Hi, Actually this is due to USB selective suspend which is taking device to the Auto Sleep mode.
There is no need to stop legato PowerMgr.
The following are the steps to be followed to disable the autosleep mode in WP8548 :
first way (not persistent after a reboot) :
To enable deep sleep, execute following shell command in console:
echo mem > /sys/power/autosleep
current firmware by default the deep sleep mode is enabled, and keep in
mind above command shall be executed upon every power cycling in order
for deep sleep mode to be disabled.
To disable deep sleep, execute following shell command in console:
echo 0 > /sys/power/autosleep