Use &raw to get fields of structs without creating an intermediate reference.
const SOME_DEVICE_REGISTER: *mut u64 = 0x800_0000 as _;
// SAFETY: Some device is mapped at this address.
unsafe {
SOME_DEVICE_REGISTER.write_volatile(0xff);
SOME_DEVICE_REGISTER.write_volatile(0x80);
assert_eq!(SOME_DEVICE_REGISTER.read_volatile(), 0xaa);
}
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 &raw to get struct field pointers from a pointer to the struct.
For compatibility with old versions of Rust you can use the addr_of! macro instead.