Intel G640T CM8062301002204 User Manual

Datasheet, Volume 2

141

This register determines the size of the graphics memory aperture in function 0 and in 
the trusted space. Only the system BIOS will write this register based on pre-boot 
address allocation efforts; however, the graphics may read this register to determine 
the correct aperture size. System BIOS needs to save this value on boot so that it can 
reset it correctly during S3 resume. 

This register is Intel TXT locked and becomes read only when the trusted environment 

is launched.

7:3

RO

0h

2

RW-K

0b

Uncore

Untrusted Aperture Size High (LHSASH)
This field is used in conjunction with LHSASL. The description 

below is for both fields (LHSASH and LHSASL).
11b = Bits [28:27] of GMADR are RO, allowing 512 MB of GMADR
10b = Illegal Programming
01b = Bit [28] of GMADR is RW but bit [27] of GMADR is RO, 

allowing 256 MB of GMADR

00b = Bits [28:27] of GMADR are RW, allowing 128 MB of GMADR

1

RW-K

1b

Uncore

Untrusted Aperture Size Low (LHSASL)
This field is used in conjunction with LHSASH. The description 

below is for both fields (LHSASH and LHSASL).
11b = Bits [28:27] of GMADR are RO, allowing 512 MB of GMADR
10b = Illegal Programming
01b = Bit [28] of GMADR is RW but bit [27] of GMADR is RO, 

allowing 256 MB of GMADR

00b = Bits [28:27] of GMADR are RW, allowing 128 MB of GMADR

0

RO

0h