657 lines
24 KiB
Rust
657 lines
24 KiB
Rust
#![cfg_attr(gpdma, allow(unused))]
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use core::future::poll_fn;
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use core::ops::Range;
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use core::sync::atomic::{compiler_fence, Ordering};
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use core::task::{Poll, Waker};
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use super::word::Word;
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/// A "read-only" ring-buffer to be used together with the DMA controller which
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/// writes in a circular way, "uncontrolled" to the buffer.
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///
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/// A snapshot of the ring buffer state can be attained by setting the `ndtr` field
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/// to the current register value. `ndtr` describes the current position of the DMA
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/// write.
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///
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/// # Buffer layout
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///
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/// ```text
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/// Without wraparound: With wraparound:
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///
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/// + buf +--- NDTR ---+ + buf +---------- NDTR ----------+
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/// | | | | | |
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/// v v v v v v
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/// +-----------------------------------------+ +-----------------------------------------+
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/// |oooooooooooXXXXXXXXXXXXXXXXoooooooooooooo| |XXXXXXXXXXXXXooooooooooooXXXXXXXXXXXXXXXX|
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/// +-----------------------------------------+ +-----------------------------------------+
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/// ^ ^ ^ ^ ^ ^
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/// | | | | | |
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/// +- start --+ | +- end ------+ |
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/// | | | |
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/// +- end --------------------+ +- start ----------------+
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/// ```
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pub struct ReadableDmaRingBuffer<'a, W: Word> {
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pub(crate) dma_buf: &'a mut [W],
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start: usize,
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}
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#[derive(Debug, PartialEq)]
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pub struct OverrunError;
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pub trait DmaCtrl {
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/// Get the NDTR register value, i.e. the space left in the underlying
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/// buffer until the dma writer wraps.
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fn get_remaining_transfers(&self) -> usize;
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/// Get the transfer completed counter.
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/// This counter is incremented by the dma controller when NDTR is reloaded,
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/// i.e. when the writing wraps.
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fn get_complete_count(&self) -> usize;
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/// Reset the transfer completed counter to 0 and return the value just prior to the reset.
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fn reset_complete_count(&mut self) -> usize;
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/// Set the waker for a running poll_fn
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fn set_waker(&mut self, waker: &Waker);
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}
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impl<'a, W: Word> ReadableDmaRingBuffer<'a, W> {
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pub fn new(dma_buf: &'a mut [W]) -> Self {
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Self { dma_buf, start: 0 }
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}
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/// Reset the ring buffer to its initial state
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pub fn clear(&mut self, dma: &mut impl DmaCtrl) {
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self.start = 0;
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dma.reset_complete_count();
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}
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/// The capacity of the ringbuffer
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pub const fn cap(&self) -> usize {
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self.dma_buf.len()
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}
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/// The current position of the ringbuffer
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fn pos(&self, dma: &mut impl DmaCtrl) -> usize {
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self.cap() - dma.get_remaining_transfers()
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}
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/// Read an exact number of elements from the ringbuffer.
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///
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/// Returns the remaining number of elements available for immediate reading.
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/// OverrunError is returned if the portion to be read was overwritten by the DMA controller.
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///
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/// Async/Wake Behavior:
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/// The underlying DMA peripheral only can wake us when its buffer pointer has reached the halfway point,
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/// and when it wraps around. This means that when called with a buffer of length 'M', when this
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/// ring buffer was created with a buffer of size 'N':
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/// - If M equals N/2 or N/2 divides evenly into M, this function will return every N/2 elements read on the DMA source.
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/// - Otherwise, this function may need up to N/2 extra elements to arrive before returning.
