Hi. I discovered a problem with USB host mode on a Nexus 7 running
Android 4.2.x: USB slave devices will become undetectable ("not
accepting address xx, error -71") after the host goes through a deep
sleep cycle (60+ seconds loss of external power; running on battery). In
this situation the methods tegra_ehci_suspend() and tegra_ehci_resume()
are being called. I am _not_ experiencing this issue at all, when the
host only goes through a light sleep cycle (less than 20 seconds of
power loss). During light sleep, the methods tegra_ehci_suspend() and
tegra_ehci_resume() are _not_ being called.
The slave device (a USB DAC; many different products have been tested)
is loosing power in both cases. But this does not seem to be the
problem, because slave devices stays accessible, when the host (N7) only
goes through light sleep.
Is anyone aware of this problem? Has it been fixed since 3.1.10?
Thank you.
Timur
Project on github:
http://mehrvarz.github.com/usb-host-mode-power-management-nexus7
Discussion: "Can you charge & USB Host mode simultaneously?"
http://rootzwiki.com/forum/512-nexus-7
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