2 files changed, 206 insertions, 25 deletions

diff --git a/embassy-usb/src/builder.rs b/embassy-usb/src/builder.rs
index 7168e077c..e1bf8041f 100644
--- a/embassy-usb/src/builder.rs
+++ b/embassy-usb/src/builder.rs
@@ -1,8 +1,8 @@
 use heapless::Vec;
 
 use crate::config::MAX_HANDLER_COUNT;
-use crate::descriptor::{BosWriter, DescriptorWriter};
-use crate::driver::{Driver, Endpoint, EndpointType};
+use crate::descriptor::{BosWriter, DescriptorWriter, SynchronizationType, UsageType};
+use crate::driver::{Driver, Endpoint, EndpointInfo, EndpointType};
 use crate::msos::{DeviceLevelDescriptor, FunctionLevelDescriptor, MsOsDescriptorWriter};
 use crate::types::{InterfaceNumber, StringIndex};
 use crate::{Handler, Interface, UsbDevice, MAX_INTERFACE_COUNT, STRING_INDEX_CUSTOM_START};
@@ -414,7 +414,7 @@ impl<'a, 'd, D: Driver<'d>> InterfaceAltBuilder<'a, 'd, D> {
     /// Descriptors are written in the order builder functions are called. Note that some
     /// classes care about the order.
     pub fn descriptor(&mut self, descriptor_type: u8, descriptor: &[u8]) {
-        self.builder.config_descriptor.write(descriptor_type, descriptor);
+        self.builder.config_descriptor.write(descriptor_type, descriptor, &[]);
     }
 
     /// Add a custom Binary Object Store (BOS) descriptor to this alternate setting.
@@ -422,26 +422,80 @@ impl<'a, 'd, D: Driver<'d>> InterfaceAltBuilder<'a, 'd, D> {
         self.builder.bos_descriptor.capability(capability_type, capability);
     }
 
-    fn endpoint_in(&mut self, ep_type: EndpointType, max_packet_size: u16, interval_ms: u8) -> D::EndpointIn {
+    /// Write a custom endpoint descriptor for a certain endpoint.
+    ///
+    /// This can be necessary, if the endpoint descriptors can only be written
+    /// after the endpoint was created. As an example, an endpoint descriptor
+    /// may contain the address of an endpoint that was allocated earlier.
+    pub fn endpoint_descriptor(
+        &mut self,
+        endpoint: &EndpointInfo,
+        synchronization_type: SynchronizationType,
+        usage_type: UsageType,
+        extra_fields: &[u8],
+    ) {
+        self.builder
+            .config_descriptor
+            .endpoint(endpoint, synchronization_type, usage_type, extra_fields);
+    }
+
+    /// Allocate an IN endpoint, without writing its descriptor.
+    ///
+    /// Used for granular control over the order of endpoint and descriptor creation.
+    pub fn alloc_endpoint_in(&mut self, ep_type: EndpointType, max_packet_size: u16, interval_ms: u8) -> D::EndpointIn {
         let ep = self
             .builder
             .driver
             .alloc_endpoint_in(ep_type, max_packet_size, interval_ms)
             .expect("alloc_endpoint_in failed");
 
-        self.builder.config_descriptor.endpoint(ep.info());
+        ep
+    }
+
+    fn endpoint_in(
+        &mut self,
+        ep_type: EndpointType,
+        max_packet_size: u16,
+        interval_ms: u8,
+        synchronization_type: SynchronizationType,
+        usage_type: UsageType,
+        extra_fields: &[u8],
+    ) -> D::EndpointIn {
+        let ep = self.alloc_endpoint_in(ep_type, max_packet_size, interval_ms);
+        self.endpoint_descriptor(ep.info(), synchronization_type, usage_type, extra_fields);
 
         ep
     }
 
-    fn endpoint_out(&mut self, ep_type: EndpointType, max_packet_size: u16, interval_ms: u8) -> D::EndpointOut {
+    /// Allocate an OUT endpoint, without writing its descriptor.
+    ///
+    /// Use for granular control over the order of endpoint and descriptor creation.
+    pub fn alloc_endpoint_out(
+        &mut self,
+        ep_type: EndpointType,
+        max_packet_size: u16,
+        interval_ms: u8,
+    ) -> D::EndpointOut {
         let ep = self
             .builder
             .driver
             .alloc_endpoint_out(ep_type, max_packet_size, interval_ms)
             .expect("alloc_endpoint_out failed");
 
