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zynq-rs/libcortex_a9/src/sync_channel.rs

105 lines
2.4 KiB
Rust
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2020-04-09 08:49:24 +08:00
use core::{
ptr::null_mut,
sync::atomic::{AtomicPtr, Ordering},
};
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;
}
}
}
/// 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();
}
}
}