Arm assembly getting started

Ref:

https://www.youtube.com/watch?v=15z_vn4H41U
https://www.youtube.com/watch?v=ViNnfoE56V8
http://goodmath.scientopia.org/2014/02/11/hello-world-in-arm-assembly-language/
http://thinkingeek.com/arm-assembler-raspberry-pi/
http://unix.stackexchange.com/questions/246463/how-can-you-find-out-which-registers-are-used-for-system-calls