USB Monitor is a tool designed to monitor and restart USB devices connected to hubs or ports that support power switching. This is useful if you for example have a device placed in a remote location, and which depends on one or more USB devices to function correctly. USB Monitor can be run as a daemon and provides a small REST API for resetting individual ports. Checking if a device is alive is done using the GET_STATUS USB control message. Control messages have the advantage that they do not interfere with the normal operation of the device, and a reply is always expected.

The tool currently supports ports where the power is controlled through GPIO, as well as the Yepkit YKUSH hub. Support for controlling power using the standardized Clear/SetPortFeature USB-messages is also implemented, but currently not implemented. Some more work on cascading hub support is needed before generic per-port power control can be used (on hubs that support it). Pull requests are welcome :)

A concrete use-case is the EU-funded research-project MONROE, which funded the development of the tool. The project will build a testbed that enables users to measure different networks across Europe, with a focus on mobile broadband. Each measurement will be equipped with multiple USB MBB-modems, which needs to be power-cycled in case of for example a firmware crash.

USB Monitor depends on libusb and is compiled using cmake. USB Monitor must be run as root in order to work.

USB monitor supports the following command line parameters:

• -o : Path to log file. This is optional, if no log file is provided then stderr is used.
• -c : Path to configuration file. Also optional. This is currently used to provide a mapping between GPIO numbers and USB paths. See archer_c5.conf for an example.
• -d : Run USB Monitor as daemon.

The REST API currently supports one GET and one POST operation. For now, we ignore the URL and only look at HTTP method.

GET is used to get the status, vid and pid of the ports. An example of the output is:

{"ports":[{"path":"3-1-2-5-4-3","mode":1,"vid":4817,"pid":5382}]}

In order to restart one or more devices, a POST request must be sent. The syntax is as follows:

{"ports": [{"path":"3-1-2-5-4-3", "cmd": 1}]}

The reply is the same as for the GET request. Only the root-user can currently send HTTP requests to USB Monitor.

Adding new handlers if fairly straight forward. A handle needs to implement three callbacks:

• print_port() : Output details about the port
• update_port() : Used to reset, or start resetting port. Will most likely be called two times.
• handle_timeout() : The code is event-loop based, so a handler needs to handle timeouts. Examples of where timeouts are used, are for sending GET_STATUS or handling the second part of a reset.

The easiest is to look at either the YKUSH- or GPIO-handlers.