This device drivers book it cool because it does into the real details you need to know and that you’d expect to know so I’m quite satisfied but its tricky. One of the examples of controlling internal hardware was controlling the CMOS by writing to the memory region(and requesting access to it) and more importantly the code required to create the device nodes in /dev/ and /sys which provide both a menas of input from user space and output. Then there was a really cool example of interfacing with the parallel port to drive LEDs on a board connected to the same parallel port interfaced with the computer. The driver would be responsible for providing /sys/led0-8 which can be written to to turn on the corresponding LEDs. Now thats cool.
I thnk my next thing on the TODO list is to build a simiar LED project myself and control it.