4 files changed, 33 insertions, 40 deletions

diff --git a/embassy-usb/src/builder.rs b/embassy-usb/src/builder.rs
index c4705d041..c06107396 100644
--- a/embassy-usb/src/builder.rs
+++ b/embassy-usb/src/builder.rs
@@ -128,7 +128,6 @@ pub struct Builder<'d, D: Driver<'d>> {
     driver: D,
     next_string_index: u8,
 
-    device_descriptor: DescriptorWriter<'d>,
     config_descriptor: DescriptorWriter<'d>,
     bos_descriptor: BosWriter<'d>,
 
@@ -144,7 +143,6 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
     pub fn new(
         driver: D,
         config: Config<'d>,
-        device_descriptor_buf: &'d mut [u8],
         config_descriptor_buf: &'d mut [u8],
         bos_descriptor_buf: &'d mut [u8],
         msos_descriptor_buf: &'d mut [u8],
@@ -167,11 +165,9 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
             _ => panic!("invalid max_packet_size_0, the allowed values are 8, 16, 32 or 64"),
         }
 
-        let mut device_descriptor = DescriptorWriter::new(device_descriptor_buf);
         let mut config_descriptor = DescriptorWriter::new(config_descriptor_buf);
         let mut bos_descriptor = BosWriter::new(DescriptorWriter::new(bos_descriptor_buf));
 
-        device_descriptor.device(&config);
         config_descriptor.configuration(&config);
         bos_descriptor.bos();
 
@@ -183,7 +179,6 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
             control_buf,
             next_string_index: STRING_INDEX_CUSTOM_START,
 
-            device_descriptor,
             config_descriptor,
             bos_descriptor,
 
@@ -199,7 +194,6 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
         self.bos_descriptor.end_bos();
 
         // Log the number of allocator bytes actually used in descriptor buffers
-        info!("USB: device_descriptor used: {}", self.device_descriptor.position());
         info!("USB: config_descriptor used: {}", self.config_descriptor.position());
         info!("USB: bos_descriptor used: {}", self.bos_descriptor.writer.position());
         info!("USB: msos_descriptor used: {}", msos_descriptor.len());
@@ -209,7 +203,6 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
             self.driver,
             self.config,
             self.handlers,
-            self.device_descriptor.into_buf(),
             self.config_descriptor.into_buf(),
             self.bos_descriptor.writer.into_buf(),
             msos_descriptor,
diff --git a/embassy-usb/src/descriptor.rs b/embassy-usb/src/descriptor.rs
index fa83ef583..eb3d1f53a 100644
--- a/embassy-usb/src/descriptor.rs
+++ b/embassy-usb/src/descriptor.rs
@@ -82,30 +82,6 @@ impl<'a> DescriptorWriter<'a> {
         self.position = start + length;
     }
 
-    pub(crate) fn device(&mut self, config: &Config) {
-        self.write(
-            descriptor_type::DEVICE,
-            &[
-                0x10,
-                0x02,                     // bcdUSB 2.1
-                config.device_class,      // bDeviceClass
-                config.device_sub_class,  // bDeviceSubClass
-                config.device_protocol,   // bDeviceProtocol
-                config.max_packet_size_0, // bMaxPacketSize0
-                config.vendor_id as u8,
-                (config.vendor_id >> 8) as u8, // idVendor
-                config.product_id as u8,
-                (config.product_id >> 8) as u8, // idProduct
-                config.device_release as u8,
-                (config.device_release >> 8) as u8,    // bcdDevice
-                config.manufacturer.map_or(0, |_| 1),  // iManufacturer
-                config.product.map_or(0, |_| 2),       // iProduct
-                config.serial_number.map_or(0, |_| 3), // iSerialNumber
-                1,                                     // bNumConfigurations
-            ],
-        );
-    }
-
     pub(crate) fn configuration(&mut self, config: &Config) {
         self.num_interfaces_mark = Some(self.position + 4);
 
