Merge #1189

1189: USB: Add MS OS Descriptors (alternate implementation) r=Dirbaio a=alexmoon

This is an alternate API for #1152 based on the work of `@mattico.` By switching to a writer-style API instead of a builder API some compile-time guarantees are lost, but it integrates better into the usb `Builder` and makes an api that can be used by USB device class implementations.

It also adds a feature flag so there is zero cost to the MS OS descriptors for devices that don't need to use them.

I've added an example based on `usb_serial` which tells Windows to use the generic `WinUSB` driver instead of the serial port driver for the device.

Comments are welcome. It would be nice to see either this or #1152 merged as my project is going to require the MS OS Descriptors soon.

Co-authored-by: Matt Ickstadt <[email protected]>
Co-authored-by: alexmoon <[email protected]>

6 files changed, 948 insertions, 8 deletions

diff --git a/embassy-usb/Cargo.toml b/embassy-usb/Cargo.toml
index 1e567bb94..eb9ba36f4 100644
--- a/embassy-usb/Cargo.toml
+++ b/embassy-usb/Cargo.toml
@@ -13,6 +13,7 @@ target = "thumbv7em-none-eabi"
 [features]
 defmt = ["dep:defmt", "embassy-usb-driver/defmt"]
 usbd-hid = ["dep:usbd-hid", "dep:ssmarshal"]
+msos-descriptor = []
 default = ["usbd-hid"]
 
 [dependencies]
diff --git a/embassy-usb/src/builder.rs b/embassy-usb/src/builder.rs
index 41b24fecf..d1cbf674b 100644
--- a/embassy-usb/src/builder.rs
+++ b/embassy-usb/src/builder.rs
@@ -3,6 +3,8 @@ use heapless::Vec;
 use crate::control::ControlHandler;
 use crate::descriptor::{BosWriter, DescriptorWriter};
 use crate::driver::{Driver, Endpoint, EndpointType};
+#[cfg(feature = "msos-descriptor")]
+use crate::msos::{DeviceLevelDescriptor, FunctionLevelDescriptor, MsOsDescriptorWriter};
 use crate::types::*;
 use crate::{DeviceStateHandler, Interface, UsbDevice, MAX_INTERFACE_COUNT, STRING_INDEX_CUSTOM_START};
 
@@ -130,6 +132,9 @@ pub struct Builder<'d, D: Driver<'d>> {
     device_descriptor: DescriptorWriter<'d>,
     config_descriptor: DescriptorWriter<'d>,
     bos_descriptor: BosWriter<'d>,
+
+    #[cfg(feature = "msos-descriptor")]
+    msos_descriptor: MsOsDescriptorWriter<'d>,
 }
 
 impl<'d, D: Driver<'d>> Builder<'d, D> {
@@ -144,6 +149,7 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
         device_descriptor_buf: &'d mut [u8],
         config_descriptor_buf: &'d mut [u8],
         bos_descriptor_buf: &'d mut [u8],
+        #[cfg(feature = "msos-descriptor")] msos_descriptor_buf: &'d mut [u8],
         control_buf: &'d mut [u8],
         handler: Option<&'d dyn DeviceStateHandler>,
     ) -> Self {
@@ -182,11 +188,17 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
             device_descriptor,
             config_descriptor,
             bos_descriptor,
+
+            #[cfg(feature = "msos-descriptor")]
+            msos_descriptor: MsOsDescriptorWriter::new(msos_descriptor_buf),
         }
     }
 
     /// Creates the [`UsbDevice`] instance with the configuration in this builder.
     pub fn build(mut self) -> UsbDevice<'d, D> {
+        #[cfg(feature = "msos-descriptor")]
+        let msos_descriptor = self.msos_descriptor.build(&mut self.bos_descriptor);
+
         self.config_descriptor.end_configuration();
         self.bos_descriptor.end_bos();
 
@@ -199,6 +211,8 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
             self.bos_descriptor.writer.into_buf(),
             self.interfaces,
             self.control_buf,
+            #[cfg(feature = "msos-descriptor")]
+            msos_descriptor,
         )
     }
 
@@ -215,14 +229,10 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
     ///
     /// If it's not set, no IAD descriptor is added.
     pub fn function(&mut self, class: u8, subclass: u8, protocol: u8) -> FunctionBuilder<'_, 'd, D> {
+        let first_interface = InterfaceNumber::new(self.interfaces.len() as u8);
         let iface_count_index = if self.config.composite_with_iads {
-            self.config_descriptor.iad(
-                InterfaceNumber::new(self.interfaces.len() as _),
-                0,
-                class,
-                subclass,
-                protocol,
-            );
+            self.config_descriptor
+                .iad(first_interface, 0, class, subclass, protocol);
 
