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Valentin Angelovski
Valentin Angelovski's picture
Joined: 12/24/2010
Odd aspect screen modes..

Hey Bill,


Can you go into a bit more detail about the "slightly squashed" screen aspect on some of those 320x200 modes? Like what the issue is and why it's like that?

Sure.. main reason for the odd screen aspect has alot to do with increasing the emulation speed - most of those games in my YouTube demos were really meant to be played on a '286 and up. Therefore, in order to give the Flea86 a little boost up into 286 territory for some of those games I basically had to do two things:

1.) Increased the host CPU clock on the Flea86 by around ~20%, so I basically used up all my margin reserved for overclocking..
2.) Increased the screen resolution of the VGA output to 800x600, with 400 viewable lines or 66% of the total screen area, this squeezes another 15-20% emulation performance overall, since the host CPU is no longer writing to ~83.3% of the screen area as per default.. You might recall the old ZX-81 had a feature where that computer blanked the display when it really had to 'think'.. well it's pretty much the same issue here..

Both of these changes push the Flea86 to nearly an IBM-AT level (6MHz 80286) of performance, with the downside of course being the odd screen aspect..

Of course, I can revert to the original 640x480, with 400 viewable lines or 83.33% of the total screen area, but at a slower emulation rate with action games like Gods/Wolf3d suffering most from any slowdown..

The only real solution for this is either:
1.) Faster system RAM, which is more expensive though perhaps worth it, or..
2.) Upgrade the host CPU to a more powerful 32-bit model..

Regards Valentin


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