@@ -269,6 +245,33 @@ impl<'a> DescriptorWriter<'a> {
     }
 }
 
+/// Create a new Device Descriptor array.
+///
+/// All device descriptors are always 18 bytes, so there's no need for
+/// a variable-length buffer or DescriptorWriter.
+pub(crate) fn device_descriptor(config: &Config) -> [u8; 18] {
+    [
+        18,   // bLength
+        0x01, // bDescriptorType
+        0x10,
+        0x02,                     // bcdUSB 2.1
+        config.device_class,      // bDeviceClass
+        config.device_sub_class,  // bDeviceSubClass
+        config.device_protocol,   // bDeviceProtocol
+        config.max_packet_size_0, // bMaxPacketSize0
+        config.vendor_id as u8,
+        (config.vendor_id >> 8) as u8, // idVendor
+        config.product_id as u8,
+        (config.product_id >> 8) as u8, // idProduct
+        config.device_release as u8,
+        (config.device_release >> 8) as u8,    // bcdDevice
+        config.manufacturer.map_or(0, |_| 1),  // iManufacturer
+        config.product.map_or(0, |_| 2),       // iProduct
+        config.serial_number.map_or(0, |_| 3), // iSerialNumber
+        1,                                     // bNumConfigurations
+    ]
+}
+
 /// A writer for Binary Object Store descriptor.
 pub struct BosWriter<'a> {
     pub(crate) writer: DescriptorWriter<'a>,
diff --git a/embassy-usb/src/lib.rs b/embassy-usb/src/lib.rs
index 241e33a78..d58950838 100644
--- a/embassy-usb/src/lib.rs
+++ b/embassy-usb/src/lib.rs
@@ -168,8 +168,6 @@ struct Interface {
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub struct UsbBufferReport {
-    /// Number of device descriptor bytes used
-    pub device_descriptor_used: usize,
     /// Number of config descriptor bytes used
     pub config_descriptor_used: usize,
     /// Number of bos descriptor bytes used
@@ -191,7 +189,7 @@ struct Inner<'d, D: Driver<'d>> {
     bus: D::Bus,
 
     config: Config<'d>,
-    device_descriptor: &'d [u8],
+    device_descriptor: [u8; 18],
     config_descriptor: &'d [u8],
     bos_descriptor: &'d [u8],
     msos_descriptor: crate::msos::MsOsDescriptorSet<'d>,
@@ -217,7 +215,6 @@ impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
         driver: D,
         config: Config<'d>,
         handlers: Vec<&'d mut dyn Handler, MAX_HANDLER_COUNT>,
-        device_descriptor: &'d [u8],
         config_descriptor: &'d [u8],
         bos_descriptor: &'d [u8],
         msos_descriptor: crate::msos::MsOsDescriptorSet<'d>,
@@ -227,6 +224,7 @@ impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
         // Start the USB bus.
         // This prevent further allocation by consuming the driver.
         let (bus, control) = driver.start(config.max_packet_size_0 as u16);
+        let device_descriptor = descriptor::device_descriptor(&config);
 
         Self {
             control_buf,
@@ -256,7 +254,6 @@ impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
     /// Useful for tuning buffer sizes for actual usage
     pub fn buffer_usage(&self) -> UsbBufferReport {
         UsbBufferReport {
-            device_descriptor_used: self.inner.device_descriptor.len(),
             config_descriptor_used: self.inner.config_descriptor.len(),
             bos_descriptor_used: self.inner.bos_descriptor.len(),
             msos_descriptor_used: self.inner.msos_descriptor.len(),
@@ -720,7 +717,7 @@ impl<'d, D: Driver<'d>> Inner<'d, D> {
 
         match dtype {
             descriptor_type::BOS => InResponse::Accepted(self.bos_descriptor),
-            descriptor_type::DEVICE => InResponse::Accepted(self.device_descriptor),
+            descriptor_type::DEVICE => InResponse::Accepted(&self.device_descriptor),
             descriptor_type::CONFIGURATION => InResponse::Accepted(self.config_descriptor),
             descriptor_type::STRING => {
                 if index == 0 {
diff --git a/embassy-usb/src/msos.rs b/embassy-usb/src/msos.rs
index 3858c0f51..a285a3ccd 100644
--- a/embassy-usb/src/msos.rs
+++ b/embassy-usb/src/msos.rs
@@ -255,7 +255,7 @@ use sealed::*;
 unsafe fn transmute_write_to<T: Sized>(t: &T, buf: &mut [u8]) {
     let bytes = core::slice::from_raw_parts((t as *const T) as *const u8, size_of::<T>());
     assert!(buf.len() >= bytes.len(), "MS OS descriptor buffer full");
-    (&mut buf[..bytes.len()]).copy_from_slice(bytes);
+    buf[..bytes.len()].copy_from_slice(bytes);
 }
 
 /// Table 9. Microsoft OS 2.0 descriptor wDescriptorType values.
@@ -444,9 +444,9 @@ impl CompatibleIdFeatureDescriptor {
     pub fn new(compatible_id: &str, sub_compatible_id: &str) -> Self {
         assert!(compatible_id.len() <= 8 && sub_compatible_id.len() <= 8);
         let mut cid = [0u8; 8];
-        (&mut cid[..compatible_id.len()]).copy_from_slice(compatible_id.as_bytes());
+        cid[..compatible_id.len()].copy_from_slice(compatible_id.as_bytes());
         let mut scid = [0u8; 8];
-        (&mut scid[..sub_compatible_id.len()]).copy_from_slice(sub_compatible_id.as_bytes());
+        scid[..sub_compatible_id.len()].copy_from_slice(sub_compatible_id.as_bytes());
         Self::new_raw(cid, scid)
     }