             Some(self.config_descriptor.position() - 5)
         } else {
@@ -232,8 +242,32 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
         FunctionBuilder {
             builder: self,
             iface_count_index,
+
+            #[cfg(feature = "msos-descriptor")]
+            first_interface,
         }
     }
+
+    #[cfg(feature = "msos-descriptor")]
+    /// Add an MS OS 2.0 Descriptor Set.
+    ///
+    /// Panics if called more than once.
+    pub fn msos_descriptor(&mut self, windows_version: u32, vendor_code: u8) {
+        self.msos_descriptor.header(windows_version, vendor_code);
+    }
+
+    #[cfg(feature = "msos-descriptor")]
+    /// Add an MS OS 2.0 Device Level Feature Descriptor.
+    pub fn msos_feature<T: DeviceLevelDescriptor>(&mut self, desc: T) {
+        self.msos_descriptor.device_feature(desc);
+    }
+
+    #[cfg(feature = "msos-descriptor")]
+    /// Gets the underlying [`MsOsDescriptorWriter`] to allow adding subsets and features for classes that
+    /// do not add their own.
+    pub fn msos_writer(&mut self) -> &mut MsOsDescriptorWriter<'d> {
+        &mut self.msos_descriptor
+    }
 }
 
 /// Function builder.
@@ -244,6 +278,16 @@ impl<'d, D: Driver<'d>> Builder<'d, D> {
 pub struct FunctionBuilder<'a, 'd, D: Driver<'d>> {
     builder: &'a mut Builder<'d, D>,
     iface_count_index: Option<usize>,
+
+    #[cfg(feature = "msos-descriptor")]
+    first_interface: InterfaceNumber,
+}
+
+impl<'a, 'd, D: Driver<'d>> Drop for FunctionBuilder<'a, 'd, D> {
+    fn drop(&mut self) {
+        #[cfg(feature = "msos-descriptor")]
+        self.builder.msos_descriptor.end_function();
+    }
 }
 
 impl<'a, 'd, D: Driver<'d>> FunctionBuilder<'a, 'd, D> {
@@ -273,6 +317,21 @@ impl<'a, 'd, D: Driver<'d>> FunctionBuilder<'a, 'd, D> {
             next_alt_setting_number: 0,
         }
     }
+
+    #[cfg(feature = "msos-descriptor")]
+    /// Add an MS OS 2.0 Function Level Feature Descriptor.
+    pub fn msos_feature<T: FunctionLevelDescriptor>(&mut self, desc: T) {
+        if !self.builder.msos_descriptor.is_in_config_subset() {
+            self.builder.msos_descriptor.configuration(0);
+        }
+
+        if !self.builder.msos_descriptor.is_in_function_subset() {
+            self.builder.msos_descriptor.function(self.first_interface.0);
+        }
+
+        #[cfg(feature = "msos-descriptor")]
+        self.builder.msos_descriptor.function_feature(desc);
+    }
 }
 
 /// Interface builder.
diff --git a/embassy-usb/src/lib.rs b/embassy-usb/src/lib.rs
index 2656af29d..aec18524b 100644
--- a/embassy-usb/src/lib.rs
+++ b/embassy-usb/src/lib.rs
@@ -13,6 +13,7 @@ pub mod class;
 pub mod control;
 pub mod descriptor;
 mod descriptor_reader;
+pub mod msos;
 pub mod types;
 
 use embassy_futures::select::{select, Either};
@@ -135,6 +136,8 @@ struct Inner<'d, D: Driver<'d>> {
     set_address_pending: bool,
 
     interfaces: Vec<Interface<'d>, MAX_INTERFACE_COUNT>,
+    #[cfg(feature = "msos-descriptor")]
+    msos_descriptor: crate::msos::MsOsDescriptorSet<'d>,
 }
 
 impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
@@ -147,6 +150,7 @@ impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
         bos_descriptor: &'d [u8],
         interfaces: Vec<Interface<'d>, MAX_INTERFACE_COUNT>,
         control_buf: &'d mut [u8],
+        #[cfg(feature = "msos-descriptor")] msos_descriptor: crate::msos::MsOsDescriptorSet<'d>,
     ) -> UsbDevice<'d, D> {
         // Start the USB bus.
         // This prevent further allocation by consuming the driver.
@@ -170,6 +174,8 @@ impl<'d, D: Driver<'d>> UsbDevice<'d, D> {
                 address: 0,
                 set_address_pending: false,
                 interfaces,
+                #[cfg(feature = "msos-descriptor")]
+                msos_descriptor,
             },
         }
     }
@@ -603,6 +609,19 @@ impl<'d, D: Driver<'d>> Inner<'d, D> {
                     None => InResponse::Rejected,
                 }
             }
+            #[cfg(feature = "msos-descriptor")]
+            (RequestType::Vendor, Recipient::Device) => {
+                if !self.msos_descriptor.is_empty() {
+                    if req.request == self.msos_descriptor.vendor_code() && req.index == 7 {
+                        // Index 7 retrieves the MS OS Descriptor Set
+                        InResponse::Accepted(self.msos_descriptor.descriptor())
+                    } else {
+                        InResponse::Rejected
+                    }
+                } else {
+                    InResponse::Rejected
+                }
+            }
             _ => InResponse::Rejected,
         }
     }
diff --git a/embassy-usb/src/msos.rs b/embassy-usb/src/msos.rs
new file mode 100644
index 000000000..19ed34979
--- /dev/null
+++ b/embassy-usb/src/msos.rs
@@ -0,0 +1,726 @@
+#![cfg(feature = "msos-descriptor")]
+
+//! Microsoft OS Descriptors
+//!
+//! <https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/microsoft-os-2-0-descriptors-specification>
+
+use core::mem::size_of;
+
+use super::{capability_type, BosWriter};
+
+/// A serialized Microsoft OS 2.0 Descriptor set.
+///
+/// Create with [`DeviceDescriptorSetBuilder`].
+pub struct MsOsDescriptorSet<'d> {
+    descriptor: &'d [u8],
+    vendor_code: u8,
+}
+
+impl<'d> MsOsDescriptorSet<'d> {
+    /// Gets the raw bytes of the MS OS descriptor
+    pub fn descriptor(&self) -> &[u8] {
+        self.descriptor
+    }
+
+    /// Gets the vendor code used by the host to retrieve the MS OS descriptor
+    pub fn vendor_code(&self) -> u8 {
+        self.vendor_code
+    }
+
+    /// Returns `true` if no MS OS descriptor data is available
+    pub fn is_empty(&self) -> bool {
+        self.descriptor.is_empty()
+    }
+}
+
+/// Writes a Microsoft OS 2.0 Descriptor set into a buffer.
+pub struct MsOsDescriptorWriter<'d> {
+    buf: &'d mut [u8],
+
+    position: usize,
+    config_mark: Option<usize>,
+    function_mark: Option<usize>,
+    vendor_code: u8,
+}
+
+impl<'d> MsOsDescriptorWriter<'d> {
+    pub(crate) fn new(buf: &'d mut [u8]) -> Self {
+        MsOsDescriptorWriter {
+            buf,
+            position: 0,
+            config_mark: None,
+            function_mark: None,
+            vendor_code: 0,
+        }
+    }
+
+    pub(crate) fn build(mut self, bos: &mut BosWriter) -> MsOsDescriptorSet<'d> {
+        self.end();
+
+        if self.is_empty() {
+            MsOsDescriptorSet {
+                descriptor: &[],
+                vendor_code: 0,
+            }
+        } else {
+            self.write_bos(bos);
+            MsOsDescriptorSet {
+                descriptor: &self.buf[..self.position],
+                vendor_code: self.vendor_code,
+            }
+        }
+    }
+
+    /// Returns `true` if the MS OS descriptor header has not yet been written
+    pub fn is_empty(&self) -> bool {
+        self.position == 0
+    }
+
+    /// Returns `true` if a configuration subset header has been started
+    pub fn is_in_config_subset(&self) -> bool {
+        self.config_mark.is_some()
+    }
+
+    /// Returns `true` if a function subset header has been started and not yet ended
+    pub fn is_in_function_subset(&self) -> bool {
+        self.function_mark.is_some()
+    }
+
+    /// Write the MS OS descriptor set header.
+    ///
+    /// - `windows_version` is an NTDDI version constant that describes a windows version. See the [`windows_version`]
+    /// module.
+    /// - `vendor_code` is the vendor request code used to read the MS OS descriptor set.
+    pub fn header(&mut self, windows_version: u32, vendor_code: u8) {
+        assert!(self.is_empty(), "You can only call MsOsDescriptorWriter::header once");
+        self.write(DescriptorSetHeader::new(windows_version));
+        self.vendor_code = vendor_code;
+    }
+
+    /// Add a device level feature descriptor.
+    ///
+    /// Note that some feature descriptors may only be used at the device level in non-composite devices.
+    /// Those features must be written before the first call to [`Self::configuration`].
