USB ROM for Nexus 7 is based on CyanogenMod 10.1 + Timur's USB Host kernel. This ROM offers extended USB functionality and support for powered USB host operation. USB ROM enables you to run your N7 in 24/7 stationary mode with many USB slave devices attached.

Whenever you connect a USB slave device to your Nexus 7, you also loose one thing: ADB over USB. In order to still be able to tinker with your tablet, or just to view logs in realtime, you need 'Boot with ADB over network'.

This page provides standalone kernel images for Android 4.2.x and CyanogenMod 10.1.

In some situations, using ADB can be a little more difficult, than just connecting your phone via USB cable. This is the case, when your Android device has only one USB socket and you are using this USB socket to connect other USB devices (for instance a USB mouse or a flash drive). In such a case, your Android device will run in USB host mode, playing the role of a PC. If you want to do some on device debugging now, you need to use ADB over WiFi.

Timur's kernel for Nexus 7 enables you to connect multiple USB devices (DAC, ethernet adapter, flash drive, hard drive, DVB/T, mouse, keyboard) and operate all of these devices from internal battery or using an external power source. When using an external power supply, there will be no battery drain and your N7 will even charge. A special variant of the kernel is available for permanent installations, such as in-car dashboard setups.

Nexus 7 in USB host mode, operating a slave device and being charged at the same time? Here is an installable kernel image that makes it possible.