trouble with Ethernet link when connecting two BBB peer to peer.

[hussain...@gmail.com]

Hi everyone,
I've faced with a problem about using ethernet cable, when i want to connect two BBB peer to peer.
When i connect one BBB through a ethernet cable to a switch or to my host computer, the link becomes successfully up and i can connect to BBB.
But when i connect two BBB peer to peer, result is different. in this case, link not brought up and the LEDs of ethernet ports not light up and hence i can't ping from one BBB to another one.
Some points are here:
1- Sometimes, after a while about 1, 2, minutes... or more, the link becomes up.
2- If we reset one of the boards, link becomes up.
3- according to smsc.c driver notes, "Due to HW bug, LAN8700 sometimes does not detect presence of energy in the Ethernet cable in Energy Detect Power-Down mode". So i disabled energy detect mode according to
 https://git.backbone.ws/linux/backbone-sources/commit/d88ecb373bd1877acc43e13311a8e0e6daffc3d
but the resule is same.
4- The phy chip on BBB is LAN8710, and debian 8.3 as OS.

Best Regards.

[Dennis Lee Bieber]

On Sat, 28 May 2016 03:05:46 -0700 (PDT),
hussain...@gmail.com declaimed the
following:

>But when i connect two BBB peer to peer, result is different. in this case,
>link not brought up and the LEDs of ethernet ports not light up and hence i
>can't ping from one BBB to another one.

Don't use a regular ethernet cable -- use a cross-over cable -- with a
regular cable you just connected Tx1 to Tx2 and Rx1 to Rx2, rather than Tx1
to Rx2 and Rx1 to Tx2

Routers/switches/hubs do the cross-over internally, and some even are
designed with auto-sense to work with either a cross-over or straight cable
(normally when linking two switches together when they don't have a
dedicated link port)

>Some points are here:
>1- Sometimes, after a while about 1, 2, minutes... or more, the link
>becomes up.

Possibly something in the BBB is capable, after enough time, to
logically swap Tx and Rx in the PHY layer.
--
Wulfraed Dennis Lee Bieber AF6VN
wlf...@ix.netcom.com HTTP://wlfraed.home.netcom.com/

[William Hermans]

It might be cheaper to just buy an inexpensive hub, or switch. For a 5ft cross over patch cable we're talking ~$6 usd . . . for less than twice that cost you can get a cheap 10/100 switch.

You can also make your own cables, but ethernet plug ends, and crimpers are pretty much out of reach( cost wise ) for the typical hobbyist.

--
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[William Hermans]

Wow I take that back RJ45 crimp tools, and cable ends have dropped a lot in price since the last time I looked. But still cost wise for a one off cable it's not worth it.

[hussain...@gmail.com]

On Saturday, May 28, 2016 at 8:38:59 PM UTC+3:30, Dennis Lee Bieber wrote:

On Sat, 28 May 2016 03:05:46 -0700 (PDT),
hussain...@gmail.com declaimed the
following:


>But when i connect two BBB peer to peer, result is different. in this case,
>link not brought up and the LEDs of ethernet ports not light up and hence i
>can't ping from one BBB to another one.

        Don't use a regular ethernet cable -- use a cross-over cable -- with a
regular cable you just connected Tx1 to Tx2 and Rx1 to Rx2, rather than Tx1
to Rx2 and Rx1 to Tx2

using cross-over cable has no effect on result.

[Dennis Lee Bieber]

On Sat, 28 May 2016 13:10:05 -0700, William Hermans
<yyr...@gmail.com> declaimed the following:

>Wow I take that back RJ45 crimp tools, and cable ends have dropped a lot in
>price since the last time I looked. But still cost wise for a one off cable
>it's not worth it.
>

That's what happens when they come out of the specialist stores into
Home Depot, next to the old phone cable stuff. {says someone who also has a
pair of lineman's test sets rotting away from lack of use, along with the
noise tracer and punch-down tools}