Merge pull request #3314 from elagil/add_iso_endpoint_support

Add ISO endpoint support

5 files changed, 430 insertions, 58 deletions

diff --git a/embassy-stm32/src/usb/usb.rs b/embassy-stm32/src/usb/usb.rs
index 9384c8688..0ab2306c8 100644
--- a/embassy-stm32/src/usb/usb.rs
+++ b/embassy-stm32/src/usb/usb.rs
@@ -80,6 +80,8 @@ impl<T: Instance> interrupt::typelevel::Handler<T::Interrupt> for InterruptHandl
 
         if istr.ctr() {
             let index = istr.ep_id() as usize;
+            CTR_TRIGGERED[index].store(true, Ordering::Relaxed);
+
             let mut epr = regs.epr(index).read();
             if epr.ctr_rx() {
                 if index == 0 && epr.setup() {
@@ -120,6 +122,10 @@ const USBRAM_ALIGN: usize = 4;
 const NEW_AW: AtomicWaker = AtomicWaker::new();
 static BUS_WAKER: AtomicWaker = NEW_AW;
 static EP0_SETUP: AtomicBool = AtomicBool::new(false);
+
+const NEW_CTR_TRIGGERED: AtomicBool = AtomicBool::new(false);
+static CTR_TRIGGERED: [AtomicBool; EP_COUNT] = [NEW_CTR_TRIGGERED; EP_COUNT];
+
 static EP_IN_WAKERS: [AtomicWaker; EP_COUNT] = [NEW_AW; EP_COUNT];
 static EP_OUT_WAKERS: [AtomicWaker; EP_COUNT] = [NEW_AW; EP_COUNT];
 static IRQ_RESET: AtomicBool = AtomicBool::new(false);
@@ -163,20 +169,37 @@ fn calc_out_len(len: u16) -> (u16, u16) {
 mod btable {
     use super::*;
 
-    pub(super) fn write_in<T: Instance>(index: usize, addr: u16) {
+    pub(super) fn write_in_tx<T: Instance>(index: usize, addr: u16) {
         USBRAM.mem(index * 4 + 0).write_value(addr);
     }
 
-    pub(super) fn write_in_len<T: Instance>(index: usize, _addr: u16, len: u16) {
+    pub(super) fn write_in_rx<T: Instance>(index: usize, addr: u16) {
+        USBRAM.mem(index * 4 + 2).write_value(addr);
+    }
+
+    pub(super) fn write_in_len_rx<T: Instance>(index: usize, _addr: u16, len: u16) {
+        USBRAM.mem(index * 4 + 3).write_value(len);
+    }
+
+    pub(super) fn write_in_len_tx<T: Instance>(index: usize, _addr: u16, len: u16) {
         USBRAM.mem(index * 4 + 1).write_value(len);
     }
 
-    pub(super) fn write_out<T: Instance>(index: usize, addr: u16, max_len_bits: u16) {
+    pub(super) fn write_out_rx<T: Instance>(index: usize, addr: u16, max_len_bits: u16) {
         USBRAM.mem(index * 4 + 2).write_value(addr);
         USBRAM.mem(index * 4 + 3).write_value(max_len_bits);
     }
 
-    pub(super) fn read_out_len<T: Instance>(index: usize) -> u16 {
+    pub(super) fn write_out_tx<T: Instance>(index: usize, addr: u16, max_len_bits: u16) {
+        USBRAM.mem(index * 4 + 0).write_value(addr);
+        USBRAM.mem(index * 4 + 1).write_value(max_len_bits);
+    }
+
+    pub(super) fn read_out_len_tx<T: Instance>(index: usize) -> u16 {
+        USBRAM.mem(index * 4 + 1).read()
+    }
+
+    pub(super) fn read_out_len_rx<T: Instance>(index: usize) -> u16 {
         USBRAM.mem(index * 4 + 3).read()
     }
 }
@@ -184,19 +207,37 @@ mod btable {
 mod btable {
     use super::*;
 
-    pub(super) fn write_in<T: Instance>(_index: usize, _addr: u16) {}
+    pub(super) fn write_in_tx<T: Instance>(_index: usize, _addr: u16) {}
 
