[clue-tech] making ethernet autonegotiation not work

[Ken MacFerrin]

Jim Ockers wrote:
> Hi Warren,
> 
>>>> Right, I should have mentioned that we have some very specific
>>>> environmental requirements and the "industrial" ethernet equipment
>>>> that meets the temperature/power/static/corrosion/hazardous location
>>>> requirements is expensive.  We can't use normal consumer grade gear.
>>> And the unmanaged $50 switch gives you all of the above?
>> Okay. So drop the 100MBps device and replace it with a ~$50 10BaseT
>> device. At [1], you'll find a 10BaseT Hub that conforms to the 802.3
>> inducstrial standard. Does that meet your needs? If the hubs won't
>> support 100MBps, it shouldn't be able to negotiate the higher speed.
> 
> That's along the right lines, thanks for the suggestion.  The thing is,
> we need to use a switch, not a hub, so that the signal gets cleaned up
> when the frames are copied to the other port(s).
> 
> We have been unable to find any unmanaged 10BaseT switches.  Also our
> selection of vendors is limited to those who make devices of a certain
> size with DIN rail mounts so we can mount them in our hazardous location
> enclosures.
> 
> Basically we have ruled out trying to solve this problem with different
> NICs (the link partners are industrial single board computers with
> built-on onboard network interfaces), hubs (because we need the switch
> signal processing), and software configuration on the link partners
> (already tried that).   

Not to beat a dead horse, but you could still try a script using
"mii-tool --watch" to monitor the interface once every second for
changes and issue an "mii-tool --force" to reset it if the link
re-negotiated itself somehow.  This should give you a "guarantee" within
1 second of any change.
-Ken