Share thoughts about Intel 855 memory pre-allocated

[LAPTOP1606]

Hi all,

 

Firstly I would like to sorry about my English. I am not native English speak so that why!

Secondly I would like to thanks this community for you work and contribution.

 

Why I open this topic? I saw many post about try to use old fashion Intel 855 graphic card with OSx 10.5.x but no post success in doing that with a proper kext. In this post I will not also give you a solution how to fix that - sorry! But we can share information/thoughts/suggest here and hopefully one day one genius could help us!

 

My intend is not going to write a new kext - how ever OSx not support Intel 855 from 10.4.1 - but to find a way around to increase the VRAM in order to run iwork, DVD...

 

My Intel 855 card is only give me 7MB of VRAM - very small when it could give more up to 64MB. Damn!

 

So I study a little bit on Intel 855 card and found one document regarding Graphic and Memory control. I copy the most related part below: (the full document could be find here: http://www.intel.com/assets/pdf/datasheet/252615.pdf)

 

GGC – GMCH Graphics Control Register (Device 0)

Address Offset: 52–53h

Default Value: 0030h

Access: Read/Write

Size: 16 bits

 

Bit (15:7) Reserved

 

Bit (6:4) Graphics Mode Select (GMS):

This field is used to select the amount of Main system memory that is

pre-allocated to support the Internal Graphics Device in VGA (non-linear) and Native (linear) modes. The

BIOS ensures that system memory is pre-allocated only when Internal Graphics is enabled.

000 = No system memory pre-allocated. Device #2 (IGD) does not claim VGA cycles (Memory and I/O),

and the Sub-Class Code field within Device #2 Function #0 Class Code register is 80.

001 = DVMT (UMA) mode, 1 MB of system memory pre-allocated for frame buffer.

010 = DVMT (UMA) mode, 4 MB of system memory pre-allocated for frame buffer.

011 = DVMT (UMA) mode, 8 MB of system memory pre-allocated for frame buffer.

100 = DVMT (UMA) mode, 16 MB of system memory pre-allocated for frame buffer.

101 = DVMT (UMA) mode, 32 MB of system memory pre-allocated for frame buffer.

All other combinations reserved.

 

Bit (3:2) Reserved

 

Bit (1) IGD VGA Disable (IVD):

1 = Disable. Device #2 (IGD) does not claim VGA Memory and I/O Mem cycles, and the Sub-Class

Code field within Device #2 Function #0 Class Code register is 80.

0 = Enable. Device #2 (IGD) claims VGA Memory and I/O cycles, the Sub-Class Code within Device #2

Class Code register is 00.

 

Bit (0) Reserved

 

In my case I guess Bit (1) set to 0 and Bit (6:4) set to 011, that why I received 7MB (why it is have 1MB different? I do not know). So if we have any tool to access to right address offset (on BIOS? I think?) and set Bit (6:4) to 101 we will receive pre-allocate memory 32 MB, which is enough to run iWork I think!.

 

I did tried to use HWDirect but to be honest, I do not know where is bit I have to change, I am new in this deeply technic.

 

Could you share some thought and may be a solution how we can manage pre-allocate video memory? I very appreciate, thank you for your time.