BALL VDEL

[Mord]

Could someone explain to me how the ball Vertical delay works? VDEL for P0 and P1, if I read the mini-dig correctly, works by writes to GRP0-A causing the contents of GRP1-A to be copied automatically into GRP1-B and vice versa. So if VDEL was turned on for P1, you'd get the delay that way... But how does the Ball work?

 

I've done a bit of testing with what I was doing and VDEL is indeed the cause of the ball triggering like 1/3 of the screen lower than it should. (I was hoping for a single scanline later but... )

[SeaGtGruff]

I've done a bit of testing with what I was doing and VDEL is indeed the cause of the ball triggering like 1/3 of the screen lower than it should. (I was hoping for a single scanline later but... )

I haven't tried it myself (and I, too, have always wondered how it works), but it should be based on a similar kind of logic as VDEL for the players-- e.g., maybe it delays the updating of the ball until you write a new value to one of the playfield registers???

 

Michael

[vdub_bobby]

What triggers writing to the visible ball when VDELBL is on is writing to GRP1.

 

Same as VDELP0.

[Mord]

What triggers writing to the visible ball when VDELBL is on is writing to GRP1.

 

Same as VDELP0.

 

Ah bugger. Looks like it's back to the code for me. This shows I'm somehow avoiding to write to GRP1 or GRP0 until so far down in the line when it should be writing to it alternately every scanline regardless - even if it's just a #0. Saw a miss in the initial write to GRP1 that followed the ball setting for instance and sure enough... Where I see it trigger almost 1/3 down the screen, that -should- be where one of the objects begin to show (Neither do at present, going to look into that tonight after I clear up the ball.)

 

Tankye. This gives me something to look into.

Edited November 27, 2006 by Mord