usb/cdc-ncm: add embassy-net Device implementation.

embassy-usb/src/class/cdc_ncm/embassy_net.rs

@@ -0,0 +1,449 @@
+use core::cell::RefCell;
+use core::mem::MaybeUninit;
+use core::task::Context;
+
+use embassy_futures::select::{select, Either};
+use embassy_net::device::{Device as DeviceTrait, DeviceCapabilities, LinkState, Medium};
+use embassy_sync::blocking_mutex::raw::NoopRawMutex;
+use embassy_sync::blocking_mutex::Mutex;
+use embassy_sync::waitqueue::WakerRegistration;
+use embassy_usb_driver::Driver;
+
+use super::{CdcNcmClass, Receiver, Sender};
+
+pub struct State<'d, const MTU: usize, const N_RX: usize, const N_TX: usize> {
+    rx: [PacketBuf<MTU>; N_RX],
+    tx: [PacketBuf<MTU>; N_TX],
+    inner: MaybeUninit<StateInner<'d, MTU>>,
+}
+
+impl<'d, const MTU: usize, const N_RX: usize, const N_TX: usize> State<'d, MTU, N_RX, N_TX> {
+    const NEW_PACKET: PacketBuf<MTU> = PacketBuf::new();
+
+    pub const fn new() -> Self {
+        Self {
+            rx: [Self::NEW_PACKET; N_RX],
+            tx: [Self::NEW_PACKET; N_TX],
+            inner: MaybeUninit::uninit(),
+        }
+    }
+}
+
+struct StateInner<'d, const MTU: usize> {
+    rx: zerocopy_channel::Channel<'d, NoopRawMutex, PacketBuf<MTU>>,
+    tx: zerocopy_channel::Channel<'d, NoopRawMutex, PacketBuf<MTU>>,
+    link_state: Mutex<NoopRawMutex, RefCell<LinkStateState>>,
+}
+
+/// State of the LinkState
+struct LinkStateState {
+    state: LinkState,
+    waker: WakerRegistration,
+}
+
+pub struct Runner<'d, D: Driver<'d>, const MTU: usize> {
+    tx_usb: Sender<'d, D>,
+    tx_chan: zerocopy_channel::Receiver<'d, NoopRawMutex, PacketBuf<MTU>>,
+    rx_usb: Receiver<'d, D>,
+    rx_chan: zerocopy_channel::Sender<'d, NoopRawMutex, PacketBuf<MTU>>,
+    link_state: &'d Mutex<NoopRawMutex, RefCell<LinkStateState>>,
+}
+
+impl<'d, D: Driver<'d>, const MTU: usize> Runner<'d, D, MTU> {
+    pub async fn run(mut self) -> ! {
+        let rx_fut = async move {
+            loop {
+                trace!("WAITING for connection");
+                self.link_state.lock(|s| {
+                    let s = &mut *s.borrow_mut();
+                    s.state = LinkState::Down;
+                    s.waker.wake();
+                });
+
+                self.rx_usb.wait_connection().await.unwrap();
+
+                trace!("Connected");
+                self.link_state.lock(|s| {
+                    let s = &mut *s.borrow_mut();
+                    s.state = LinkState::Up;
+                    s.waker.wake();
+                });
+
+                loop {
+                    let p = self.rx_chan.send().await;
+                    match self.rx_usb.read_packet(&mut p.buf).await {
+                        Ok(n) => {
+                            p.len = n;
+                            self.rx_chan.send_done();
+                        }
+                        Err(e) => {
+                            warn!("error reading packet: {:?}", e);
+                            break;
+                        }
+                    };
+                }
+            }
+        };
+        let tx_fut = async move {
+            loop {
+                let p = self.tx_chan.recv().await;
+                if let Err(e) = self.tx_usb.write_packet(&p.buf[..p.len]).await {
+                    warn!("Failed to TX packet: {:?}", e);
+                }
+                self.tx_chan.recv_done();
+            }
+        };
+        match select(rx_fut, tx_fut).await {
+            Either::First(x) => x,
+            Either::Second(x) => x,
+        }
+    }
+}
+
+impl<'d, D: Driver<'d>> CdcNcmClass<'d, D> {
+    pub fn into_embassy_net_device<const MTU: usize, const N_RX: usize, const N_TX: usize>(
+        self,
+        state: &'d mut State<'d, MTU, N_RX, N_TX>,
+        ethernet_address: [u8; 6],
+    ) -> (Runner<'d, D, MTU>, Device<'d, MTU>) {