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pub async fn read_exact(&mut self, dma: &mut impl DmaCtrl, buffer: &mut [W]) -> Result<usize, OverrunError> {
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let mut read_data = 0;
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let buffer_len = buffer.len();
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poll_fn(|cx| {
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dma.set_waker(cx.waker());
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compiler_fence(Ordering::SeqCst);
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match self.read(dma, &mut buffer[read_data..buffer_len]) {
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Ok((len, remaining)) => {
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read_data += len;
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if read_data == buffer_len {
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Poll::Ready(Ok(remaining))
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} else {
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Poll::Pending
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}
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}
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Err(e) => Poll::Ready(Err(e)),
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}
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})
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.await
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}
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/// Read elements from the ring buffer
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/// Return a tuple of the length read and the length remaining in the buffer
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/// If not all of the elements were read, then there will be some elements in the buffer remaining
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/// The length remaining is the capacity, ring_buf.len(), less the elements remaining after the read
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/// OverrunError is returned if the portion to be read was overwritten by the DMA controller.
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pub fn read(&mut self, dma: &mut impl DmaCtrl, buf: &mut [W]) -> Result<(usize, usize), OverrunError> {
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/*
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This algorithm is optimistic: we assume we haven't overrun more than a full buffer and then check
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after we've done our work to see we have. This is because on stm32, an interrupt is not guaranteed
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to fire in the same clock cycle that a register is read, so checking get_complete_count early does
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not yield relevant information.
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Therefore, the only variable we really need to know is ndtr. If the dma has overrun by more than a full
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buffer, we will do a bit more work than we have to, but algorithms should not be optimized for error
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conditions.
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After we've done our work, we confirm that we haven't overrun more than a full buffer, and also that
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the dma has not overrun within the data we could have copied. We check the data we could have copied
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rather than the data we actually copied because it costs nothing and confirms an error condition
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earlier.
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*/
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let end = self.pos(dma);
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if self.start == end && dma.get_complete_count() == 0 {
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// No elements are available in the buffer
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Ok((0, self.cap()))
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} else if self.start < end {
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// The available, unread portion in the ring buffer DOES NOT wrap
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// Copy out the elements from the dma buffer
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let len = self.copy_to(buf, self.start..end);
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compiler_fence(Ordering::SeqCst);
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/*
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first, check if the dma has wrapped at all if it's after end
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or more than once if it's before start
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this is in a critical section to try to reduce mushy behavior.
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it's not ideal but it's the best we can do
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then, get the current position of of the dma write and check
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if it's inside data we could have copied
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*/
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let (pos, complete_count) = critical_section::with(|_| (self.pos(dma), dma.get_complete_count()));
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if (pos >= self.start && pos < end) || (complete_count > 0 && pos >= end) || complete_count > 1 {
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Err(OverrunError)
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} else {
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self.start = (self.start + len) % self.cap();
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Ok((len, self.cap() - self.start))
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}
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} else if self.start + buf.len() < self.cap() {
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// The available, unread portion in the ring buffer DOES wrap
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// The DMA writer has wrapped since we last read and is currently
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// writing (or the next byte added will be) in the beginning of the ring buffer.
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// The provided read buffer is not large enough to include all elements from the tail of the dma buffer.
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// Copy out from the dma buffer
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let len = self.copy_to(buf, self.start..self.cap());
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compiler_fence(Ordering::SeqCst);
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/*
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first, check if the dma has wrapped around more than once
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then, get the current position of of the dma write and check
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if it's inside data we could have copied
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*/
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let pos = self.pos(dma);
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if pos > self.start || pos < end || dma.get_complete_count() > 1 {
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Err(OverrunError)
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} else {
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self.start = (self.start + len) % self.cap();
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Ok((len, self.start + end))
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}
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} else {
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// The available, unread portion in the ring buffer DOES wrap
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// The DMA writer has wrapped since we last read and is currently
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// writing (or the next byte added will be) in the beginning of the ring buffer.
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// The provided read buffer is large enough to include all elements from the tail of the dma buffer,
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// so the next read will not have any unread tail elements in the ring buffer.