-    pub(super) fn write_in_len<T: Instance>(index: usize, addr: u16, len: u16) {
+    pub(super) fn write_in_rx<T: Instance>(_index: usize, _addr: u16) {}
+
+    pub(super) fn write_in_len_tx<T: Instance>(index: usize, addr: u16, len: u16) {
         USBRAM.mem(index * 2).write_value((addr as u32) | ((len as u32) << 16));
     }
 
-    pub(super) fn write_out<T: Instance>(index: usize, addr: u16, max_len_bits: u16) {
+    pub(super) fn write_in_len_rx<T: Instance>(index: usize, addr: u16, len: u16) {
+        USBRAM
+            .mem(index * 2 + 1)
+            .write_value((addr as u32) | ((len as u32) << 16));
+    }
+
+    pub(super) fn write_out_tx<T: Instance>(index: usize, addr: u16, max_len_bits: u16) {
+        USBRAM
+            .mem(index * 2)
+            .write_value((addr as u32) | ((max_len_bits as u32) << 16));
+    }
+
+    pub(super) fn write_out_rx<T: Instance>(index: usize, addr: u16, max_len_bits: u16) {
         USBRAM
             .mem(index * 2 + 1)
             .write_value((addr as u32) | ((max_len_bits as u32) << 16));
     }
 
-    pub(super) fn read_out_len<T: Instance>(index: usize) -> u16 {
+    pub(super) fn read_out_len_tx<T: Instance>(index: usize) -> u16 {
+        (USBRAM.mem(index * 2).read() >> 16) as u16
+    }
+
+    pub(super) fn read_out_len_rx<T: Instance>(index: usize) -> u16 {
         (USBRAM.mem(index * 2 + 1).read() >> 16) as u16
     }
 }
@@ -327,6 +368,13 @@ impl<'d, T: Instance> Driver<'d, T> {
                 return false; // reserved for control pipe
             }
             let used = ep.used_out || ep.used_in;
+            if used && (ep.ep_type == EndpointType::Isochronous || ep.ep_type == EndpointType::Bulk) {
+                // Isochronous and bulk endpoints are double-buffered.
+                // Their corresponding endpoint/channel registers are forced to be unidirectional.
+                // Do not reuse this index.
+                return false;
+            }
+
             let used_dir = match D::dir() {
                 Direction::Out => ep.used_out,
                 Direction::In => ep.used_in,
@@ -350,7 +398,11 @@ impl<'d, T: Instance> Driver<'d, T> {
                 let addr = self.alloc_ep_mem(len);
 
                 trace!("  len_bits = {:04x}", len_bits);
-                btable::write_out::<T>(index, addr, len_bits);
+                btable::write_out_rx::<T>(index, addr, len_bits);
+
+                if ep_type == EndpointType::Isochronous {
+                    btable::write_out_tx::<T>(index, addr, len_bits);
+                }
 
                 EndpointBuffer {
                     addr,
@@ -366,7 +418,11 @@ impl<'d, T: Instance> Driver<'d, T> {
                 let addr = self.alloc_ep_mem(len);
 
                 // ep_in_len is written when actually TXing packets.
-                btable::write_in::<T>(index, addr);
+                btable::write_in_tx::<T>(index, addr);
+
+                if ep_type == EndpointType::Isochronous {
+                    btable::write_in_rx::<T>(index, addr);
+                }
 
                 EndpointBuffer {
                     addr,
@@ -656,6 +712,18 @@ impl Dir for Out {
     }
 }
 
+/// Selects the packet buffer.
+///
+/// For double-buffered endpoints, both the `Rx` and `Tx` buffer from a channel are used for the same
+/// direction of transfer. This is opposed to single-buffered endpoints, where one channel can serve
+/// two directions at the same time.
+enum PacketBuffer {
+    /// The RX buffer - must be used for single-buffered OUT endpoints
+    Rx,
+    /// The TX buffer - must be used for single-buffered IN endpoints
+    Tx,
+}
+
 /// USB endpoint.
 pub struct Endpoint<'d, T: Instance, D> {
     _phantom: PhantomData<(&'d mut T, D)>,
@@ -664,15 +732,46 @@ pub struct Endpoint<'d, T: Instance, D> {
 }
 