+        let (tx_usb, rx_usb) = self.split();
+
+        let mut caps = DeviceCapabilities::default();
+        caps.max_transmission_unit = 1514; // 1500 IP + 14 ethernet header
+        caps.medium = Medium::Ethernet;
+
+        let state = state.inner.write(StateInner {
+            rx: zerocopy_channel::Channel::new(&mut state.rx[..]),
+            tx: zerocopy_channel::Channel::new(&mut state.tx[..]),
+            link_state: Mutex::new(RefCell::new(LinkStateState {
+                state: LinkState::Down,
+                waker: WakerRegistration::new(),
+            })),
+        });
+
+        let (rx_sender, rx_receiver) = state.rx.split();
+        let (tx_sender, tx_receiver) = state.tx.split();
+
+        (
+            Runner {
+                tx_usb,
+                tx_chan: tx_receiver,
+                rx_usb,
+                rx_chan: rx_sender,
+                link_state: &state.link_state,
+            },
+            Device {
+                caps,
+                ethernet_address,
+                link_state: &state.link_state,
+                rx: rx_receiver,
+                tx: tx_sender,
+            },
+        )
+    }
+}
+
+pub struct PacketBuf<const MTU: usize> {
+    len: usize,
+    buf: [u8; MTU],
+}
+
+impl<const MTU: usize> PacketBuf<MTU> {
+    pub const fn new() -> Self {
+        Self { len: 0, buf: [0; MTU] }
+    }
+}
+
+pub struct Device<'d, const MTU: usize> {
+    rx: zerocopy_channel::Receiver<'d, NoopRawMutex, PacketBuf<MTU>>,
+    tx: zerocopy_channel::Sender<'d, NoopRawMutex, PacketBuf<MTU>>,
+    link_state: &'d Mutex<NoopRawMutex, RefCell<LinkStateState>>,
+    caps: DeviceCapabilities,
+    ethernet_address: [u8; 6],
+}
+
+impl<'d, const MTU: usize> DeviceTrait for Device<'d, MTU> {
+    type RxToken<'a> = RxToken<'a, MTU> where Self: 'a ;
+    type TxToken<'a> = TxToken<'a, MTU> where Self: 'a ;
+
+    fn receive(&mut self, cx: &mut Context) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
+        if self.rx.poll_recv(cx).is_ready() && self.tx.poll_send(cx).is_ready() {
+            Some((RxToken { rx: self.rx.borrow() }, TxToken { tx: self.tx.borrow() }))
+        } else {
+            None
+        }
+    }
+
+    /// Construct a transmit token.
+    fn transmit(&mut self, cx: &mut Context) -> Option<Self::TxToken<'_>> {
+        if self.tx.poll_send(cx).is_ready() {
+            Some(TxToken { tx: self.tx.borrow() })
+        } else {
+            None
+        }
+    }
+
+    /// Get a description of device capabilities.
+    fn capabilities(&self) -> DeviceCapabilities {
+        self.caps.clone()
+    }
+
+    fn ethernet_address(&self) -> [u8; 6] {
+        self.ethernet_address
+    }
+
+    fn link_state(&mut self, cx: &mut Context) -> LinkState {
+        self.link_state.lock(|s| {
+            let s = &mut *s.borrow_mut();
+            s.waker.register(cx.waker());
+            s.state
+        })
+    }
+}
+
+pub struct RxToken<'a, const MTU: usize> {
+    rx: zerocopy_channel::Receiver<'a, NoopRawMutex, PacketBuf<MTU>>,
+}
+
+impl<'a, const MTU: usize> embassy_net::device::RxToken for RxToken<'a, MTU> {
+    fn consume<R, F>(mut self, f: F) -> R
+    where
+        F: FnOnce(&mut [u8]) -> R,
+    {
+        // NOTE(unwrap): we checked the queue wasn't full when creating the token.
+        let pkt = unwrap!(self.rx.try_recv());
+        let r = f(&mut pkt.buf[..pkt.len]);
+        self.rx.recv_done();
+        r
+    }
+}
+
+pub struct TxToken<'a, const MTU: usize> {
+    tx: zerocopy_channel::Sender<'a, NoopRawMutex, PacketBuf<MTU>>,
+}
+
+impl<'a, const MTU: usize> embassy_net::device::TxToken for TxToken<'a, MTU> {
+    fn consume<R, F>(mut self, len: usize, f: F) -> R
+    where
+        F: FnOnce(&mut [u8]) -> R,
+    {
+        // NOTE(unwrap): we checked the queue wasn't full when creating the token.