+    pub fn device_feature<T: DeviceLevelDescriptor>(&mut self, desc: T) {
+        assert!(
+            !self.is_empty(),
+            "device features may only be added after the header is written"
+        );
+        assert!(
+            self.config_mark.is_none(),
+            "device features must be added before the first configuration subset"
+        );
+        self.write(desc);
+    }
+
+    /// Add a configuration subset.
+    pub fn configuration(&mut self, config: u8) {
+        assert!(
+            !self.is_empty(),
+            "MsOsDescriptorWriter: configuration must be called after header"
+        );
+        Self::end_subset::<ConfigurationSubsetHeader>(self.buf, self.position, &mut self.config_mark);
+        self.config_mark = Some(self.position);
+        self.write(ConfigurationSubsetHeader::new(config));
+    }
+
+    /// Add a function subset.
+    pub fn function(&mut self, first_interface: u8) {
+        assert!(
+            self.config_mark.is_some(),
+            "MsOsDescriptorWriter: function subset requires a configuration subset"
+        );
+        self.end_function();
+        self.function_mark = Some(self.position);
+        self.write(FunctionSubsetHeader::new(first_interface));
+    }
+
+    /// Add a function level feature descriptor.
+    ///
+    /// Note that some features may only be used at the function level. Those features must be written after a call
+    /// to [`Self::function`].
+    pub fn function_feature<T: FunctionLevelDescriptor>(&mut self, desc: T) {
+        assert!(
+            self.function_mark.is_some(),
+            "function features may only be added to a function subset"
+        );
+        self.write(desc);
+    }
+
+    /// Ends the current function subset (if any)
+    pub fn end_function(&mut self) {
+        Self::end_subset::<FunctionSubsetHeader>(self.buf, self.position, &mut self.function_mark);
+    }
+
+    fn write<T: Descriptor>(&mut self, desc: T) {
+        desc.write_to(&mut self.buf[self.position..]);
+        self.position += desc.size();
+    }
+
+    fn end_subset<T: DescriptorSet>(buf: &mut [u8], position: usize, mark: &mut Option<usize>) {
+        if let Some(mark) = mark.take() {
+            let len = position - mark;
+            let p = mark + T::LENGTH_OFFSET;
+            buf[p..(p + 2)].copy_from_slice(&(len as u16).to_le_bytes());
+        }
+    }
+
+    fn end(&mut self) {
+        if self.position > 0 {
+            Self::end_subset::<FunctionSubsetHeader>(self.buf, self.position, &mut self.function_mark);
+            Self::end_subset::<ConfigurationSubsetHeader>(self.buf, self.position, &mut self.config_mark);
+            Self::end_subset::<DescriptorSetHeader>(self.buf, self.position, &mut Some(0));
+        }
+    }
+
+    fn write_bos(&mut self, bos: &mut BosWriter) {
+        let windows_version = &self.buf[4..8];
+        let len = (self.position as u16).to_le_bytes();
+        bos.capability(
+            capability_type::PLATFORM,
+            &[
+                0, // reserved
+                // platform capability UUID, Microsoft OS 2.0 platform compabitility
+                0xdf,
+                0x60,
+                0xdd,
+                0xd8,
+                0x89,
+                0x45,
+                0xc7,
+                0x4c,
+                0x9c,
+                0xd2,
+                0x65,
+                0x9d,
+                0x9e,
+                0x64,
+                0x8a,
+                0x9f,
+                // Minimum compatible Windows version
+                windows_version[0],
+                windows_version[1],
+                windows_version[2],
+                windows_version[3],
+                // Descriptor set length
+                len[0],
+                len[1],
+                self.vendor_code,
+                0x0, // Device does not support alternate enumeration
+            ],
+        );
+    }
+}
+
+/// Microsoft Windows version codes
+///
+/// Windows 8.1 is the minimum version allowed for MS OS 2.0 descriptors.
+pub mod windows_version {
+    /// Windows 8.1 (aka `NTDDI_WINBLUE`)
+    pub const WIN8_1: u32 = 0x06030000;
+    /// Windows 10
+    pub const WIN10: u32 = 0x0A000000;
+}
+
+mod sealed {
+    use core::mem::size_of;
+
+    /// A trait for descriptors
+    pub trait Descriptor: Sized {
+        const TYPE: super::DescriptorType;
+
+        /// The size of the descriptor's header.
+        fn size(&self) -> usize {
+            size_of::<Self>()
+        }
+
+        fn write_to(&self, buf: &mut [u8]);
+    }
+
+    pub trait DescriptorSet: Descriptor {
+        const LENGTH_OFFSET: usize;
+    }
+}
+
+use sealed::*;
+
+/// Copies the data of `t` into `buf`.
+///
+/// # Safety
+/// The type `T` must be able to be safely cast to `&[u8]`. (e.g. it is a `#[repr(packed)]` struct)
+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);
+}
+
+/// Table 9. Microsoft OS 2.0 descriptor wDescriptorType values.
