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Slowdown in games
Posted: Wed Oct 28, 2020 8:29 am
by redmoonlevel9
I experience a lot of slowdown in a few cores on games that I wouldn't expect it.
I'm curious about it since in theory if the fpga is emulating the clock/memory and bus speeds then should it not be identical to the original hardware?
A case in point is Rainbow Islands on the Amiga, there's a ton of slowdown in it and the game overall feels like it's running at a few fps lower than it should.
I have it on my original hardware and so can directly compare it and it's definitely slower - if you reach the top of the first level, when the prizes come out of the chest it starts lagging badly but doesn't on my 1200.
Also I've noticed a lot of lag in some arcade cores (Strider for example) and the NeoGeo which almost makes them unplayable at times.
This is over and above any original hardware slowdown which I know the NeoGeo does suffer from in some games (i.e. metal slug).
So my question is if the mister is cycle-accurate how come it's slower than the original hardware?
Re: Slowdown in games
Posted: Wed Oct 28, 2020 8:41 am
by mahen
Hi ! Regarding Rainbow Islands on the Amiga, did you use the cycle accurate 68000 mode (from the floppy disk ?) or a WHDLoad install with the (not cycle accurate) 68020 ?
That's not supposed to be related but do you use the low lag vsync adjust mode ?
Re: Slowdown in games
Posted: Wed Oct 28, 2020 9:07 am
by redmoonlevel9
Hi, yes I did, I tried both actually and the results are very similar.
Although this isn't specific to Rainbow Islands on the Amiga, I experience it in other games and cores too.
It was more of a general question on clock, memory and bus speeds not translating to real-world performance.
I'm happy to see that graftgold games now work from by WHDLoad installation though, Uridium 2 runs perfectly but I think that was coded in a very slick manner.
I haven't adjusted the vsync mode, I'll give that a try, not sure if it has any effect running on a CRT though?
Re: Slowdown in games
Posted: Thu Oct 29, 2020 1:23 pm
by redmoonlevel9
VSync setting makes no difference as I suspected it wouldn't, I don't even think it's active when using VGA out.
So my initial question still stands, if the memory, cpu and bus speeds are the same why is the overall system performance seemingly slower?
The main reason I use a mister is for clean video output to my CRT, I have most of the original hardware but it just can't complete in terms of video output, and in this regard it is excellent so this is not a gripe.
More of a curiosity question really since I would have thought that by matching the clock, bus etc. you would get the same performance.
Re: Slowdown in games
Posted: Thu Feb 15, 2024 10:01 am
by Armakuni
A lot of slowdown on systems and arcades is the same on the original hardware
The 608020 CPU module is not cycle accurate and the Amiga chipset is still not 100% but i cant say i have noticed that many issues with the Minimig core
A lot of arcade boards , Neo Geo, SNES, PC engine and some other systems were prone to slowdown
EDIT
I just tried some Rainbow Islands on the Amiga core via MegaAGS and it was fine, no slowdowns at all including when you reach the top of the level, exactly as i remember it
Re: Slowdown in games
Posted: Sat Feb 17, 2024 5:00 pm
by FoxbatStargazer
Wonder if bad or missing SDRAM could be a cause?
Re: Slowdown in games
Posted: Sat Feb 17, 2024 5:07 pm
by dshadoff
In general, slowdown on an FPGA system would be either due to “the original system also had slowdown”, or some element of the original system is not properly emulated, leading to signals not occurring at the correct time. It’s not the same as software emulation where a slow CPU can give a different outcome than a fast one.
Having said that, the idea that original hardware didn’t have slowdowns is inaccurate. Many times, original programmers had issues where the processing wasn’t fast enough to complete in one video frame, and the user experienced slowdowns. While this happened occasionally on arcade hardware, it was much more common on computers, and a couple of consoles had bad records on releasing games containing slowdown (Neo Geo, SNES especially).
Re: Slowdown in games
Posted: Sat Feb 17, 2024 6:31 pm
by retrodroid
Yes, slowdown is authentic to the arcade/computer experience and usually means that something awesome is happening! 
Often the slowdown also has a helpful side-effect in giving the player a sort of slow-motion mode to better react to many things happening on the screen at once. Sometimes though, the slowdown just messes with your timing for jumping, etc.
All part of the OG magic, IMHO.
Re: Slowdown in games
Posted: Sat Feb 17, 2024 6:45 pm
by Bristles
This thread started nearly 4 years ago, why bump it up ?
4 years ago, the Amiga core wasn't as good as it is today, so it might have had slowdowns in 2020.
Re: Slowdown in games
Posted: Sun Feb 18, 2024 9:20 am
by Armakuni
Bristles wrote: ↑Sat Feb 17, 2024 6:45 pm
This thread started nearly 4 years ago, why bump it up ?
4 years ago, the Amiga core wasn't as good as it is today, so it might have had slowdowns in 2020.
I didnt notice the date sorry but seeing as Minimig was 15 years old by the time of this post, it was very mature anyway
Re: Slowdown in games
Posted: Sun Feb 18, 2024 12:56 pm
by Chris23235
Bristles wrote: ↑Sat Feb 17, 2024 6:45 pm
This thread started nearly 4 years ago, why bump it up ?
4 years ago, the Amiga core wasn't as good as it is today, so it might have had slowdowns in 2020.
The core wasn't affected by slowdowns back then either. The Minimig was able to simulate an A500 by around 2008 and the current core is derived from this project.