+        let pkt = unwrap!(self.tx.try_send());
+        let r = f(&mut pkt.buf[..len]);
+        pkt.len = len;
+        self.tx.send_done();
+        r
+    }
+}
+
+mod zerocopy_channel {
+    use core::cell::RefCell;
+    use core::future::poll_fn;
+    use core::marker::PhantomData;
+    use core::task::{Context, Poll};
+
+    use embassy_sync::blocking_mutex::raw::RawMutex;
+    use embassy_sync::blocking_mutex::Mutex;
+    use embassy_sync::waitqueue::WakerRegistration;
+
+    pub struct Channel<'a, M: RawMutex, T> {
+        buf: *mut T,
+        phantom: PhantomData<&'a mut T>,
+        state: Mutex<M, RefCell<State>>,
+    }
+
+    impl<'a, M: RawMutex, T> Channel<'a, M, T> {
+        pub fn new(buf: &'a mut [T]) -> Self {
+            let len = buf.len();
+            assert!(len != 0);
+
+            Self {
+                buf: buf.as_mut_ptr(),
+                phantom: PhantomData,
+                state: Mutex::new(RefCell::new(State {
+                    len,
+                    front: 0,
+                    back: 0,
+                    full: false,
+                    send_waker: WakerRegistration::new(),
+                    recv_waker: WakerRegistration::new(),
+                })),
+            }
+        }
+
+        pub fn split(&mut self) -> (Sender<'_, M, T>, Receiver<'_, M, T>) {
+            (Sender { channel: self }, Receiver { channel: self })
+        }
+    }
+
+    pub struct Sender<'a, M: RawMutex, T> {
+        channel: &'a Channel<'a, M, T>,
+    }
+
+    impl<'a, M: RawMutex, T> Sender<'a, M, T> {
+        pub fn borrow(&mut self) -> Sender<'_, M, T> {
+            Sender { channel: self.channel }
+        }
+
+        pub fn try_send(&mut self) -> Option<&mut T> {
+            self.channel.state.lock(|s| {
+                let s = &mut *s.borrow_mut();
+                match s.push_index() {
+                    Some(i) => Some(unsafe { &mut *self.channel.buf.add(i) }),
+                    None => None,
+                }
+            })
+        }
+
+        pub fn poll_send(&mut self, cx: &mut Context) -> Poll<&mut T> {
+            self.channel.state.lock(|s| {
+                let s = &mut *s.borrow_mut();
+                match s.push_index() {
+                    Some(i) => Poll::Ready(unsafe { &mut *self.channel.buf.add(i) }),
+                    None => {
+                        s.recv_waker.register(cx.waker());
+                        Poll::Pending
+                    }
+                }
+            })
+        }
+
+        pub async fn send(&mut self) -> &mut T {
+            let i = poll_fn(|cx| {
+                self.channel.state.lock(|s| {
+                    let s = &mut *s.borrow_mut();
+                    match s.push_index() {
+                        Some(i) => Poll::Ready(i),
+                        None => {
+                            s.recv_waker.register(cx.waker());
+                            Poll::Pending
+                        }
+                    }
+                })
+            })
+            .await;
+            unsafe { &mut *self.channel.buf.add(i) }
+        }
+
+        pub fn send_done(&mut self) {
+            self.channel.state.lock(|s| s.borrow_mut().push_done())
+        }
+    }
+    pub struct Receiver<'a, M: RawMutex, T> {
+        channel: &'a Channel<'a, M, T>,
+    }
+
+    impl<'a, M: RawMutex, T> Receiver<'a, M, T> {
+        pub fn borrow(&mut self) -> Receiver<'_, M, T> {
+            Receiver { channel: self.channel }
+        }
+
+        pub fn try_recv(&mut self) -> Option<&mut T> {
+            self.channel.state.lock(|s| {
+                let s = &mut *s.borrow_mut();
+                match s.pop_index() {
+                    Some(i) => Some(unsafe { &mut *self.channel.buf.add(i) }),
+                    None => None,
+                }
+            })
+        }
+
+        pub fn poll_recv(&mut self, cx: &mut Context) -> Poll<&mut T> {
+            self.channel.state.lock(|s| {
+                let s = &mut *s.borrow_mut();
+                match s.pop_index() {
+                    Some(i) => Poll::Ready(unsafe { &mut *self.channel.buf.add(i) }),
+                    None => {
+                        s.send_waker.register(cx.waker());
+                        Poll::Pending
+                    }
+                }
+            })
+        }
+
+        pub async fn recv(&mut self) -> &mut T {
+            let i = poll_fn(|cx| {
+                self.channel.state.lock(|s| {
+                    let s = &mut *s.borrow_mut();
+                    match s.pop_index() {
+                        Some(i) => Poll::Ready(i),
+                        None => {
+                            s.send_waker.register(cx.waker());
+                            Poll::Pending
+                        }
+                    }
+                })
+            })
+            .await;
+            unsafe { &mut *self.channel.buf.add(i) }
+        }
+
+        pub fn recv_done(&mut self) {
+            self.channel.state.lock(|s| s.borrow_mut().pop_done())
+        }
+    }
+
+    struct State {
+        len: usize,
+
+        /// Front index. Always 0..=(N-1)
+        front: usize,
+        /// Back index. Always 0..=(N-1).
