his document describes, as completely as I am aware of, the ARM instruction set. If, however, you are only interested in the instructions relating to programming under RISC OS, you may prefer to read the shorter quick finder document...
Here are links to various resources for ARMLinux. Mostly off-site but some are maintained here. <a target=_blank href=http://www.aleph1.co.uk/armlinux/>http://www.aleph1.co.uk/armlinux/</a>