The instruction set reference (the architecture manual, to give it its proper title) has been freely available from ARM for some time, though you needed to cre

The instruction set reference (the architecture manual, to give it its proper title) has been freely available from ARM for some time, though you needed to create a website account and agree to a clickthrough license. It's more recently been made available as a simple download: https://developer.arm.com/products/architecture/a-profile/docs https://developer.arm.com/products/architecture/a-profile/do... for cortex-a profile https://developer.arm.com/products/architecture/m-profile/docs https://developer.arm.com/products/architecture/m-profile/do... for cortex-m profile For documentation of the devices in a particular SoC you'll need the reference manual from the SoC manufacturer -- they of course vary in how easy it is to find those docs.