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Old 13 September 2010, 00:03   #33
Join Date: Jun 2010
Location: out in the wild
Posts: 1,251
Originally Posted by desiv View Post
Just wondering.. Is an Amiga FPU basically pointless?
Although it's floating-point-less (if that's the "bad joke" you wanted to throw - pardon the question from a German), I don't know of any useful software that requires an FPU these days. If you want to render something with an Amiga, you either go '060 or emulation, but not '030.

I created these cards because I was amazed about the prices that A1200 memory expansions go for on eBay. The goal was to make an accelerator at the price of a memory expansion. Now that 72-pin SIMM sockets are more expensive than SD-Ram memory chips (and hardly available RoHS-compliant), a new logic design was required. I have access to brand new Winbond 200MHz SD-Rams (AFAIK, I'm the first in Europe who has them in quantities), and I wanted to play with them.

To take advantage of 3.3V rams in a 5V system, you need 5V-tolerant drivers between the voltage domains. The drivers I'm using have a guaranteed propagation delay for up to 50pF capacitive load. If I add the pin capacity of the translators, the data bus drivers and the CPU to the trace capacity of the board, I end up barely below 50pF, so the 2-cycle access that I use here is within spec. If an FPU would be on the data bus as well, I'd have to add another waitstate to the memory timing, which would add up to 4 waitstates for a cache line burst, which is currently 2-1-1-1. Although my target was never "high performance", the 28MHz-A1200 version (which is the only functional model at the moment) is probably the fastest non-static mem 28-MHz-68030 ever made for the Amiga.

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