feat: add helper to read/write full transfer blocks

instead of always transferring only USB packets, add a provided method
to transmit an entire data block by using a simple loop construct.

Signed-off-by: Felipe Balbi <febalbi@microsoft.com>

embassy-usb-driver/CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 <!-- next-header -->
 ## Unreleased - ReleaseDate
 
+- Add `EndpointOut::read_data()` and `EndpointIn::write_data()` provided methods.
+
 ## 0.2.0 - 2025-07-16
 
 - Make USB endpoint allocator methods accept an optional `EndpointAddress`.

embassy-usb-driver/src/lib.rs

@@ -236,6 +236,22 @@ pub trait EndpointOut: Endpoint {
     ///
     /// This should also clear any NAK flags and prepare the endpoint to receive the next packet.
     async fn read(&mut self, buf: &mut [u8]) -> Result<usize, EndpointError>;
+
+    /// Read until the buffer is full or we receive a short packet from the USB host returning the
+    /// actual length of the entire data block.
+    ///
+    /// This should also clear any NAK flags and prepare the endpoint to receive the next packet or
+    /// data block.
+    async fn read_data(&mut self, buf: &mut [u8]) -> Result<usize, EndpointError> {
+        let mut n = 0;
+        loop {
+            let i = self.read(&mut buf[n..]).await?;
+            n += i;
+            if i < self.info().max_packet_size as usize {
+                return Ok(n);
+            }
+        }
+    }
 }
 
 /// USB control pipe trait.
@@ -349,6 +365,20 @@ pub trait ControlPipe {
 pub trait EndpointIn: Endpoint {
     /// Write a single packet of data to the endpoint.
     async fn write(&mut self, buf: &[u8]) -> Result<(), EndpointError>;
+
+    /// Write all the data from buf to the endpoint one wMaxPacketSize chunk at a time.
+    ///
+    /// If the buffer size is evenly divisible by wMaxPacketSize, this will also ensure the
+    /// terminating zero-length-packet is transmitted.
+    async fn write_data(&mut self, buf: &[u8]) -> Result<(), EndpointError> {
+        for chunk in buf.chunks(self.info().max_packet_size as usize) {
+            self.write(chunk).await?;
+        }
+        if buf.len() % self.info().max_packet_size as usize == 0 {
+            self.write(&[]).await?;
+        }
+        Ok(())
+    }
 }
 
 #[derive(Copy, Clone, Eq, PartialEq, Debug)]