Quoting Jonas Smedegaard (2019-04-26 09:54:37) > Quoting Sunil Mohan Adapa (2019-04-25 21:30:03) > > > Were your Lime2 boards connected with a cross-over cable or via a > > > switch during those tests? > > > > Lime2 was connected to a laptop via a cross-over cable (actually > > regular cable but the hardware actually detects cross-over setup and > > automatically swaps TX/RX). > > Thanks. Makes good sense to me now (sorry for being dense).
It seems wiring while testing _is_ relevant after all: Concretely, wiring affects MDI/MDI-X, commonly emulated transparently in both hosts and switches nowadays (because it is an optional part of the standard for gigabit ethernet), with no need for actually using a "cross-over cable". I do not suspect any flaws in MDI/MDI-X handling itself, but indirectly the _need_ for NDI-X matters anyway: The cause for the packet loss issues is likely a timing issue. Ethernet is tied to a clock signal fed from one end of the wiring - the "master". When using a switch the switch end of the wiring becomes master, but in "cross-over" wiring (no matter if a cross-over cable is used or whichever of the host PHYs emulate cross-over by flipping from the normal MDI to MDI-X) it is _undefined_ which end gets becomes master. It can seem more reliable to setup a minimal test involving only two hosts and a cable, but in reality that introduces less reliable results than using a switch in-between. Sunil: It would be helpful to know who from Olimex you talked to, so that we can try get back to them and figure out if their tests leading to 20% failure was done "head-to-head" (where it is undefined which end becomes master but perhaps just a fancier chipset at the peer end wins a random race 80% of the time), or they used a switch (where I cannot think of such obvious explanation for the 20% failure, and fall back on "20% of the chips are behaving differently than the rest"). What I am hoping for is to that all chips behave the same - that the 20% can be explained by the wiring in the test setup. - Jonas -- * Jonas Smedegaard - idealist & Internet-arkitekt * Tlf.: +45 40843136 Website: http://dr.jones.dk/ [x] quote me freely [ ] ask before reusing [ ] keep private
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