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Shadow
Account closed
Registered: Apr 2002
Posts: 355 |
How to find a C64 capable of HW-scroll?
I have had my C64-C for more than 20 years, and I love the thing.
However, it always, ALWAYS locks up on hardware scrolling effects (VSP/AGSP or whatever it is called).
That meant that I could never watch for exaple the Horizon demos with large x/y scrolling pictures back in the day.
Then there was the 'pc-style' period from 1994 and the rest of the nineties where demos wasn't using such tricks much more, and all was good.
Lately though I have seen more and more demos use the hardware scrolling tricks again, which means lockups for me and not being able to watch the demo.
The fact that I am pissed of that people use code that is not compatible with all C64s will probably not make much difference, so I guess I am forced to track down another C64, but how do I make sure that it can cope with hardware scrolling?
I think it is a question the average eBay seller is unable to answer, but maybe there is something I should look for? Are old breadbox ones generally better? |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
I've never seen a demo crash on my first C64.
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Shadow
Account closed
Registered: Apr 2002
Posts: 355 |
OK, this is just plain weird. I have tested with "1 Year Totally Stoned", and the AGSP part runs without problem (tested three times, let it run for a minute or so)!
However the vector part that followed messed up two times out of three tests, almost as running the AGSP before it has somehow put the computer in an unstable state... However there is a loading break in between, so that seems unlikely that any memory corruption would carry over. Strangeness...
Oh and Jackasser - had I lived closer to Lund I would totally have brought my machine for some measuring. Perhaps if there is another BFP/LCP nearby sometime...
-edit- OK, now I was able to watch Royal Arte from start to finish without problems as well! I used to get lockups in the DYCP part. Maybe my C64 got the feeling that I was going to replace it and got its act together! :D |
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HCL
Registered: Feb 2003
Posts: 716 |
@Shadow: Yeah, i think you're right about the feelings of your c64 ;). But that test you made sort of sums up my view of this problem also. VSP on the top of the screen, like the bitmap mover (AGSP.. hate that abbreviation..) in "1 Year Totally Stoned" is less error prone than VSP somewhere in the middle of the screen, like the vector-part after. Strange but true. |
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Shadow
Account closed
Registered: Apr 2002
Posts: 355 |
HCL: Ahh.. The vector part uses VSP as well, didn't realize that. |
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Codey
Registered: Oct 2005
Posts: 79 |
Quote: The $d021 bug on new VICs also only occurs sometimes on some machines. When it occurs, it's "persistent" until power off, regardless of resets. And when it doesn't occur, it doesn't occur until power cycle.
Lotus has a machine that toggles this bug every second time on average. Now, back when we discovered this, we didn't know about the $d011 bug. If this particular c64 is prone to the $d011 bug, and someone could give a demo example which exposes both the $d021 and the $d011 bug it just migt be interresting to see if the two bugs are related.
i had a breadbox 64 that would crash on vsp routines after a period of time.
what exactly is the $d021 bug? |
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assiduous
Account closed
Registered: Jun 2007
Posts: 343 |
Quote:what exactly is the $d021 bug? loop lda#$00 sta $d021 jmp loop gives random gray (half)pixels on the 8565 VIC-II chip. |
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Danzig
Registered: Jun 2002
Posts: 429 |
Quote: @Shadow: Yeah, i think you're right about the feelings of your c64 ;). But that test you made sort of sums up my view of this problem also. VSP on the top of the screen, like the bitmap mover (AGSP.. hate that abbreviation..) in "1 Year Totally Stoned" is less error prone than VSP somewhere in the middle of the screen, like the vector-part after. Strange but true.
i agree! in an old x-rated intro doom used vsp on the top of the screen to move a little X-R bitmap. that intro worked even on my first c64c that fuxxored usually on any vsp. he also used vsp to compensate it later on the screen but coded "in the same way". whatever that means for the discussion. it might also depend on "the width of the wank", i never spotted fuxxor with accidently happening vsp when doing f.e. fli without stable raster before. that said, the vsp from doom was also only about 10 to 12 chars wide °":) (iirc!)
EDIT: i quicky found it: its in here (the metallica like XR)
Examples 4 AFL
[/url] |
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algorithm
Registered: May 2002
Posts: 702 |
Quote: Quote:what exactly is the $d021 bug? loop lda#$00 sta $d021 jmp loop gives random gray (half)pixels on the 8565 VIC-II chip.
Funnily enough this bug sometimes disappears after power off/on on the same machine.
VSP seems to crash more easily when the grey pixels appear. Its not just a $d021 bug, same issue for $d020 with the same color. |
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HCL
Registered: Feb 2003
Posts: 716 |
My c128 *always* shows those d020-d021-bugs, but with the VSP-bug it's totally different. I remember i had to heat it up for ~5 minutes before i started to code on my VSP-shit (and that was totally the coolest shit you could code by then), and then i had about 30-45 minutes to work when the VSP-bug didn't appear as frequently. Then it started to ruin the memory, and if i didn't save before that, it was all lost :D. Madness!! Especially during "1 year totally stoned" that was my every day madness.. |
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algorithm
Registered: May 2002
Posts: 702 |
Yes VSP was a nightmare. I remember my poor C64 setup. AR cartridge and Tapedeck. Had to turn off and on c64 multiple times and to run a VSP crash tester until the machine did not crash to continue coding something VSP based.
Have mentioned this quite a few times but i had purchased a reject c64 with a new powersupply and using this new powersupply, every single vsp part worked with NO CRASHES on the same c64 that had problems initially with the previous psu.
It certainly must partially be a Power related issue as well although not sure how VSP sometimes worked when cycling power off/on using even the older psu. |
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