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XMP values for tRC, tRRDS, tRRDL and tFAW on AM4 for QVL, and termination

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  • XMP values for tRC, tRRDS, tRRDL and tFAW on AM4 for QVL, and termination

    This is really just something I have been curious about. I know XMP is an Intel specification, and how the platforms handle tRC or tRAS is a bit different.

    When the ram is tested on motherboards for the QVL, are these timings set manually or are the motherboard automatic values used? For example, I have the F4-3600C14D-32GVK set, and the XMP values of those timings seem to be tRC 50, tRRDS 4, tRRDL 9, and tFAW 44. At least if tools like AIDA or thaiphoon are reporting those correctly.

    But the various AM4 motherboards I have owned seem to calculate those timings based on the base SPD timing, which for this kit works out to tRC 83, tRRDS 6, tRRDL 9, tFAW 38.

    Only somewhat related since it just has to do with setting XMP and forgetting it, are the termination values (ProcODT, RTT) used the motherboard automatic values?

    Thanks in advance!

  • #2
    Originally posted by UrdnotTex View Post
    But the various AM4 motherboards I have owned seem to calculate those timings based on the base SPD timing...
    Which makes sense, since the AMD platforms don't natively support Intel Extreme Memory Profiles. So it depends upon the workarounds of the motherboard manufacturers (A-XMP, D.O.C.P. etc) what programmed timings get applied 1:1 and which ones are ignored or calculated/determined by other means during DRAM training*.

    *originally some implementations were more faithful to the programmed timings, but that did limit compatibility of higher frequency SKUs

    Originally posted by UrdnotTex View Post
    Only somewhat related since it just has to do with setting XMP and forgetting it, are the termination values (ProcODT, RTT) used the motherboard automatic values?
    Those are not part of the XMP Standard for DDR4. The motherboard uses presets for that and/or adjusts them during DRAM training.
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    • #3
      Thank you for the reply. So the assumption should be that if they list a motherboard in the QVL for a kit, the compatibility would be at whatever values the motherboard generates for anything except primaries on AMD?

      I suppose that is academic. Also if one intends to run out of specification anyway it probably doesn't matter.

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      • #4
        As far as I know, QVL testing is done with just the XMP enabled and no other adjustments.

        Back during the DDR3 era the differences between the AMD and Intel memory controllers could also be problematic. The AMD platforms suffered with only 5 static tRFC values (90/110/160/300/350). So in theory the AMD based Motherboards should have always used the next larger value of what is programmed. However that was not always the case and resulted in lot's of issues with high frequency SKUs and/or higher density ICs. If you were aware of that, it was enough to fix by adjusting the tRFC manually though.

        Compatibility by QVL does not matter for manual overclocks. What you can get out of a specific kit, mostly depends upon your OC skills, CPU and MB(BIOS).
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        • #5
          It is helpful to have a QVL kit so you know the combination has been tested and optimized, and as a result it should have great OC results. It is possible to have a memory kit not listed to not work well at all, such as not OC well or it can only boot up; the latter being more possible with new platforms that have yet to have proper BIOS coding for the hardware.

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