I'm trying to use VESA 2.0 modes with linear framebuffer with this ISA graphic card. The idea is to run certain software (like my port of C-Ray32 for DOS: C-Ray 32 : a FPU intensive benchmark for retro PCs testing ) on OLD pre-VLB/PCI motherboards

Both the chip (Cirrus Logic GD-5434) and the card support LFB operation. The only caveat is that ISA cards have the memory address limited to 16MB, but this is not a problem because I don't install more than 8 x 1MB memory sticks and these old motherboards also support a 1 MB "hole" in the memory address range exactly for the purpose of mapping external memory present on add on card.

I'm using SciTech's Display Doctor 5.3a to enable VESA 2.0 modes. The software reports that has created a LFB at 14MB (on newer VLB/PCI cards usually the LFB is located much higher in memory, but this is expected)

If I run any software using VESA 2.0 LFB modes, however, all I get is a blank screen. The card is actually outputting the required screen mode (checked with the monitor OSD utility that displays resolution and frequency of the VGA signal). Note also that the program DOES run, but any output is simply not shown. For example, the afore mentioned C-Ray benchmark is doing its number crunching routines and, when it has finished, it reverts back to text mode to display the execution time in seconds.

The same happens i.e. with Dos Quake. VID_DESCRIBEMODES lists all of the available VESA 2.0 modes, but when I choose one with VID_MODE, all I get is a black screen. If I've sound enabled and run a demo, I can hear the sounds. That means that Quake hasn't crashed: whatever it sends to the screen is -simply- not displayed.

Any idea? I've tried with two different motherboards with different chipsets, so there's something else I'm missing...