 impl<'d, T: Instance, D> Endpoint<'d, T, D> {
-    fn write_data(&mut self, buf: &[u8]) {
+    /// Write to a double-buffered endpoint.
+    ///
+    /// For double-buffered endpoints, the data buffers overlap, but we still need to write to the right counter field.
+    /// The DTOG_TX bit indicates the buffer that is currently in use by the USB peripheral, that is, the buffer in
+    /// which the next transmit packet will be stored, so we need to write the counter of the OTHER buffer, which is
+    /// where the last transmitted packet was stored.
+    fn write_data_double_buffered(&mut self, buf: &[u8], packet_buffer: PacketBuffer) {
         let index = self.info.addr.index();
         self.buf.write(buf);
-        btable::write_in_len::<T>(index, self.buf.addr, buf.len() as _);
+
+        match packet_buffer {
+            PacketBuffer::Rx => btable::write_in_len_rx::<T>(index, self.buf.addr, buf.len() as _),
+            PacketBuffer::Tx => btable::write_in_len_tx::<T>(index, self.buf.addr, buf.len() as _),
+        }
     }
 
-    fn read_data(&mut self, buf: &mut [u8]) -> Result<usize, EndpointError> {
+    /// Write to a single-buffered endpoint.
+    fn write_data(&mut self, buf: &[u8]) {
+        self.write_data_double_buffered(buf, PacketBuffer::Tx);
+    }
+
+    /// Read from a double-buffered endpoint.
+    ///
+    /// For double-buffered endpoints, the data buffers overlap, but we still need to read from the right counter field.
+    /// The DTOG_RX bit indicates the buffer that is currently in use by the USB peripheral, that is, the buffer in
+    /// which the next received packet will be stored, so we need to read the counter of the OTHER buffer, which is
+    /// where the last received packet was stored.
+    fn read_data_double_buffered(
+        &mut self,
+        buf: &mut [u8],
+        packet_buffer: PacketBuffer,
+    ) -> Result<usize, EndpointError> {
         let index = self.info.addr.index();
-        let rx_len = btable::read_out_len::<T>(index) as usize & 0x3FF;
+
+        let rx_len = match packet_buffer {
+            PacketBuffer::Rx => btable::read_out_len_rx::<T>(index),
+            PacketBuffer::Tx => btable::read_out_len_tx::<T>(index),
+        } as usize
+            & 0x3FF;
+
         trace!("READ DONE, rx_len = {}", rx_len);
         if rx_len > buf.len() {
             return Err(EndpointError::BufferOverflow);
@@ -680,6 +779,11 @@ impl<'d, T: Instance, D> Endpoint<'d, T, D> {
         self.buf.read(&mut buf[..rx_len]);
         Ok(rx_len)
     }
+
+    /// Read from a single-buffered endpoint.
+    fn read_data(&mut self, buf: &mut [u8]) -> Result<usize, EndpointError> {
+        self.read_data_double_buffered(buf, PacketBuffer::Rx)
+    }
 }
 
 impl<'d, T: Instance> driver::Endpoint for Endpoint<'d, T, In> {
@@ -734,25 +838,53 @@ impl<'d, T: Instance> driver::EndpointOut for Endpoint<'d, T, Out> {
             EP_OUT_WAKERS[index].register(cx.waker());
             let regs = T::regs();
             let stat = regs.epr(index).read().stat_rx();
-            if matches!(stat, Stat::NAK | Stat::DISABLED) {
-                Poll::Ready(stat)
+            if self.info.ep_type == EndpointType::Isochronous {
+                // The isochronous endpoint does not change its `STAT_RX` field to `NAK` when receiving a packet.
+                // Therefore, this instead waits until the `CTR` interrupt was triggered.
+                if matches!(stat, Stat::DISABLED) || CTR_TRIGGERED[index].load(Ordering::Relaxed) {
+                    Poll::Ready(stat)
+                } else {
+                    Poll::Pending
+                }
             } else {
-                Poll::Pending
+                if matches!(stat, Stat::NAK | Stat::DISABLED) {
+                    Poll::Ready(stat)
+                } else {
+                    Poll::Pending
+                }
             }
         })
         .await;
 
+        CTR_TRIGGERED[index].store(false, Ordering::Relaxed);
+
         if stat == Stat::DISABLED {
             return Err(EndpointError::Disabled);
         }
 
