5 docs tagged with "volatile"

CV-qualifiers (const and volatile) modify type behavior. const prevents modification; volatile prevents compiler optimization.

Raising the optimization level is the one build change that routinely alters what a firmware does. Not what it does more quickly — what it does. A delay loop disappears. A register write that was there at -O0 is gone at -O2. Code that worked for two years starts failing, and nothing in the source changed.

A peripheral is a piece of digital logic sitting on the same bus as your RAM. It has no API, no calling convention and no way to be invoked. The only interface it exposes is a small block of addresses: write a word to one of them and some flip-flops change state; read from another and you get the current state of some wires. That is the whole model.

volatile tells compiler that a variable can change unexpectedly (hardware, interrupts, other threads). Prevents certain optimizations. Not for thread synchronization - use atomics instead.

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.