[atari7800] Re: DMA TIMING

  • From: Christopher Tumber <christophertumber@xxxxxxxxxx>
  • To: atari7800@xxxxxxxxxxxxx
  • Date: Tue, 02 Nov 2004 14:01:21 -0500

>yes - indirect mode = character mode.

Okay, so then does that mean:

Sprites: 3 cycles per byte
Characters: 9 cycles per byte (1 byte characters)
Characters: 12 cycles per 2 bytes (2 byte characters)

Plus overhead (Startup, Headers, Shutdown)

>iirc it just states that DLL's and DL's must be in ram.

Okay, then can they be in ROM, but with slower access and therefore more time 
spent in overhead which equals less time for sprite/character display? Or does 
putting them in ROM "break" DMA?

Is there any benefit then to putting bitmap data into RAM? It should be read 
faster then, no? (ie: Are the timings I've listed above for sprites/characters 
for ROM or RAM or does it make a difference?)

The attached file works on MESS but not on a real 7800 due to the DMA timing 
(uses character mode which is, apparently, prohibitively slow). However, if I 
can get 2 cycles per byte (in sprite mode) then it should be possible if I 
"simply" rework it as sprites.


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