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// Copy out from the dma buffer
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let tail = self.copy_to(buf, self.start..self.cap());
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let head = self.copy_to(&mut buf[tail..], 0..end);
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compiler_fence(Ordering::SeqCst);
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/*
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first, check if the dma has wrapped around more than once
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then, get the current position of of the dma write and check
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if it's inside data we could have copied
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*/
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let pos = self.pos(dma);
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if pos > self.start || pos < end || dma.reset_complete_count() > 1 {
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Err(OverrunError)
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} else {
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self.start = head;
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Ok((tail + head, self.cap() - self.start))
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}
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}
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}
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/// Copy from the dma buffer at `data_range` into `buf`
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fn copy_to(&mut self, buf: &mut [W], data_range: Range<usize>) -> usize {
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// Limit the number of elements that can be copied
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let length = usize::min(data_range.len(), buf.len());
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// Copy from dma buffer into read buffer
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// We need to do it like this instead of a simple copy_from_slice() because
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// reading from a part of memory that may be simultaneously written to is unsafe
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unsafe {
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let dma_buf = self.dma_buf.as_ptr();
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for i in 0..length {
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buf[i] = core::ptr::read_volatile(dma_buf.offset((data_range.start + i) as isize));
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}
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}
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length
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}
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}
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pub struct WritableDmaRingBuffer<'a, W: Word> {
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pub(crate) dma_buf: &'a mut [W],
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end: usize,
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}
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impl<'a, W: Word> WritableDmaRingBuffer<'a, W> {
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pub fn new(dma_buf: &'a mut [W]) -> Self {
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Self { dma_buf, end: 0 }
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}
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/// Reset the ring buffer to its initial state
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pub fn clear(&mut self, dma: &mut impl DmaCtrl) {
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self.end = 0;
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dma.reset_complete_count();
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}
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/// The capacity of the ringbuffer
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pub const fn cap(&self) -> usize {
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self.dma_buf.len()
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}
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/// The current position of the ringbuffer
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fn pos(&self, dma: &mut impl DmaCtrl) -> usize {
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self.cap() - dma.get_remaining_transfers()
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}
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/// Write an exact number of elements to the ringbuffer.
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pub async fn write_exact(&mut self, dma: &mut impl DmaCtrl, buffer: &[W]) -> Result<usize, OverrunError> {
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let mut written_data = 0;
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let buffer_len = buffer.len();
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poll_fn(|cx| {
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dma.set_waker(cx.waker());
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compiler_fence(Ordering::SeqCst);
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match self.write(dma, &buffer[written_data..buffer_len]) {
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Ok((len, remaining)) => {
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written_data += len;
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if written_data == buffer_len {
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Poll::Ready(Ok(remaining))
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} else {
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Poll::Pending
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}
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}
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Err(e) => Poll::Ready(Err(e)),
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}
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})
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.await
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}
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/// Write elements from the ring buffer
