how to code for ARM in C Programming Urgent Please Need References
You have not specified which processor you are using, but to give some general info, the toolchain documentation should provide some insight, for example the Arm Compiler for Embedded documentation:https://developer.arm.com/documentation/100748/0617/Writing-Optimized-Code
There is general information in various application notes:https://www2.keil.com/mdk5/learn
For a thorough description, I recommend this book (similar exist for other processors):https://www.oreilly.com/library/view/the-definitive-guide/9780124080829/