I had this book https://archive.org/details/arm-arc...complete-programming-course-se-covers-risc-os and my dad bought me the RiscOS Programmers Reference Guide (a set of books that documented all the SWIs etc).
At uni I shared my final year house with Berty (Tom Cooper) who wrote and sold a number of games on the arch. Xymox who wrote the music for many of tom's games was on the campus too.
Heh I've still got one for 6502 assembly language for the BBC Micro somewhere or other can still remember most of thatI still have this one (Martyn not Martin) covered the fundamentals decently, I've got the RISC OS Programmers Reference Guide somewhere as well but probably in storage now - couldn't find it from a quick dig.
Sadly I've forgotten most of what I know now about ARM programming - I look back at some of the stuff I did and was like "I did that!?!" - OK some techniques are extremely dated now hah.