+#[derive(Clone, Copy, PartialEq, Eq)]
+#[repr(u16)]
+pub enum DescriptorType {
+    /// MS OS descriptor set header
+    SetHeaderDescriptor = 0,
+    /// Configuration subset header
+    SubsetHeaderConfiguration = 1,
+    /// Function subset header
+    SubsetHeaderFunction = 2,
+    /// Compatible device ID feature descriptor
+    FeatureCompatibleId = 3,
+    /// Registry property feature descriptor
+    FeatureRegProperty = 4,
+    /// Minimum USB resume time feature descriptor
+    FeatureMinResumeTime = 5,
+    /// Vendor revision feature descriptor
+    FeatureModelId = 6,
+    /// CCGP device descriptor feature descriptor
+    FeatureCcgpDevice = 7,
+    /// Vendor revision feature descriptor
+    FeatureVendorRevision = 8,
+}
+
+/// Table 5. Descriptor set information structure.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct DescriptorSetInformation {
+    dwWindowsVersion: u32,
+    wMSOSDescriptorSetTotalLength: u16,
+    bMS_VendorCode: u8,
+    bAltEnumCode: u8,
+}
+
+/// Table 4. Microsoft OS 2.0 platform capability descriptor header.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct PlatformDescriptor {
+    bLength: u8,
+    bDescriptorType: u8,
+    bDevCapabilityType: u8,
+    bReserved: u8,
+    platformCapabilityUUID: [u8; 16],
+    descriptor_set_information: DescriptorSetInformation,
+}
+
+/// Table 10. Microsoft OS 2.0 descriptor set header.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct DescriptorSetHeader {
+    wLength: u16,
+    wDescriptorType: u16,
+    dwWindowsVersion: u32,
+    wTotalLength: u16,
+}
+
+impl DescriptorSetHeader {
+    /// Creates a MS OS descriptor set header.
+    ///
+    /// `windows_version` is the minimum Windows version the descriptor set can apply to.
+    pub fn new(windows_version: u32) -> Self {
+        DescriptorSetHeader {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+            dwWindowsVersion: windows_version.to_le(),
+            wTotalLength: 0,
+        }
+    }
+}
+
+impl Descriptor for DescriptorSetHeader {
+    const TYPE: DescriptorType = DescriptorType::SetHeaderDescriptor;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl DescriptorSet for DescriptorSetHeader {
+    const LENGTH_OFFSET: usize = 8;
+}
+
+/// Table 11. Configuration subset header.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct ConfigurationSubsetHeader {
+    wLength: u16,
+    wDescriptorType: u16,
+    bConfigurationValue: u8,
+    bReserved: u8,
+    wTotalLength: u16,
+}
+
+impl ConfigurationSubsetHeader {
+    /// Creates a configuration subset header
+    pub fn new(config: u8) -> Self {
+        ConfigurationSubsetHeader {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+            bConfigurationValue: config,
+            bReserved: 0,
+            wTotalLength: 0,
+        }
+    }
+}
+
+impl Descriptor for ConfigurationSubsetHeader {
+    const TYPE: DescriptorType = DescriptorType::SubsetHeaderConfiguration;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl DescriptorSet for ConfigurationSubsetHeader {
+    const LENGTH_OFFSET: usize = 6;
+}
+
+/// Table 12. Function subset header.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct FunctionSubsetHeader {
+    wLength: u16,
+    wDescriptorType: u16,
+    bFirstInterface: u8,
+    bReserved: u8,
+    wSubsetLength: u16,
+}
+
+impl FunctionSubsetHeader {
+    /// Creates a function subset header
+    pub fn new(first_interface: u8) -> Self {
+        FunctionSubsetHeader {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+            bFirstInterface: first_interface,
+            bReserved: 0,
+            wSubsetLength: 0,
+        }
+    }
+}
+
+impl Descriptor for FunctionSubsetHeader {
+    const TYPE: DescriptorType = DescriptorType::SubsetHeaderFunction;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl DescriptorSet for FunctionSubsetHeader {
+    const LENGTH_OFFSET: usize = 6;
+}
+
+// Feature Descriptors
+
+/// A marker trait for feature descriptors that are valid at the device level.
+pub trait DeviceLevelDescriptor: Descriptor {}
+
+/// A marker trait for feature descriptors that are valid at the function level.
+pub trait FunctionLevelDescriptor: Descriptor {}
+
+/// Table 13. Microsoft OS 2.0 compatible ID descriptor.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct CompatibleIdFeatureDescriptor {
+    wLength: u16,
+    wDescriptorType: u16,
+    compatibleId: [u8; 8],
+    subCompatibleId: [u8; 8],
+}
+
+impl DeviceLevelDescriptor for CompatibleIdFeatureDescriptor {}
+impl FunctionLevelDescriptor for CompatibleIdFeatureDescriptor {}
+
+impl Descriptor for CompatibleIdFeatureDescriptor {
+    const TYPE: DescriptorType = DescriptorType::FeatureCompatibleId;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl CompatibleIdFeatureDescriptor {
+    /// Creates a compatible ID feature descriptor
+    ///
+    /// The ids must be 8 ASCII bytes or fewer.
+    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());
