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|
//! Stack Resource Policy for Cortex-M processors
//!
//! NOTE ARMv6-M is not supported at the moment.
#![feature(asm)]
#![feature(const_fn)]
#![no_std]
// NOTE Only the 4 highest bits of the priority byte (BASEPRI / NVIC.IPR) are
// considered when determining priorities.
const PRIORITY_BITS: u8 = 4;
extern crate cortex_m;
use cortex_m::interrupt::CsToken;
use cortex_m::register::{basepri, basepri_max};
use core::cell::UnsafeCell;
use core::marker::PhantomData;
// XXX why is this needed?
#[inline(always)]
fn compiler_barrier() {
unsafe {
asm!(""
:
:
: "memory"
: "volatile")
}
}
// XXX why is this needed?
#[inline(always)]
fn memory_barrier() {
unsafe {
asm!("dsb
isb"
:
:
: "memory"
: "volatile")
}
}
pub struct Peripheral<T>
where T: 'static
{
_ty: PhantomData<&'static mut T>,
address: usize,
ceiling: u8,
}
impl<T> Peripheral<T> {
pub const unsafe fn new(address: usize, ceiling: u8) -> Self {
Peripheral {
_ty: PhantomData,
address: address,
ceiling: ceiling,
}
}
pub fn claim<F, R>(&self, f: F) -> R
where F: FnOnce(&T) -> R
{
unsafe {
let old_basepri = basepri::read();
basepri_max::write(priority(self.ceiling));
memory_barrier();
let ret = f(&*(self.address as *const T));
compiler_barrier();
basepri::write(old_basepri);
ret
}
}
pub fn claim_mut<F, R>(&self, f: F) -> R
where F: FnOnce(&mut T) -> R
{
unsafe {
let old_basepri = basepri::read();
basepri_max::write(priority(self.ceiling));
memory_barrier();
let ret = f(&mut *(self.address as *mut T));
compiler_barrier();
basepri::write(old_basepri);
ret
}
}
pub fn take<'a>(&self, _token: &'a CsToken) -> &'a T {
unsafe {
&*(self.address as *const T)
}
}
pub fn take_mut<'a>(&self, _token: &'a CsToken) -> &'a mut T {
unsafe {
&mut *(self.address as *mut T)
}
}
}
pub struct Resource<T> {
ceiling: u8,
data: UnsafeCell<T>,
}
impl<T> Resource<T> {
pub const fn new(data: T, ceiling: u8) -> Self {
Resource {
ceiling: ceiling,
data: UnsafeCell::new(data),
}
}
pub fn claim<F, R>(&self, f: F) -> R
where F: FnOnce(&T) -> R
{
unsafe {
let old_basepri = basepri::read();
basepri_max::write(priority(self.ceiling));
memory_barrier();
let ret = f(&*self.data.get());
compiler_barrier();
basepri::write(old_basepri);
ret
}
}
pub fn claim_mut<F, R>(&self, f: F) -> R
where F: FnOnce(&mut T) -> R
{
unsafe {
let old_basepri = basepri::read();
basepri_max::write(priority(self.ceiling));
memory_barrier();
let ret = f(&mut *self.data.get());
compiler_barrier();
basepri::write(old_basepri);
ret
}
}
pub fn take<'a>(&self, _token: &'a CsToken) -> &'a T {
unsafe {
&*self.data.get()
}
}
pub fn take_mut<'a>(&self, _token: &'a CsToken) -> &'a mut T {
unsafe {
&mut *self.data.get()
}
}
}
unsafe impl<T> Sync for Resource<T> {}
/// Turns a `logical` priority into a NVIC-style priority
///
/// With `logical` priorities, `2` has HIGHER priority than `1`.
///
/// With NVIC priorities, `32` has LOWER priority than `16`. (Also, NVIC
/// priorities encode the actual priority in the highest bits of a byte so
/// priorities like `1` and `2` aren't actually different)
// TODO review the handling extreme value
pub fn priority(logical: u8) -> u8 {
((1 << PRIORITY_BITS) - logical) << (8 - PRIORITY_BITS)
}
|
