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Old 18 February 2014, 23:31   #1
hooverphonique
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A3640 burst

I was wondering if the A3640, in an A3000 with static column ram, will do bursts to fastram??

What I actually would like to know is, if the A3640 generates 68030 burst accesses on the CPU slot connector, and without a lot of inside info, answering the above question is probably the easiest way to find out.

Since the 6840 always bursts when caches are on (and thus has no specific burst mode pins like the 68030), it would be nice if the A3640 translated these into 68030 burst cycles for the motherboard to know and then optimize memory access (which currently only works for static column ram, i.e. A3000).

I think it was a huge oversight of Commodore to not support fast page mode in Ramsey as almost every simm out there supports it (even at the cost of static column support because static column chips support fpm as well), unless they thought that it didn't matter because the A3640 (and maybe even the A3630) doesn't support burst cycles.
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Old 19 February 2014, 00:57   #2
alenppc
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According to this guide

"The A3640 also does not support burst mode access."

...which makes sense cause it's really slow in RAM access.

There is a mod that SpeedGeek made on Amibay to speed the access up by removing 1 waitstate. It's definitely a nice improvement but it doesn't seem to be compatible with every A3640. Some refuse to boot with it installed.
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Old 19 February 2014, 09:27   #3
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Removing 2 wait states

http://www.amibay.com/showpost.php?p...8&postcount=16
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Old 19 February 2014, 16:10   #4
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The A3640 does NOT support burst access and probably never will.

If you look at the A3640 schematic you may see the signal /TBI is connected to a 1K pull-down resistor... and just in case you don't have an 040 manual handy /TBI = Transfer Burst Inhibit.

You may also notice the signal /CBREQ is present on the 200 pin CPU slot connector but an N/C to the A3640 on-board logic... and just in case you don't have an 030 manual handy /CBREQ = Cache Burst Request.

Now, this completely disables A3640 burst and for a very good reason... the state machine logic does NOT support burst and probably never will.

I'm sorry the state machine logic upgrade doesn't work with all A3640s but as with other hacks (e.g. CLK90 mod, PIO2) it's always a case of "Your mileage will vary".

P.S. The latest archive has some updates (to fix problems with the A3000T and A4000T). I don't know if these updates will help with "No Boot" A3640s but it might be worth a try. Thanks to alexh for the link!

Last edited by SpeedGeek; 19 February 2014 at 16:33.
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Old 19 February 2014, 16:38   #5
alenppc
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@alexh indeed.

Speaking of which, in theory it should be possible to clone the A3640 and make a new production run, since we have the GAL code. They are currently selling for unbelievable amounts, the only problem is that some components are extremely hard to find nowadays.
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Old 19 February 2014, 22:09   #6
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Quote:
Originally Posted by alenppc View Post
They are currently selling for unbelievable amounts
I bought a rev3.0 from eBay Italy last month for €35 inc postage. You just have to keep looking.
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Old 20 February 2014, 03:56   #7
alenppc
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alexh, that seems more an exception than a rule, they usually go for 100-150 euros on amibay. Althought I suppose the fact that my local ebay site does not show European auctions other than UK by default doesn't help.
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