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Discussing the Open Source FPGA Amiga Project
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 Post subject: Music notes skipped in turbo mode
PostPosted: Sun Feb 03, 2013 3:12 pm 
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Posts: 349
Another question for Minimig V1.1 gurus:

When I set Turbo mode, some games (Loom, Elvira, Waxworks, Ishar) skip music notes. Just take a look at their intros. There are sounds that are only played in normal mode, and omited in TURBO mode.
Now, the cause for this could be the following:
-Some kind of instruction cache that is only activated when TURBO mode is ON.
-TOO fast CPU for these games. That's a problem because LucasArts games (Loom, Monkey Island) are too slow at stock 7MHZ normal mode, but they miss musical notes in TURBO mode. So in the end they never play as intended...

So, could it be possible to build a core version (from the great FSB130117 version) with
A) No extra instruction cache in TURBO mode, if there's one at all or
B) A more moderated speed step in TURBO mode, let's say 14MHz?


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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Mon Feb 04, 2013 11:27 am 
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Yes I also notice that, in many (mega)demo title too.
But its totally normal! Some MOD player routine uses CPU counter to determine sample loop time and those counter are "designed" for a 7.09/7.14 MHz running 68000.
Its a bad way and even in any real Amiga with faster the same effect will appear.
Minimig provide ~50MHz CPU speed at Turbo mode, so this effect is quite strong and many notes are skiped in those player.
In general the Turbo mode is "less compatible" due to also speed-up Blitter and some game/demo show graphics problems.

HINT:
In my cores I disabled the 4KB cache in Turbo mode at scanlines: BLK setting.
But even without the cache and only 14MHz clock rate those note skip will appear.

There is no way to fix this via the FPGA core. In those case the Normal mode is required and suggested.
To compare compatibility to a real Amiga, the Normal mode is the best way. If something don't act there as it should be, it need to be checked :)

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Mon Feb 04, 2013 4:05 pm 
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Thanks for the detailed explanation, Boing4000, I really appreciate it because it's complete yet easy to understand :)
However, I never noticed any note skipping on my Amiga 1200 (stock 14Mhz 68020), even with Amiga 500 games. For example, Loom, Waxworks and Monkey Island played great in this machine and they sound as intended without any skipped notes.

What I'm trying to say is that maybe a 14 Mhz-TURBO version would make these skips less frequent to almost inexistant, and would make a great compromise: great speed (almost twice faster than stock 7Mhz Amiga 500, I know it's not exact) while mantaining good sound.
In the "7 OR 50Mhz" situation we're in "one or the other!" situation.

Moreover, some games are prepared for higher clock speeds (Monkey Island: intro clouds only appear in 14+ Mhz Amigas, Loom: has smooth animation in 14+ Mhz Amigas) but at the same time they have broken sound with the 50 Mhz "excessive" speed. 14Mhz would make a perfect compromise: good sound, no skipped notes (I know them pretty well on A1200), with fast and smooth animations.


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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Mon Feb 04, 2013 9:16 pm 
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I will take a look (or ear ;)) at this games. Until now I only played "Indiana Jones - The Fate Of Atlantis" on the Minimig installed on HDF and there was no note-skips.

I made a special core with 28MHz cpu clock at Turbo mode.
(14MHz did not work, the bootloader stall after Agnus & Denise detection)
Maybe this already solve the sound-skip issue of the mentioned title. Some old demo may stil have note-skips, it also appear at 14MHz in real Amiga too.

Take it as some sort of a test-core :)


Attachments:
FSB130117_28mhz.zip [94.83 KiB]
Downloaded 223 times

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Mon Feb 04, 2013 10:57 pm 
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Results with this core are GREAT and very promissing!

-Monkey Island: no more notes skipped + game running as intended, smooth and fast. (It's SLOW in 7Mhz mode)
-Loom: no more notes skipped + game running as intended, smooth and fast. (It's SLOW in 7Mhz mode)
-Waxworks: Some notes skipped, but much less than 50Mhz TURBO! A great improvement!
-Ishar - Legend of the fortress: Some notes skipped, but much less than 50Mhz TURBO! A great improvement!

So I fired up the 1200 (stock 14Mhz), re-installed Waxworks and Ishar OCS and tried them again: zero notes skipped. Perfect. I'd go for 14Mhz turbo mode...or at least as an optional middle-step mode with perfect audio yet way faster than stock 7Mhz mode.
A 14MHz mode would be ideal to leave Minimig always running at that speed.

Thanks a lot, as always, for making the Minimig V1.1 even better :D


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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Mon Feb 04, 2013 11:14 pm 
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The other option that might be worth exploring is leaving the clock speed at 50Mhz, but introducing some wait states into the cache. That way you still get some of the advantage of the faster clock speed for anything math intensive, but the tight delay loops in the sound routines won't run so fast.

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Mon Feb 04, 2013 11:54 pm 
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Seems even without the cache (scanlines: blk) the problems with note skip is still present.
And its not fully gone at "only" 28MHz. Those title are badly coded and I guess they would show same trouble at a stock A3000 (030@25MHz).

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Tue Feb 05, 2013 10:23 am 
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I also suspect those problems would persist on a 25Mhz CPU, but the problems disapear at 14Mhz (these games perform great on an A1200) yet the system is way faster than stock 7MHz.
Of course 7Mhz will still be needed for a lot of demos and games really bad coded and depending on cpu speed for timing, but 14Mhz would give both speed and perfect musics on most games.
Is a middle-step setting possible? Something like: NORMAL - 14MHZ - TURBO


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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Tue Feb 05, 2013 11:01 am 
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Sure a multiple cpu speed setting is possible.
But as always, I am unable to adapt the PIC or ARM firmware for this kind of changed.
The OSD is static to me, so the only changes is inside the FPGA.

Perhaps I can make the 14MHz get to work in time.
But I will not drop the 7MHz setting since this is very important for many things and offer the best compatibility :)

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 Post subject: Re: Music notes skipped in turbo mode
PostPosted: Tue Feb 05, 2013 11:06 am 
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Quote:
But I will not drop the 7MHz setting since this is very important for many things and offer the best compatibility


Of course not, sir! The 7Mhz setting is the Amiga 1000 and Amiga 500 cpu setting, the standard Amiga cpu speed, if there's such a thing :D
It must be there, I agree!


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