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White Flame
Registered: Sep 2002
Posts: 136 |
VSP/DMA delay compatibility
I've been playing around with these routines lately, and remember hearing that some older C64 models couldn't properly do this effect without bugging all over or locking up. Is that really worth worrying about, or can I write a small game or demo using VSP and simply assume it'll work on basically every 64? It autodetects the cycles per line of the chip being used, so the various VIC-II flavors should theoretically all work. |
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WVL
Registered: Mar 2002
Posts: 902 |
I've noticed that the speed at which you shift the screen matters a lot. If i make a routine that shifts the screen to a certain position and just holds it there, I almost never experience crashes. When I make the same routine shift the screen very fast all over, I experience a lot of crashes.
-> make the game move the screen slow, is the only remedy on some c='s, dont ask me why though. |
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algorithm
Registered: May 2002
Posts: 705 |
The VSP trick probably interferes with the C64 Ram refresh?. A C64 with a worn out power supply will experience crashes when using the screen shifting trick. I had the same problem when coding VSP. With the purchase of a new power supply all the crashes disappeared!
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WVL
Registered: Mar 2002
Posts: 902 |
anyway : if you use VSP in a demo only use it at the beginning, and make a selector, so you can skip it. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Anyway, what is VSP? Variable Screen Positioning? On a C64? Or is this some special 128 or Vic20 stuff? |
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Stryyker
Registered: Dec 2001
Posts: 468 |
Standard C64 can do VSP. IT's just some $D011 trickery. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Haha, ok. So VSP is just a newsk00l name for the standard forced badline conditions? |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
a term which has been established in 1987 isn't really "newschool". also, it's not just forced badline condition, but some specific way to use it. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
=) OK. |