+        back: usize,
+
+        /// Used to distinguish "empty" and "full" cases when `front == back`.
+        /// May only be `true` if `front == back`, always `false` otherwise.
+        full: bool,
+
+        send_waker: WakerRegistration,
+        recv_waker: WakerRegistration,
+    }
+
+    impl State {
+        fn increment(&self, i: usize) -> usize {
+            if i + 1 == self.len {
+                0
+            } else {
+                i + 1
+            }
+        }
+
+        fn is_full(&self) -> bool {
+            self.full
+        }
+
+        fn is_empty(&self) -> bool {
+            self.front == self.back && !self.full
+        }
+
+        fn push_index(&mut self) -> Option<usize> {
+            match self.is_full() {
+                true => None,
+                false => Some(self.back),
+            }
+        }
+
+        fn push_done(&mut self) {
+            assert!(!self.is_full());
+            self.back = self.increment(self.back);
+            if self.back == self.front {
+                self.full = true;
+            }
+            self.send_waker.wake();
+        }
+
+        fn pop_index(&mut self) -> Option<usize> {
+            match self.is_empty() {
+                true => None,
+                false => Some(self.front),
+            }
+        }
+
+        fn pop_done(&mut self) {
+            assert!(!self.is_empty());
+            self.front = self.increment(self.front);
+            self.full = false;
+            self.recv_waker.wake();
+        }
+    }
+}

embassy-usb/src/class/cdc_ncm/mod.rs

@@ -0,0 +1,496 @@
+/// CDC-NCM, aka Ethernet over USB.
+///
+/// # Compatibility
+///
+/// Windows: NOT supported in Windows 10. Supported in Windows 11.
+///
+/// Linux: Well-supported since forever.
+///
+/// Android: Support for CDC-NCM is spotty and varies across manufacturers.
+///
+/// - On Pixel 4a, it refused to work on Android 11, worked on Android 12.
+/// - if the host's MAC address has the "locally-administered" bit set (bit 1 of first byte),
+///   it doesn't work! The "Ethernet tethering" option in settings doesn't get enabled.
+///   This is due to regex spaghetti: https://android.googlesource.com/platform/frameworks/base/+/refs/tags/android-mainline-12.0.0_r84/core/res/res/values/config.xml#417
+///   and this nonsense in the linux kernel: https://github.com/torvalds/linux/blob/c00c5e1d157bec0ef0b0b59aa5482eb8dc7e8e49/drivers/net/usb/usbnet.c#L1751-L1757
+use core::intrinsics::copy_nonoverlapping;
+use core::mem::{size_of, MaybeUninit};
+
+use crate::control::{self, ControlHandler, InResponse, OutResponse, Request};
+use crate::driver::{Driver, Endpoint, EndpointError, EndpointIn, EndpointOut};
+use crate::types::*;
+use crate::Builder;
+
+#[cfg(feature = "embassy-net")]
+pub mod embassy_net;
+
+/// This should be used as `device_class` when building the `UsbDevice`.
