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Zer0-X
Registered: Aug 2008
Posts: 78 |
VSP crash (not solved yet)
I recently found my C64C to be very prone to crash with certain demos and finally managed to create a reproducible crash while banging the $d011 register so I hooked up my logic analyzer and here are some logs of the event taking place.
http://oms.wmhost.com/misc/VSP_Crash_100MHz.zip
A testprogram was looped at address $0ff0. It could've been placed at pretty much any $xxf0 address and it still would crash within few seconds. Running the code at lower offset on the memorypage quite effectively prevented it from crashing on the machine used for testing. A shorter version with only inc/dec/inc/jmp not crossing the page boundary crashes.
The symptoms were always the same; low address byte of the 2nd inc at $xxf7 and/or the opcode of the jmp at $xxff are suddenly trashed. The byte at $xxf7 ends up being 0x00, 0x01, 0x10 or 0x1d. Byte at $xxff ends up being 0x0c, 0x40, 0x48 or 0x4d.
As a post-work the decoupling caps of the memorychips in the C64C used were replaced and a new thick wire delivering power directly to the memorychips was soldered in place. This had no effect and the machine still crashes with this code, as well as with Booze Design demos Royal Arte and Tsunami for example. Powersupply used is a C128 PSU with C64 powercable soldered next to the C128 powercable.
Logfiles VSP Crash 100MHz 3_31.csv/txt have the actual crash event taking place.
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lft
Registered: Jul 2007
Posts: 369 |
Remember that the VSP crash could occur even when we don't deliberately try to use VSP. For instance, consider a very simple up-scrolling game that does everything by the book and doesn't even have a raster interrupt. It would still have to change YSCROLL from 3 to 0 during initialisation, and if this happens during the visible portion of rasterline $30 (and there's a 0.2% probability of this), it could trigger a VSP crash. So it is a real bug (in the sense that specifications are violated) that some machines have. Do we fix those machines or do we avoid changing YSCROLL? |
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raven
Account closed
Registered: Jan 2002
Posts: 137 |
Shadow: You'll be surprised how many demos don't work on my 128D due to loaders that don't like the 1571 drive.
A few recent examples are "Trick and Treat" and "Edge of Disgrace".
With other demos there are random crashes after file loading ("Artphosis" and "Vicious SID 2" are such examples).
As for VSP, since the 80's I owned or had access to over 50 different C64 and C128/D machines.
I still haven't found a machine that would crash with VSP and I tried really hard to find one back when testing "Insomnia", which uses VSP quite heavily.
My only assumption is that these machines are rare, which is why I don't think VSP should be "banned" :)
I agree with Oswald, get a machine that can handle it ;) |
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Oswald
Registered: Apr 2002
Posts: 5021 |
"I still haven't found a machine that would crash with VSP "
maybe try older ones. back in the days I had an old sid machine which couldnt handle it at all.
btw, another funny thing happened once at one of my friend, the machine did not erase its ram on a power cycle. some game screen came back over and over again (more and more trashed), while we tried to get the basic prompt by power cycling :) |
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Shadow
Account closed
Registered: Apr 2002
Posts: 355 |
No fucking way - I've had my C64C for 24 years now and it will remain my main machine forever! :P
I actually bought an old breadbox C64 just to be able to watch demos using VSP-crap but it just didn't feel right somehow, graphics output not as crisp, sound not as good.
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chatGPZ
Registered: Dec 2001
Posts: 11123 |
that often happens with certain batches of machines that have chinese ram chips (which hold their data for literally seconds without power) |
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Danzig
Registered: Jun 2002
Posts: 429 |
Quote: "I still haven't found a machine that would crash with VSP "
maybe try older ones. back in the days I had an old sid machine which couldnt handle it at all.
btw, another funny thing happened once at one of my friend, the machine did not erase its ram on a power cycle. some game screen came back over and over again (more and more trashed), while we tried to get the basic prompt by power cycling :)
I got such a machine, too, (my first C64 (C64C)) and I could switch it off, wait 2 minutes, switch it on and still start V3-Turbo with Sys. BUT that machine suffered from VSP-bug IMMEDIATELY! I have seen lots of demoparts years later on other peoples machine :/ The mentioned "feature" was the fact that I never believed the "ram-refresh is fuxxored"-explanation about VSP. In my head there is still the simple rule of thumb: "Breadcase=VSP works - Any other case including C128=VSP crashes" I never ever had a Breadbox that crashed on VSP. |
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raven
Account closed
Registered: Jan 2002
Posts: 137 |
Oswald: most of my C64's are the old type (breadbox), only have a few C64C. |
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Zer0-X
Registered: Aug 2008
Posts: 78 |
I just had to try it. I put 8565R2 into a breadbox and couldn't get that to crash. I also put 6569R3 into the new board (running from SIDs 9 volts just fine) and so far haven't been able to crash that one either. |
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encore
Registered: Aug 2010
Posts: 61 |
Quoting Skate@encore: i wish i knew who Bil Herd was. :))) http://en.wikipedia.org/wiki/Bil_Herd |
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Oswald
Registered: Apr 2002
Posts: 5021 |
uhh, Bil Herd is one of the greatest C= engineers, designed single handedly the TED machines, c128, and more. read "on the edge" its a must :) |
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