How should I get started on writing device drivers? [closed]

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).

Writing a device driver can be pretty simple, or it can be almost arbitrarily complicated. For instance, I've been involved in a project where it took six of us almost three years to solve ONE bug in a device driver. Of course, we cleared out dozens of other bugs while looking for it... the code improved immensely. The fix turned out to be an eight line patch, that cost, conservatively, about a million dollars.

But, as a side project to that, I wrote an ethernet driver from the chip data sheet in a week, and took another week to debug it. Haven't needed to touch it since.

There's no way to say in general how much work a driver will be; a GPU driver could cost hundreds of millions, a driver for a single LED costs a couple of hours work at the most.

If you want to go for Linux device driver development, the freely available O'Reilly book Linux Device Drivers, Third Edition is a must read.

In order to find unsupported hardware pieces for which you could write a driver, ask on the Linux mailing lists. Maybe some USB 3.0 device? ;)