I would like to learn how to write device drivers because I think it would be fun. I use a Mac OS X Macbook, but I also have an Ubuntu machine (running on a Mac Min). I am pretty familiar with C and currently am reading this book. I have found some links online such as Mac Dev Center. I am doing this because it would be fun. I think there would be real gratification to see hardware operate because of software I wrote.
I guess what I would like is some tips or advice and guidance, and does anyone know of a list of devices that don't have drivers or can I write a driver for something that's already supported (would prefer the former so I'm actually providing value). What's a good device to get started with? Am I biting off more than I can chew? I'm not afraid of low level programming or assembly or whatever amount of effort is required. I'd like a challenge really!
For Linux, you might look into picking up the O'Reilly Linux Device Drivers book or reading PDFs online. In my opinion, it is one of the better texts around on the subject.
The Linux Kernel Module Programming Guide is another good resource.
You may also want to pick up a book specifically on the Linux Kernel. I picked up a copy of Robert Love's Linux Kernel Development (2nd Edition) for this purpose (3rd Edition on the way).