Hi, edonkey

    Please check your PM. Below is the topology I suggested for your 20 DMs.  The Inside Orico P10-U2 diagram partly explained why leave one bottom port empty.
http://i.imgur.com/F7KYlq0.jpg

    As we know, USB is a very tricky interface and has painful compatibility issues lack of unified solution and theory explanation. If we are so luck to find out a stable topology with specified hub assembly, we appreciate the hard work of test engineers and patient costumers.
    How to explain it in theory is a question which we could think while we watching it running stably.
    Looking forward your feedback.

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dmsp
DualMiner Support