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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: AmmoJammo on March 11, 2013, 06:35:22 AM
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Been looking in to this, and it seems the issue with the A500 and overclocking the stock cpu, is that the "E-clock" signal that feeds other parts on the motherboard comes from the CPU, so if you double the speed of the cpu, this frequency also doubles.
However, the "E-clock" on the A600 is generated by the Gayle chip, so the E output from the CPU doesn't go anywhere, meaning if its the wrong frequency, it shouldn't matter.
BUT! I can't actually find any conclusive answer as to whether or not it will even work....
You can overclock a Sega Mega Drive using a 10Mhz crystal oscillator, feeding the signal into pin 15 (clock in) on the cpu, and this works fine on 99.9% of machines...
So, can this method potentially work on an A600? can I take the 14Mhz output from the Agnus chip and feed it into the 68000?
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170 views, zero replies.
Either its a stupid question.
It simply doesn't work.
Or, no one has really tried it properly?
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well, did you see this thread?
http://eab.abime.net/showthread.php?t=54474
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I've seen that thread, but there's no one in there who has actually done it.
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Haven't tried, did have an A600 a few years ago but it was stock. Probably possible but didn't see anything on aminet. Usually there's some text documents were someone has tried.
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Never heard of an overclock on a stock cpu. I did overclock, only a modest one, on a 030. was like excrement off a wet shovel after I did it. But stock..... I honestly don't know if it would sustain it without some lasting damage to the cpu.
WOOO POST 999 - I am in the emergency services lol.
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Having the 68000 run any faster would only speed up a few instructions taking several cycles, the rest of the time the CPU would be waiting for the RAM. Without any form of cache or fast(er) RAM it'll be pretty pointless.
The only way is to speed up RAM as well - and since it's chip RAM, you'd need to overclock the whole chipset. Provided your monitor can cope with that (multisync, no 1084 derivative) you can replace the main crystal with a faster one. I've tried a 32 MHz crystal once (A500) and my monitor was whining terribly, so I stopped after seeing it boot.
(I had a sync switch installed to be able to use composite input without unplugging RGB and used that to run the monitor unsynced for most of the time - wouldn't recommend letting it run for more than a few seconds on 17+ kHz, if at all.)
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I modified my newly acquired A600, connected the 14mhz output from agnus to the clock input on the 68000 (after cutting a track)
did nothing. no video output at all.
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It is pointless to do this. You get a 5% speed increase. Just adding fast ram to the Amiga gives you a 10% speed increase.
As an alternative, has anyone tried adding faster RAM in chip and fast RAM?
Could you then raise the clock speed a little to take advantage of it?
btw, With the specs of the 68000 available could you add some external cache RAM to and run it at 14mhz or 28mhz. That sound like an easy project for someone with a little experience.
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I modified my newly acquired A600, connected the 14mhz output from agnus to the clock input on the 68000 (after cutting a track)
did nothing. no video output at all.
There are several reasons: Either the CPU did not like the higher clock rate. Or one of the timings are out. A simple one, but check the track for continuity.