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/// Return a tuple of the length written and the capacity remaining to be written in the buffer
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pub fn write(&mut self, dma: &mut impl DmaCtrl, buf: &[W]) -> Result<(usize, usize), OverrunError> {
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let start = self.pos(dma);
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if start > self.end {
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// The occupied portion in the ring buffer DOES wrap
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let len = self.copy_from(buf, self.end..start);
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compiler_fence(Ordering::SeqCst);
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// Confirm that the DMA is not inside data we could have written
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let (pos, complete_count) = critical_section::with(|_| (self.pos(dma), dma.get_complete_count()));
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if (pos >= self.end && pos < start) || (complete_count > 0 && pos >= start) || complete_count > 1 {
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Err(OverrunError)
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} else {
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self.end = (self.end + len) % self.cap();
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Ok((len, self.cap() - (start - self.end)))
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}
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} else if start == self.end && dma.get_complete_count() == 0 {
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Ok((0, 0))
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} else if start <= self.end && self.end + buf.len() < self.cap() {
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// The occupied portion in the ring buffer DOES NOT wrap
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// and copying elements into the buffer WILL NOT cause it to
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// Copy into the dma buffer
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let len = self.copy_from(buf, self.end..self.cap());
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compiler_fence(Ordering::SeqCst);
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// Confirm that the DMA is not inside data we could have written
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let pos = self.pos(dma);
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if pos > self.end || pos < start || dma.get_complete_count() > 1 {
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Err(OverrunError)
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} else {
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self.end = (self.end + len) % self.cap();
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Ok((len, self.cap() - (self.end - start)))
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}
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} else {
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// The occupied portion in the ring buffer DOES NOT wrap
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// and copying elements into the buffer WILL cause it to
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let tail = self.copy_from(buf, self.end..self.cap());
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let head = self.copy_from(&buf[tail..], 0..start);
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compiler_fence(Ordering::SeqCst);
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// Confirm that the DMA is not inside data we could have written
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let pos = self.pos(dma);
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if pos > self.end || pos < start || dma.reset_complete_count() > 1 {
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Err(OverrunError)
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} else {
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self.end = head;
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Ok((tail + head, self.cap() - (start - self.end)))
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}
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}
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}
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/// Copy into the dma buffer at `data_range` from `buf`
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fn copy_from(&mut self, buf: &[W], data_range: Range<usize>) -> usize {
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// Limit the number of elements that can be copied
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let length = usize::min(data_range.len(), buf.len());
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// Copy into dma buffer from read buffer
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// We need to do it like this instead of a simple copy_from_slice() because
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// reading from a part of memory that may be simultaneously written to is unsafe
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unsafe {
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let dma_buf = self.dma_buf.as_mut_ptr();
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for i in 0..length {
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core::ptr::write_volatile(dma_buf.offset((data_range.start + i) as isize), buf[i]);
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}
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}
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length
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}
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}
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#[cfg(test)]
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mod tests {
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use core::array;
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use std::{cell, vec};
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use super::*;
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#[allow(dead_code)]
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#[derive(PartialEq, Debug)]
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enum TestCircularTransferRequest {
