317610-001 Datasheet, PDF (53/342 Pages) Intel Corporation – Express Chipset

MCH Register Description
4 MCH Register Description
The MCH contains two sets of software accessible registers, accessed via the Host
processor I/O address space: Control registers and internal configuration registers.
• Control registers are I/O mapped into the processor I/O space, which control
access to PCI and PCI Express configuration space (see Chapter 6).
• Internal configuration registers residing within the MCH are partitioned into two
logical device register sets (“logical” since they reside within a single physical
device). The first register set is dedicated to Host Bridge functionality (i.e., DRAM
configuration, other chipset operating parameters and optional features). The
second register block is dedicated to Host-to-PCI Express Bridge functions (controls
PCI Express interface configurations and operating parameters).
The MCH internal registers (I/O Mapped, Configuration and PCI Express Extended
Configuration registers) are accessible by the processor. The registers that reside within
the lower 256 bytes of each device can be accessed as Byte, Word (16-bit), or DWord
(32-bit) quantities, with the exception of CONFIG_ADDRESS, which can only be
accessed as a DWord. All multi-byte numeric fields use “little-endian” ordering (i.e.,
lower addresses contain the least significant parts of the field). Registers that reside in
bytes 256 through 4095 of each device may only be accessed using memory-mapped
transactions in DWord (32-bit) quantities.
Some of the MCH registers described in this section contain reserved bits. These bits
are labeled “Reserved”. 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, and write
operation for the Configuration Address Register.
In addition to reserved bits within a register, the MCH contains address locations in the
configuration space of the Host Bridge entity that are marked either “Reserved” or
“Intel Reserved”. The MCH responds to accesses to “Reserved” address locations by
completing the host cycle. When a “Reserved” register location is read, a zero value is
returned. (“Reserved” registers can be 8-, 16-, or 32-bits in size). Writes to “Reserved”
registers have no effect on the MCH. Registers that are marked as “Intel Reserved”
must not be modified by system software. Writes to “Intel Reserved” registers may
cause system failure. Reads from “Intel Reserved” registers may return a non-zero
value.
Upon a Full Reset, the MCH sets its entire set of internal configuration registers to
predetermined default states. Some register values at reset are determined by external
strapping options. The default state represents the minimum functionality feature set
required to successfully bringing up the system. Hence, it does not represent the
optimal system configuration. It is the responsibility of the system initialization
software (usually BIOS) to properly determine the DRAM configurations, operating
parameters and optional system features that are applicable, and to program the MCH
registers accordingly.
Datasheet
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