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Author Topic: 2GB of RAM  (Read 2593 times)
glee_hokie
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« on: August 18, 2009, 03:19:33 PM »

I'm working on a custom design based on the SheevaPlug reference design.  I would like to incorporate 2GB of RAM on my design, but I've not been able to locate any DRAM chips that will work properly with the Kirkwood processor in a 2GB configuration.

Has anyone else done a Kirkwood based design that supports 2GB of RAM?  If so, what DRAM parts are you using and in what configuration?
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restamp
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« Reply #1 on: August 18, 2009, 06:19:47 PM »

I thought the Marvell processor only brought out 30 bits of address space, so unless you are talking externally segmenting the memory, 1G is the limit.
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glee_hokie
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« Reply #2 on: August 18, 2009, 08:31:03 PM »

I thought the Marvell processor only brought out 30 bits of address space, so unless you are talking externally segmenting the memory, 1G is the limit.

Where do you see that there are 30 bits of address space?  According to section 4 of the 88F6281 functional spec (http://www.marvell.com/files/products/embedded_processors/kirkwood/FS_88F6180_9x_6281_OpenSource.pdf):

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The device integrates an DDR SDRAM (Double Data Rate-Synchronous DRAM) controller that supports up to four DRAM banks (four DRAM chip selects). It incorporates an 18-bit address bus (M_A[14:0] and M_BA[2:0]) and a 16-bit data bus (M_DQ[15:0]).

The device supports 256 Mb, 512 Mb, 1 Gb, and 2 Gb DDR2 SDRAM devices, with up to 2 GB total address space.

I want to know what parts are suitable to achieve a design with 2 GB of RAM.
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restamp
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« Reply #3 on: August 19, 2009, 12:56:10 PM »

I thought the Marvell processor only brought out 30 bits of address space, so unless you are talking externally segmenting the memory, 1G is the limit.

Where do you see that there are 30 bits of address space?  According to section 4 of the 88F6281 functional spec (http://www.marvell.com/files/products/embedded_processors/kirkwood/FS_88F6180_9x_6281_OpenSource.pdf):
You're apparently right, glee_hokie.  I must have been thinking about the 88F5182.  So guess it would have been nice, and not out of the realm of possibility, if the Plug had come with another 512MB of DRAM in it.
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