ECS' Workbench color limitations?

[utri007]

Havin OS open with screen resolution 320 x 256 gives possibility to use OS with 32 colors. Using hires modes drops colors to 16.

Question is where this limitation comes? Is it by hardware or software?

Would it be possible hack WB to use 32 colors or even Halfbrite 64 colors mode?

There is P96 and FBlit to reduce Chip ram usage generated higher number of colors.

[Daedalus]

It's a hardware limitation. The display data is "fetched" from chip RAM using a finite number of DMA slots on every line. There's a limit to how much information the chipset can fetch during these slots, and when the screen is 640 pixels wide there's only enough time to fetch 4 bitplanes' worth of colour information (and takes up every available slot in doing so). Dropping the screen width to 320 pixels halves the number of DMA slots required for each line, allowing all 6 bitplanes' worth of data to be fetched.

[utri007]

Originally Posted by Daedalus

It's a hardware limitation. The display data is "fetched" from chip RAM using a finite number of DMA slots on every line. There's a limit to how much information the chipset can fetch during these slots, and when the screen is 640 pixels wide there's only enough time to fetch 4 bitplanes' worth of colour information (and takes up every available slot in doing so). Dropping the screen width to 320 pixels halves the number of DMA slots required for each line, allowing all 6 bitplanes' worth of data to be fetched.

Thanks, for a good explanation. It would have been weird if it had been hackable, and nobody would have done it already.

[SpeedGeek]

Originally Posted by utri007

Thanks, for a good explanation. It would have been weird if it had been hackable, and nobody would have done it already.

Circa 1990 and just before Commodore announced the A4000 with the AGA chip set. Newtek and Lake Forrest Logic created a new display mode called "Dynamic Hi-Res".

This was a hack which used the CPU to modify the palette on each scan line. This allowed 4096 colors to be displayed on a high res (4 bit plane) screen. It would probably not be a useful hack for displaying a workbench screen because of the slow screen updates, but just because it was never implemented that doesn't mean it can't be done.