models).

Integrated

 

Slot 1

 

Slot 2

 

Slot 3 or R

 

Slot 4 (MT)

graphics

 

 

 

 

 

 

 

 

 

 

 

 

A

 

A B C D

 

A B C D

 

A B C D

 

A B C D

A

B PCI/ISA

Bridge

C

D

PCI interrupts are then mapped into ISA interrupts inside the PCI/ISA

Bridge (in the PIIX3 chip), by configuring registers 60h through 63h.

Bit

Description

 

 

7

Routing of interrupts: when enabled, this bit routes the PCI interrupt signal to the PC-

 

compatible interrupt signal specified in bits[3:0]. At reset, this bit is disabled (set to 1)

 

 

6:4

Reserved: read as 000

 

 

3:0

IRQx# Routing Bits: these bits specify which IRQ signal to generate.

 

Possible values are: 3, 4, 5, 6, 7, 9, 10, 11, 12, 14, 15.

 

 

The possible choices given by the Setup program are 9, 10, 11, 15. If some of these are unavailable due to ISA cards, some interrupts will have to be shared.

The IDE controller is actually configured in legacy mode, and uses IRQ 14 (IRQ 15 for the secondary channel). The mode setting is in configuration byte 09h of the IDE controller, device 01h.

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