Many mbed users are dreaming of getting a bit closer to the hardware. A systematic approach is offered with BMPTK. You can read about it here: http://www.voti.nl/bmptk/docs/index.html.

Though I have no experience with it, I know that the writer (Wouter van Ooijen) is an experienced professional and he is an excellent teacher. So you may expect that BMPTK is well designed and documented. You also can expect good help. Wouter likes it to assist when you want to learn something new.

I had a look at it, and maybe I am missing something, but how is that related to getting closer to the hardware? The mbed environment allows you easily to get close to the hardware since stuff like all register names follow the standard convention and are easily accessible. Most of my own published libraries directly access registers.

And just like with for example an arduino it helps alot you still got your framework, so you can do for example printf style debugging, or flashing a LED, while at the same time using the ADC directly via its registers.