Functional Description

R

Table 15. AGP Commands Supported by the Intel® MCH When Acting as an AGP Target

AGP

C/BE[3:0]#

 

MCH Host Bridge

Command

Encoding

 

 

 

 

 

Cycle Destination

 

Response as PCIx Target

 

 

 

 

 

Read

0000

System memory

 

Low-priority read

 

 

 

 

 

 

0000

Hub interface

 

Complete with random data

 

 

 

 

 

Hi-Priority Read

0001

System memory

 

High-priority read

 

 

 

 

 

 

0000

The Hub interface

 

Complete with random data

 

 

 

 

 

Reserved

0010

N/A

 

No response

 

 

 

 

 

Reserved

0011

N/A

 

No response

 

 

 

 

 

Write

0100

System memory

 

Low-priority write

 

 

 

 

 

 

0100

Hub interface

 

Cycle goes to DRAM with byte

 

 

 

 

enables inactive

 

 

 

 

 

Hi-Priority Write

0101

System memory

 

High-priority write

 

 

 

 

 

 

0101

Hub interface

 

Cycle goes to DRAM with byte

 

 

 

 

enables inactive; does not go to

 

 

 

 

the hub interface

 

 

 

 

 

Reserved

0110

N/A

 

No response

 

 

 

 

 

Reserved

0111

N/A

 

No response

 

 

 

 

 

Long Read

1000

System memory

 

Low-priority read

 

 

 

 

 

 

 

Hub interface

 

Complete locally with random data;

 

 

 

 

does not go to the hub interface

 

 

 

 

 

Hi-Priority Long

1001

System memory

 

High-priority read

Read

 

 

 

 

 

 

 

 

 

 

 

Hub interface

 

Complete with random data

 

 

 

 

 

Flush

1010

MCH

 

Complete with QW of random data

 

 

 

 

 

Reserved

1011

N/A

 

No response

 

 

 

 

 

Fence

1100

MCH

 

No response; Flag inserted in

 

 

 

 

MCH request queue

 

 

 

 

 

Reserved

1101

N/A

 

No response

 

 

 

 

 

Reserved

1110

N/A

 

No response

 

 

 

 

 

Reserved

1111

N/A

 

No response

 

 

 

 

 

NOTES:

1. N/A refers to a function that is not applicable

As a target of an AGP cycle, the MCH supports all the transactions targeting system memory (summarized in Table 15). The MCH supports both normal and high-priority read and write requests. The MCH does not support AGP cycles to the hub interface. PIPE# and SBA cycles do not require coherency management and all AGP initiator accesses to system memory, using AGP PIPE# or SBA protocol, are treated as non-snoopable cycles. These accesses are directed to the AGP aperture in system memory that is programmed as either uncacheable (UC) memory or write combining (WC) in the processor’s MTRRs.

Intel® 82845 MCH for SDR Datasheet

113

Page 113
Image 113
Intel 845 manual BE30# MCH Host Bridge Command Encoding, Response as PCIx Target