Do you need to write a Linux driver for a new USB device? Did you ask 
for help on a community mailing list, but the answer was "Use the 
Source, Luke"?

This was wise advice. The Linux sources contain hundreds of USB driver 
sources which you can learn from. You are also likely to find code for 
devices which are pretty similar to yours. You could then reuse some of 
this code for your device!

Now, you realize how fortunate you are compared to when you had to write 
the equivalent driver for a proprietary operating system! The only 
documentation you could find was the OS driver manual, and there was 
just one example from that manual. In addition, you couldn't even reuse 
that sample driver code as it was copyright protected by the OS vendor!!!

Now, you should be ready to use the Source. Just the Source? Some 
documentation would still help in understanding existing code faster.

Fortunately, an increasing number of documentation sources exist for 
Free and Open Source Software.

Free Electrons, a training and consulting company in Free and Open 
Source Software for embedded systems, has just released a new set of 
free training slides on USB device driver development: 
http://free-electrons.com/news/news.2007-01-21 .

These slides give details about the Linux USB implementation and the 
data structure it uses. They explains the API to create, transmit, and 
process the completion of USB Request Blocks, and details the resources 
a driver needs to register to support a USB device. They also give the 
most useful resources that were used by Free Electrons to create them.

Free Electrons also takes advantage of this announcement to send its 
best wishes to the whole user and developer community. Let 2007 be the 
Year of the Penguin! More details in our New Year's card: 
http://free-electrons.com/news/news.2007-01-01 . Just like everything 
produced by Free Electrons, this card is available under a free license. 
You can reuse it if you like it!

-- 
Michael Opdenacker, Free Electrons
Free Embedded Linux Training Materials
on http://free-electrons.com/training
(More than 1500 pages!)