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Intel
®
82854 Graphics Memory Controller Hub (GMCH)
52 D15343-003
4.8.3 PCICMD – PCI Command Register
Since GMCH Device #0 does not physically reside on PCI_A many of the bits are not
implemented.
Address Offset:
Default Value:
Access:
Size:
04-05h
0006h
Read only, Read/Write
16 bits
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.
8 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.