-        let rx_len = self.read_data(buf)?;
-
         let regs = T::regs();
+
+        let packet_buffer = if self.info.ep_type == EndpointType::Isochronous {
+            // Find the buffer, which is currently in use. Read from the OTHER buffer.
+            if regs.epr(index).read().dtog_rx() {
+                PacketBuffer::Rx
+            } else {
+                PacketBuffer::Tx
+            }
+        } else {
+            PacketBuffer::Rx
+        };
+
+        let rx_len = self.read_data_double_buffered(buf, packet_buffer)?;
+
         regs.epr(index).write(|w| {
             w.set_ep_type(convert_type(self.info.ep_type));
             w.set_ea(self.info.addr.index() as _);
-            w.set_stat_rx(Stat::from_bits(Stat::NAK.to_bits() ^ Stat::VALID.to_bits()));
+            if self.info.ep_type == EndpointType::Isochronous {
+                w.set_stat_rx(Stat::from_bits(0)); // STAT_RX remains `VALID`.
+            } else {
+                w.set_stat_rx(Stat::from_bits(Stat::NAK.to_bits() ^ Stat::VALID.to_bits()));
+            }
             w.set_stat_tx(Stat::from_bits(0));
             w.set_ctr_rx(true); // don't clear
             w.set_ctr_tx(true); // don't clear
@@ -776,25 +908,54 @@ impl<'d, T: Instance> driver::EndpointIn for Endpoint<'d, T, In> {
             EP_IN_WAKERS[index].register(cx.waker());
             let regs = T::regs();
             let stat = regs.epr(index).read().stat_tx();
-            if matches!(stat, Stat::NAK | Stat::DISABLED) {
-                Poll::Ready(stat)
+            if self.info.ep_type == EndpointType::Isochronous {
+                // The isochronous endpoint does not change its `STAT_RX` field to `NAK` when receiving a packet.
+                // Therefore, this instead waits until the `CTR` interrupt was triggered.
+                if matches!(stat, Stat::DISABLED) || CTR_TRIGGERED[index].load(Ordering::Relaxed) {
+                    Poll::Ready(stat)
+                } else {
+                    Poll::Pending
+                }
             } else {
-                Poll::Pending
+                if matches!(stat, Stat::NAK | Stat::DISABLED) {
+                    Poll::Ready(stat)
+                } else {
+                    Poll::Pending
+                }
             }
         })
         .await;
 
+        CTR_TRIGGERED[index].store(false, Ordering::Relaxed);
+
         if stat == Stat::DISABLED {
             return Err(EndpointError::Disabled);
         }
 
-        self.write_data(buf);
+        let regs = T::regs();
+
+        let packet_buffer = if self.info.ep_type == EndpointType::Isochronous {
+            // Find the buffer, which is currently in use. Write to the OTHER buffer.
+            if regs.epr(index).read().dtog_tx() {
+                PacketBuffer::Tx
+            } else {
+                PacketBuffer::Rx
+            }
+        } else {
+            PacketBuffer::Tx
+        };
+
+        self.write_data_double_buffered(buf, packet_buffer);
 
         let regs = T::regs();
         regs.epr(index).write(|w| {
             w.set_ep_type(convert_type(self.info.ep_type));
             w.set_ea(self.info.addr.index() as _);
-            w.set_stat_tx(Stat::from_bits(Stat::NAK.to_bits() ^ Stat::VALID.to_bits()));
+            if self.info.ep_type == EndpointType::Isochronous {
+                w.set_stat_tx(Stat::from_bits(0)); // STAT_TX remains `VALID`.
+            } else {
+                w.set_stat_tx(Stat::from_bits(Stat::NAK.to_bits() ^ Stat::VALID.to_bits()));
+            }
             w.set_stat_rx(Stat::from_bits(0));
             w.set_ctr_rx(true); // don't clear
             w.set_ctr_tx(true); // don't clear
diff --git a/embassy-usb-synopsys-otg/src/lib.rs b/embassy-usb-synopsys-otg/src/lib.rs
index 5fb82db42..b145f4aa8 100644
--- a/embassy-usb-synopsys-otg/src/lib.rs
+++ b/embassy-usb-synopsys-otg/src/lib.rs
@@ -1071,6 +1071,21 @@ impl<'d> embassy_usb_driver::EndpointOut for Endpoint<'d, Out> {
                         w.set_pktcnt(1);
                     });
 
