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  1. #1
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    BRAM vs LUTRAM resources

    I am implementing a small memory, which after implementation takes the smallest possible BRAM block of 18kb in Zedboard. Then I force it not to take BRAM, so it takes the distributed RAM resources. The resources utilized are: LUT : 342, LUTRAM : 256. Now my question is: Does it mean the resouces utilized equals 342 LUT out of which 256 are LUTRAMs Or 342 LUTs plus 256 LUTRAMs? Also I believe that LUTRAMs are special LUTs for implementing distributed RAMs. Is that it?

    •   Alt27th November 2017, 07:16

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  2. #2
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    Re: BRAM vs LUTRAM resources

    Yes, look at the CLB guide for whatever device you have. The short explanation is that Xilinx FPGAs have SLICEL, SLICEM, and SLICEX. The SLICEM can be used as DMEM/SRL32 as well as anything in a SLICEL. THe SLICEX is only on lower end devices and has less features than a SLICEL. At least, from what I can recall.

    I suspect this is 256 LUTs from SLICEM's for the ram, and 342 SLICE*'s for any clock enable and muxing.

    --edit:

    in general, any depth over 256 or maybe 512 is probably better done in a BRAM. This is based on the DMEM configurations. Likewise, ram configs below 32 might be better served by a DMEM of size 32. These are because a SLICEM can be a 1 bit, 256 depth RAM, or a 6 bit, 32 depth RAM. (the latter is because the SLICEM is 4 LUTs with a shared write address, but 3 independent read addresses. It also has f7/f8 muxes to allow 2-4 LUT outputs to be quickly muxed.)



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