C64 - timing(?) problem in The Space is Broken demo

[F-RX]

I found a C64 core synchronization problem in Space is Broken - great demo by FAIRLIGHT.
In some scenes, artifacts appear that are not visible on real hardware or in the VICE emulator.
https://csdb.dk/release/?id=234768
https://www.youtube.com/watch?v=M2fCRbLwU74
On C128 the demo works fine.

[gyurco]

mist-devel/c64@fe99275

[sorgelig]

@gyurco thanks!

[sorgelig]

should be fixed in upcoming unstable/nightly build

[F-RX]

Thanx a lot :)

[paich64]

@gyurco @sorgelig @F-RX I was testing an our established list of demos before considering pushing this fix in the Mega65 C64 core (which is a port of the mister core). We have a few demos having visual glitches (the same as on mister). So i compared the behviour with and without this fix on mister, and it obviously introduces a regression in at least one demo :

https://csdb.dk/release/?id=198283

in this XMAS mega demo we have a visual glitch on both Mister and Mega65 C64 core which you can see here :

https://www.youtube.com/watch?v=OUUgmUE7avs&t=17s

in the bottom right corner 4 black pixels are showing up during a few seconds, while the expected behaviour is the following :

https://www.youtube.com/watch?v=p0ddV07WC8o&t=561s

With your new fix, we now get an even more unexpected behaviour : The top and bottom borders which are supposed to be opened, now get closed and the Star at the top of the screen gets now half hidden :

Can you guess what could be the link between your fix and this unexpected behaviour ?

Thanks,
Olivier.

[gyurco]

Try this:
mist-devel/c64@17c452b

[paich64]

@sorgelig could you backport to mister so that i can test on mister ? thanks !

[makigumo]

Thanks, this seems to fix the XMAS demo issue.
Below is the patch adapted to mister. Apply with git am 17c452b94a37c4eda3d4080c0daf018c6a1a022f.patch.

17c452b94a37c4eda3d4080c0daf018c6a1a022f.patch

[paich64]

@makigumo many thanks will ask the person generating the core for me to provide a fixed build

[sorgelig]

i've pushed the changes

[paich64]

@sorgelig @gyurco @makigumo Many thanks, Xmas Megademo 2020 is back to its original state (the little glitch is still here but top/bottom borders are now again opened) and Fairlight demo is still fixed.

I will keep testing demos on the Mister and report if i find a demo with regressions.

[paich64]

@gyurco @sorgelig @F-RX @sy2002
while the fix seems to have no side defect on a few other tested demo, I have to report this regression :

Plush 1997 +H2K (https://csdb.dk/release/?id=11755)
=> while this demo has allready known issues :

• disk flip not detected (on Mister only)
• visual glitch 1 (https://www.youtube.com/watch?v=GeShKqdEc50&t=22s)
  expected behaviour (https://www.youtube.com/watch?v=XbpJA-SQ-5Y&t=10s)
• visual glitch 2 (https://www.youtube.com/watch?v=GeShKqdEc50&t=229s)
  expected behaviour (https://www.youtube.com/watch?v=GeShKqdEc50&t=220s)

The fix introduced another slight glitch :

On the picture, the 2 circled rectangles will shortly blink while it does not happen without the fix.

I know that this demo is old, has already known glitches, but it's an additional one, and even it's not the best demo out there, we can't garantee for sure that it will no impact other demos. I also recognize it's probably very complex to figure out why we have another additional slight glitch.

In such a situation it's quite complex to decide what to do and i won't have time to run our full 180 demos benchmark.
This will be done when we are done with our own C64 core refactoring on Mega65 [we first want to ensure our refactoring doesn't introduce new issues and then only we will consider this fix and run of course the whole 180 demos benchmar].

If you have any idea about what could produce this additional glitch ...

Olivier.

[paich64]

@sorgelig @gyurco @makigumo @sy2002
To be as much clear as possible :

• If we call FIX1 the original fix provided to fix Fairlight demo (and which broke the Xmas Mega demo)
• if we call FIX2 the fix provided on top of FIX1 and which fixed Xmas Mega demo

Then +H2K was broken by FIX1.

though it was not fixed by FIX2 as Xmas Mega demo was.

Also, while so far i only tested our 180 demos bench on the Mega65 C64 core i will probably consider at some point to perform the same tests with Mister Core each time you provide a Fix. I just have to include this in my schedule.

To be as much clear as possible : We have a huge milestone in the pipe for the Mega65 C64 core. We are currently refactoring it and we want to be sure that in case of regression it's only related to our refactoring and not related to this addional Fix you have provided. When the refactoring is done and we know we did not introduce regressions, then we will obviously test this Fix with the MEGA65 C64 core. I will have to run again an inspect each and every single demo of this 180 demos bench.

I will do this for the Mega65 C64 core and the C64 Mister core.

Olivier.

[gyurco]

This should fix the regression:
mist-devel/c64@a04e0d9

The shaking at the beginning is a problem of a stable raster, I'm not sure how to fix it without breaking everything else (if the raster interrupt is fired one cycle earlier or later, then the scene is fixed, but a lot more is broken).

[sorgelig]

This should fix the regression:
mist-devel/c64@a04e0d9

pushed