Acquire semaphore in transfer wait

Author: kalkyl

examples/spis-demo/src/main.rs

@@ -61,7 +61,6 @@ const APP: () = {
         ctx.resources.gpiote.reset_events();
         rprintln!("Reset buffer");
         let (buf, spis) = ctx.resources.transfer.take().unwrap().wait();
-        spis.acquire(); // Acquire the SPIS semaphore to be able to safely update `buf`
         buf.copy_from_slice(&[0; 8][..]);
         rprintln!("{:?}", buf);
         *ctx.resources.transfer = spis.transfer(buf).ok();

nrf-hal-common/src/spis.rs

@@ -470,6 +470,7 @@ impl<T: Instance, B> Transfer<T, B> {
             .take()
             .unwrap_or_else(|| unsafe { core::hint::unreachable_unchecked() });
         while !inner.spis.is_done() {}
+        inner.spis.acquire();
         compiler_fence(Ordering::Acquire);
         (inner.buffer, inner.spis)
     }
@@ -513,6 +514,7 @@ impl<T: Instance, TxB, RxB> TransferSplit<T, TxB, RxB> {
             .take()
             .unwrap_or_else(|| unsafe { core::hint::unreachable_unchecked() });
         while !inner.spis.is_done() {}
+        inner.spis.acquire();
         compiler_fence(Ordering::Acquire);
         (inner.tx_buffer, inner.rx_buffer, inner.spis)
     }