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Visitor kalajian
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Newbie Spartan-6 MIG user interface command address question

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Hi there, 

 

I have a MIG/MCB running on my Spartan-6 evaluation board. This is the board by the way -- https://numato.com/product/mimas-v2-spartan-6-fpga-development-board-with-ddr-sdram

 

Anyway, I am wondering what is the maximum address I can use for my user interface logic (i.e., "c3_p0_cmd_byte_addr")?

 

This is 30-bits wide because the lower two must be 0, but the actual external RAM chip is only 512Mb, so surely I cannot write to ‭0x3FFFFFFF‬, or can I (if I understand, the MCB does some kind of address translation at a lower layer)?

 

Thanks for any help!

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回复: Newbie Spartan-6 MIG user interface command address question

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@kalajian

Note that your data bus width is x16, so row + col + bank sum is 25. If you choose X8 model, you will see 26 bits.

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回复: Newbie Spartan-6 MIG user interface command address question

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@kalajian

512Mb is 64MB, so the address bus needs 26 bits.
If the data bus width is 32 bits (4 byte), then the maximum address value is 0x3FFFFFC. It is meaningless to read and write beyond this range.

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Visitor kalajian
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回复: Newbie Spartan-6 MIG user interface command address question

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Doing some more reading, it seems like the user address is specified with some bits allocated to BANK, ROW, and COLUMN -- https://www.xilinx.com/support/answers/44094.html

My specific memory part has 25 bits for those fields, 

mcb.pngSo I am guessing that I simply cannot use the upper 5 bits for addressing? That would be ‭0x07FFFFFC‬.. but you're right, that's > 64MB so I'm still a little confused

 

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回复: Newbie Spartan-6 MIG user interface command address question

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@kalajian

Note that your data bus width is x16, so row + col + bank sum is 25. If you choose X8 model, you will see 26 bits.