Fix compilation when async feature is disabled

boards/atsame54_xpro/Cargo.toml

@@ -40,6 +40,9 @@ rtt-target = { version = "0.3", features = ["cortex-m"] }
 [features]
 default = ["rt", "atsamd-hal/same54p"]
 dma = ["atsamd-hal/dma"]
+max-channels = ["dma", "atsamd-hal/max-channels"]
+# Enable async support from atsamd-hal
+async = ["atsamd-hal/async"]
 rt = ["cortex-m-rt", "atsamd-hal/same54p-rt"]
 usb = ["atsamd-hal/usb", "usb-device"]
 can = ["atsamd-hal/can"]

boards/feather_m4/Cargo.toml

@@ -48,6 +48,8 @@ rt = ["cortex-m-rt", "atsamd-hal/samd51j-rt"]
 usb = ["atsamd-hal/usb", "usb-device"]
 dma = ["atsamd-hal/dma"]
 max-channels = ["dma", "atsamd-hal/dma"]
+# Enable async support from atsamd-hal
+async = ["atsamd-hal/async"]
 use_semihosting =  []
 
 [[example]]

boards/metro_m0/Cargo.toml

@@ -43,6 +43,8 @@ cortex-m-rtic = "1.0"
 default = ["rt", "atsamd-hal/samd21g"]
 dma = ["atsamd-hal/dma"]
 max-channels = ["dma", "atsamd-hal/max-channels"]
+# Enable async support from atsamd-hal
+async = ["atsamd-hal/async"]
 rt = ["cortex-m-rt", "atsamd-hal/samd21g-rt"]
 rtic = ["atsamd-hal/rtic"]
 use_rtt = ["atsamd-hal/use_rtt"]

boards/metro_m4/Cargo.toml

@@ -55,6 +55,7 @@ version = "0.3"
 [features]
 # ask the HAL to enable atsamd51j support
 default = ["rt", "atsamd-hal/samd51j"]
+# Enable async support from atsamd-hal
 async = ["atsamd-hal/async"]
 dma = ["atsamd-hal/dma"]
 max-channels = ["dma", "atsamd-hal/max-channels"]

boards/pygamer/Cargo.toml

@@ -49,6 +49,10 @@ default = ["rt", "atsamd-hal/samd51j"]
 panic_led = []
 rt = ["cortex-m-rt", "atsamd-hal/samd51j-rt"]
 usb = ["atsamd-hal/usb", "usb-device"]
+dma = ["atsamd-hal/dma"]
+max-channels = ["dma", "atsamd-hal/max-channels"]
+# Enable async support from atsamd-hal
+async = ["atsamd-hal/async"]
 
 # for cargo flash
 [package.metadata]

boards/samd11_bare/Cargo.toml

@@ -38,6 +38,8 @@ rtt-target = { version = "0.3.0", features = ["cortex-m"] }
 default = ["rt", "atsamd-hal/samd11c"]
 dma = ["atsamd-hal/dma"]
 max-channels = ["dma", "atsamd-hal/max-channels"]
+# Enable async support from atsamd-hal
+async = ["atsamd-hal/async"]
 rt = ["cortex-m-rt", "atsamd-hal/samd11c-rt"]
 use_semihosting = []
 

hal/src/dmac/channel/mod.rs

@@ -628,7 +628,6 @@ impl<Id: ChId> Channel<Id, ReadyFuture> {
     /// [`ManuallyDrop`]: core::mem::ManuallyDrop
     /// [`Future`]: core::future::Future
     /// [`poll`]: core::future::Future::poll
-    #[cfg(feature = "async")]
     #[inline]
     pub async fn transfer_future<S, D>(
         &mut self,
@@ -655,7 +654,7 @@ impl<Id: ChId> Channel<Id, ReadyFuture> {
 
         self.configure_trigger(trig_src, trig_act);
 
-        TransferFuture::start(self, trig_src).await;
+        transfer_future::TransferFuture::start(self, trig_src).await;
 
         // No need to defensively disable channel here; it's automatically stopped when
         // TransferFuture is dropped. Even though `stop()` is implicitly called
@@ -669,61 +668,78 @@ impl<Id: ChId> Channel<Id, ReadyFuture> {
     }
 }
 
-struct TransferFuture<'a, Id: ChId> {
-    triggered: bool,
-    trig_src: TriggerSource,
-    chan: &'a mut Channel<Id, ReadyFuture>,
-}
+#[cfg(feature = "async")]
+mod transfer_future {
+    use super::*;
 
