Infinity Fabric = PCIe

By: Michael S (, March 16, 2017 4:32 am
Room: Moderated Discussions
Adrian ( on March 16, 2017 2:51 am wrote:
> slacker ( on March 15, 2017 11:11 pm wrote:
> > Groo ( on March 15, 2017 5:35 pm wrote:
> > >
> > > Did you see the part about physical layer agnostic?
> >
> > That is part of what concerns me (i.e.: they don't care about
> > the physical layer, so they're happy to rely on PCIe).
> >
> > > What little tech there was was somewhat a rehash of the Hot Chips arch talk
> > > and a little more about the device itself rather than just the core. This
> > > is the long way of saying the audience wasn't right for an IF talk
> >
> > I understand that AMD has to balance the timing of their marketing, but I can't find technical details
> > on IF anywhere, including patent filings. Aren't chips supposed to be released in 2Q17? It's a little
> > late to be disclosing surprises in the interconnect of a server-class microprocessor.
> I believe that the information we have is consistent with the following interpretation:
> 1. The higher-level protocol is an improved version of the coherent HyperTransport protocol
> 2. The physical interface is PCIe, i.e. with embedded clocks, not with separate clock signals. This is the
> main difference from HyperTransport. Keeping separate clock signals would have been exceedingly difficult
> at the current speeds (>= 8 Gb/s) and at the very large number of signals that connect the 2 AMD sockets.

It depends on the number of signals in clock group. Intel demonstrated that with 5 data signal per group it's doable for much longer distances and much less controlled PCBs than one targeted by AMD.
Hypertransport has 8+1 data signal per clock. That's a little harder than 5, but, then again, environment within MCM is very tightly controlled.

As to "very large number of signals", I don't see how a total number of signals matters at all.
As as far as "total number" goes, multilane serial with per lane CDR protocols (like PCIe) and multisection parallel source-synchronous protocols with provision for adaptive deskewing (like HT3) face very similar challenges.

> 3. Even if the physical interface is mostly identical with PCIe (same serializing algorithm), it must have
> a few non-standard differences. Almost certainly the speed is higher, possibly a little larger than 10 Gb/s.

I don't think so. 8 Gb/s is fast. Running faster will require more complex processing that will impact latency. If anything, I'd expect that inter-processor links would run slower than PCIe Gen3. I'd bet on 6.4 GT/s.

> It might be that the speed is a multiple of the memory speed, e.g. with DDR4-2667 it might be 10.67 Gb/s

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TopicPosted ByDate
What is infinity fabric?slacker03/12/17 06:41 PM
  What is infinity fabric?Jason Creighton03/13/17 12:26 AM
    What is infinity fabric?Klimax03/13/17 12:42 AM
      What is infinity fabric?Kevin G03/13/17 04:39 AM
  What is infinity?Anon03/13/17 04:44 AM
  What is infinity fabric?Groo03/13/17 07:33 AM
    What is infinity fabric?Ireland03/13/17 09:12 AM
      Another way to put same questionIreland03/13/17 09:16 AM
      What is infinity fabric?Groo03/13/17 12:12 PM
        What is infinity fabric?Ireland03/13/17 02:07 PM
          What is infinity fabric?Ireland03/13/17 02:32 PM
            What is infinity fabric?Seni03/14/17 12:38 PM
          What is infinity fabric?Brendan03/14/17 05:28 AM
            What is infinity fabric?Ireland03/14/17 06:09 AM
            What is infinity fabric?Groo03/14/17 07:35 AM
              What is infinity fabric?Ireland03/14/17 08:35 AM
    Infinity Fabric = PCIeslacker03/15/17 02:59 PM
      Infinity Fabric = PCIeMichael S03/15/17 04:19 PM
        Infinity Fabric = PCIeIreland03/15/17 04:49 PM
        Infinity Fabric = PCIeRicardo B03/15/17 10:25 PM
        Infinity Fabric = PCIeslacker03/15/17 10:45 PM
          Infinity Fabric = PCIeRicardo B03/15/17 11:02 PM
            Infinity Fabric = PCIeAaron Spink03/16/17 01:08 AM
              Infinity Fabric = PCIeRicardo B03/16/17 05:30 AM
                Infinity Fabric = PCIeAaron Spink03/16/17 10:58 AM
        Infinity Fabric = PCIeGabriele Svelto03/16/17 03:48 AM
          Latency vs. bandwidthDavid Kanter03/16/17 08:04 AM
      Infinity Fabric = PCIeGroo03/15/17 05:35 PM
        Infinity Fabric = PCIeslacker03/15/17 11:11 PM
          Infinity Fabric = PCIeAdrian03/16/17 02:51 AM
            Infinity Fabric = PCIeMichael S03/16/17 04:32 AM
              Infinity Fabric = PCIeAdrian03/16/17 07:58 AM
                Infinity Fabric = PCIeRicardo B03/16/17 09:16 AM
                  Infinity Fabric = PCIeMichael S03/16/17 09:54 AM
                    Infinity Fabric = PCIeRicardo B03/16/17 10:07 AM
                      Infinity Fabric = PCIeMichael S03/16/17 02:33 PM
                        Infinity Fabric = PCIeGabriele Svelto03/17/17 03:35 AM
                          Infinity Fabric = PCIeAaron Spink03/17/17 10:25 AM
                            Thanks, your posts on this thread have been extremely informative (NT)Gabriele Svelto03/17/17 01:08 PM
                            Infinity Fabric = PCIeRicardo B03/17/17 06:08 PM
                              Infinity Fabric = PCIeAaron Spink03/17/17 06:27 PM
                              Quickpath papers - circuits and implementationslacker03/18/17 06:50 PM
                                Quickpath papers - circuits and implementationRicardo B03/19/17 08:07 AM
                    Infinity Fabric = PCIeAaron Spink03/16/17 11:11 AM
                      Infinity Fabric = PCIeMichael S03/16/17 02:46 PM
                        Infinity Fabric = PCIeRicardo B03/16/17 03:07 PM
                          Infinity Fabric = PCIeMichael S03/16/17 05:13 PM
                            Infinity Fabric = PCIeAaron Spink03/16/17 11:04 PM
                            Infinity Fabric = PCIeRicardo B03/16/17 11:30 PM
                              Infinity Fabric = PCIeMichael S03/17/17 07:24 AM
                                Infinity Fabric = PCIeRicardo B03/17/17 06:07 PM
              Infinity Fabric = PCIeDavid Kanter03/16/17 08:36 AM
                Infinity Fabric = PCIeMichael S03/16/17 08:50 AM
                  Infinity Fabric = PCIeAaron Spink03/16/17 11:24 AM
                    Infinity Fabric = PCIeMichael S03/16/17 02:45 PM
                      Infinity Fabric = PCIeAaron Spink03/16/17 11:21 PM
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