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 Post subject: Overclocking 68SEC000
PostPosted: Tue Sep 15, 2009 9:31 am 
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Joined: Mon Dec 01, 2008 10:11 am
Posts: 197
Hi guys,

I have made some tests with clocking the CPU asynchronously. Guess what frequency it was able to run stable (my CPU is 20 MHz part).

Jakub


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 Post subject: Re: Overclocking 68SEC000
PostPosted: Tue Sep 15, 2009 9:51 am 
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Joined: Mon Aug 24, 2009 1:21 am
Posts: 27
Location: Warsaw/Poland
yaqube wrote:
Guess what frequency it was able to run stable (my CPU is 20 MHz part).


I would say it can be close to 40 MHz...

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 Post subject: Re: Overclocking 68SEC000
PostPosted: Tue Sep 15, 2009 12:14 pm 
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Joined: Mon Dec 01, 2008 9:58 pm
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Location: .de
Yep for the 20MHz version I also would guess about 40-45MHz, perhaps more.
I have tested my 16MHz version and it works at leat at 38MHz without any error.

This MHz lable could also just be a marketing issue of Freescale to present some product bandwidth for customers. The DIE core may be the same for both (all) SEC000 version. Since this is totally new 3v3 static design, its clock rate may be able to wort far above its lable.
I also could imagine about 150-180% overclocking... ?

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 Post subject: Re: Overclocking 68SEC000
PostPosted: Tue Sep 15, 2009 5:22 pm 
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To my surprise the CPU on my Minimig board is able to run stable at 52.67 MHz.

Clocking the CPU faster than the memory can be accessed is of little advantage. Fortunately my board is equipped with 10ns SRAMs and I'm very curious what performance can be achieved with zero-waitstate memory subsystem.


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 Post subject: Re: Overclocking 68SEC000
PostPosted: Tue Sep 15, 2009 5:40 pm 
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Wow, >50MHz is very overclocked and impressive ;)
Without s-ram waitstate the performance should rise up extreme and could possibly gain 25MHz 68020 level.
Unfortunately the 68000 dont have any cache and require more clock tick per instruction and, so it can not perform as a real 68020 at same clock rate.

Still it would be fun to let Minimig run at approx. 50MHz :D
Is your cpu getting any warm at this clock rate? The 16MHz version running at 28.36MHz become a bit warm at benchmark or strong IDE access. Still its cool compared to any real 68000 and the Spartan3!

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 Post subject: Re: Overclocking 68SEC000
PostPosted: Tue Sep 15, 2009 8:07 pm 
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On another board I was able to run the CPU stable at 56.72 MHz (I haven't tried any higher rate yet). The first board has some problems with keeping the PLL locked (probably caused by insufficient decoupling).


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 Post subject: Re: Overclocking 68SEC000
PostPosted: Tue Sep 15, 2009 8:13 pm 
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Location: .de
A 68SEC000 running close to 60MHz really is :shock:!
If asynchronous clock is possible, I can provide a test bench using "A'Nel Speedmaker" from 1MHz up to 120MHz in at least 1MHz step. This would require a tristate cpu_clk setting at fpga output and the async. core of course ;)

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 Post subject: Re: Overclocking 68SEC000
PostPosted: Fri Sep 18, 2009 7:38 am 
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Joined: Sat Jan 31, 2009 9:01 pm
Posts: 82
Location: Malta
This is really interesting news! The Minimig with ARM controller is already faster and easier to use than any Amiga I ever owned, and here you tell us it goes up to 56MHZ+

With 10ns RAM how does it perform in benchmarks? Maybe it's time to start promoting the Minimig as a demo coder's ideal platform.

Slightly OT. Would it be possible to expose a couple of the hardware multipliers as memory mapped peripherals/registers? This would make for a killer 3D vector demo tool, given that these require matrix multiplication (very expensive instructions on 68k).

Cheers!
Edwin

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 Post subject: Re: Overclocking 68SEC000
PostPosted: Fri Sep 18, 2009 2:05 pm 
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Joined: Sat May 16, 2009 5:15 pm
Posts: 31
Very interesting!

What sort of performance gains (if any) could one realistically expect from a stock ACube minimig board with 45ns ram?


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 Post subject: Re: Overclocking 68SEC000
PostPosted: Fri Sep 18, 2009 3:47 pm 
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Posts: 197
wolfchild wrote:
With 10ns RAM how does it perform in benchmarks?

I haven't tested that yet but when the CPU is clocked at 28 MHz and memory runs zero-waitstate cycles the performance gain is 5.0 over a stock A500. I expect this value to double when the CPU is clocked at 56 MHz (unfortunately only one of my boards is able to run that fast). The performance should be comparable with a 030 @ 25 MHz.

wolfchild wrote:
Would it be possible to expose a couple of the hardware multipliers as memory mapped peripherals/registers? This would make for a killer 3D vector demo tool, given that these require matrix multiplication (very expensive instructions on 68k).

It should be possible but without software support it's pretty useless (like chunky to planar converter in CD32). If we go this way why not implement a real DSP?


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