Intel® 945G/945GZ/945GC/ 945P/945PL Express Chipset Family ...

Host-PCI Express* Bridge Registers (D1:F0) (Intel® 82945G/82945GC/82945P/82945PL Only)
5.1.16 MLIMIT1—Memory Limit Address (D1:F0)
PCI Device: 1
Address Offset: 22h
Default Value: 0000h
Access: R/W
Size: 16 bits
This register controls the processor-to-PCI Express non-prefetchable memory access routing
based on the following formula:
MEMORY_BASE � address � MEMORY_LIMIT
The upper 12 bits of the register are read/write and correspond to the upper 12 address bits
A[31:20] of the 32-bit address. The bottom 4 bits of this register are read-only and return zeroes
when read. The configuration software must initialize this register. For the purpose of address
decode, address bits A[19:0] are assumed to be FFFFFh. Thus, the top of the defined memory
address range will be at the top of a 1-MB aligned memory block.
Note: Memory range covered by MBASE and MLIMIT registers are used to map non-pre-fetchable PCI
Express address ranges (typically where control/status memory-mapped I/O data structures of the
graphics controller will reside) and PMBASE and PMLIMIT are used to map pre-fetchable
address ranges (typically, graphics local memory).
This segregation allows application of USWC space attribute to be performed in a true plug-andplay
manner to the pre-fetchable address range for improved processor -PCI Express memory
access performance.
Note: Configuration software is responsible for programming all address range registers (pre-fetchable,
non-prefetchable) with the values that provide exclusive address ranges (i.e., prevent overlap with
each other and/or with the ranges covered with the main memory). There is no provision in the
(G)MCH hardware to enforce prevention of overlap and operations of the system in the case of
overlap may be affected.
Bit Access &
Default
15:4 R/W
000h
3:0 Reserved
Description
Memory Address Limit (MLIMIT): This field corresponds to A[31:20] of the
upper limit of the address range passed to PCI Express.
122 Intel ® 82945G/82945GZ/82945GC GMCH and 82945P/82945PL MCH Datasheet