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GetCompleteCount(usize),
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ResetCompleteCount(usize),
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PositionRequest(usize),
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}
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struct TestCircularTransfer {
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len: usize,
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requests: cell::RefCell<vec::Vec<TestCircularTransferRequest>>,
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}
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impl DmaCtrl for TestCircularTransfer {
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fn get_remaining_transfers(&self) -> usize {
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match self.requests.borrow_mut().pop().unwrap() {
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TestCircularTransferRequest::PositionRequest(pos) => {
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let len = self.len;
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assert!(len >= pos);
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len - pos
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}
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_ => unreachable!(),
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}
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}
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fn get_complete_count(&self) -> usize {
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match self.requests.borrow_mut().pop().unwrap() {
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TestCircularTransferRequest::GetCompleteCount(complete_count) => complete_count,
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_ => unreachable!(),
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}
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}
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fn reset_complete_count(&mut self) -> usize {
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match self.requests.get_mut().pop().unwrap() {
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TestCircularTransferRequest::ResetCompleteCount(complete_count) => complete_count,
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_ => unreachable!(),
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}
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}
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fn set_waker(&mut self, waker: &Waker) {}
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}
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impl TestCircularTransfer {
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pub fn new(len: usize) -> Self {
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Self {
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requests: cell::RefCell::new(vec![]),
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len,
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}
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}
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pub fn setup(&self, mut requests: vec::Vec<TestCircularTransferRequest>) {
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requests.reverse();
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self.requests.replace(requests);
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}
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}
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#[test]
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fn empty_and_read_not_started() {
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let mut dma_buf = [0u8; 16];
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let ringbuf = ReadableDmaRingBuffer::new(&mut dma_buf);
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assert_eq!(0, ringbuf.start);
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}
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#[test]
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fn can_read() {
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let mut dma = TestCircularTransfer::new(16);
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let mut dma_buf: [u8; 16] = array::from_fn(|idx| idx as u8); // 0, 1, ..., 15
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let mut ringbuf = ReadableDmaRingBuffer::new(&mut dma_buf);
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assert_eq!(0, ringbuf.start);
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assert_eq!(16, ringbuf.cap());
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dma.setup(vec![
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TestCircularTransferRequest::PositionRequest(8),
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TestCircularTransferRequest::PositionRequest(10),
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TestCircularTransferRequest::GetCompleteCount(0),
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]);
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let mut buf = [0; 2];
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assert_eq!(2, ringbuf.read(&mut dma, &mut buf).unwrap().0);
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assert_eq!([0, 1], buf);
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assert_eq!(2, ringbuf.start);
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dma.setup(vec![
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TestCircularTransferRequest::PositionRequest(10),
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TestCircularTransferRequest::PositionRequest(12),
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TestCircularTransferRequest::GetCompleteCount(0),
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]);
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let mut buf = [0; 2];
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assert_eq!(2, ringbuf.read(&mut dma, &mut buf).unwrap().0);
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assert_eq!([2, 3], buf);
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assert_eq!(4, ringbuf.start);
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dma.setup(vec![
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TestCircularTransferRequest::PositionRequest(12),
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TestCircularTransferRequest::PositionRequest(14),