-        self.builder.config_descriptor.endpoint(ep.info());
+        ep
+    }
+
+    fn endpoint_out(
+        &mut self,
+        ep_type: EndpointType,
+        max_packet_size: u16,
+        interval_ms: u8,
+        synchronization_type: SynchronizationType,
+        usage_type: UsageType,
+        extra_fields: &[u8],
+    ) -> D::EndpointOut {
+        let ep = self.alloc_endpoint_out(ep_type, max_packet_size, interval_ms);
+        self.endpoint_descriptor(ep.info(), synchronization_type, usage_type, extra_fields);
 
         ep
     }
@@ -451,7 +505,14 @@ impl<'a, 'd, D: Driver<'d>> InterfaceAltBuilder<'a, 'd, D> {
     /// Descriptors are written in the order builder functions are called. Note that some
     /// classes care about the order.
     pub fn endpoint_bulk_in(&mut self, max_packet_size: u16) -> D::EndpointIn {
-        self.endpoint_in(EndpointType::Bulk, max_packet_size, 0)
+        self.endpoint_in(
+            EndpointType::Bulk,
+            max_packet_size,
+            0,
+            SynchronizationType::NoSynchronization,
+            UsageType::DataEndpoint,
+            &[],
+        )
     }
 
     /// Allocate a BULK OUT endpoint and write its descriptor.
@@ -459,7 +520,14 @@ impl<'a, 'd, D: Driver<'d>> InterfaceAltBuilder<'a, 'd, D> {
     /// Descriptors are written in the order builder functions are called. Note that some
     /// classes care about the order.
     pub fn endpoint_bulk_out(&mut self, max_packet_size: u16) -> D::EndpointOut {
-        self.endpoint_out(EndpointType::Bulk, max_packet_size, 0)
+        self.endpoint_out(
+            EndpointType::Bulk,
+            max_packet_size,
+            0,
+            SynchronizationType::NoSynchronization,
+            UsageType::DataEndpoint,
+            &[],
+        )
     }
 
     /// Allocate a INTERRUPT IN endpoint and write its descriptor.
@@ -467,24 +535,66 @@ impl<'a, 'd, D: Driver<'d>> InterfaceAltBuilder<'a, 'd, D> {
     /// Descriptors are written in the order builder functions are called. Note that some
     /// classes care about the order.
     pub fn endpoint_interrupt_in(&mut self, max_packet_size: u16, interval_ms: u8) -> D::EndpointIn {
-        self.endpoint_in(EndpointType::Interrupt, max_packet_size, interval_ms)
+        self.endpoint_in(
+            EndpointType::Interrupt,
+            max_packet_size,
+            interval_ms,
+            SynchronizationType::NoSynchronization,
+            UsageType::DataEndpoint,
+            &[],
+        )
     }
 
     /// Allocate a INTERRUPT OUT endpoint and write its descriptor.
     pub fn endpoint_interrupt_out(&mut self, max_packet_size: u16, interval_ms: u8) -> D::EndpointOut {
-        self.endpoint_out(EndpointType::Interrupt, max_packet_size, interval_ms)
+        self.endpoint_out(
+            EndpointType::Interrupt,
+            max_packet_size,
+            interval_ms,
+            SynchronizationType::NoSynchronization,
+            UsageType::DataEndpoint,
+            &[],
+        )
     }
 
     /// Allocate a ISOCHRONOUS IN endpoint and write its descriptor.
     ///
     /// Descriptors are written in the order builder functions are called. Note that some
     /// classes care about the order.
-    pub fn endpoint_isochronous_in(&mut self, max_packet_size: u16, interval_ms: u8) -> D::EndpointIn {
-        self.endpoint_in(EndpointType::Isochronous, max_packet_size, interval_ms)
+    pub fn endpoint_isochronous_in(
+        &mut self,
+        max_packet_size: u16,
+        interval_ms: u8,
+        synchronization_type: SynchronizationType,
+        usage_type: UsageType,
+        extra_fields: &[u8],
+    ) -> D::EndpointIn {
+        self.endpoint_in(
+            EndpointType::Isochronous,
+            max_packet_size,
+            interval_ms,
+            synchronization_type,
+            usage_type,
+            extra_fields,
+        )
     }
 
