Display Lists and Scanlines Question

[Mord]

Trying to wrap my mind around a few things.

 

"There are a total of 262 rasters per frame (1/60th second). The "visible" screen (during which MARIA attempts display) starts on raster 16 and ends on raster 258."

 

 

What happens if when you set up your DLLs that it doesn't hold enough zones to cover the entire 242 lines Maria tries to do stuff.

 

What happens if you set up your DLLs and it tries to cover more than 242 lines?

 

My assumption would be that in the first case it'd just stop displaying things for the rest of the frame. In the second case it would get cut off after the first 242 lines are cleared, then it would get reset to the beginning of the DLL again at the start of the next frame. (Meaning the excess lines/zones are simply ignored/wasted)

 

Am I correct, or does something else happen.

[RevEng]

Unlike the DLs, the DLL doesn't have an end marker. If you don't have enough line coverage, Maria will keep pulling bytes after your DLL and will interpret them as DLL data. This can result in random garbage being displayed and/or crashing or unexpected behavior from NMIs being triggered inappropriately.

 

Having too many DLL lines defined is fine. As you surmise, Maria just gives up after displaying its fill. (NTSC=243, PAL=293) For this reason, if you're making an NTSC game, its a good idea to give it enough blank lines so it will run nicely on a PAL console. (bonus points if you detect PAL and center your display vertically)

[PacManPlus]

Excellent explanation - I was coming here to try and explain, but you did it better than I ever could.

[RevEng]

Thanks, Bob!