http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=3105/4 [Linux kernel calling convention]
file:///usr/include/arm-linux-gnueabihf/asm/unistd.h [System calls]
https://community.arm.com/processors/b/blog/posts/useful-assembler-directives-and-macros-for-the-gnu-assembler [Useful assembler directives and macros for gas]
http://bob.cs.sonoma.edu/IntroCompOrg-RPi/intro-co-rpi.html [Bob’s intro to assembler on the RPi]
https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/ [Alex’s into to assembler on the RPi (Model A and Pi zero)]
https://elinux.org/RPi_Low-level_peripherals [PIN Header description]