Some notes on USB Device Driver development and debugging

embeddedlinuxenea — Sun, 11 Sep 2011 20:04:37 +0000

The USB protocol is quite complex. Luckily (for those of us developing USB device drivers) there are drivers in the kernel designed specifically to test USB drivers.

These can be used to test both Host Controller Drivers (HCDs) and USB Device Controllers (UDCs). To run the tests, you need the “USB testing driver” on the USB host. This driver can be found at

Device drivers -> USB support -> USB testing driver (CONFIG_USB_TEST)

For the device, there are several options, but the simplest seem to be to find some hardware capable of being a USB Device (“Gadget”) and of running Linux (of course, if you are developing a driver for a UDC, then the test gadget is the gadget you are writing the UDC driver for). The gadget kernel should then be configured with

Device drivers -> USB support -> USB Gadget Support -> USB Gadget Drivers -> Gadget Zero (CONFIG_USB_ZERO)

You then need to visit http://www.linux-usb.org/usbtest/ and download the testusb.c program and the test.sh shell script. For a simple test, build testusb.c on your host and hook up your gadget. Then run

./testusb -a

… and wait a few minutes. (Test 14 might fail due to a bug in the test itself; you may need to specify the “vary” parameter for this test to pass.)

If everything seems fine, well, it’s too soon to congratulate yourself. The usbtest homepage above explains how to use the test.sh script to really excercise your hardware and software.

If you DO find problems, you need to start looking into the source code of the test program and kernel to find out what goes wrong.

A great help in finding out what goes wrong is the usbmon interface, with in-kernel documentation at

Documentation/usb/usbmon.txt

Also, don’t forget the Linux USB maillist, where you can ask incredibly knowledgeable people (the people who wrote the code ) what is going on. Information about the linux-usb maillist can be found at

http://vger.kernel.org/vger-lists.html#linux-usb

Arvid Brodin
Linux developer
Enea Experts Stockholm

New article by Anders Törnqvist

embeddedlinuxenea — Tue, 28 Jun 2011 08:43:37 +0000

The Enea Experts Embedded Linux Hub is proud to have Anders Törnqvist contributing with recurring articles on interesting and current topics in the field of embedded Linux.

This time Anders presents a Linux system overview. The article can be found on the Enea Experts Embedded Linux Hub webpage. A previous article in this series discussed Linux and other FOSS in embedded systems.

Anders’ articles will be recurring monthly throughout the year, so make sure to check back in for more!

Welcome!

embeddedlinuxenea — Mon, 23 May 2011 06:17:55 +0000

This blog will be maintained by the Embedded Linux Expert Hub, which collects employees of Enea Experts that work with Embedded Linux and open source software each day, professionally and as an personal interest.

We will try to share some of our thoughts and experiences on the subject, describe current and topical stories and problems, as well as provide you with tips for upcoming events and seminars etc.