HP A2Y15AV ユーザーズマニュアル

72

Datasheet, Volume 2

This 8-bit register controls steering of MDA cycles and a fixed DRAM hole from 15–
16 MB.

There can only be at most one MDA device in the system.

7

RW

0b

Uncore

Hole Enable (HEN) 
This field enables a memory hole in DRAM space. The DRAM that 

lies "behind" this space is not remapped.
0 = No memory hole.
1 = Memory hole from 15 MB to 16 MB.
This bit is Intel TXT lockable.

6:4

RO

0h

3

RW

0b

Uncore

PEG60 MDA Present (MDAP60) 
This bit works with the VGA Enable bits in the BCTRL register of 

Device 6 Function 0 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 6 VGA Enable bit is 

not set.
If Device 6 Function 0 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 6 Function 0 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 6 Function 0.

0

1

Illegal combination

1

0

All VGA and MDA references are routed to 

PCI Express Graphics Attach Device 6 

function 0.

1

1

All VGA references are routed to PCI Express 

Graphics Attach Device 6 Function 0. MDA 

references are not claimed by Device 6 

Function 0.

VGA and MDA memory cycles can only be routed across PEG60 

when MAE (PCICMD60[1]) is set. VGA and MDA I/O cycles can 

only be routed across PEG60 if IOAE (PCICMD60[0]) is set.
0 = No MDA
1 = MDA Present