Re: link-up link-down ethernet switch tale of woe
briand@aracnet.com put forth on 2/2/2010 12:11 AM:
> I take the linksys apart, and here's where things get kind of
> interesting. Those of you who have any hardware experience with
> ethernet phy's are probably aware that they typically use a 25MHz clock.
> This crazy piece of dung has a 25.0006 MHz crystal. That is not a
> typo.
>
> I've heard rumors of manufacturers overseas grabbing anything in the
> way of parts so they can ship it out the door, and I _know_ they don't
> test. Too expensive, it's cheaper for you to test it. Probably happens
> in the US too - I mean it would if we actually made anything anymore.
>
> I'm really interested if anybody with some hardware experience can shed
> light on the crystal I found. I even measured it in the lab and it's
> 25.0006MHz alright. I'm 99% sure that it's the wrong frequency for
> proper ethernet operation, but the level of incompetence that it implies
> is amazing.
You're barking up the wrong tree Brian. That crystal isn't the source of your
problem. It's well within spec. I'm sure the system design tolerance is much
greater than 0.0006%. PHYs use PLL circuits to clean up the clock anyway, so
even if that clock crystal chip was running at 25.05 MHz it wouldn't cause
problems. BTW, what "lab" equipment did you use to "test" this crystal and
verify its frequency? /laughs
I'd say you probably just got a defective switch. It happens. And probably
more frequently with the cheap stuff than the more expensive stuff. No surprise
there.
Here's a somewhat reverse example. I recently purchased a $10 Rosewill 8 port
10/100 desktop switch from Newegg just to have some extra bench testing ports.
The uplink to the closet switch works fine, and it works great using full auto
negotiation with my main desktop. But if I force 100FDX in the driver the link
won't come up *period*. Some gear will *only* work with auto negotiation.
Speaking of which...
What's interesting in your case is that you're dealing with 1000BaseTX. IEEE
802.3ab *requires* auto negotiation for all copper gigabit ethernet; manual
settings aren't allowed, period.
Again, I'd say you just got a bad switch. And it has nothing to do with the
clock crystal being 0.0006% off target. Check the crystals in some of your
other electronics and see how far off they are. I bet most are off by more than
0.0006% The problem with the Linky could be the power supply, the transformer,
the switch chip, a marginal or cracked trace on the board, a defective capacitor
(one of those itty bitty suckers you can barely see soldered to the board),
could be any number of things. But it ain't that crystal.
--
Stan
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