301467-005 Datasheet, PDF (138/426 Pages) Intel Corporation – Express Chipset

Host-PCI Express* Bridge Registers (D1:F0)
(Intel® 82915G/82915P/82915PL Only)
R
8.1.16
MLIMIT1—Memory Limit Address (D1:F0)
PCI Device:
Address Offset:
Default Value:
Access:
Size:
1
22h
0000h
R/W
16 bits
This register controls the processor-to-PCI Express Graphics 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. 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-prefetchable PCI
Express Graphics 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
prefetchable address ranges (typically, graphics local memory). This segregation allows
application of USWC space attribute to be performed in a true plug-and-play manner to the
prefetchable address range for improved processor-PCI Express memory access performance.
Note:
Configuration software is responsible for programming all address range registers (prefetchable,
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 are not guaranteed.
Bit
Access &
Default
Description
15:4
R/W
Memory Address Limit (MLIMIT): This field corresponds to A[31:20] of the
000h
upper limit of the address range passed to PCI Express*.
3:0
Reserved
138
Datasheet