+        let mut scid = [0u8; 8];
+        (&mut scid[..sub_compatible_id.len()]).copy_from_slice(sub_compatible_id.as_bytes());
+        Self::new_raw(cid, scid)
+    }
+
+    fn new_raw(compatible_id: [u8; 8], sub_compatible_id: [u8; 8]) -> Self {
+        Self {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+            compatibleId: compatible_id,
+            subCompatibleId: sub_compatible_id,
+        }
+    }
+}
+
+/// Table 14. Microsoft OS 2.0 registry property descriptor
+#[allow(non_snake_case)]
+pub struct RegistryPropertyFeatureDescriptor<'a> {
+    name: &'a str,
+    data: PropertyData<'a>,
+}
+
+/// Data values that can be encoded into a registry property descriptor
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum PropertyData<'a> {
+    /// A registry property containing a string.
+    Sz(&'a str),
+    /// A registry property containing a string that expands environment variables.
+    ExpandSz(&'a str),
+    /// A registry property containing binary data.
+    Binary(&'a [u8]),
+    /// A registry property containing a little-endian 32-bit integer.
+    DwordLittleEndian(u32),
+    /// A registry property containing a big-endian 32-bit integer.
+    DwordBigEndian(u32),
+    /// A registry property containing a string that contains a symbolic link.
+    Link(&'a str),
+    /// A registry property containing multiple strings.
+    RegMultiSz(&'a [&'a str]),
+}
+
+fn write_bytes(val: &[u8], buf: &mut [u8]) -> usize {
+    assert!(buf.len() >= val.len());
+    buf[..val.len()].copy_from_slice(val);
+    val.len()
+}
+
+fn write_utf16(val: &str, buf: &mut [u8]) -> usize {
+    let mut pos = 0;
+    for c in val.encode_utf16() {
+        pos += write_bytes(&c.to_le_bytes(), &mut buf[pos..]);
+    }
+    pos + write_bytes(&0u16.to_le_bytes(), &mut buf[pos..])
+}
+
+impl<'a> PropertyData<'a> {
+    /// Gets the `PropertyDataType` for this property value
+    pub fn kind(&self) -> PropertyDataType {
+        match self {
+            PropertyData::Sz(_) => PropertyDataType::Sz,
+            PropertyData::ExpandSz(_) => PropertyDataType::ExpandSz,
+            PropertyData::Binary(_) => PropertyDataType::Binary,
+            PropertyData::DwordLittleEndian(_) => PropertyDataType::DwordLittleEndian,
+            PropertyData::DwordBigEndian(_) => PropertyDataType::DwordBigEndian,
+            PropertyData::Link(_) => PropertyDataType::Link,
+            PropertyData::RegMultiSz(_) => PropertyDataType::RegMultiSz,
+        }
+    }
+
+    /// Gets the size (in bytes) of this property value when encoded.
+    pub fn size(&self) -> usize {
+        match self {
+            PropertyData::Sz(val) | PropertyData::ExpandSz(val) | PropertyData::Link(val) => {
+                core::mem::size_of::<u16>() * (val.encode_utf16().count() + 1)
+            }
+            PropertyData::Binary(val) => val.len(),
+            PropertyData::DwordLittleEndian(val) | PropertyData::DwordBigEndian(val) => core::mem::size_of_val(val),
+            PropertyData::RegMultiSz(val) => {
+                core::mem::size_of::<u16>() * val.iter().map(|x| x.encode_utf16().count() + 1).sum::<usize>() + 1
+            }
+        }
+    }
+
+    /// Encodes the data for this property value and writes it to `buf`.
+    pub fn write(&self, buf: &mut [u8]) -> usize {
+        match self {
+            PropertyData::Sz(val) | PropertyData::ExpandSz(val) | PropertyData::Link(val) => write_utf16(val, buf),
+            PropertyData::Binary(val) => write_bytes(val, buf),
+            PropertyData::DwordLittleEndian(val) => write_bytes(&val.to_le_bytes(), buf),
+            PropertyData::DwordBigEndian(val) => write_bytes(&val.to_be_bytes(), buf),
+            PropertyData::RegMultiSz(val) => {
+                let mut pos = 0;
+                for s in *val {
+                    pos += write_utf16(s, &mut buf[pos..]);
+                }
+                pos + write_bytes(&0u16.to_le_bytes(), &mut buf[pos..])
+            }
+        }
+    }
+}
+
+/// Table 15. wPropertyDataType values for the Microsoft OS 2.0 registry property descriptor.
+#[derive(Clone, Copy, PartialEq, Eq)]
+#[repr(u16)]
+pub enum PropertyDataType {
+    /// A registry property containing a string.
+    Sz = 1,
+    /// A registry property containing a string that expands environment variables.
+    ExpandSz = 2,
+    /// A registry property containing binary data.
+    Binary = 3,
+    /// A registry property containing a little-endian 32-bit integer.
+    DwordLittleEndian = 4,
+    /// A registry property containing a big-endian 32-bit integer.
+    DwordBigEndian = 5,
+    /// A registry property containing a string that contains a symbolic link.
+    Link = 6,
+    /// A registry property containing multiple strings.
+    RegMultiSz = 7,
+}
+
+impl<'a> DeviceLevelDescriptor for RegistryPropertyFeatureDescriptor<'a> {}
+impl<'a> FunctionLevelDescriptor for RegistryPropertyFeatureDescriptor<'a> {}
+
+impl<'a> Descriptor for RegistryPropertyFeatureDescriptor<'a> {
