usb: merge alloc_control_pipe and into_bus into start.

This prevents calling `alloc_control_pipe` twice at compile time, which was
always an error.

embassy-nrf/src/usb.rs

@@ -147,7 +147,7 @@ impl<'d, T: Instance> driver::Driver<'d> for Driver<'d, T> {
         packet_size: u16,
         interval: u8,
     ) -> Result<Self::EndpointIn, driver::EndpointAllocError> {
-        let index = self.alloc_in.allocate(ep_type, packet_size, interval)?;
+        let index = self.alloc_in.allocate(ep_type)?;
         let ep_addr = EndpointAddress::from_parts(index, UsbDirection::In);
         Ok(Endpoint::new(EndpointInfo {
             addr: ep_addr,
@@ -163,7 +163,7 @@ impl<'d, T: Instance> driver::Driver<'d> for Driver<'d, T> {
         packet_size: u16,
         interval: u8,
     ) -> Result<Self::EndpointOut, driver::EndpointAllocError> {
-        let index = self.alloc_out.allocate(ep_type, packet_size, interval)?;
+        let index = self.alloc_out.allocate(ep_type)?;
         let ep_addr = EndpointAddress::from_parts(index, UsbDirection::Out);
         Ok(Endpoint::new(EndpointInfo {
             addr: ep_addr,
@@ -173,24 +173,16 @@ impl<'d, T: Instance> driver::Driver<'d> for Driver<'d, T> {
         }))
     }
 
-    fn alloc_control_pipe(
-        &mut self,
-        max_packet_size: u16,
-    ) -> Result<Self::ControlPipe, driver::EndpointAllocError> {
-        self.alloc_in.used |= 0x01;
-        self.alloc_in.lens[0] = max_packet_size as u8;
-        self.alloc_out.used |= 0x01;
-        self.alloc_out.lens[0] = max_packet_size as u8;
-        Ok(ControlPipe {
-            _phantom: PhantomData,
-            max_packet_size,
-        })
-    }
-
-    fn into_bus(self) -> Self::Bus {
+    fn start(self, control_max_packet_size: u16) -> (Self::Bus, Self::ControlPipe) {
+        (
             Bus {
                 phantom: PhantomData,
-        }
+            },
+            ControlPipe {
+                _phantom: PhantomData,
+                max_packet_size: control_max_packet_size,
+            },
+        )
     }
 }
 
@@ -791,24 +783,14 @@ fn dma_end() {
 
 struct Allocator {
     used: u16,
-    // Buffers can be up to 64 Bytes since this is a Full-Speed implementation.
-    lens: [u8; 9],
 }
 
 impl Allocator {
     fn new() -> Self {
-        Self {
-            used: 0,
-            lens: [0; 9],
-        }
+        Self { used: 0 }
     }
 
-    fn allocate(
-        &mut self,
-        ep_type: EndpointType,
-        max_packet_size: u16,
-        _interval: u8,
-    ) -> Result<usize, driver::EndpointAllocError> {
+    fn allocate(&mut self, ep_type: EndpointType) -> Result<usize, driver::EndpointAllocError> {
         // Endpoint addresses are fixed in hardware:
         // - 0x80 / 0x00 - Control        EP0
         // - 0x81 / 0x01 - Bulk/Interrupt EP1
@@ -840,7 +822,6 @@ impl Allocator {
         }
 
         self.used |= 1 << alloc_index;
-        self.lens[alloc_index] = max_packet_size as u8;
 
         Ok(alloc_index)
     }

embassy-usb/src/driver.rs

@@ -14,7 +14,7 @@ pub trait Driver<'a> {
 
     /// Allocates an endpoint and specified endpoint parameters. This method is called by the device
     /// and class implementations to allocate endpoints, and can only be called before
-    /// [`enable`](UsbBus::enable) is called.
+    /// [`start`](UsbBus::start) is called.
     ///
     /// # Arguments
     ///
@@ -37,14 +37,15 @@ pub trait Driver<'a> {
         interval: u8,
     ) -> Result<Self::EndpointIn, EndpointAllocError>;
 
-    fn alloc_control_pipe(
-        &mut self,
-        max_packet_size: u16,
-    ) -> Result<Self::ControlPipe, EndpointAllocError>;
-
-    /// Enables and initializes the USB peripheral. Soon after enabling the device will be reset, so
-    /// there is no need to perform a USB reset in this method.
-    fn into_bus(self) -> Self::Bus;
+    /// Start operation of the USB device.
+    ///
+    /// This returns the `Bus` and `ControlPipe` instances that are used to operate
+    /// the USB device. Additionally, this makes all the previously allocated endpoints
+    /// start operating.
+    ///
+    /// This consumes the `Driver` instance, so it's no longer possible to allocate more
+    /// endpoints.
+    fn start(self, control_max_packet_size: u16) -> (Self::Bus, Self::ControlPipe);
 
     /// Indicates that `set_device_address` must be called before accepting the corresponding
     /// control transfer, not after.

embassy-usb/src/lib.rs

@@ -126,7 +126,7 @@ struct Inner<'d, D: Driver<'d>> {
 
 impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
     pub(crate) fn build(
-        mut driver: D,
+        driver: D,
         config: Config<'d>,
         handler: Option<&'d dyn DeviceStateHandler>,
         device_descriptor: &'d [u8],
@@ -135,13 +135,9 @@ impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
         interfaces: Vec<Interface<'d>, MAX_INTERFACE_COUNT>,
         control_buf: &'d mut [u8],
     ) -> UsbDevice<'d, D> {
-        let control = driver
-            .alloc_control_pipe(config.max_packet_size_0 as u16)
-            .expect("failed to alloc control endpoint");
-
-        // Enable the USB bus.
+        // Start the USB bus.
         // This prevent further allocation by consuming the driver.
-        let bus = driver.into_bus();
+        let (bus, control) = driver.start(config.max_packet_size_0 as u16);
 
         Self {
             control_buf,