+                    if self.info.ep_type == EndpointType::Isochronous {
+                        // Isochronous endpoints must set the correct even/odd frame bit to
+                        // correspond with the next frame's number.
+                        let frame_number = self.regs.dsts().read().fnsof();
+                        let frame_is_odd = frame_number & 0x01 == 1;
+
+                        self.regs.doepctl(index).modify(|r| {
+                            if frame_is_odd {
+                                r.set_sd0pid_sevnfrm(true);
+                            } else {
+                                r.set_sd1pid_soddfrm(true);
+                            }
+                        });
+                    }
+
                     // Clear NAK to indicate we are ready to receive more data
                     self.regs.doepctl(index).modify(|w| {
                         w.set_cnak(true);
@@ -1158,6 +1173,21 @@ impl<'d> embassy_usb_driver::EndpointIn for Endpoint<'d, In> {
                 w.set_xfrsiz(buf.len() as _);
             });
 
+            if self.info.ep_type == EndpointType::Isochronous {
+                // Isochronous endpoints must set the correct even/odd frame bit to
+                // correspond with the next frame's number.
+                let frame_number = self.regs.dsts().read().fnsof();
+                let frame_is_odd = frame_number & 0x01 == 1;
+
+                self.regs.diepctl(index).modify(|r| {
+                    if frame_is_odd {
+                        r.set_sd0pid_sevnfrm(true);
+                    } else {
+                        r.set_sd1pid_soddfrm(true);
+                    }
+                });
+            }
+
             // Enable endpoint
             self.regs.diepctl(index).modify(|w| {
                 w.set_cnak(true);
diff --git a/embassy-usb-synopsys-otg/src/otg_v1.rs b/embassy-usb-synopsys-otg/src/otg_v1.rs
index a8530980c..d3abc328d 100644
--- a/embassy-usb-synopsys-otg/src/otg_v1.rs
+++ b/embassy-usb-synopsys-otg/src/otg_v1.rs
@@ -795,15 +795,15 @@ pub mod regs {
         pub fn set_sd0pid_sevnfrm(&mut self, val: bool) {
             self.0 = (self.0 & !(0x01 << 28usize)) | (((val as u32) & 0x01) << 28usize);
         }
-        #[doc = "SODDFRM/SD1PID"]
+        #[doc = "SD1PID/SODDFRM"]
         #[inline(always)]
-        pub const fn soddfrm_sd1pid(&self) -> bool {
+        pub const fn sd1pid_soddfrm(&self) -> bool {
             let val = (self.0 >> 29usize) & 0x01;
             val != 0
         }
-        #[doc = "SODDFRM/SD1PID"]
+        #[doc = "SD1PID/SODDFRM"]
         #[inline(always)]
-        pub fn set_soddfrm_sd1pid(&mut self, val: bool) {
+        pub fn set_sd1pid_soddfrm(&mut self, val: bool) {
             self.0 = (self.0 & !(0x01 << 29usize)) | (((val as u32) & 0x01) << 29usize);
         }
         #[doc = "EPDIS"]
@@ -1174,15 +1174,15 @@ pub mod regs {
         pub fn set_sd0pid_sevnfrm(&mut self, val: bool) {
             self.0 = (self.0 & !(0x01 << 28usize)) | (((val as u32) & 0x01) << 28usize);
         }
-        #[doc = "SODDFRM"]
+        #[doc = "SD1PID/SODDFRM"]
         #[inline(always)]
-        pub const fn soddfrm(&self) -> bool {
+        pub const fn sd1pid_soddfrm(&self) -> bool {
             let val = (self.0 >> 29usize) & 0x01;
             val != 0
         }
-        #[doc = "SODDFRM"]
+        #[doc = "SD1PID/SODDFRM"]
         #[inline(always)]
-        pub fn set_soddfrm(&mut self, val: bool) {
+        pub fn set_sd1pid_soddfrm(&mut self, val: bool) {
             self.0 = (self.0 & !(0x01 << 29usize)) | (((val as u32) & 0x01) << 29usize);
         }
         #[doc = "EPDIS"]
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 c4d79e39f..06ebe0481 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,
         );
     }
 
@@ -318,6 +388,7 @@ impl<'a> BosWriter<'a> {
                 0x00, 0x00, // wTotalLength
                 0x00, // bNumDeviceCaps
             ],
+            &[],
         );
 
         self.capability(capability_type::USB_2_0_EXTENSION, &[0; 4]);