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eth-v2: Fix bug in Rx descriptors and add docs art

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This commit is contained in:
Thales Fragoso 2021-06-13 08:02:38 -03:00 committed by Dario Nieuwenhuis
parent 6daa55a897
commit ffc19a54d6
1 changed files with 49 additions and 24 deletions
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73
embassy-stm32/src/eth/v2/descriptors.rs
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@ -230,11 +230,34 @@ impl RDes {
}
}
/// Rx ring of descriptors and packets
///
/// This ring has three major locations that work in lock-step. The DMA will never write to the tail
/// index, so the `read_index` must never pass the tail index. The `next_tail_index` is always 1
/// slot ahead of the real tail index, and it must never pass the `read_index` or it could overwrite
/// a packet still to be passed to the application.
///
/// nt can't pass r (no alloc)
/// +---+---+---+---+ Read ok +---+---+---+---+ No Read +---+---+---+---+
/// | | | | | ------------> | | | | | ------------> | | | | |
/// +---+---+---+---+ Allocation ok +---+---+---+---+ +---+---+---+---+
/// ^ ^t ^t ^ ^t ^
/// |r |r |r
/// |nt |nt |nt
///
///
/// +---+---+---+---+ Read ok +---+---+---+---+ Can't read +---+---+---+---+
/// | | | | | ------------> | | | | | ------------> | | | | |
/// +---+---+---+---+ Allocation fail +---+---+---+---+ Allocation ok +---+---+---+---+
/// ^ ^t ^ ^t ^ ^ ^ ^t
/// |r | |r | | |r
/// |nt |nt |nt
///
pub(crate) struct RDesRing<const N: usize> {
rd: [RDes; N],
buffers: [Option<PacketBox>; N],
read_idx: usize,
tail_idx: usize,
next_tail_idx: usize,
}
impl<const N: usize> RDesRing<N> {
@ -246,7 +269,7 @@ impl<const N: usize> RDesRing<N> {
rd: [RDES; N],
buffers: [BUFFERS; N],
read_idx: 0,
tail_idx: 0,
next_tail_idx: 0,
}
}
@ -274,7 +297,7 @@ impl<const N: usize> RDesRing<N> {
self.rd[index].set_ready(addr);
last_index = index;
}
self.tail_idx = (last_index + 1) % N;
self.next_tail_idx = (last_index + 1) % N;
unsafe {
let dma = ETH.ethernet_dma();
@ -294,7 +317,9 @@ impl<const N: usize> RDesRing<N> {
}
pub(crate) fn on_interrupt(&mut self) {
// TODO!
// XXX: Do we need to do anything here ? Maybe we should try to advance the tail ptr, but it
// would soon hit the read ptr anyway, and we will wake smoltcp's stack on the interrupt
// which should try to pop a packet...
}
pub(crate) fn pop_packet(&mut self) -> Option<PacketBuf> {
@ -304,12 +329,9 @@ impl<const N: usize> RDesRing<N> {
fence(Ordering::SeqCst);
let read_available = self.rd[self.read_idx].available();
if !read_available && self.read_idx == self.tail_idx {
// Nothing to do
return None;
}
let tail_index = (self.next_tail_idx + N - 1) % N;
let pkt = if read_available {
let pkt = if read_available && self.read_idx != tail_index {
let pkt = self.buffers[self.read_idx].take();
let len = (self.rd[self.read_idx].rdes3.get() & EMAC_RDES3_PKTLEN) as usize;
@ -326,25 +348,28 @@ impl<const N: usize> RDesRing<N> {
None
};
match PacketBox::new(Packet::new()) {
Some(b) => {
let addr = b.as_ptr() as u32;
self.buffers[self.tail_idx].replace(b);
self.rd[self.tail_idx].set_ready(addr);
// Try to advance the tail_idx
if self.next_tail_idx != self.read_idx {
match PacketBox::new(Packet::new()) {
Some(b) => {
let addr = b.as_ptr() as u32;
self.buffers[self.next_tail_idx].replace(b);
self.rd[self.next_tail_idx].set_ready(addr);
// "Preceding reads and writes cannot be moved past subsequent writes."
fence(Ordering::Release);
// "Preceding reads and writes cannot be moved past subsequent writes."
fence(Ordering::Release);
// NOTE(unsafe) atomic write
unsafe {
ETH.ethernet_dma()
.dmacrx_dtpr()
.write(|w| w.0 = &self.rd[self.tail_idx] as *const _ as u32);
// NOTE(unsafe) atomic write
unsafe {
ETH.ethernet_dma()
.dmacrx_dtpr()
.write(|w| w.0 = &self.rd[self.next_tail_idx] as *const _ as u32);
}
self.next_tail_idx = (self.next_tail_idx + 1) % N;
}
self.tail_idx = (self.tail_idx + 1) % N;
None => {}
}
None => {}
}
pkt
}