Register Description

R

3.6.19PMBASE1—Prefetchable Memory Base Address Register (Device 1)

Address Offset:

24–25h

Default Value:

FFF0h

Access:

R/W

Size:

16 bits

This register controls the host to AGP prefetchable memory accesses routing based on the following formula:

PREFETCHABLE_MEMORY_BASE1 address PREFETCHABLE_MEMORY_LIMIT1

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 0s when read. The configuration software must initialize this register. For the purpose of address decode, address bits A[19:0] are assumed to be 0. Thus, the bottom of the defined memory address range will be aligned to a 1 MB boundary.

Bit

Description

 

 

15:4

Prefetchable Memory Address Base 1(PMEM_BASE1). Corresponds to A[31:20] of the

 

memory address.

 

 

3:0

Reserved.

 

 

3.6.20PMLIMIT1—Prefetchable Memory Limit Address Register (Device 1)

Address Offset:

26–27h

Default Value:

0000h

Access:

R/W

Size:

16 bits

This register controls the host to AGP prefetchable memory accesses routing based on the following formula:

PREFETCHABLE_MEMORY_BASE1 address PREFETCHABLE_MEMORY_LIMIT1

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 0s 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.

Bit

Description

 

 

15:4

Prefetchable Memory Address Limit 1(PMEM_LIMIT1). Corresponds to A[31:20] of the

 

memory address. (Default=00h)

 

 

3:0

Reserved.

 

 

Note: Prefetchable memory range is supported to allow segregation by the configuration software between the memory ranges that must be defined as UC and the ones that can be designated as a USWC (i.e., prefetchable) from the processor perspective.

Intel® 82845 MCH for SDR Datasheet

91

Page 91
Image 91
Intel 845 manual PMBASE1-Prefetchable Memory Base Address Register Device