Datasheet

Datasheet 61

4.8.3 PCICMD – PCI Command Register

Address Offset: 04-05h

Default Value: 0006h

Access: Read Only, Read/Write

Size: 16 bits

Since GMCH Device #0 does not physically reside on PCI_A many of the bits are not

implemented.

Bit Descriptions

15:10 Reserved

9 Fast Back-to-Back Enable (FB2B): This bit controls whether or not the master can do fast back-to-

back Write. Since Device #0 is strictly a target, this bit is not implemented and is hardwired to 0. Writes

to this bit position have no affect.

SERR Enable (SERRE): This bit is a global enable bit for Device #0 SERR messaging. The GMCH

does not have an SERR# signal, but communicates the SERR# condition by sending an SERR

message to the ICH4-M.

1 = Enable. GMCH is enabled to generate SERR messages over Hub interface for specific Device #0

error conditions that are individually enabled in the ERRCMD register. The error status is reported in the

ERRSTS and PCISTS registers.

0 = SERR message is not generated by the GMCH for Device #0.

NOTE: This bit only controls SERR messaging for the Device #0. Device #1 has its own SERRE bit to

control error reporting for error conditions occurring on Device #1. The two control bits are used in a

logical OR manner to enable the SERR Hub interface message mechanism.

7 Address/Data Stepping Enable (ADSTEP): Address/data stepping is not implemented in the GMCH,

and this bit is hardwired to 0. Writes to this bit position have no effect.

6 Parity Error Enable (PERRE): PERR# is not implemented by GMCH and this bit is hardwired to 0.

Writes to this bit position have no effect.

5 VGA Palette Snoop Enable (VGASNOOP): The GMCH does not implement this bit and it is hardwired

to a 0. Writes to this bit position have no effect.

4 Memory Write and Invalidate Enable (MWIE): The GMCH will never issue memory write and

invalidate commands. This bit is therefore hardwired to 0. Writes to this bit position will have no effect.

3 Special Cycle Enable (SCE): The GMCH does not implement this bit and it is hardwired to a 0. Writes

to this bit position have no effect.

2 Bus Master Enable (BME): The GMCH is always enabled as a master on HI. This bit is hardwired to a

1. Writes to this bit position have no effect.

1 Memory Access Enable (MAE): The GMCH always allows access to main system memory. This bit is

not implemented and is hardwired to 1. Writes to this bit position have no effect.

0 I/O Access Enable (IOAE): This bit is not implemented in the GMCH and is hardwired to a 0. Writes to

this bit position have no effect.