+pub const USB_CLASS_CDC: u8 = 0x02;
+
+const USB_CLASS_CDC_DATA: u8 = 0x0a;
+const CDC_SUBCLASS_NCM: u8 = 0x0d;
+
+const CDC_PROTOCOL_NONE: u8 = 0x00;
+const CDC_PROTOCOL_NTB: u8 = 0x01;
+
+const CS_INTERFACE: u8 = 0x24;
+const CDC_TYPE_HEADER: u8 = 0x00;
+const CDC_TYPE_UNION: u8 = 0x06;
+const CDC_TYPE_ETHERNET: u8 = 0x0F;
+const CDC_TYPE_NCM: u8 = 0x1A;
+
+const REQ_SEND_ENCAPSULATED_COMMAND: u8 = 0x00;
+//const REQ_GET_ENCAPSULATED_COMMAND: u8 = 0x01;
+//const REQ_SET_ETHERNET_MULTICAST_FILTERS: u8 = 0x40;
+//const REQ_SET_ETHERNET_POWER_MANAGEMENT_PATTERN_FILTER: u8 = 0x41;
+//const REQ_GET_ETHERNET_POWER_MANAGEMENT_PATTERN_FILTER: u8 = 0x42;
+//const REQ_SET_ETHERNET_PACKET_FILTER: u8 = 0x43;
+//const REQ_GET_ETHERNET_STATISTIC: u8 = 0x44;
+const REQ_GET_NTB_PARAMETERS: u8 = 0x80;
+//const REQ_GET_NET_ADDRESS: u8 = 0x81;
+//const REQ_SET_NET_ADDRESS: u8 = 0x82;
+//const REQ_GET_NTB_FORMAT: u8 = 0x83;
+//const REQ_SET_NTB_FORMAT: u8 = 0x84;
+//const REQ_GET_NTB_INPUT_SIZE: u8 = 0x85;
+const REQ_SET_NTB_INPUT_SIZE: u8 = 0x86;
+//const REQ_GET_MAX_DATAGRAM_SIZE: u8 = 0x87;
+//const REQ_SET_MAX_DATAGRAM_SIZE: u8 = 0x88;
+//const REQ_GET_CRC_MODE: u8 = 0x89;
+//const REQ_SET_CRC_MODE: u8 = 0x8A;
+
+//const NOTIF_MAX_PACKET_SIZE: u16 = 8;
+//const NOTIF_POLL_INTERVAL: u8 = 20;
+
+const NTB_MAX_SIZE: usize = 2048;
+const SIG_NTH: u32 = 0x484d434e;
+const SIG_NDP_NO_FCS: u32 = 0x304d434e;
+const SIG_NDP_WITH_FCS: u32 = 0x314d434e;
+
+const ALTERNATE_SETTING_DISABLED: u8 = 0x00;
+const ALTERNATE_SETTING_ENABLED: u8 = 0x01;
+
+/// Simple NTB header (NTH+NDP all in one) for sending packets
+#[repr(packed)]
+#[allow(unused)]
+struct NtbOutHeader {
+    // NTH
+    nth_sig: u32,
+    nth_len: u16,
+    nth_seq: u16,
+    nth_total_len: u16,
+    nth_first_index: u16,
+
+    // NDP
+    ndp_sig: u32,
+    ndp_len: u16,
+    ndp_next_index: u16,
+    ndp_datagram_index: u16,
+    ndp_datagram_len: u16,
+    ndp_term1: u16,
+    ndp_term2: u16,
+}
+
+#[repr(packed)]
+#[allow(unused)]
+struct NtbParameters {
+    length: u16,
+    formats_supported: u16,
+    in_params: NtbParametersDir,
+    out_params: NtbParametersDir,
+}
+
+#[repr(packed)]
+#[allow(unused)]
+struct NtbParametersDir {
+    max_size: u32,
+    divisor: u16,
+    payload_remainder: u16,
+    out_alignment: u16,
+    max_datagram_count: u16,
+}
+
+fn byteify<T>(buf: &mut [u8], data: T) -> &[u8] {
+    let len = size_of::<T>();
+    unsafe { copy_nonoverlapping(&data as *const _ as *const u8, buf.as_mut_ptr(), len) }
+    &buf[..len]
+}
+
+pub struct State<'a> {
+    comm_control: MaybeUninit<CommControl<'a>>,
+    data_control: MaybeUninit<DataControl>,
+    shared: ControlShared,
+}
+
+impl<'a> State<'a> {
+    pub fn new() -> Self {
+        Self {
+            comm_control: MaybeUninit::uninit(),
+            data_control: MaybeUninit::uninit(),
+            shared: Default::default(),
+        }
+    }
+}
+
+/// Shared data between Control and CdcAcmClass
+struct ControlShared {
+    mac_addr: [u8; 6],
+}
+
+impl Default for ControlShared {
+    fn default() -> Self {
+        ControlShared { mac_addr: [0; 6] }
+    }
+}
+
+struct CommControl<'a> {
+    mac_addr_string: StringIndex,
+    shared: &'a ControlShared,
+    mac_addr_str: [u8; 12],
+}
+
+impl<'d> ControlHandler for CommControl<'d> {
+    fn control_out(&mut self, req: control::Request, _data: &[u8]) -> OutResponse {
+        match req.request {
+            REQ_SEND_ENCAPSULATED_COMMAND => {
+                // We don't actually support encapsulated commands but pretend we do for standards
+                // compatibility.
