zynq-rs/libcortex_a9/src/sync_channel.rs

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use core::{
future::Future,
pin::Pin,
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ptr::null_mut,
sync::atomic::{AtomicPtr, Ordering},
task::{Context, Poll},
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};
use alloc::{
boxed::Box,
sync::Arc,
vec::Vec,
};
use super::asm::*;
type Channel<T> = Vec<AtomicPtr<T>>;
/// Create a bounded channel
///
/// Returns `(tx, rx)` where one should be used one the local core,
/// and the other is to be shared with another core.
pub fn sync_channel<T>(bound: usize) -> (Sender<T>, Receiver<T>) {
// allow for bound=0
let len = bound + 1;
let mut channel = Vec::with_capacity(len);
for _ in 0..len {
channel.push(AtomicPtr::default());
}
let channel = Arc::new(channel);
let sender = Sender {
channel: channel.clone(),
pos: 0,
};
let receiver = Receiver {
channel: channel,
pos: 0,
};
(sender, receiver)
}
/// Sending half of a channel
pub struct Sender<T> {
channel: Arc<Channel<T>>,
pos: usize,
}
impl<T> Sender<T> {
/// Blocking send
pub fn send<B: Into<Box<T>>>(&mut self, content: B) {
let ptr = Box::into_raw(content.into());
let entry = &self.channel[self.pos];
// try to write the new pointer if the current pointer is
// NULL, retrying while it is not NULL
while entry.compare_and_swap(null_mut(), ptr, Ordering::Acquire) != null_mut() {
// power-saving
wfe();
}
dsb();
// wake power-saving receivers
sev();
// advance
self.pos += 1;
// wrap
if self.pos >= self.channel.len() {
self.pos = 0;
}
}
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/// Non-blocking send, handing you back ownership of the content on **failure**
pub fn try_send<B: Into<Box<T>>>(&mut self, content: B) -> Option<Box<T>> {
let ptr = Box::into_raw(content.into());
let entry = &self.channel[self.pos];
// try to write the new pointer if the current pointer is
// NULL
if entry.compare_and_swap(null_mut(), ptr, Ordering::Acquire) == null_mut() {
dsb();
// wake power-saving receivers
sev();
// advance
self.pos += 1;
// wrap
if self.pos >= self.channel.len() {
self.pos = 0;
}
// success
None
} else {
let content = unsafe { Box::from_raw(ptr) };
// failure
Some(content)
}
}
pub async fn async_send<B: Into<Box<T>>>(&mut self, content: B) {
struct Send<'a, T> {
sender: &'a mut Sender<T>,
content: Option<Box<T>>,
}
impl<T> Future for Send<'_, T> {
type Output = ();
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
match self.content.take() {
Some(content) => {
if let Some(content) = self.sender.try_send(content) {
// failure
self.content = Some(content);
cx.waker().wake_by_ref();
Poll::Pending
} else {
// success
Poll::Ready(())
}
}
None => panic!("Send future polled after success"),
}
}
}
Send {
sender: self,
content: Some(content.into()),
}.await
}
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}
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/// Receiving half of a channel
pub struct Receiver<T> {
channel: Arc<Channel<T>>,
pos: usize,
}
impl<T> Receiver<T> {
/// Blocking receive
pub fn recv(&mut self) -> Box<T> {
let entry = &self.channel[self.pos];
loop {
dmb();
let ptr = entry.swap(null_mut(), Ordering::Release);
if ptr != null_mut() {
dsb();
// wake power-saving senders
sev();
let content = unsafe { Box::from_raw(ptr) };
// advance
self.pos += 1;
// wrap
if self.pos >= self.channel.len() {
self.pos = 0;
}
return content;
}
// power-saving
wfe();
}
}
/// Non-blocking receive
pub fn try_recv(&mut self) -> Option<Box<T>> {
let entry = &self.channel[self.pos];
dmb();
let ptr = entry.swap(null_mut(), Ordering::Release);
if ptr != null_mut() {
dsb();
// wake power-saving senders
sev();
let content = unsafe { Box::from_raw(ptr) };
// advance
self.pos += 1;
// wrap
if self.pos >= self.channel.len() {
self.pos = 0;
}
Some(content)
} else {
None
}
}
pub async fn async_recv(&mut self) -> Box<T> {
struct Recv<'a, T> {
receiver: &'a mut Receiver<T>,
}
impl<T> Future for Recv<'_, T> {
type Output = Box<T>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
if let Some(content) = self.receiver.try_recv() {
Poll::Ready(content)
} else {
cx.waker().wake_by_ref();
Poll::Pending
}
}
}
Recv {
receiver: self,
}.await
}
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}
impl<T> Iterator for Receiver<T> {
type Item = Box<T>;
fn next(&mut self) -> Option<Self::Item> {
Some(self.recv())
}
}