Newsgroups: comp.sys.amiga.hardware
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From: taab5@isuvax.iastate.edu (Marc Barrett)
Subject: Re: Accellerator Hack
Message-ID: <1991Jun6.104357.12137@news.iastate.edu>
Sender: news@news.iastate.edu (USENET News System)
Reply-To: taab5@isuvax.iastate.edu
Organization: Iowa State University, Ames, IA.
References: <Edward_Braswell.3260@a68k.UUCP>
Date: Thu, 6 Jun 1991 10:43:57 GMT
Lines: 72

In article <Edward_Braswell.3260@a68k.UUCP>, Edward_Braswell@a68k.UUCP (Edward Braswell) writes:
>Some of you may remember the old "14 MHz Hack" that's been floating around
>for A500's (and presumably A2000's).  After MUCH! trying, I finally
>decided it wouldn't work for the A1000, due to differences in timing, in
>that the A1000 uses a couple of 74F74's and some other logic to generate
>it's 7M clock for the 68000, while the A500 has all of that stuff
>integrated into the "Fat Agnus" chip.
> 
>But, I did find an accellerator that does work.  It's not 14 MHz, it's
>only 8 MHz (7.14 -> 8 MHz => 12% increase in speed).  And, it only cost me
>$2.50 for a 32 MHz crystal oscillator. 
[stuff deleted]

   I tried exactly this a couple of years ago, only I tried it with both 
32Mhz and 40Mhz clock oscillators.  I found that the monitor I was using
at the time (a cheap composite monochrome monitor, to alleviate the
interlace flicker) was able to sink up to the higher video frequency when
the 32Mhz oscillator was used, but not when the 40Mhz crystal was used.
For this reason, I think a multisync monitor should be able to sort
everything out and produce a solid display when this hack is done.  Now
that I have a multisync monitor, I've been wanting to try the hack again,
but I now longer have the thing (it was cheaply wire-wrapped, and I 
threw it out long ago).

   The next time I get around to it, I will try the hack with the multisync
monitor and report my results.  BTW, this hack, when used with the 40Mhz
clock oscillator, can produce a 40% speedup clear across the board on
everything from the blitter to the sound chip to the CPU.  This is because,
unlike all other acclerator boards or speedup hacks, this speeds up the
custom chips as well as the CPU.    

> Actually, there _IS_ one small problem with this hack:  while in the fast
>mode, the RGB and video outputs are UNREADABLE.  The screens get very
>messed up, as their Syncs are not at the specified NTSC frequencies, and
>my monitors can't "sync up".  OK, yes, this is a major problem, but there
>are 2 solutions:
> 
> 1. Modify the monitors so that they CAN sync with the new speed.
> 2. Use FAST mode blind.

  Or 3. Use a multisync monitor.  See above.

> 
>Yes, I know, what's the use of an accellerator if you can't see an output?
>  Well, one use is for things you don't need to see, like ray-tracing.  If
>you're doing heavy-duty ray tracing on an unaccellerated 68000 system, then
>the FAST mode would cut the time by 12% (and getting a 68010 would bring the
>saving to 17%!).  Let's say the picture would normally take 2 hours to draw. 
>You could save 15 minutes!
> 
> Another good use for it is in LZHing / UN LZHing  / Warping / unwarping,
>etc.. large files.  If you don't mind waiting until it's done to see
>anything,
>this hack will save you time.
> 
> Ultimately, what can you expect from a $2.50 accellerator?    I think it's a
>bargain.
> 
> Oh, if anyone wants specific pin outs / schematic, just ask and I'll upload
>them.

   It's very simple.  Just send the output of the clock oscillator to the
external clock input pin, and tie the external_clock_enable to the ground
pin specifically for the external_clock_enable.  

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