Volatile memory access for MMIO

  • Use pointer::read_volatile and pointer::write_volatile.
  • Never hold a reference.
  • addr_of! lets you get fields of structs without creating an intermediate reference.
  • Volatile access: read or write operations may have side-effects, so prevent the compiler or hardware from reordering, duplicating or eliding them.
    • Usually if you write and then read, e.g. via a mutable reference, the compiler may assume that the value read is the same as the value just written, and not bother actually reading memory.
  • Some existing crates for volatile access to hardware do hold references, but this is unsound. Whenever a reference exist, the compiler may choose to dereference it.
  • Use the addr_of! macro to get struct field pointers from a pointer to the struct.