On 10/7/2011 8:08 AM, Michael J. Mahon wrote:
Are you saying that a SecondSight or Carte Blanche will correctly render an Apple display in which a "window" of a different video mode (say, hi-res) is created by synchronous mode switching within a page of a different mode (say, text)? That's a pretty tall order...
Can't comment on the Second Sight but the CB is definitely capable of this. Not sure if it will work with the default configuration - it's been a while since I designed it an I don't quite remember what made it to the release.
The simplest possible approach I used in the very first FPGApple was re-implementing the original Apple video hardware in configurable logic. No buffers needed - just scan the video buffer and display it. As long as the emulated 6502 is cycle accurate this should re-create all the video effects perfectly, switching or not.
The problem is that this requires a video monitor that supports 16 MHz line rate. Not many did in those days. So the next step was to double scan the lines at 32 KHz. Worked great with an analog VGA monitor, but looked horrible on LCD - the pixel clock of 14.xx MHz didn't map well to any VGA rate. The solution was to buffer each line and scan at 25 MHz. This of course sacrifices compatibility with trick video modes even more but provides great text and standard graphics on an LCD.
If I had to implement as good an emulation of the video as possible today on modern LCDs I would probably target the new breed of TV/monitors. In addition to DVI and VGA some have component video inputs. Generating RGB (or YPbPr) at Apple native NTSC rate with improved sync it not hard at all.
-Alex.