Changing Memory Allocation in BIOS? [SOLVED-Bad Idea]

UberPinguin · Last edited by UberPinguin on Sun Nov 05, 2006 6:09 am; edited 1 time in total

I have a Compaq Evo N610c notebook. It has an integrated ATI Radeon Mobility 7500 graphics card with shared memory. I've got 1024MB of RAM in the thing, but the BIOS will only allocate 32MB to video. There is no place in the setup menu to change this value.

The challenge: hack the BIOS to change the memory mappings and give more RAM to the video card. It should be able to handle 128MB.

Relevant details:

NeddySeagoon · Posted: Fri Nov 03, 2006 4:09 pm Post subject:

UberPinguin,

What are you trying to achieve ?

The pixel buffer requires HorDots x VertDots X ColourBytes x 2 bytes per independent display surface. Thats 15360000 bytes for 1600x1200 in 32 bit colour. or 15Mb in round numbers. With the graphics pixel buffer in shared main memory, more dedicate RAM than you need is wasted.

With a dedicated memory graphics card, excess on card RAM is used to hold 3D textures, which is only useful for 3D applications.
When on card RAM is used up, the graphics card requests some of main memory, via the AGP Aperture. This is slower than on card RAM.
However, you have zero on card RAM. By allocating more graphics RAM than you need for your pixel buffers, you prevent the kernel from allocating this RAM to applications and you have no speed loss using the AGP Aperture, since its effectively all you have anyway.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

UberPinguin · Posted: Fri Nov 03, 2006 4:23 pm Post subject:

When you put it like that, it almost seems pointless...
I guess I'm a little confused. I've seen other systems where the BIOS has a setting for increasing or decreasing the amount of RAM dedicated to the video card. On these systems, changing the value definitely had an impact on video performance.
My main objective is to achieve better rendering speed/quality in X. Right now, with EXA enabled, everything is very choppy - even moving terminal windows around when no other applications are open. Changing to XAA gives slight speed improvements, but is ugly compared to EXA and still pretty slow. I thought that by increasing the amount of RAM reserved for video, I could improve this performance.

Your point that there is zero on card RAM and all the memory operations are running through the AGP aperture clarifies something for me: I've seen other machines (notably a PowerBook I have) with the same (at least, nominally) video card in them that perform far better. Perhaps they are, in fact, built differently.

BTW, thanks for the quick response. I wasn't expecting anything for at least a few hours!
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NeddySeagoon · Posted: Fri Nov 03, 2006 4:36 pm Post subject:

UberPinguin,

What graphics driver are you using ?
If ati-drivers works for you, it will give the best performance.

What applications are choppy ?
What screen resolution and refresh rate are you using?

For some video drivers Xorg can change the amount of RAM allocated.

UberPinguin · Posted: Fri Nov 03, 2006 5:09 pm Post subject:

I'm using the open-source radeon driver. ATI's binary driver doesn't support my card. I tried setting VideoRAM, but it didn't seem to have any effect.

I'm using a dual-headed MergedFB setup: 1024x768 on the built-in LCD and 1280x1024 on an external CRT. Both monitors are running at 60Hz refresh.

I'm trying some options from the radeon man page, will report results..

[EDIT]Adding