     /// Allocate a ISOCHRONOUS OUT endpoint and write its descriptor.
-    pub fn endpoint_isochronous_out(&mut self, max_packet_size: u16, interval_ms: u8) -> D::EndpointOut {
-        self.endpoint_out(EndpointType::Isochronous, max_packet_size, interval_ms)
+    pub fn endpoint_isochronous_out(
+        &mut self,
+        max_packet_size: u16,
+        interval_ms: u8,
+        synchronization_type: SynchronizationType,
+        usage_type: UsageType,
+        extra_fields: &[u8],
+    ) -> D::EndpointOut {
+        self.endpoint_out(
+            EndpointType::Isochronous,
+            max_packet_size,
+            interval_ms,
+            synchronization_type,
+            usage_type,
+            extra_fields,
+        )
     }
 }
diff --git a/embassy-usb/src/descriptor.rs b/embassy-usb/src/descriptor.rs
index f1773fa8a..0f2931c38 100644
--- a/embassy-usb/src/descriptor.rs
+++ b/embassy-usb/src/descriptor.rs
@@ -1,4 +1,5 @@
 //! Utilities for writing USB descriptors.
+use embassy_usb_driver::EndpointType;
 
 use crate::builder::Config;
 use crate::driver::EndpointInfo;
@@ -38,6 +39,40 @@ pub mod capability_type {
     pub const PLATFORM: u8 = 5;
 }
 
+/// USB endpoint synchronization type. The values of this enum can be directly
+/// cast into `u8` to get the bmAttributes synchronization type bits.
+/// Values other than `NoSynchronization` are only allowed on isochronous endpoints.
+#[repr(u8)]
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum SynchronizationType {
+    /// No synchronization is used.
+    NoSynchronization = 0b00,
+    /// Unsynchronized, although sinks provide data rate feedback.
+    Asynchronous = 0b01,
+    /// Synchronized using feedback or feedforward data rate information.
+    Adaptive = 0b10,
+    /// Synchronized to the USB’s SOF.
+    Synchronous = 0b11,
+}
+
+/// USB endpoint usage type. The values of this enum can be directly cast into
+/// `u8` to get the bmAttributes usage type bits.
+/// Values other than `DataEndpoint` are only allowed on isochronous endpoints.
+#[repr(u8)]
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum UsageType {
+    /// Use the endpoint for regular data transfer.
+    DataEndpoint = 0b00,
+    /// Endpoint conveys explicit feedback information for one or more data endpoints.
+    FeedbackEndpoint = 0b01,
+    /// A data endpoint that also serves as an implicit feedback endpoint for one or more data endpoints.
+    ImplicitFeedbackDataEndpoint = 0b10,
+    /// Reserved usage type.
+    Reserved = 0b11,
+}
+
 /// A writer for USB descriptors.
 pub(crate) struct DescriptorWriter<'a> {
     pub buf: &'a mut [u8],
@@ -65,23 +100,26 @@ impl<'a> DescriptorWriter<'a> {
         self.position
     }
 
-    /// Writes an arbitrary (usually class-specific) descriptor.
-    pub fn write(&mut self, descriptor_type: u8, descriptor: &[u8]) {
-        let length = descriptor.len();
+    /// Writes an arbitrary (usually class-specific) descriptor with optional extra fields.
+    pub fn write(&mut self, descriptor_type: u8, descriptor: &[u8], extra_fields: &[u8]) {
+        let descriptor_length = descriptor.len();
+        let extra_fields_length = extra_fields.len();
+        let total_length = descriptor_length + extra_fields_length;
 
         assert!(
-            (self.position + 2 + length) <= self.buf.len() && (length + 2) <= 255,
+            (self.position + 2 + total_length) <= self.buf.len() && (total_length + 2) <= 255,
             "Descriptor buffer full"
         );
 
