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Riddle me this: in KUKOO2 demo, on ARK1000PV & S3 Trio 64V2/DX the VGA palette is correct via FC, but not via VGA?

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First post, by clb

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Here is something quite peculiar that I discovered while running signal stability tests on CRT Terminator Digital VGA Feature Card ISA DV1000:

when I run the KUKOO2 demo, I observe that on Hercules Stingray Pro card with ARK1000PV chip:

The attachment HerculesStingrayProARK1000PV.jpg is no longer available

as well as on S3 Trio64V2/DX:

The attachment S3Trio64V2DX.jpg is no longer available

the graphics palette does not show up correctly. On both cards, the background colors are missing:

ARK1000PV via VGA:

The attachment KUKOO2_vga_output_palette_broken.jpg is no longer available

and S3:

The attachment KUKOO2-S3-missing-colors-on-vga-output.jpg is no longer available

but when I observe the demo on CRT Terminator via the Feature Connector line, both of these cards show the palette colors in the demo properly:

The attachment KUKOO2_HerculesStingrayProARK1000PV.png is no longer available

The raster bars that are missing from VGA are seen properly here. I presume they are racing the scanlines, but how on earth would that specifically just work on FC, but not on VGA? Weird.

I haven't observed any other palette omissions or discrepancies on these two cards on any other games or apps, just this demo.

Reply 1 of 1, by mkarcher

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l33t

The Feature Connector is on the digital end before the RAMDAC. The CRTC terminator has its own palette implementation (it relies on "palette snooping" to know what's on the VGA palette). For some reason, the KUKOO2 demo implements raster bars in a way that is compatible with the CRTC terminator, but incompatible with the ARK1000 and Trio64 palette implementation. One idea that comes to mind: You need to set up palette reads differently than palette writes. Some cards don't care if you use the wrong setup procedure, while other cards do. So maybe KUKOO2 sets up the RAMDAC for "read color 0" and then is going to write RGB values.

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