(S)GC memory

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Giorgio Garabello
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(S)GC memory

Postby Giorgio Garabello » Fri Apr 13, 2018 12:33 pm

I ask a question from inexperienced: is it possible to increase the memory of the GoldCard or SUperGoldCard by replacing the memory banks?
(I suppose not, otherwise someone would have already done so)


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Re: (S)GC memory

Postby Pr0f » Fri Apr 13, 2018 12:54 pm

The addressing for the memory comes from the large ingot chip - which is a programmable logic device. The design is quite pin constrained, so upping the memory is not an option I'm afraid.

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Re: (S)GC memory

Postby Dave » Fri Apr 13, 2018 4:57 pm

This is correct, but it's a bit more nuanced too.

Memory geometry is as important as memory size.

The GC uses 4x 514400 DRAMs organized as 1M x 4 bit. This gives 1M x 16 memory - that is one IC deep and four ICs wide. 1M x 16 = 2MB.

The SGC uses 8x 514400 DRAMs organized as 1M x 4 bit. This gives 1M x 32 memory - that is one IC deep and eight ICs wide. 1M x 32 = 4MB.

The Ingot IC is managing DRAM reads and writes, but also refresh. It has no pins remaining. If you expanded the memory by doubling it, you would change the memory geometry so instead of 1x4 or 1x8 ICs it would be 2x4 or 2x8 ICs. This would also require a couple of pins for chip select and a rewrite of the DRAM refresh code. The (S)GC expects a single bank of DRAM and rewriting that to support two our four banks would be an extensive rework that would require a LOT of validation for a LOT of very obscure use cases. Driving two ICS per pin may also, depending on the drive of the pins, require some kind of buffering.

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