If you&#x27;re interested in low-level code (assembly, JITs, Forth, etc.), note that official documentation for the ARM ISA has considerable encumbrance. It&#x27;s not like most architectures where you just go to the manufacturer&#x27;s website and download a PDF of the programming manual; ARM makes you register an account and agree to a rather restrictive clickwrap license (something to the effect of &quot;you&#x27;re only allowed to use this manual to support our products, not to compete with us&quot;).<p>This seems to not be common knowledge. Maybe the atmosphere of typical ARM applications is already so buried under NDAs that nobody cares, or maybe people just punch &quot;ARM Architecture Reference Manual&quot; into Google and grab one of the many slightly-outdated copies that are floating around on .edu servers. But I found it pretty surprising after seeing how widespread ARM is in &quot;open&quot; hardware.