[atari7800] Re: DMA TIMING

  • From: "Mitch Orman" <Msorman@xxxxxxxxxxxxx>
  • To: <atari7800@xxxxxxxxxxxxx>
  • Date: Fri, 5 Nov 2004 18:29:10 -0800

The whole picture is kind of jumpy as well. The picture seems to be a bit
shorter then the last version, as well, hence the garbage at the bottom of
the screen.


-----Original Message-----
From: atari7800-bounce@xxxxxxxxxxxxx [mailto:atari7800-bounce@xxxxxxxxxxxxx]
On Behalf Of Ken Siders
Sent: Friday, November 05, 2004 6:19 PM
To: atari7800@xxxxxxxxxxxxx
Subject: [atari7800] Re: DMA TIMING

Picture looks pretty much the same as the one posted on atariage that 
someone posted of a screen capture.  Pressing fire changes the color of 
everything from redish to purplish.  The sprites are not visible at all.
There is some flickering garbage at the very bottom of the screen.

----- Original Message ----- 
From: "Christopher Tumber" <christophertumber@xxxxxxxxxx>
To: <atari7800@xxxxxxxxxxxxx>
Sent: Friday, November 05, 2004 9:02 PM
Subject: [atari7800] Re: DMA TIMING

>>It appears that the Indirect cycle counts include the character map access
> Yeh, it must be 3 cycles per byte, regardless of character or sprite and 
> the only difference is in the overhead.
> The only real remaining question is whether or not reading the bitmaps 
> from RAM gives a performance boost or not (2 cycles instead of 3 cycles 
> would rock!)
> Attached is the latest version on my layered scroll. I've made some 
> changes that should tell us if RAM vs ROM makes a difference.
> - The DLL, DLs and character map are in RAM
> - The bitmaps default to ROM
> - Pressing and holding the fire button switches to RAM bitmaps. This also 
> inverses the palette so it should be obvious. (Releasing returns to ROM)
> - In addition, I've added 17 sprites in the middle of the screen, just to 
> see how they behave (ie: how many sprites can go over 320x2 characters). 
> They also switch from ROM to RAM. They're only 2 byte sprites, but should 
> be a decent test (17 'cuz that's how many fit my DL without moving stuff 
> around in memory)...
> Strangely, the sprites are not transparent and I'm not sure why that is. 
> It's not the Kagaroo bit as setting that is obvious and affects the scroll

> layers. Maybe a MESS problem? But other games must uses sprites over 
> character??
> Anyway, you have a CC2, right? Would you mind...?
> If reading from RAM makes the difference, then cool, it works! If not, 
> well, it'd definately be possible in 160x2. But to me 160 modes are just 
> glorified 2600 graphics. 320x2, however, kicks NES ass!
> Ah well, we'll see... I had a completely different idea today that could 
> really show off the 7800's capabilities. If this doesn't work I might 
> change gears completely. Or do both. I dunno...
>>With two bytes per character, we only need two 5 byte headers,
> That's a really good point, if it's close, I can maybe eliminate some 
> overhead by going with 2 byte characters and dropping some headers.
> Chris...

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