+                OutResponse::Accepted
+            }
+            REQ_SET_NTB_INPUT_SIZE => {
+                // TODO
+                OutResponse::Accepted
+            }
+            _ => OutResponse::Rejected,
+        }
+    }
+
+    fn control_in<'a>(&'a mut self, req: Request, buf: &'a mut [u8]) -> InResponse<'a> {
+        match req.request {
+            REQ_GET_NTB_PARAMETERS => {
+                let res = NtbParameters {
+                    length: size_of::<NtbParameters>() as _,
+                    formats_supported: 1, // only 16bit,
+                    in_params: NtbParametersDir {
+                        max_size: NTB_MAX_SIZE as _,
+                        divisor: 4,
+                        payload_remainder: 0,
+                        out_alignment: 4,
+                        max_datagram_count: 0, // not used
+                    },
+                    out_params: NtbParametersDir {
+                        max_size: NTB_MAX_SIZE as _,
+                        divisor: 4,
+                        payload_remainder: 0,
+                        out_alignment: 4,
+                        max_datagram_count: 1, // We only decode 1 packet per NTB
+                    },
+                };
+                InResponse::Accepted(byteify(buf, res))
+            }
+            _ => InResponse::Rejected,
+        }
+    }
+
+    fn get_string(&mut self, index: StringIndex, _lang_id: u16) -> Option<&str> {
+        if index == self.mac_addr_string {
+            let mac_addr = self.shared.mac_addr;
+            let s = &mut self.mac_addr_str;
+            for i in 0..12 {
+                let n = (mac_addr[i / 2] >> ((1 - i % 2) * 4)) & 0xF;
+                s[i] = match n {
+                    0x0..=0x9 => b'0' + n,
+                    0xA..=0xF => b'A' + n - 0xA,
+                    _ => unreachable!(),
+                }
+            }
+
+            Some(unsafe { core::str::from_utf8_unchecked(s) })
+        } else {
+            warn!("unknown string index requested");
+            None
+        }
+    }
+}
+
+struct DataControl {}
+
+impl ControlHandler for DataControl {
+    fn set_alternate_setting(&mut self, alternate_setting: u8) {
+        match alternate_setting {
+            ALTERNATE_SETTING_ENABLED => info!("ncm: interface enabled"),
+            ALTERNATE_SETTING_DISABLED => info!("ncm: interface disabled"),
+            _ => unreachable!(),
+        }
+    }
+}
+
+pub struct CdcNcmClass<'d, D: Driver<'d>> {
+    _comm_if: InterfaceNumber,
+    comm_ep: D::EndpointIn,
+
+    data_if: InterfaceNumber,
+    read_ep: D::EndpointOut,
+    write_ep: D::EndpointIn,
+
+    _control: &'d ControlShared,
+}
+
+impl<'d, D: Driver<'d>> CdcNcmClass<'d, D> {
+    pub fn new(
+        builder: &mut Builder<'d, D>,
+        state: &'d mut State<'d>,
+        mac_address: [u8; 6],
+        max_packet_size: u16,
+    ) -> Self {
+        state.shared.mac_addr = mac_address;
+
+        let mut func = builder.function(USB_CLASS_CDC, CDC_SUBCLASS_NCM, CDC_PROTOCOL_NONE);
+
+        // Control interface
+        let mut iface = func.interface();
+        let mac_addr_string = iface.string();
+        iface.handler(state.comm_control.write(CommControl {
+            mac_addr_string,
+            shared: &state.shared,
+            mac_addr_str: [0; 12],
+        }));
+        let comm_if = iface.interface_number();
+        let mut alt = iface.alt_setting(USB_CLASS_CDC, CDC_SUBCLASS_NCM, CDC_PROTOCOL_NONE);
+
+        alt.descriptor(
+            CS_INTERFACE,
+            &[
+                CDC_TYPE_HEADER, // bDescriptorSubtype
+                0x10,
+                0x01, // bcdCDC (1.10)
+            ],
+        );
