
Register and Memory Mapping
6-2
82801AA and 82801AB Datasheet
6.1
PCI Devices and Functions
The ICH incorporates a variety of PCI functions as shown in
Table 6-1
. These functions are divided
into two logical devices (30, and 31). Device 30 is the Hub Interface-To-PCI bridge. Device 31
contains all the other PCI functions.
If for some reason, the particular system platform does not want to support any one of the
Functions 1-6, they can individually be disabled. When a function is disabled, it does not appear at
all to the software. A disabled function will not respond to any register reads or writes. This is
intended to prevent software from thinking that a function is present (and reporting it to the end-
user).
6.1.1
PCI Configuration Map
Each PCI function on the ICH has a set of PCI configuration registers. The register address map
tables for these register sets are included at the beginning of the chapter for the particular function.
Refer to
Table A-1
for a complete list of all PCI Configuration Registers.
Configuration Space registers are accessed through configuration cycles on the PCI bus by the
Host bridge using configuration mechanism #1 detailed in the
PCI 2.1 Specification
.
Some of the PCI registers contain reserved bits. Software must deal correctly with fields that are
reserved. On reads, software must use appropriate masks to extract the defined bits and not rely on
reserved bits being any particular value. On writes, software must ensure that the values of
reserved bit positions are preserved. That is, the values of reserved bit positions must first be read,
merged with the new values for other bit positions and then written back. Note the software does
not need to perform read, merge, write operation for the configuration address register.
In addition to reserved bits within a register, the configuration space contains reserved locations.
Software should not write to reserved PCI configuration locations in the device-specific region
(above address offset 3Fh).
Table 6-1. PCI Devices and Functions
Device:Function
Function Description
Device 30:Function 0
Hub Interface to PCI Bridge
Device 31:Function 0
PCI to LPC Bridge
(includes: DMA, Timers, compatible interrupt controller, APIC, RTC, processor
interface control, power management control, System Management control,
and GPIO control)
Device 31:Function 1
IDE Controller
Device 31:Function 2
USB Controller
Device 31:Function 3
SMBus Controller
Device 31:Function 4
Reserved
Device 31:Function 5
AC’97 Audio Controller
Device 31:Function 6
AC’97 Modem Controller