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Radiant
Registered: Sep 2004
Posts: 639 |
FLI and stable raster
Ok, now I'm starting to tire of this. :-)
Several people claim, and I have no reason to doubt them, that you don't need a stable raster to do FLI, because, "FLI is self-stabilizing". What does this mean, exactly? I've coded FLI routines, but I've always utilized an already stable raster (since you need to time the $d011 write to cycle 14 of each FLI raster line). I can't for the life of me figure out another way of doing FLI than actually writing to $d011 at cycle 14, and in order to do so you need a stable, predictable raster.
I guess my question is; where am I thinking wrong? |
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Cruzer
Registered: Dec 2001
Posts: 1048 |
I think it stabilizes after the first line or something. Typically you'll have the FLI bug jittering a few cycles at the first line and after that it's stable. There are also cases when the whole thing jitters, but that can quickly be fixed by inserting some nops before the first d011 sta. Haven't wondered too much about this, since it always works, but I guess FLI's self-stabilizing feature is caused by the DMA delay being reduced by the number of cycles that the first d011 sta is "too late" compared to normally. E.g. if you store it 10 cycles too late, the FLI bug will be 10 char bigger, and 10 chars less will be fetched, causing the delay to be 10 cycles less.
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Radiant
Registered: Sep 2004
Posts: 639 |
Cruzer: Wouldn't delaying it into cycle 15 or more cause normal VSP? |
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Danzig
Registered: Jun 2002
Posts: 429 |
some people even used writing to $d011 based on the actual rasterline and then back to $?b afterwards to GET stable raster :P quite a "single pixel fld" |
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HCL
Registered: Feb 2003
Posts: 716 |
Yeah, that's how i always made it in 1992 :). trigger a badline with sta $d011 with #$7x, then back to #$1x or whatever visible. |
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Radiant
Registered: Sep 2004
Posts: 639 |
But you lose height that way! OMG! OMG! :-)
Please disregard my previous post; of course you won't trigger VSP unless the VIC is in idle state. I blame teh tired. |
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cavey
Registered: Jul 2002
Posts: 68 |
something like:
ldx #$7x
lda $d011
stx $d011
sta $d011
?
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