+    const TYPE: DescriptorType = DescriptorType::FeatureRegProperty;
+
+    fn size(&self) -> usize {
+        10 + self.name_size() + self.data.size()
+    }
+
+    fn write_to(&self, buf: &mut [u8]) {
+        assert!(buf.len() >= self.size(), "MS OS descriptor buffer full");
+
+        let mut pos = 0;
+        pos += write_bytes(&(self.size() as u16).to_le_bytes(), &mut buf[pos..]);
+        pos += write_bytes(&(Self::TYPE as u16).to_le_bytes(), &mut buf[pos..]);
+        pos += write_bytes(&(self.data.kind() as u16).to_le_bytes(), &mut buf[pos..]);
+        pos += write_bytes(&(self.name_size() as u16).to_le_bytes(), &mut buf[pos..]);
+        pos += write_utf16(self.name, &mut buf[pos..]);
+        pos += write_bytes(&(self.data.size() as u16).to_le_bytes(), &mut buf[pos..]);
+        self.data.write(&mut buf[pos..]);
+    }
+}
+
+impl<'a> RegistryPropertyFeatureDescriptor<'a> {
+    /// A registry property.
+    pub fn new(name: &'a str, data: PropertyData<'a>) -> Self {
+        Self { name, data }
+    }
+
+    fn name_size(&self) -> usize {
+        core::mem::size_of::<u16>() * (self.name.encode_utf16().count() + 1)
+    }
+}
+
+/// Table 16. Microsoft OS 2.0 minimum USB recovery time descriptor.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct MinimumRecoveryTimeDescriptor {
+    wLength: u16,
+    wDescriptorType: u16,
+    bResumeRecoveryTime: u8,
+    bResumeSignalingTime: u8,
+}
+
+impl DeviceLevelDescriptor for MinimumRecoveryTimeDescriptor {}
+
+impl Descriptor for MinimumRecoveryTimeDescriptor {
+    const TYPE: DescriptorType = DescriptorType::FeatureMinResumeTime;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl MinimumRecoveryTimeDescriptor {
+    /// Times are in milliseconds.
+    ///
+    /// `resume_recovery_time` must be >= 0 and <= 10.
+    /// `resume_signaling_time` must be >= 1 and <= 20.
+    pub fn new(resume_recovery_time: u8, resume_signaling_time: u8) -> Self {
+        assert!(resume_recovery_time <= 10);
+        assert!(resume_signaling_time >= 1 && resume_signaling_time <= 20);
+        Self {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+            bResumeRecoveryTime: resume_recovery_time,
+            bResumeSignalingTime: resume_signaling_time,
+        }
+    }
+}
+
+/// Table 17. Microsoft OS 2.0 model ID descriptor.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct ModelIdDescriptor {
+    wLength: u16,
+    wDescriptorType: u16,
+    modelId: [u8; 16],
+}
+
+impl DeviceLevelDescriptor for ModelIdDescriptor {}
+
+impl Descriptor for ModelIdDescriptor {
+    const TYPE: DescriptorType = DescriptorType::FeatureModelId;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl ModelIdDescriptor {
+    /// Creates a new model ID descriptor
+    ///
+    /// `model_id` should be a uuid that uniquely identifies a physical device.
+    pub fn new(model_id: u128) -> Self {
+        Self {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+            modelId: model_id.to_le_bytes(),
+        }
+    }
+}
+
+/// Table 18. Microsoft OS 2.0 CCGP device descriptor.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct CcgpDeviceDescriptor {
+    wLength: u16,
+    wDescriptorType: u16,
+}
+
+impl DeviceLevelDescriptor for CcgpDeviceDescriptor {}
+
+impl Descriptor for CcgpDeviceDescriptor {
+    const TYPE: DescriptorType = DescriptorType::FeatureCcgpDevice;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl CcgpDeviceDescriptor {
+    /// Creates a new CCGP device descriptor
+    pub fn new() -> Self {
+        Self {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+        }
+    }
+}
+
+/// Table 19. Microsoft OS 2.0 vendor revision descriptor.
+#[allow(non_snake_case)]
+#[repr(C, packed(1))]
+pub struct VendorRevisionDescriptor {
+    wLength: u16,
+    wDescriptorType: u16,
+    /// Revision number associated with the descriptor set. Modify it every time you add/modify a registry property or
+    /// other MS OS descriptor. Shell set to greater than or equal to 1.
+    VendorRevision: u16,
+}
+
+impl DeviceLevelDescriptor for VendorRevisionDescriptor {}
+impl FunctionLevelDescriptor for VendorRevisionDescriptor {}
+
+impl Descriptor for VendorRevisionDescriptor {
+    const TYPE: DescriptorType = DescriptorType::FeatureVendorRevision;
+    fn write_to(&self, buf: &mut [u8]) {
+        unsafe { transmute_write_to(self, buf) }
+    }
+}
+
+impl VendorRevisionDescriptor {
+    /// Creates a new vendor revision descriptor
+    pub fn new(revision: u16) -> Self {
+        assert!(revision >= 1);
+        Self {
+            wLength: (size_of::<Self>() as u16).to_le(),
+            wDescriptorType: (Self::TYPE as u16).to_le(),
+            VendorRevision: revision.to_le(),
+        }
+    }
+}
diff --git a/examples/nrf52840/Cargo.toml b/examples/nrf52840/Cargo.toml
index 95d939873..cfdda076e 100644
--- a/examples/nrf52840/Cargo.toml
+++ b/examples/nrf52840/Cargo.toml
@@ -6,6 +6,7 @@ license = "MIT OR Apache-2.0"
 
