Intel i7-3920XM Extreme AW8063801009607 User Manual

Datasheet, Volume 2

73

Processor Configuration Registers 

2

RW

0b

Uncore

PEG12 MDA Present (MDAP12) 
This bit works with the VGA Enable bits in the BCTRL register of 

Device 1 Function 2 to control the routing of processor initiated 

transactions targeting MDA compatible I/O and memory address 

ranges. This bit should not be set if Device 1 Function 2 VGA 

Enable bit is not set.
If Device 1 Function 2 VGA enable bit is not set, then accesses to 

I/O address range x3BCh-x3BFh remain on the backbone.
If the VGA enable bit is set and MDA is not present, then 

accesses to I/O address range x3BCh–x3BFh are forwarded to 

PCI Express through Device 1 Function 2 if the address is within 

the corresponding IOBASE and IOLIMIT, otherwise they remain 

on the backbone.
MDA resources are defined as the following:

Memory:

0B0000h–0B7FFFh

I/O:

3B4h, 3B5h, 3B8h, 3B9h, 3BAh, 3BFh,
(including ISA address aliases, A[15:10] are not 

used in decode)

Any I/O reference that includes the I/O locations listed above, or 

their aliases, will remain on the backbone even if the reference 

also includes I/O locations not listed above.
The following table shows the behavior for all combinations of 

MDA and VGA:

0

0

All References to MDA and VGA space are 

not claimed by Device 1 Function 2.

0

1

Illegal combination

1

0

All VGA and MDA references are routed to 

PCI Express Graphics Attach Device 1 

Function 2.

1

1

All VGA references are routed to PCI 

Express Graphics Attach Device 1 Function 

2. MDA references are not claimed by 

Device 1 Function 2.

VGA and MDA memory cycles can only be routed across PEG12 

when MAE (PCICMD12[1]) is set. VGA and MDA I/O cycles can 

only be routed across PEG12 if IOAE (PCICMD12[0]) is set.