There is unlikely to be any LFB for your ISA VGA card on a pentium 3.

You would either need less than 16meg ram, which is REALLY rare for a P3 class machine, or a specific option in the bios to disable the mapping of memory between 15meg and 16meg.

May I ask a dumb question .... why? If you want the video on your P3 to go faster, why not install a quicker video card (anything PCI/AGP would be way faster)

canthearu wrote on 2021-08-10, 02:37:

May I ask a dumb question .... why? If you want the video on your P3 to go faster, why not install a quicker video card (anything PCI/AGP would be way faster)

Because it's fun an interesting?

Kahenraz wrote on 2021-08-10, 03:38:

canthearu wrote on 2021-08-10, 02:37:

May I ask a dumb question .... why? If you want the video on your P3 to go faster, why not install a quicker video card (anything PCI/AGP would be way faster)

Because it's fun an interesting?

Well I approve then 😀

It was interesting to discover, for example, that Quake will happily run at over 30fps on a basic ISA VGA card. 😀

Kahenraz wrote on 2021-08-10, 02:27:

There is a very small performance gain when VGA Write Combining is enabled. Is this change unrelated to the PCI bus?

It's CPU related. Also VGA write combining at least on P6 micro-architecture has some disadvantages depending of the card, when mode X is in use some images gets screwed up. I recommend only enabling it for LFB.

I have several questions to this topic:

Acumos AVGA2 is only VBE 1.1 card, so UNIVBE refuse to install VESA VBE 2.0 extension
But it happens on Trident 8900CL. Even VBE 3.0 extensions are installed.

Is possible to use Linear Frame Buffer on ISA 512KB VRAM card, or 1MB Video RAM memory is ALWAYS needed as minimum?
When I use Phil's Fastvid, it wants me to enter Linear Frame Buffer address, but only allows greater addresses than 80.000.000
I quess it's unusable, as with ISA, I need to allocate Frame Buffer at ISA memory Hole at 15-16MB.

So, is there a way, how to use Linear Frame Buffer on Trident 8900 cards with 512KB VRAM? Is there a different program than Fastvid for that?
(second question is, if it is possible to load VBE extensions on Acumos AVGA2 (CL-GD5402) card somehow, different way then with UNIVBE tool)

Ok, my second question is answered. To my suprise, I've found out, that UNIVBE works with Acumos AVGA2, but you need to use older version. It was dropped in newest version 6.7.
I've tried 5.1 and it works. That contains VBE 2.0 only.

W.x. wrote on 2024-01-10, 15:50:

Acumos AVGA2 is only VBE 1.1 card, so UNIVBE refuse to install VESA VBE 2.0 extension
But it happens on Trident 8900CL. Even VBE 3.0 extensions are installed.

Is possible to use Linear Frame Buffer on ISA 512KB VRAM card, or 1MB Video RAM memory is ALWAYS needed as minimum?

You seem to misunderstand what VBE 2.0 or 3.0 implies. VBE 2.0 does not imply that you will always have a linear frame buffer. The linear frame buffer is an option provided with VBE 2.0, which need not be implemented for all modes, and in fact, a VBE 2.0 implementation reporting "no LFB support" for all VESA modes is perfectly compliant, as long as it recognizes all VBE 2.0 API calls and properly rejects every optional functionality it does not support.

There is no general minimum amount for LFB support. Even a card with just 256KB of RAM could support LFB for easy access to the video memory in 640x400 at 8bpp. The 4bpp modes heavily rely on the VGA memory interface logic and often do not support LFB access.

And last but not least, it is possible for a protected mode kernel to implement a "virtual linear frame buffer". In this case, the application gets the address of a linear frame buffer, but only 64KB of that buffer is actually accessible, and remapped to the standard VGA memory range. As soon as the application accesses a different part of the linear frame buffer, the kernel catches the exception, re-banks the VGA memory, re-maps the memory in a way that the area accessed right now is permitted in the LFB range, and returns to the application. IIRC later UNIVBE versions implement this, which is great for marketing, and which makes Quake run in high resolution in cards without LFB support - but is not generally advantageous to performance. A notable example for "virtual LFB" is the Windows 3.1/95 graphics driver subsystem: Most SVGA drivers that do not support LFB (or operate with LFB disabled due to system incompatibility) rely on the Microsoft-provided VFB driver that implements the strategy I just described. During initialization of the graphics driver, VFB is requested to generate a virtual LFB given a pointer to the hardware bank switching funtion.