-        self.buf[self.position] = (length + 2) as u8;
+        self.buf[self.position] = (total_length + 2) as u8;
         self.buf[self.position + 1] = descriptor_type;
 
         let start = self.position + 2;
 
-        self.buf[start..start + length].copy_from_slice(descriptor);
+        self.buf[start..start + descriptor_length].copy_from_slice(descriptor);
+        self.buf[start + descriptor_length..start + total_length].copy_from_slice(extra_fields);
 
-        self.position = start + length;
+        self.position = start + total_length;
     }
 
     pub(crate) fn configuration(&mut self, config: &Config) {
@@ -99,6 +137,7 @@ impl<'a> DescriptorWriter<'a> {
                     | if config.supports_remote_wakeup { 0x20 } else { 0x00 }, // bmAttributes
                 (config.max_power / 2) as u8, // bMaxPower
             ],
+            &[],
         );
     }
 
@@ -145,6 +184,7 @@ impl<'a> DescriptorWriter<'a> {
                 function_protocol,
                 0,
             ],
+            &[],
         );
     }
 
@@ -195,6 +235,7 @@ impl<'a> DescriptorWriter<'a> {
                 interface_protocol,  // bInterfaceProtocol
                 str_index,           // iInterface
             ],
+            &[],
         );
     }
 
@@ -204,21 +245,50 @@ impl<'a> DescriptorWriter<'a> {
     ///
     /// * `endpoint` - Endpoint previously allocated with
     ///   [`UsbDeviceBuilder`](crate::bus::UsbDeviceBuilder).
-    pub fn endpoint(&mut self, endpoint: &EndpointInfo) {
+    /// * `synchronization_type` - The synchronization type of the endpoint.
+    /// * `usage_type` - The usage type of the endpoint.
+    /// * `extra_fields` - Additional, class-specific entries at the end of the endpoint descriptor.
+    pub fn endpoint(
+        &mut self,
+        endpoint: &EndpointInfo,
+        synchronization_type: SynchronizationType,
+        usage_type: UsageType,
+        extra_fields: &[u8],
+    ) {
         match self.num_endpoints_mark {
             Some(mark) => self.buf[mark] += 1,
             None => panic!("you can only call `endpoint` after `interface/interface_alt`."),
         };
 
+        let mut bm_attributes = endpoint.ep_type as u8;
+
+        // Synchronization types other than `NoSynchronization`,
+        // and usage types other than `DataEndpoint`
+        // are only allowed for isochronous endpoints.
+        if endpoint.ep_type != EndpointType::Isochronous {
+            assert_eq!(synchronization_type, SynchronizationType::NoSynchronization);
+            assert_eq!(usage_type, UsageType::DataEndpoint);
+        } else {
+            if usage_type == UsageType::FeedbackEndpoint {
+                assert_eq!(synchronization_type, SynchronizationType::NoSynchronization)
+            }
+
+            let synchronization_bm_attibutes: u8 = (synchronization_type as u8) << 2;
+            let usage_bm_attibutes: u8 = (usage_type as u8) << 4;
+
+            bm_attributes |= usage_bm_attibutes | synchronization_bm_attibutes;
+        }
+
         self.write(
             descriptor_type::ENDPOINT,
             &[
-                endpoint.addr.into(),   // bEndpointAddress
-                endpoint.ep_type as u8, // bmAttributes
+                endpoint.addr.into(), // bEndpointAddress
+                bm_attributes,        // bmAttributes
                 endpoint.max_packet_size as u8,
                 (endpoint.max_packet_size >> 8) as u8, // wMaxPacketSize
                 endpoint.interval_ms,                  // bInterval
             ],
+            extra_fields,
         );
     }
 
@@ -315,6 +385,7 @@ impl<'a> BosWriter<'a> {
                 0x00, 0x00, // wTotalLength
                 0x00, // bNumDeviceCaps
             ],
+            &[],
         );
 
         self.capability(capability_type::USB_2_0_EXTENSION, &[0; 4]);