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TestCircularTransferRequest::GetCompleteCount(0),
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]);
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let mut buf = [0; 8];
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assert_eq!(8, ringbuf.read(&mut dma, &mut buf).unwrap().0);
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assert_eq!([4, 5, 6, 7, 8, 9], buf[..6]);
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assert_eq!(12, ringbuf.start);
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}
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#[test]
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fn can_read_with_wrap() {
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let mut dma = TestCircularTransfer::new(16);
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let mut dma_buf: [u8; 16] = array::from_fn(|idx| idx as u8); // 0, 1, ..., 15
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let mut ringbuf = ReadableDmaRingBuffer::new(&mut dma_buf);
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assert_eq!(0, ringbuf.start);
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assert_eq!(16, ringbuf.cap());
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/*
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Read to close to the end of the buffer
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*/
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dma.setup(vec![
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TestCircularTransferRequest::PositionRequest(14),
|
|
TestCircularTransferRequest::PositionRequest(16),
|
|
TestCircularTransferRequest::GetCompleteCount(0),
|
|
]);
|
|
let mut buf = [0; 14];
|
|
assert_eq!(14, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(14, ringbuf.start);
|
|
|
|
/*
|
|
Now, read around the buffer
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(6),
|
|
TestCircularTransferRequest::PositionRequest(8),
|
|
TestCircularTransferRequest::ResetCompleteCount(1),
|
|
]);
|
|
let mut buf = [0; 6];
|
|
assert_eq!(6, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(4, ringbuf.start);
|
|
}
|
|
|
|
#[test]
|
|
fn can_read_when_dma_writer_is_wrapped_and_read_does_not_wrap() {
|
|
let mut dma = TestCircularTransfer::new(16);
|
|
|
|
let mut dma_buf: [u8; 16] = array::from_fn(|idx| idx as u8); // 0, 1, ..., 15
|
|
let mut ringbuf = ReadableDmaRingBuffer::new(&mut dma_buf);
|
|
|
|
assert_eq!(0, ringbuf.start);
|
|
assert_eq!(16, ringbuf.cap());
|
|
|
|
/*
|
|
Read to close to the end of the buffer
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(14),
|
|
TestCircularTransferRequest::PositionRequest(16),
|
|
TestCircularTransferRequest::GetCompleteCount(0),
|
|
]);
|
|
let mut buf = [0; 14];
|
|
assert_eq!(14, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(14, ringbuf.start);
|
|
|
|
/*
|
|
Now, read to the end of the buffer
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(6),
|
|
TestCircularTransferRequest::PositionRequest(8),
|
|
TestCircularTransferRequest::ResetCompleteCount(1),
|
|
]);
|
|
let mut buf = [0; 2];
|
|
assert_eq!(2, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(0, ringbuf.start);
|
|
}
|
|
|
|
#[test]
|
|
fn can_read_when_dma_writer_wraps_once_with_same_ndtr() {
|
|
let mut dma = TestCircularTransfer::new(16);
|
|
|
|
let mut dma_buf: [u8; 16] = array::from_fn(|idx| idx as u8); // 0, 1, ..., 15
|
|
let mut ringbuf = ReadableDmaRingBuffer::new(&mut dma_buf);
|
|
|
|
assert_eq!(0, ringbuf.start);
|
|
assert_eq!(16, ringbuf.cap());
|
|
|
|
/*
|
|
Read to about the middle of the buffer
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(6),
|
|
TestCircularTransferRequest::PositionRequest(6),
|
|
TestCircularTransferRequest::GetCompleteCount(0),
|
|
]);
|
|
let mut buf = [0; 6];
|
|
assert_eq!(6, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(6, ringbuf.start);
|
|
|
|
/*
|
|
Now, wrap the DMA controller around
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(6),
|
|
TestCircularTransferRequest::GetCompleteCount(1),
|
|
TestCircularTransferRequest::PositionRequest(6),
|
|
TestCircularTransferRequest::GetCompleteCount(1),
|
|
]);
|
|
let mut buf = [0; 6];
|
|
assert_eq!(6, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(12, ringbuf.start);
|
|
}
|
|
|
|
#[test]
|
|
fn cannot_read_when_dma_writer_overwrites_during_not_wrapping_read() {
|
|
let mut dma = TestCircularTransfer::new(16);
|
|
|
|
let mut dma_buf: [u8; 16] = array::from_fn(|idx| idx as u8); // 0, 1, ..., 15
|
|
let mut ringbuf = ReadableDmaRingBuffer::new(&mut dma_buf);
|
|
|
|
assert_eq!(0, ringbuf.start);
|
|
assert_eq!(16, ringbuf.cap());
|
|
|
|
/*
|
|
Read a few bytes
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(2),
|
|
TestCircularTransferRequest::PositionRequest(2),
|
|
TestCircularTransferRequest::GetCompleteCount(0),
|
|
]);
|
|
let mut buf = [0; 6];
|
|
assert_eq!(2, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(2, ringbuf.start);
|
|
|
|
/*
|
|
Now, overtake the reader
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(4),
|
|
TestCircularTransferRequest::PositionRequest(6),
|
|
TestCircularTransferRequest::GetCompleteCount(1),
|
|
]);
|
|
let mut buf = [0; 6];
|
|
assert_eq!(OverrunError, ringbuf.read(&mut dma, &mut buf).unwrap_err());
|
|
}
|
|
|
|
#[test]
|
|
fn cannot_read_when_dma_writer_overwrites_during_wrapping_read() {
|
|
let mut dma = TestCircularTransfer::new(16);
|
|
|
|
let mut dma_buf: [u8; 16] = array::from_fn(|idx| idx as u8); // 0, 1, ..., 15
|
|
let mut ringbuf = ReadableDmaRingBuffer::new(&mut dma_buf);
|
|
|
|
assert_eq!(0, ringbuf.start);
|
|
assert_eq!(16, ringbuf.cap());
|
|
|
|
/*
|
|
Read to close to the end of the buffer
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(14),
|
|
TestCircularTransferRequest::PositionRequest(16),
|
|
TestCircularTransferRequest::GetCompleteCount(0),
|
|
]);
|
|
let mut buf = [0; 14];
|
|
assert_eq!(14, ringbuf.read(&mut dma, &mut buf).unwrap().0);
|
|
assert_eq!(14, ringbuf.start);
|
|
|
|
/*
|
|
Now, overtake the reader
|
|
*/
|
|
dma.setup(vec![
|
|
TestCircularTransferRequest::PositionRequest(8),
|
|
TestCircularTransferRequest::PositionRequest(10),
|
|
TestCircularTransferRequest::ResetCompleteCount(2),
|
|
]);
|
|
let mut buf = [0; 6];
|
|
assert_eq!(OverrunError, ringbuf.read(&mut dma, &mut buf).unwrap_err());
|
|
}
|
|
}
|