ERROR::dwc_otg_hcd_urb_enqueue:515: Not connected
Running /etc/init.d/networking restart is deprecated because it may not enable again some interfaces
Failed to bring up wlan0.
Running /etc/init.d/networking restart is deprecated because it may not re-enable
以上提示，是因为电源电压不足导致
raspberryPI 电源不足引起usb wifi模块 出现的问题
原文：http://www.cnblogs.com/2zhyi/p/3561195.html