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|
//! Safe wrapper for closure-based interrupt handlers.
//!
//! # Notes
//!
//! The number of entries allowed is defined by Cargo features. The
//! default is 32 as this seems a reasonable comprimise between the
//! size of the array and utility. Each array entry costs two words of
//! space for the closure reference. Thus a full array of 256 entries
//! on a 32-bit architecture costs 2048 bytes of memory, which can be
//! quite a lot on resource constrained devices.
//!
//! One day, when const-generics are stabilized, this will be more
//! elegant.
//!
//! # Examples
//!
//! ``` no_run
//! use clint::HandlerArray;
//! use cortex_m_rt::exception;
//!
//! static HANDLERS: HandlerArray = HandlerArray::new();
//!
//! fn main() {
//! // NB: This closure has to be created outside of `with_overrides` to
//! // ensure it lives as long as `with_overrides` scope lasts.
//! let mut cl = || {
//! // Your interrupt handling code.
//! };
//! HANDLERS.with_overrides(|arr| {
//! arr.register(0, &mut cl);
//!
//! loop {
//! // Your main loop.
//! }
//! })
//! }
//!
//! #[exception]
//! fn SysTick() {
//! HANDLERS.call(0);
//! }
//! ```
use crate::cs::{CriticalSection, Locker};
use crate::Handler;
use core::cell::UnsafeCell;
// Define features for the underlying array size so that we can
// statically allocate it.
// TODO: Use const generics when available.
#[cfg(feature = "isr-8")]
const NR_ISR: usize = 8;
#[cfg(feature = "isr-16")]
const NR_ISR: usize = 16;
#[cfg(feature = "isr-32")]
const NR_ISR: usize = 32;
#[cfg(feature = "isr-64")]
const NR_ISR: usize = 64;
#[cfg(feature = "isr-128")]
const NR_ISR: usize = 128;
#[cfg(feature = "isr-256")]
const NR_ISR: usize = 256;
/// Safely use `Handler`s by enclosing them in an array.
///
/// This type provides a safe wrapper around `Handler` by ensuring
/// that closures are swapped safely using critical sections, and that
/// the lifetime of those handlers is sufficient by using the inner
/// scope of `with_overrides`/`lock_overrides`.
#[derive(Debug)]
pub struct HandlerArray<'a> {
h: UnsafeCell<[Handler<'a>; NR_ISR]>,
}
impl<'a> HandlerArray<'a> {
/// Create a new `HandlerArray` filled with no-op handlers.
pub const fn new() -> Self {
Self {
h: UnsafeCell::new([Handler::new(); NR_ISR]),
}
}
/// Register `f` for entry `nr` in this array using the default
/// critical section locker.
pub fn register<F>(&self, nr: usize, f: &'a mut F)
where
F: FnMut() + Send + 'a,
{
self.lock_register(&Locker::new(), nr, f)
}
/// Register `f` for entry `nr` in this array using `cs` to create
/// a critical section for updating the array.
pub fn lock_register<F, CS>(&self, cs: &CS, nr: usize, f: &'a mut F)
where
F: FnMut() + Send + 'a,
CS: CriticalSection,
{
cs.with_lock(|| unsafe { (*self.h.get())[nr].replace(f) });
}
/// Call the handler for entry `nr`.
pub fn call(&self, nr: usize) {
// Unsafe: there's always a valid handler to call except for
// when it's being actively replaced. As long as that happens
// while in a critical section, there's no risk of data races.
unsafe { (*self.h.get())[nr].call() }
}
/// Create a new array for use in `f`'s scope. The existing
/// handlers can be overridden using `register` or
/// `lock_register`. When `f` exits, all previous handlers are
/// restored.
pub fn with_overrides<'b>(&self, f: impl FnOnce(&HandlerArray<'b>)) {
self.lock_overrides(&Locker::new(), f)
}
/// Same as `with_overrides` but allows you to specify your own
/// implementation of `CriticalSection` instead of using the
/// default.
pub fn lock_overrides<'b, CS>(&self, cs: &CS, f: impl FnOnce(&HandlerArray<'b>))
where
CS: CriticalSection,
{
// Create a shorter-lived array from `self` that matches the
// lifetime of `f` so we can make sure `register` is only
// called with closures that will live as long as `f` does.
//
// Unsafe: This requires that we back up and restore the handlers
// in the array to make sure there's always something alive in
// whatever the real scope of `array' is.
let tmp: &HandlerArray<'b> = unsafe { core::mem::transmute(self) };
// Back up old handlers before entering inner scope so we can
// restore them on exit.
let bk = HandlerArray::new();
unsafe { core::ptr::copy_nonoverlapping(tmp.h.get(), bk.h.get(), 1) }
f(tmp);
// Put the old handlers back inside a critical section to avoid
// data races.
cs.with_lock(|| unsafe { core::ptr::copy_nonoverlapping(bk.h.get(), tmp.h.get(), 1) });
}
}
// Unsafe: as long as `register` and `with_overrides` use critical
// sections appropriately, it should be safe to share this between
// threads.
unsafe impl<'a> Sync for HandlerArray<'a> {}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn overrides_unwind() {
static mut CALLS: usize = 0;
let mut cl = || unsafe { CALLS += 1 };
let cl_ref = &mut cl;
let ht = HandlerArray::new();
ht.with_overrides(|t| {
t.register(0, cl_ref);
ht.call(0);
});
unsafe { assert_eq!(CALLS, 1) };
ht.call(0);
unsafe { assert_eq!(CALLS, 1) };
}
}
|
