1 files changed, 146 insertions, 0 deletions

diff --git a/embassy-sync/src/ring_buffer.rs b/embassy-sync/src/ring_buffer.rs
new file mode 100644
index 000000000..521084024
--- /dev/null
+++ b/embassy-sync/src/ring_buffer.rs
@@ -0,0 +1,146 @@
+pub struct RingBuffer<const N: usize> {
+    buf: [u8; N],
+    start: usize,
+    end: usize,
+    empty: bool,
+}
+
+impl<const N: usize> RingBuffer<N> {
+    pub const fn new() -> Self {
+        Self {
+            buf: [0; N],
+            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;
+    }
+
+    pub fn is_full(&self) -> bool {
+        self.start == self.end && !self.empty
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.empty
+    }
+
+    #[allow(unused)]
+    pub fn len(&self) -> usize {
+        if self.empty {
+            0
+        } else if self.start < self.end {
+            self.end - self.start
+        } else {
+            N + self.end - self.start
+        }
+    }
+
+    pub fn clear(&mut self) {
+        self.start = 0;
+        self.end = 0;
+        self.empty = true;
+    }
+
+    fn wrap(&self, n: usize) -> usize {
+        assert!(n <= self.buf.len());
+        if n == self.buf.len() {
+            0
+        } else {
+            n
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn push_pop() {
+        let mut rb: RingBuffer<4> = RingBuffer::new();
+        let buf = rb.push_buf();
+        assert_eq!(4, buf.len());
+        buf[0] = 1;
+        buf[1] = 2;
+        buf[2] = 3;
+        buf[3] = 4;
+        rb.push(4);
+
+        let buf = rb.pop_buf();
+        assert_eq!(4, buf.len());
+        assert_eq!(1, buf[0]);
+        rb.pop(1);
+
+        let buf = rb.pop_buf();
+        assert_eq!(3, buf.len());
+        assert_eq!(2, buf[0]);
+        rb.pop(1);
+
+        let buf = rb.pop_buf();
+        assert_eq!(2, buf.len());
+        assert_eq!(3, buf[0]);
+        rb.pop(1);
+
+        let buf = rb.pop_buf();
+        assert_eq!(1, buf.len());
+        assert_eq!(4, buf[0]);
+        rb.pop(1);
+
+        let buf = rb.pop_buf();
+        assert_eq!(0, buf.len());
+
+        let buf = rb.push_buf();
+        assert_eq!(4, buf.len());
+    }
+}