 [features]
 default = ["nightly"]
+msos-descriptor = ["embassy-usb/msos-descriptor"]
 nightly = ["embassy-executor/nightly", "embassy-nrf/nightly", "embassy-net/nightly", "embassy-nrf/unstable-traits", "embassy-usb", "embedded-io/async", "embassy-net",
            "embassy-lora", "lorawan-device", "lorawan"]
 
@@ -34,4 +35,8 @@ futures = { version = "0.3.17", default-features = false, features = ["async-awa
 rand = { version = "0.8.4", default-features = false }
 embedded-storage = "0.3.0"
 usbd-hid = "0.6.0"
-serde = { version = "1.0.136", default-features = false }
\ No newline at end of file
+serde = { version = "1.0.136", default-features = false }
+
+[[bin]]
+name = "usb_serial_winusb"
+required-features = ["msos-descriptor"]
diff --git a/examples/nrf52840/src/bin/usb_serial_winusb.rs b/examples/nrf52840/src/bin/usb_serial_winusb.rs
new file mode 100644
index 000000000..f4b828de6
--- /dev/null
+++ b/examples/nrf52840/src/bin/usb_serial_winusb.rs
@@ -0,0 +1,130 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use core::mem;
+
+use defmt::{info, panic};
+use embassy_executor::Spawner;
+use embassy_futures::join::join;
+use embassy_nrf::usb::{Driver, HardwareVbusDetect, Instance, VbusDetect};
+use embassy_nrf::{interrupt, pac};
+use embassy_usb::class::cdc_acm::{CdcAcmClass, State};
+use embassy_usb::driver::EndpointError;
+use embassy_usb::msos::{self, windows_version};
+use embassy_usb::{Builder, Config};
+use {defmt_rtt as _, panic_probe as _};
+
+// This is a randomly generated GUID to allow clients on Windows to find our device
+const DEVICE_INTERFACE_GUIDS: &[&str] = &["{EAA9A5DC-30BA-44BC-9232-606CDC875321}"];
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_nrf::init(Default::default());
+    let clock: pac::CLOCK = unsafe { mem::transmute(()) };
+
+    info!("Enabling ext hfosc...");
+    clock.tasks_hfclkstart.write(|w| unsafe { w.bits(1) });
+    while clock.events_hfclkstarted.read().bits() != 1 {}
+
+    // Create the driver, from the HAL.
+    let irq = interrupt::take!(USBD);
+    let power_irq = interrupt::take!(POWER_CLOCK);
+    let driver = Driver::new(p.USBD, irq, HardwareVbusDetect::new(power_irq));
+
+    // Create embassy-usb Config
+    let mut config = Config::new(0xc0de, 0xcafe);
+    config.manufacturer = Some("Embassy");
+    config.product = Some("USB-serial example");
+    config.serial_number = Some("12345678");
+    config.max_power = 100;
+    config.max_packet_size_0 = 64;
+
+    // Required for windows compatiblity.
+    // https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.9.1/kconfig/CONFIG_CDC_ACM_IAD.html#help
+    config.device_class = 0xEF;
+    config.device_sub_class = 0x02;
+    config.device_protocol = 0x01;
+    config.composite_with_iads = true;
+
+    // Create embassy-usb DeviceBuilder using the driver and config.
+    // It needs some buffers for building the descriptors.
+    let mut device_descriptor = [0; 256];
+    let mut config_descriptor = [0; 256];
+    let mut bos_descriptor = [0; 256];
+    let mut msos_descriptor = [0; 256];
+    let mut control_buf = [0; 64];
+
+    let mut state = State::new();
+
+    let mut builder = Builder::new(
+        driver,
+        config,
+        &mut device_descriptor,
+        &mut config_descriptor,
+        &mut bos_descriptor,
+        &mut msos_descriptor,
+        &mut control_buf,
+        None,
+    );
+
+    builder.msos_descriptor(windows_version::WIN8_1, 2);
+
+    // Create classes on the builder.
+    let mut class = CdcAcmClass::new(&mut builder, &mut state, 64);
+
+    // Since we want to create MS OS feature descriptors that apply to a function that has already been added to the
+    // builder, need to get the MsOsDescriptorWriter from the builder and manually add those descriptors.
+    // Inside a class constructor, you would just need to call `FunctionBuilder::msos_feature` instead.
+    let msos_writer = builder.msos_writer();
+    msos_writer.configuration(0);
+    msos_writer.function(0);
+    msos_writer.function_feature(msos::CompatibleIdFeatureDescriptor::new("WINUSB", ""));
+    msos_writer.function_feature(msos::RegistryPropertyFeatureDescriptor::new(
+        "DeviceInterfaceGUIDs",
+        msos::PropertyData::RegMultiSz(DEVICE_INTERFACE_GUIDS),
+    ));
+
+    // Build the builder.
+    let mut usb = builder.build();
+
+    // Run the USB device.
+    let usb_fut = usb.run();
+
+    // Do stuff with the class!
+    let echo_fut = async {
+        loop {
+            class.wait_connection().await;
+            info!("Connected");
+            let _ = echo(&mut class).await;
+            info!("Disconnected");
+        }
+    };
+
+    // Run everything concurrently.
+    // If we had made everything `'static` above instead, we could do this using separate tasks instead.
+    join(usb_fut, echo_fut).await;
+}
+
+struct Disconnected {}
+
+impl From<EndpointError> for Disconnected {
+    fn from(val: EndpointError) -> Self {
+        match val {
+            EndpointError::BufferOverflow => panic!("Buffer overflow"),
+            EndpointError::Disabled => Disconnected {},
+        }
+    }
+}
+
+async fn echo<'d, T: Instance + 'd, P: VbusDetect + 'd>(
+    class: &mut CdcAcmClass<'d, Driver<'d, T, P>>,
+) -> Result<(), Disconnected> {
+    let mut buf = [0; 64];
+    loop {
+        let n = class.read_packet(&mut buf).await?;
+        let data = &buf[..n];
+        info!("data: {:x}", data);
+        class.write_packet(data).await?;
+    }
+}