Reduce memory overhead and simplify logic for merging endpoint and control request output reports.

embassy-usb/src/driver.rs

@@ -120,6 +120,9 @@ pub trait Endpoint {
 
 pub trait EndpointOut: Endpoint {
     type ReadFuture<'a>: Future<Output = Result<usize, ReadError>> + 'a
+    where
+        Self: 'a;
+    type DataReadyFuture<'a>: Future<Output = ()> + 'a
     where
         Self: 'a;
 
@@ -128,6 +131,11 @@ pub trait EndpointOut: Endpoint {
     ///
     /// This should also clear any NAK flags and prepare the endpoint to receive the next packet.
     fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Self::ReadFuture<'a>;
+
+    /// Waits until a packet of data is ready to be read from the endpoint.
+    ///
+    /// A call to[`read()`](Self::read()) after this future completes should not block.
+    fn wait_data_ready<'a>(&'a mut self) -> Self::DataReadyFuture<'a>;
 }
 
 pub trait ControlPipe {