1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52

//! Just like [`Cell`] but with [volatile] read / write operations
//!
//! [`Cell`]: https://doc.rust-lang.org/std/cell/struct.Cell.html
//! [volatile]: https://doc.rust-lang.org/std/ptr/fn.read_volatile.html

#![deny(missing_docs)]
#![deny(warnings)]
#![no_std]

use core::cell::UnsafeCell;
use core::ptr;

/// Just like [`Cell`] but with [volatile] read / write operations
///
/// [`Cell`]: https://doc.rust-lang.org/std/cell/struct.Cell.html
/// [volatile]: https://doc.rust-lang.org/std/ptr/fn.read_volatile.html
#[repr(transparent)]
pub struct VolatileCell<T> {
    value: UnsafeCell<T>,
}

impl<T> VolatileCell<T> {
    /// Creates a new `VolatileCell` containing the given value
    pub const fn new(value: T) -> Self {
        VolatileCell { value: UnsafeCell::new(value) }
    }

    /// Returns a copy of the contained value
    #[inline(always)]
    pub fn get(&self) -> T
        where T: Copy
    {
        unsafe { ptr::read_volatile(self.value.get()) }
    }

    /// Sets the contained value
    #[inline(always)]
    pub fn set(&self, value: T)
        where T: Copy
    {
        unsafe { ptr::write_volatile(self.value.get(), value) }
    }

    /// Returns a raw pointer to the underlying data in the cell
    #[inline(always)]
    pub fn as_ptr(&self) -> *mut T {
        self.value.get()
    }
}

// NOTE implicit because of `UnsafeCell`
// unsafe impl<T> !Sync for VolatileCell<T> {}