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Old 15 February 2012, 22:13   #2310
Join Date: Jun 2010
Location: out in the wild
Posts: 1,251
Originally Posted by SpeedGeek View Post
Now, I have contemplated hacking some SDRAM into my A2630 just to prove their is NO INHERENT compatibility problem with the MC68881/2. But that's quite a lot of work just to prove a point and I can still squeeze a bit more performance from my DKB2632 with some comparatively minor modifications.
I have even contemplated making a fastmem expansion for the 2630, because it's fairly easy-going at 25MHz. However, I fear that capacitive load on the data bus plus the resistor packs (pull-downs) will put enough load on the LXC16245 drivers that timing specs can't be achieved. For a 2-1-1-1 burst, you may have to remove all onboard memory chips (they hang off the data bus without drivers).

Of course you can work with an even higher clock (not x2 but x3) and make data valid a good 5ns earlier, but that goes into the same direction as hacking the card to over 50MHz ;-)

For some real speed gain, I'd pull the EXTERN signal for pretty much every bit of memory that the 2630 can address - including 00c0.0000, the Z2 memory area and (optionally) kickstart. Drawback: DMA would not work any more. Advantage: The whole system would be a lot faster, because any slower memory (except chipmem) would be switched off.

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