Okay, so we really do need this: zeroing out the descriptors is important!

Author: datdenkikniet

src/dma/mod.rs

@@ -39,7 +39,7 @@ const _TXDESC_SIZE: usize = core::mem::size_of::<TxDescriptor>();
 /// value which applies to both TX and RX descriptors.
 const _ASSERT_DESCRIPTOR_SIZES: () = assert!(_RXDESC_SIZE == _TXDESC_SIZE);
 
-const DESC_WORD_SKIP: u8 = (core::mem::size_of::<RxDescriptor>() / 4 - DESC_SIZE) as u8;
+const DESC_WORD_SKIP: u8 = ((_RXDESC_SIZE / 4) - DESC_SIZE) as u8;
 
 const _ASSERT_DESC_WORD_SKIP_SIZE: () = assert!(DESC_WORD_SKIP <= 0b111);
 

src/dma/tx/h_desc.rs

@@ -144,17 +144,26 @@ impl TxDescriptor {
         }
     }
 
+    #[allow(unused)]
     fn is_last(&self) -> bool {
         (self.inner_raw.read(3) & TXDESC_3_LD) == TXDESC_3_LD
     }
 
     // Placeholder for API parity with f-series descriptor.
-    pub(super) fn setup(&mut self, _: &[u8]) {}
+    pub(super) fn setup(&mut self, _: &[u8]) {
+        // Zero-out all fields in the descriptor
+        (0..4).for_each(|n| unsafe { self.inner_raw.write(n, 0) });
+    }
 
     pub(super) fn is_owned(&self) -> bool {
         (self.inner_raw.read(3) & TXDESC_3_OWN) == TXDESC_3_OWN
     }
 
+    #[allow(unused)]
+    pub(super) fn is_context(&self) -> bool {
+        (self.inner_raw.read(3) & TXDESC_3_CTXT) == TXDESC_3_CTXT
+    }
+
     #[allow(unused)]
     pub(super) fn packet_id(&self) -> Option<&PacketId> {
         self.packet_id.as_ref()
@@ -238,12 +247,3 @@ impl TxDescriptor {
         self.cached_timestamp.as_ref()
     }
 }
-
-impl TxDescriptor {
-    /// The initial value for a TxDescriptor
-    pub const TX_INIT: Self = Self::new();
-
-    pub(crate) fn prepare_packet(&mut self) -> bool {
-        !self.is_owned()
-    }
-}

src/dma/tx/mod.rs

@@ -117,8 +117,8 @@ impl<'data> TxRing<'data, NotRunning> {
             // Assert that the descriptors are properly aligned.
             assert!(ring_ptr as u32 & !0b11 == ring_ptr as u32);
             assert!(
-                self.ring.last_descriptor_mut() as *const _ as u32 & !0b11
-                    == self.ring.last_descriptor_mut() as *const _ as u32
+                self.ring.last_descriptor() as *const _ as u32 & !0b11
+                    == self.ring.last_descriptor() as *const _ as u32
             );
 
             // Set the start pointer.
@@ -175,7 +175,7 @@ impl<'data> TxRing<'data, Running> {
 
         assert!(length <= buffer.len());
 
-        if descriptor.prepare_packet() {
+        if !descriptor.is_owned() {
             let r = f(&mut buffer[0..length]);
 
             descriptor.send(packet_id, &buffer[0..length]);