> Andrew, pardon my ignorance in these matters, can a PHY driver in > general determine that the issue is with the cable, even without running > the fairly expensive cable test?
No. To diagnose a problem, you need the link to be idle. If the link peer is sending frames, they interfere with TDR. So all the cable testing i've seen first manipulates the auto-negotiation to make the link peer go quiet. That takes 1 1/2 seconds. There are some optimizations possible, e.g. if the cable is so broken it never establishes link, you can skip this. But Ethernet tends to be robust, it drops back to 100Mbps only using two pairs if one of the four pairs is broken, for example. Andrew
