I recently got my new HEM27 with iPolar and encountered similar issue. As I know RPi itself has very limited current supplied for its alll USB ports. Before I got a "powered" USB hub, my USB devices that connect to my HEM27, then to RPi, were quite unstable on the connection. Then I noticed the message below in dmesg,
attempt power cycle
Cannot enable. Maybe the USB cable is bad?
That reminds me that RPi is weak on the USB ports. So I got a powered USB hub, then connected HEM27 USB that integrated all USB rigs. Now my RPi is quite stable to communicate all USB devices on my mount.

Lucian

Read More...