Book/docs for advanced Arduino programming

Hello,

I am relatively new to Arduino, and was wondering if someone could suggest books or documentation on AVR programming. In my search for some PCM ideas, I came across Arduino code that uses direct port manipulation, and code that sets up timers/interrupts. I'd appreciate pointers to any books or online docs that would help me understand the AVR architecture and the C API calls.

Thanks

MV

Have a look at:- Arduino Playground - HomePage

I came across Arduino code that uses direct port manipulation

and:- Arduino Reference - Arduino Reference

Thanks!