Ethernet connection

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I use uip in my MCU project. However, I need to save power as the
device uses battery. So I set the ethernet chip sleeping and then wake
up for every one minute.

After waking up, it is connected to the remote computer and then
several bytes are transmitted. However, several seconds delay for the
remote side hub/computer is required to detect the insertion of lan

In uip, could I know instantly when the remote side hub/computer is
ready to be connected after the device is waking up?

Besides, could I know this by reading the ARP state?


Re: Ethernet connection

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I won't comment on the uIP stack specifically, but in general one does
not know the state of the connected Ethernet port beyond the link status
(which the driver can detect).

The ARP table could be a way to tell if you can reach the defaut gateway
or the local neighbor, as long as the ARP isn't cached across sleep
cycles.  Maybe you can force an ARP flush right after awakening, then
monitor the table.  Although, if the host is local, this won't tell you
any more than a missing ACK - you'll need to send traffic to cause ARP
to trigger, and that traffic could just as well be your data.

FYI, different Ethernet switches will behave differently regarding
Spanning Tree.  For example, by default, Cisco switches will put a newly
activated port into "blocking" mode for up to 45 seconds until it can
determine the new port does not create a loop on the network.  During
this 45 seconds, you will have a link to the switch, but cannot talk to
any devices.

To plan for this scenario, you might want to ping the remote device, or
be very tolerant of retries and use some sort of acknowledged traffic
(TCP, or UDP with your own ACK scheme).  You might also find that waking
up every 60 seconds is too frequent due to this issue.  Or, that there
may be a way to drop the Ethernet controller into a sleeping mode
without dropping the link signal (but this will draw power).

Some things to consider.


Re: Ethernet connection

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As sidenote, there is now power over ethernet
standardized. Have a look at the chips of various
manufacturers such as Linear Technology.

Depending on the technology, you could also implemnt your own.
I've seen systems using coax (RG58 or RG214) with several hundred
volts of DC, supplying remote equipment.

Ing.Buero R.Tschaggelar -
& commercial newsgroups -

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