-impl<'a, Id: ChId> TransferFuture<'a, Id> {
-    fn start(chan: &'a mut Channel<Id, ReadyFuture>, trig_src: TriggerSource) -> Self {
-        Self {
-            triggered: false,
-            trig_src,
-            chan,
+    /// [`Future`](core::future::Future) which starts, then waits on a DMA
+    /// transfer.
+    ///
+    /// This implementation is a standalone struct instead of using
+    /// [`poll_fn`](core::future::poll_fn), because we want to implement
+    /// [`Drop`] for the future returned by the
+    /// [`transfer_future`](super::Channel::transfer_future) method. This way we
+    /// can stop transfers when they are dropped, thus avoiding undefined
+    /// behaviour.
+    pub(super) struct TransferFuture<'a, Id: ChId> {
+        triggered: bool,
+        trig_src: TriggerSource,
+        chan: &'a mut Channel<Id, ReadyFuture>,
+    }
+
+    impl<'a, Id: ChId> TransferFuture<'a, Id> {
+        pub(super) fn start(
+            chan: &'a mut Channel<Id, ReadyFuture>,
+            trig_src: TriggerSource,
+        ) -> Self {
+            Self {
+                triggered: false,
+                trig_src,
+                chan,
+            }
         }
     }
-}
 
-impl<Id: ChId> Drop for TransferFuture<'_, Id> {
-    fn drop(&mut self) {
-        self.chan.stop();
+    impl<Id: ChId> Drop for TransferFuture<'_, Id> {
+        fn drop(&mut self) {
+            self.chan.stop();
+        }
     }
-}
 
-impl<Id: ChId> core::future::Future for TransferFuture<'_, Id> {
-    type Output = ();
+    impl<Id: ChId> core::future::Future for TransferFuture<'_, Id> {
+        type Output = ();
 
-    fn poll(
-        mut self: core::pin::Pin<&mut Self>,
-        cx: &mut core::task::Context<'_>,
-    ) -> core::task::Poll<Self::Output> {
-        use crate::dmac::waker::WAKERS;
-        use core::task::Poll;
+        fn poll(
+            mut self: core::pin::Pin<&mut Self>,
+            cx: &mut core::task::Context<'_>,
+        ) -> core::task::Poll<Self::Output> {
+            use crate::dmac::waker::WAKERS;
+            use core::task::Poll;
 
-        self.chan._enable_private();
+            self.chan._enable_private();
 
-        if !self.triggered && self.trig_src == TriggerSource::Disable {
-            self.triggered = true;
-            self.chan._trigger_private();
-        }
+            if !self.triggered && self.trig_src == TriggerSource::Disable {
+                self.triggered = true;
+                self.chan._trigger_private();
+            }
 
-        let flags_to_check = InterruptFlags::new().with_tcmpl(true).with_terr(true);
+            let flags_to_check = InterruptFlags::new().with_tcmpl(true).with_terr(true);
 
-        if self.chan.check_and_clear_interrupts(flags_to_check).tcmpl() {
-            return Poll::Ready(());
-        }
+            if self.chan.check_and_clear_interrupts(flags_to_check).tcmpl() {
+                return Poll::Ready(());
+            }
 
-        WAKERS[Id::USIZE].register(cx.waker());
-        self.chan.enable_interrupts(flags_to_check);
+            WAKERS[Id::USIZE].register(cx.waker());
+            self.chan.enable_interrupts(flags_to_check);
 
-        if self.chan.check_and_clear_interrupts(flags_to_check).tcmpl() {
-            self.chan.disable_interrupts(flags_to_check);
+            if self.chan.check_and_clear_interrupts(flags_to_check).tcmpl() {
+                self.chan.disable_interrupts(flags_to_check);
 
-            return Poll::Ready(());
-        }
+                return Poll::Ready(());
+            }
 
-        Poll::Pending
+            Poll::Pending
+        }
     }
 }
 

hal/src/lib.rs

@@ -2,12 +2,15 @@
 
 use embedded_hal_02 as ehal_02;
 pub use embedded_hal_1 as ehal;
-pub use embedded_hal_async as ehal_async;
 pub use embedded_hal_nb as ehal_nb;
 pub use embedded_io;
 pub use fugit;
 pub use nb;
 pub use paste;
+
+#[cfg(feature = "async")]
+pub use embedded_hal_async as ehal_async;
+
 pub mod typelevel;
 mod util;