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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Fri May 31, 2013 12:30 pm 
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Joined: Thu Jun 18, 2009 9:54 am
Posts: 349
Sorry to bring this old thread back to life, but I found this other old thread on Amiga.org that seems to suggest that, at least in the distant past (back in 2008 when all this Amiga hardware resurrection fever started!) the Minimig CPU worked fine at 14MHz:

http://www.amiga.org/forums/archive/index.php/t-47510.html

Just to refresh your memory, 14MHz would be a very good intermediate speed to have set as Minimig's default (after the real, original 7MHz speed of course) because it would avoid slowdowns in games AND it wouldn't cause music notes to be skipped since A1200 CPU ran at that speed and an A1200 doesn't show any skipped notes in games (Monkey, Loom, Ishar...).
Now that minimig_emu has published his AWESOME new arm firmware, we could have NORMAL (7MHz), FAST (14MHz) and TURBO (50MHz) cpu speeds.

Maybe there's info on that thread regarding why 14MHz doesn't work anymore?


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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Fri May 31, 2013 5:26 pm 
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I will try again to make the 14MHz CPU clock work.
Currently the CPU bridge or RAM module can not work at this frequency, 28MHz is the minimum right now.

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Fri May 31, 2013 5:42 pm 
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boing4000 wrote:
I will try again to make the 14MHz CPU clock work.
Currently the CPU bridge or RAM module can not work at this frequency, 28MHz is the minimum right now.


Would it be possible to leave it at 28Mhz but just put some selectable delays on the DTACK signal?
(Whether that would solve the problem depends, I guess, on whether it's possible for a dbra loop to run from prefetch on the 68K?)

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Fri May 31, 2013 7:26 pm 
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I don't have useable experience in 68k cpu handling to do this quickly.
It would be a possible solution and I will try it out. Thanks for the hint :)

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Fri May 31, 2013 10:16 pm 
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Having just checked with a bit of Googling, the 68010 can run a dbra loop from prefetch, but the 68000 can't, so delaying DTACK should work.

Try adding a delayed copy of the cache_hit signal and using it instead of cache_hit in the _dtack assignment.

In fact I suspect the cache is having more impact than the clock frequency, so maybe making it separately selectable would be a simpler solution?

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~ Amiga 4000/030 ~ Amiga 1200 030/50MHz ~ Turbo Chameleon 64 ~ Altera DE1 with Minimig core ~
Details of my projects: http://retroramblings.net


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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Fri May 31, 2013 10:41 pm 
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Quote:
In fact I suspect the cache is having more impact than the clock frequency


If you mean that cache has impact on the notes being lost, I believe it, too. For exaple, FS-UAE configured with a 68040 CPU on a quad-core X86 Linux system doesn't show missing notes on Monkey Island nor causes Loom to hang, while Minimig @50Mhz does both things.


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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Sat Jun 01, 2013 9:56 am 
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The cache already is switchable via the "scanline BLK" option.
But the CPU still is too fast at the current Turbo clockrate to let those dbf loops work properly.

I can try to "play" with the _DTACK signal to force a slow-down.
Lets see how it works. But it may take some time, other private issue have higher priority right now.

For those who do have a MinimigV1 board and can synthesize the core, a co-work is welcome.
But please all in Verilog and no softcore mix-up since the Minimig core timing is quite fragile ;)

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