Thanks!! You definitively set me to the right point. Problem was indeed the broken support to Andorid USB host API. Your link was a good starting point, but did not fix completely the problem. I explain what I did for others with my problem.
1) have root access
2) install from Google Play "USB Host Diagnostics"
3) run the diagnostic, in my case it reads:
Android API
Claims support: No
Classes found: Yes
Device detected: No
so classes are there but unused. The complete list of results from USB Host Diagnostics App is available here, to find out in advance:
http://usbhost.chainfire.eu/ If classes are not found, you should upgrade to a new firmware.
4) in case /system is read only, remount it read/write. In my case:
mount -o remount,rw /dev/block/mtdblock8 /system
5) as indicated in the link by harrison, a file must be added. But in my case also tablet_core_hardware.xml needed an update, not mentioned in the previous link but explained here instead:
http://stackoverflow.com/questions/11183792/android-usb-host-and-hidden-devices :
add the file /system/etc/permissions/android.hardware.usb.host.xml with the following content:
<permissions>
<feature name="android.hardware.usb.host"/>
</permissions>
Edit /system/etc/permissions/tablet_core_hardware.xml adding in the section where other permissions are:
<feature name="android.hardware.usb.host" />
Note the ending slash, missing in original link!!
6) Reboot.
7) run again USB diagnostic, in my case now it reads:
Android API
Claims support: Yes
Classes found: Yes
Device detected: Yes
Best Regards,
Francesco.
