What volatile Does and Does Not Do
volatile has a reputation for being either a magic word that makes hardware access work or a deprecated relic that nobody should use. Both readings come from the same place: people learn what it does by observing that adding it fixed a bug, and never learn the boundary of the guarantee. The boundary is narrow, it is written down precisely in the C standard, and knowing exactly where it stops is what separates code that works from code that works on your desk.