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

3 files changed, 468 insertions, 0 deletions

diff --git a/embassy-usb/Cargo.toml b/embassy-usb/Cargo.toml
index b59ba8a22..1e72ce682 100644
--- a/embassy-usb/Cargo.toml
+++ b/embassy-usb/Cargo.toml
@@ -19,6 +19,7 @@ default = ["usbd-hid"]
 embassy-futures = { version = "0.1.0", path = "../embassy-futures" }
 embassy-usb-driver = { version = "0.1.0", path = "../embassy-usb-driver" }
 embassy-sync = { version = "0.1.0", path = "../embassy-sync" }
+embassy-net = { version = "0.1.0", path = "../embassy-net", optional = true }
 
 defmt = { version = "0.3", optional = true }
 log = { version = "0.4.14", optional = true }
diff --git a/embassy-usb/src/class/cdc_ncm/embassy_net.rs b/embassy-usb/src/class/cdc_ncm/embassy_net.rs
new file mode 100644
index 000000000..60bbfd8d4
--- /dev/null
+++ b/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();
+        }
+    }
+}
diff --git a/embassy-usb/src/class/cdc_ncm.rs b/embassy-usb/src/class/cdc_ncm/mod.rs
index a39b87e9b..2ee47f68c 100644
--- a/embassy-usb/src/class/cdc_ncm.rs
+++ b/embassy-usb/src/class/cdc_ncm/mod.rs
@@ -1,3 +1,18 @@
+/// 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};
 
@@ -6,6 +21,9 @@ 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;