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whitebird · 08 September 2010, 20:25

Thanks all for your answers.

What I understand is that some (most) amiga games and demos use amiga specific resolutions/refresh rates. So those programs need for example 50Hz refresh rate to run synchronously, and it would be difficult to accomodate higher refresh rates because VBL will occur more often, so everything would go out of sync.

But to display a desktop or internet content, the timing constraint isn't crucial and this can be done through a VGA board connected through a PCI mediator.

To be able to play games and watch demos on an amiga with PCI board, we still must consider the signal coming out from the RGB connector, pass it through a PAL => VGA converter (like SCAN DOUBLEUR) which changes (X2) the timings so that it can feed a VGA display.

So if I understand well, amigas with PCI graphics have dual display, that works fine for desktop etc... but for games only the RGB is usable? Right?

For me there are two different problems with video:

1. Software pixel drawing is purely a logical concept. It fills some memory but has nothing to do with video signal timings.

2. Hardware scrollings, dynamic changes of color are video signal clocked. So it needs the native video timings. To output correctly, the VGA board, need to:

-Receive the video memory content built by amiga chips under PAL timings or
-Convert the video timings to VGA. (have an internal SCANDoubler built arround an FPGA for example)

Hope I understand well the challenge...

08 September 2010, 20:25	#6
whitebird Registered User Join Date: May 2006 Location: France Age: 48 Posts: 211	Thanks all for your answers. What I understand is that some (most) amiga games and demos use amiga specific resolutions/refresh rates. So those programs need for example 50Hz refresh rate to run synchronously, and it would be difficult to accomodate higher refresh rates because VBL will occur more often, so everything would go out of sync. But to display a desktop or internet content, the timing constraint isn't crucial and this can be done through a VGA board connected through a PCI mediator. To be able to play games and watch demos on an amiga with PCI board, we still must consider the signal coming out from the RGB connector, pass it through a PAL => VGA converter (like SCAN DOUBLEUR) which changes (X2) the timings so that it can feed a VGA display. So if I understand well, amigas with PCI graphics have dual display, that works fine for desktop etc... but for games only the RGB is usable? Right? For me there are two different problems with video: 1. Software pixel drawing is purely a logical concept. It fills some memory but has nothing to do with video signal timings. 2. Hardware scrollings, dynamic changes of color are video signal clocked. So it needs the native video timings. To output correctly, the VGA board, need to: -Receive the video memory content built by amiga chips under PAL timings or -Convert the video timings to VGA. (have an internal SCANDoubler built arround an FPGA for example) Hope I understand well the challenge...