82870P2P64H2 Datasheet, PDF (35/217 Pages) –

Register Description
R
3.1
Register Nomenclature and Access Attributes
Symbol
RO
R/W
R/W/L
R/WC
R/WO
L
Reserved
Bits
Reserved
Registers
Default
Value Upon
Reset
Description
Read Only. If a register is read only, writes to this register have no effect.
Read/Write. A register with this attribute can be read and written
Read/Write/Lock. A register with this attribute can be read, written, and Locked.
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.
Read/Write Once. A register bit with this attribute can be written to only once after power
up. After the first write, the bit becomes read only.
Lock. A register bit with this attribute becomes Read Only after a lock bit is set.
Some of the Intel® P64H2 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 operations for the
configuration address register.
In addition to reserved bits within a register, the P64H2 contains address locations in the
configuration space that are marked "Reserved. When a “Reserved” register location is
read, a random value can be returned. (“Reserved” registers can be 8-, 16-, or 32-bit in
size). Registers that are marked as “Reserved” must not be modified by system software.
Writes to “Reserved” registers may cause system failure.
Upon a Full Reset, the P64H2 sets its internal configuration registers to predetermined
default states. The default state represents the minimum functionality feature set required
to successfully bring 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 operating parameters and optional system features that are
applicable, and to program the P64H2 registers accordingly.
Intel^® 82870P2 P64H2 Datasheet
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