Merge pull request #4566 from mkj/pr/otg-rx

otg: Use chunks_exact for more efficient rx copy

2 files changed, 18 insertions, 14 deletions

diff --git a/embassy-usb-synopsys-otg/CHANGELOG.md b/embassy-usb-synopsys-otg/CHANGELOG.md
index 9ca90f5e9..45353d907 100644
--- a/embassy-usb-synopsys-otg/CHANGELOG.md
+++ b/embassy-usb-synopsys-otg/CHANGELOG.md
@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## 0.3.1 - 2025-08-26
 
+- Improve receive performance, more efficient copy from FIFO
+
 ## 0.3.0 - 2025-07-22
 
 - Bump `embassy-usb-driver` to v0.2.0
diff --git a/embassy-usb-synopsys-otg/src/lib.rs b/embassy-usb-synopsys-otg/src/lib.rs
index 9d74c046d..6b4a87bdf 100644
--- a/embassy-usb-synopsys-otg/src/lib.rs
+++ b/embassy-usb-synopsys-otg/src/lib.rs
@@ -76,10 +76,16 @@ pub unsafe fn on_interrupt<const MAX_EP_COUNT: usize>(r: Otg, state: &State<MAX_
                     let buf =
                         unsafe { core::slice::from_raw_parts_mut(*state.ep_states[ep_num].out_buffer.get(), len) };
 
-                    for chunk in buf.chunks_mut(4) {
+                    let mut chunks = buf.chunks_exact_mut(4);
+                    for chunk in &mut chunks {
                         // RX FIFO is shared so always read from fifo(0)
                         let data = r.fifo(0).read().0;
-                        chunk.copy_from_slice(&data.to_ne_bytes()[0..chunk.len()]);
+                        chunk.copy_from_slice(&data.to_ne_bytes());
+                    }
+                    let rem = chunks.into_remainder();
+                    if !rem.is_empty() {
+                        let data = r.fifo(0).read().0;
+                        rem.copy_from_slice(&data.to_ne_bytes()[0..rem.len()]);
                     }
 
                     state.ep_states[ep_num].out_size.store(len as u16, Ordering::Release);
@@ -1229,23 +1235,19 @@ impl<'d> embassy_usb_driver::EndpointIn for Endpoint<'d, In> {
             });
 
             // Write data to FIFO
-            let chunks = buf.chunks_exact(4);
-            // Stash the last partial chunk
-            let rem = chunks.remainder();
-            let last_chunk = (!rem.is_empty()).then(|| {
-                let mut tmp = [0u8; 4];
-                tmp[0..rem.len()].copy_from_slice(rem);
-                u32::from_ne_bytes(tmp)
-            });
-
             let fifo = self.regs.fifo(index);
-            for chunk in chunks {
+            let mut chunks = buf.chunks_exact(4);
+            for chunk in &mut chunks {
                 let val = u32::from_ne_bytes(chunk.try_into().unwrap());
                 fifo.write_value(regs::Fifo(val));
             }
             // Write any last chunk
-            if let Some(val) = last_chunk {
-                fifo.write_value(regs::Fifo(val));
+            let rem = chunks.remainder();
+            if !rem.is_empty() {
+                let mut tmp = [0u8; 4];
+                tmp[0..rem.len()].copy_from_slice(rem);
+                let tmp = u32::from_ne_bytes(tmp);
+                fifo.write_value(regs::Fifo(tmp));
             }
         });