845GL datasheet(112/193 Pages) INTEL

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Functional Description

112

Intel® 82845G/82845GL/82845GV GMCH Datasheet

4.3.1.2

AGP Target Operations

As an initiator, the GMCH does not initiate cycles using AGP enhanced protocols. The GMCH

supports AGP target interface to main memory only. The GMCH supports interleaved AGP and

PCI transactions. The Table 4-6 summarizes target operation support of GMCH for AGP masters.

NOTE:

N/A refers to a function that is not applicable

As a target of an AGP cycle, the GMCH supports all the transactions targeted at main memory and

summarized in Table 4-6. The GMCH supports both normal and high priority read and write

requests. The GMCH does not support AGP cycles to the hub interface. AGP cycles do not require

coherency management and all AGP-initiator accesses to main memory using AGP protocol are

treated as non-snoopable cycles. These accesses are directed to the AGP aperture in main memory

that is programmed as either uncacheable (UC) memory or write combining (WC) in the

processor’s MTRRs.

Table 4-6. AGP Commands Supported by GMCH When Acting As an AGP Target

AGP Command

GC/BE[3:0]#

Encoding

GMCH Host Bridge

Cycle Destination

Response As AGP Target

Read

0000

Main Memory

Low Priority Read

0000

Hub Interface

Complete with random data

Hi-Priority Read

0001

Main Memory

High Priority Read

0000

Hub Interface

Complete with random data

Reserved

0010

N/A

No Response

Reserved

0011

N/A

No Response

Write

0100

Main Memory

Low Priority Write

0100

Hub Interface

Cycle goes to SDRAM with BEs inactive

Hi-Priority Write

0101

Main Memory

High Priority Write

0101

Hub Interface

Cycle goes to SDRAM with BEs inactive -

does not go to hub interface

Reserved

0110

N/A

No Response

Reserved

0111

N/A

No Response

Long Read

1000

Main Memory

Low Priority Read

Hub Interface

Complete locally with random data - does

not go to hub interface

Hi-Priority Long

Read

1001

Main Memory

High Priority Read

Hub Interface

Complete with random data

Flush

1010

GMCH

Complete with QW of Random Data

Reserved

1011

N/A

No Response

Fence

1100

GMCH

No Response – Flag inserted in GMCH

request queue

Reserved

1101

N/A

No Response

Reserved

1110

N/A

No Response

Reserved

1111

N/A

No Response

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