Intel 460GX manual IFB Register Mapping, PCI / LPC / FWH Configuration

IFB Register Mapping 9

The IFB internal registers are organized into four Functions–LPC/FWH interface bridge, IDE Controller, USB Host Controller, and Enhanced Power Management. Each Function has its registers divided into 1 set of PCI Configuration Registers and one or more register sets located in system I/O space.

Software should not map programmable memory or I/O address registers such that any part of the range overlaps addresses decoded by other IFB devices.

Some of the IFB 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.

In addition to reserved bits within a register, the IFB contains address locations in the PCI configuration space that are marked “Reserved”. The IFB responds to accesses to these address locations by completing the Host cycle. Software should not write to reserved IFB configuration locations in the device-specific region (above address offset 3Fh).

During a hard reset, the IFB sets its internal registers to predetermined default states. The default values are indicated in the individual register descriptions.

The following notation is used to describe register access attributes:

RO	Read Only. If a register is read only, writes have no effect.
WO	Write Only. If a register is write only, reads have no effect.
R/W	Read/Write. A register with this attribute can be read and written. Note that individual
	bits in some read/write registers may be read only.
R/WC	Read/Write Clear. A register bit with this attribute can be read and written. However, a
	write of a 1 clears (sets to 0) the corresponding bit and a write of a 0 has no effect.

9.1PCI / LPC / FWH Configuration

The IFB PCI Function 0 contains a LPC/FWH interface, interrupt controller and counter / timers, including the real time clock. The register set associated with this Functionality and associated logic is shown below with actual register descriptions given in this section.

9.1.1PCI Configuration Registers (Function 0)

Table 9-1. PCI Configuration Registers–Function 0(PCI to LPC/FWH Interface Bridge)

Configuration Offset	Mnemonic	Register	Register Access
00–01h	VID	Vendor Identification	RO
02–03h	DID	Device Identification	RO
04–05h	PCICMD	PCI Command	R/W

Intel® 460GX Chipset Software Developer’s Manual 9-1