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Re: CB030, A 68030 SBC for hobbyists [message #7054 is a reply to message #7052] Thu, 06 February 2020 19:14 Go to previous messageGo to previous message
plasmo is currently offline  plasmo
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Registered: March 2017
Location: New Mexico, USA
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The swap register is a hack. I didn't want to deal with MMU translation initially, so I use swap register to exchange first 64meg memory with 2nd 64 meg memory. The first 64 meg is EPROM and DRAM starts from 2nd 64 meg. So if I do have 128meg of DRAM, then the memory map after swap is
lower half DRAM at 1st 64meg (0-3FFFFFF)
EPROM at 2nd 64 meg (4000000-7FFFFFF)
upper half DRAM at 3rd 64 meg (8000000-BFFFFFF)

The reason I don't just swap the first 128meg with 2nd 128 meg is because I ran out of pins so the total decoded memory space is 256meg and the top 64 meg is I/O space. I don't want to change I/O mapping when swapping.

Swap register probably won't be in use once MMU translation is turned on.

Bill
 
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