EricBall's Tech Projects - 7800 cycle counting

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I've done some cycle counting of the display list builder for SpaceWar! 7800 and the results aren't pretty:

 

103 cycles per display list (25 NTSC, 30 PAL)

403 cycles per player sprite, +191 for horizontal wrap around

248 cycles per non-player sprite, +82 for horizontal wrap around

50 cycles per sprite header vertical wrap around

200+ cycles of overhead

 

At 114 cycles per raster, just the display list builder is going to chew through all 62 lines of VBLANK.

 

So, what to do?

1. Optimize where possible, but otherwise ignore it and risk having the display stutter.

2. Alternate frames building display lists and game processing. I'd need to recalculate (or fudge) all of the gravity & velocity tables since it would be effectively 30fps instead of 60fps.

 

#2 sounds feasible, just need to add the DLI wait routine after the display list builder.

 

Note: SpaceWar! 7800 doesn't do itself any favors when it comes to the display list builder:

1. 4 way scrolling tiled background

2. 4 way wrap around

3. player sprites are double height versus the zones

 

 

 

http://www.atariage.com/forums/index.php?a...;showentry=3089