Hi all,
i'm wondering if the autonegotiation process can be performed by a PHY port that is not connected to another device, but simply electrically closed in loopback by itself (I mean, TX on RX on a full duplex connection.
I've done some tests, and after the startup on the line only the FLP pulses can be seen:
And this autonegotiation phase, that if a real devices is connected takes a very little time, let say 1 sec, can remain for a random amount of time, maybe minutes.
This behavior (the long time with only FLP pulses) is frequent if the loopback connection is realized with a short ethernet cable (30 cm), while with a long cable (10 m) typically ends with success within few seconds, as expected.
After a random time, the FLP phase ends and the carrier appears; if I read PHY register at this moment, the link is declared as present (see image below). Of course, when the autonegotiation ends up and the link is established, ethernet messages can be sent over this "loopback" and received correctly.
In your opinion this type of "external loopback" (which i'm trying because I have a ring of units and I want to route back answers) can be realized or there is some error in my meaning?
thank you
