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Old 20 June 2012, 17:17   #2515
Join Date: Jun 2010
Location: out in the wild
Posts: 1,251
Originally Posted by alenppc View Post
Excellent, thanks. Most A1200 accelerators identify themselves as Zorro cards, which is how, I suspect, the memory gets added to the system by any kickstart. Did you decide not to use this technique for cost reasons or does it have other benefits?
Most previous accelerators have SIMM slots where the user can add different sizes of memory, and that needs to be identified. The Zorro-autoconfig that you see on many other accelerators is not a memory card, but a ROM that runs a bit of code with memory-test/add-routines. Since my 1200 accelerators always have the same size memory, I found it to be a waste to use a ROM, and I also saved a bunch of pins on the CPLD by not doing autoconfig.

The A600 accel is slightly different, because it must be compatible with Kick2.0. I'm avoiding the ROM, but still give this thing 32-bit autoconfig-mem by pretending to be a Z3 memory card. It's almost like the Kick3.1 accelerator-mem routine: Looks for memory and adds whatever it finds in 1-MByte increments. I could have done the same on the 1200 accelerator, but that would have cost me more pins on the CPLD, thus requiring a larger, more expensive chip. I know it looks like a compromise, but the trick with the same-speed-memory at $c0 will locate any OS stuff in true fastmem, so you don't have any drawback under kick3.0. It's just a different approach: Fewer components, less power consumption, same (or even better) effect:

You'll find that many OCS/ECS programs that were previously incompatible with the A1200, will now work with the ACA1231. That's because some of those old programs expect memory at $c0 without checking if it's actually there. It was *the* standard address for the 512k expansion of the A500, and the majority of the market back in the days was A500 users with a trapdoor mem expansion.

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