+        alt.descriptor(
+            CS_INTERFACE,
+            &[
+                CDC_TYPE_UNION,        // bDescriptorSubtype
+                comm_if.into(),        // bControlInterface
+                u8::from(comm_if) + 1, // bSubordinateInterface
+            ],
+        );
+        alt.descriptor(
+            CS_INTERFACE,
+            &[
+                CDC_TYPE_ETHERNET,      // bDescriptorSubtype
+                mac_addr_string.into(), // iMACAddress
+                0,                      // bmEthernetStatistics
+                0,                      // |
+                0,                      // |
+                0,                      // |
+                0xea,                   // wMaxSegmentSize = 1514
+                0x05,                   // |
+                0,                      // wNumberMCFilters
+                0,                      // |
+                0,                      // bNumberPowerFilters
+            ],
+        );
+        alt.descriptor(
+            CS_INTERFACE,
+            &[
+                CDC_TYPE_NCM, // bDescriptorSubtype
+                0x00,         // bcdNCMVersion
+                0x01,         // |
+                0,            // bmNetworkCapabilities
+            ],
+        );
+
+        let comm_ep = alt.endpoint_interrupt_in(8, 255);
+
+        // Data interface
+        let mut iface = func.interface();
+        iface.handler(state.data_control.write(DataControl {}));
+        let data_if = iface.interface_number();
+        let _alt = iface.alt_setting(USB_CLASS_CDC_DATA, 0x00, CDC_PROTOCOL_NTB);
+        let mut alt = iface.alt_setting(USB_CLASS_CDC_DATA, 0x00, CDC_PROTOCOL_NTB);
+        let read_ep = alt.endpoint_bulk_out(max_packet_size);
+        let write_ep = alt.endpoint_bulk_in(max_packet_size);
+
+        CdcNcmClass {
+            _comm_if: comm_if,
+            comm_ep,
+            data_if,
+            read_ep,
+            write_ep,
+            _control: &state.shared,
+        }
+    }
+
+    pub fn split(self) -> (Sender<'d, D>, Receiver<'d, D>) {
+        (
+            Sender {
+                write_ep: self.write_ep,
+                seq: 0,
+            },
+            Receiver {
+                data_if: self.data_if,
+                comm_ep: self.comm_ep,
+                read_ep: self.read_ep,
+            },
+        )
+    }
+}
+
+pub struct Sender<'d, D: Driver<'d>> {
+    write_ep: D::EndpointIn,
+    seq: u16,
+}
+
+impl<'d, D: Driver<'d>> Sender<'d, D> {
+    pub async fn write_packet(&mut self, data: &[u8]) -> Result<(), EndpointError> {
+        let seq = self.seq;
+        self.seq = self.seq.wrapping_add(1);
+
+        const MAX_PACKET_SIZE: usize = 64; // TODO unhardcode
+        const OUT_HEADER_LEN: usize = 28;
+
+        let header = NtbOutHeader {
+            nth_sig: SIG_NTH,
+            nth_len: 0x0c,
+            nth_seq: seq,
+            nth_total_len: (data.len() + OUT_HEADER_LEN) as u16,
+            nth_first_index: 0x0c,
+
+            ndp_sig: SIG_NDP_NO_FCS,
+            ndp_len: 0x10,
+            ndp_next_index: 0x00,
+            ndp_datagram_index: OUT_HEADER_LEN as u16,
+            ndp_datagram_len: data.len() as u16,
+            ndp_term1: 0x00,
+            ndp_term2: 0x00,
+        };
+
+        // Build first packet on a buffer, send next packets straight from `data`.
+        let mut buf = [0; MAX_PACKET_SIZE];
+        let n = byteify(&mut buf, header);
+        assert_eq!(n.len(), OUT_HEADER_LEN);
+
+        if OUT_HEADER_LEN + data.len() < MAX_PACKET_SIZE {
+            // First packet is not full, just send it.
+            // No need to send ZLP because it's short for sure.
