Intel B940 Datasheet download pdf (Page 126)

Processor Configuration Registers

126 Datasheet, Volume 2

2.10.16 MLIMIT1—Memory Limit Address Register

This register controls the processor to PCI Express-G 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. This register must be initialized by the configuration

software. 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-G 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

(that is, prevent overlap with each other and/or with the ranges covered with the main

memory). There is no provision in the processor hardware to enforce prevention of

overlap and operations of the system in the case of overlap are not ensured.

B/D/F/Type: 0/1/0/PCI

Address Offset: 22–23h

Reset Value: 0000h

Access: RW, RO

Bit Attr

Reset

Value

Description

15:4 RW 000h

Memory Address Limit (MLIMIT)

This field corresponds to A[31:20] of the upper limit of the address range

passed to PCI Express-G.

3:0 RO 0h Reserved

1 2 ... 121 122 123 124 125 126 127 128 129 130 131 ... 359 360

No comments

Intel B940 Datasheet Page 126