Introduce "peripheral" abstraction to share state between main and interrupt.

embassy-nrf/src/util/mod.rs

@@ -0,0 +1,2 @@
+pub mod peripheral;
+pub mod ring_buffer;

embassy-nrf/src/util/peripheral.rs

@@ -0,0 +1,107 @@
+use core::mem;
+use core::mem::MaybeUninit;
+use core::ptr;
+use core::sync::atomic::{compiler_fence, Ordering};
+use core::{cell::UnsafeCell, marker::PhantomData};
+
+use crate::interrupt::OwnedInterrupt;
+
+pub struct Store<T>(MaybeUninit<UnsafeCell<T>>);
+impl<T> Store<T> {
+    pub const fn uninit() -> Self {
+        Self(MaybeUninit::uninit())
+    }
+
+    unsafe fn as_mut_ptr(&self) -> *mut T {
+        (*self.0.as_ptr()).get()
+    }
+
+    unsafe fn as_mut(&self) -> &mut T {
+        &mut *self.as_mut_ptr()
+    }
+
+    unsafe fn write(&self, val: T) {
+        ptr::write(self.as_mut_ptr(), val)
+    }
+
+    unsafe fn drop_in_place(&self) {
+        ptr::drop_in_place(self.as_mut_ptr())
+    }
+
+    unsafe fn read(&self) -> T {
+        ptr::read(self.as_mut_ptr())
+    }
+}
+unsafe impl<T> Send for Store<T> {}
+unsafe impl<T> Sync for Store<T> {}
+
+pub trait State: Sized {
+    type Interrupt: OwnedInterrupt;
+    fn on_interrupt(&mut self);
+    #[doc(hidden)]
+    fn store<'a>() -> &'a Store<Self>;
+}
+
+pub struct Registration<P: State> {
+    irq: P::Interrupt,
+    not_send: PhantomData<*mut P>,
+}
+
+impl<P: State> Registration<P> {
+    pub fn new(irq: P::Interrupt, state: P) -> Self {
+        // safety:
+        // - No other PeripheralRegistration can already exist because we have the owned interrupt
+        // - therefore, storage is uninitialized
+        // - therefore it's safe to overwrite it without dropping the previous contents
+        unsafe { P::store().write(state) }
+
+        irq.set_handler(|| {
+            // safety:
+            // - If a PeripheralRegistration instance exists, P::storage() is initialized.
+            // - It's OK to get a &mut to it since the irq is disabled.
+            unsafe { P::store().as_mut() }.on_interrupt();
+        });
+
+        compiler_fence(Ordering::SeqCst);
+        irq.enable();
+
+        Self {
+            irq,
+            not_send: PhantomData,
+        }
+    }
+
+    pub fn with<R>(&mut self, f: impl FnOnce(&mut P, &mut P::Interrupt) -> R) -> R {
+        self.irq.disable();
+        compiler_fence(Ordering::SeqCst);
+
+        // safety:
+        // - If a PeripheralRegistration instance exists, P::storage() is initialized.
+        // - It's OK to get a &mut to it since the irq is disabled.
+        let r = f(unsafe { P::store().as_mut() }, &mut self.irq);
+
+        compiler_fence(Ordering::SeqCst);
+        self.irq.enable();
+
+        r
+    }
+
+    pub fn free(self) -> (P::Interrupt, P) {
+        let irq = unsafe { ptr::read(&self.irq) };
+        irq.disable();
+        irq.set_handler(|| ());
+        mem::forget(self);
+        let storage = P::store();
+        (irq, unsafe { storage.read() })
+    }
+}
+
+impl<P: State> Drop for Registration<P> {
+    fn drop(&mut self) {
+        self.irq.disable();
+        self.irq.set_handler(|| ());
+
+        let storage = P::store();
+        unsafe { storage.drop_in_place() };
+    }
+}

embassy-nrf/src/util/ring_buffer.rs

@@ -0,0 +1,80 @@
+use crate::fmt::{assert, panic, todo, *};
+
+pub struct RingBuffer<'a> {
+    buf: &'a mut [u8],
+    start: usize,
+    end: usize,
+    empty: bool,
+}
+
+impl<'a> RingBuffer<'a> {
+    pub fn new(buf: &'a mut [u8]) -> Self {
+        Self {
+            buf,
+            start: 0,
+            end: 0,
+            empty: true,
+        }
+    }
+
+    pub fn push_buf(&mut self) -> &mut [u8] {
+        if self.start == self.end && !self.empty {
+            trace!("  ringbuf: push_buf empty");
+            return &mut self.buf[..0];
+        }
+
+        let n = if self.start <= self.end {
+            self.buf.len() - self.end
+        } else {
+            self.start - self.end
+        };
+
+        trace!("  ringbuf: push_buf {:?}..{:?}", self.end, self.end + n);
+        &mut self.buf[self.end..self.end + n]
+    }
+
+    pub fn push(&mut self, n: usize) {
+        trace!("  ringbuf: push {:?}", n);
+        if n == 0 {
+            return;
+        }
+
+        self.end = self.wrap(self.end + n);
+        self.empty = false;
+    }
+
+    pub fn pop_buf(&mut self) -> &mut [u8] {
+        if self.empty {
+            trace!("  ringbuf: pop_buf empty");
+            return &mut self.buf[..0];
+        }
+
+        let n = if self.end <= self.start {
+            self.buf.len() - self.start
+        } else {
+            self.end - self.start
+        };
+
+        trace!("  ringbuf: pop_buf {:?}..{:?}", self.start, self.start + n);
+        &mut self.buf[self.start..self.start + n]
+    }
+
+    pub fn pop(&mut self, n: usize) {
+        trace!("  ringbuf: pop {:?}", n);
+        if n == 0 {
+            return;
+        }
+
+        self.start = self.wrap(self.start + n);
+        self.empty = self.start == self.end;
+    }
+
+    fn wrap(&self, n: usize) -> usize {
+        assert!(n <= self.buf.len());
+        if n == self.buf.len() {
+            0
+        } else {
+            n
+        }
+    }
+}