+            buf[OUT_HEADER_LEN..][..data.len()].copy_from_slice(data);
+            self.write_ep.write(&buf[..OUT_HEADER_LEN + data.len()]).await?;
+        } else {
+            let (d1, d2) = data.split_at(MAX_PACKET_SIZE - OUT_HEADER_LEN);
+
+            buf[OUT_HEADER_LEN..].copy_from_slice(d1);
+            self.write_ep.write(&buf).await?;
+
+            for chunk in d2.chunks(MAX_PACKET_SIZE) {
+                self.write_ep.write(&chunk).await?;
+            }
+
+            // Send ZLP if needed.
+            if d2.len() % MAX_PACKET_SIZE == 0 {
+                self.write_ep.write(&[]).await?;
+            }
+        }
+
+        Ok(())
+    }
+}
+
+pub struct Receiver<'d, D: Driver<'d>> {
+    data_if: InterfaceNumber,
+    comm_ep: D::EndpointIn,
+    read_ep: D::EndpointOut,
+}
+
+impl<'d, D: Driver<'d>> Receiver<'d, D> {
+    /// Reads a single packet from the OUT endpoint.
+    pub async fn read_packet(&mut self, buf: &mut [u8]) -> Result<usize, EndpointError> {
+        // Retry loop
+        loop {
+            // read NTB
+            let mut ntb = [0u8; NTB_MAX_SIZE];
+            let mut pos = 0;
+            loop {
+                let n = self.read_ep.read(&mut ntb[pos..]).await?;
+                pos += n;
+                if n < self.read_ep.info().max_packet_size as usize || pos == NTB_MAX_SIZE {
+                    break;
+                }
+            }
+
+            let ntb = &ntb[..pos];
+
+            // Process NTB header (NTH)
+            let nth = match ntb.get(..12) {
+                Some(x) => x,
+                None => {
+                    warn!("Received too short NTB");
+                    continue;
+                }
+            };
+            let sig = u32::from_le_bytes(nth[0..4].try_into().unwrap());
+            if sig != SIG_NTH {
+                warn!("Received bad NTH sig.");
+                continue;
+            }
+            let ndp_idx = u16::from_le_bytes(nth[10..12].try_into().unwrap()) as usize;
+
+            // Process NTB Datagram Pointer (NDP)
+            let ndp = match ntb.get(ndp_idx..ndp_idx + 12) {
+                Some(x) => x,
+                None => {
+                    warn!("NTH has an NDP pointer out of range.");
+                    continue;
+                }
+            };
+            let sig = u32::from_le_bytes(ndp[0..4].try_into().unwrap());
+            if sig != SIG_NDP_NO_FCS && sig != SIG_NDP_WITH_FCS {
+                warn!("Received bad NDP sig.");
+                continue;
+            }
+            let datagram_index = u16::from_le_bytes(ndp[8..10].try_into().unwrap()) as usize;
+            let datagram_len = u16::from_le_bytes(ndp[10..12].try_into().unwrap()) as usize;
+
+            if datagram_index == 0 || datagram_len == 0 {
+                // empty, ignore. This is allowed by the spec, so don't warn.
+                continue;
+            }
+
+            // Process actual datagram, finally.
+            let datagram = match ntb.get(datagram_index..datagram_index + datagram_len) {
+                Some(x) => x,
+                None => {
+                    warn!("NDP has a datagram pointer out of range.");
+                    continue;
+                }
+            };
+            buf[..datagram_len].copy_from_slice(datagram);
+
+            return Ok(datagram_len);
+        }
+    }
+
+    /// Waits for the USB host to enable this interface
+    pub async fn wait_connection(&mut self) -> Result<(), EndpointError> {
+        loop {
+            self.read_ep.wait_enabled().await;
+            self.comm_ep.wait_enabled().await;
+
+            let buf = [
+                0xA1, //bmRequestType
+                0x00, //bNotificationType = NETWORK_CONNECTION
+                0x01, // wValue = connected
+                0x00,
+                self.data_if.into(), // wIndex = interface
+                0x00,
+                0x00, // wLength
+                0x00,
+            ];
+            match self.comm_ep.write(&buf).await {
+                Ok(()) => break,                   // Done!
+                Err(EndpointError::Disabled) => {} // Got disabled again, wait again.
+                Err(e) => return Err(e),
+            }
+        }
+
+        Ok(())
+    }
+}