Explain cancel code

esp-hal/src/dma/mod.rs

@@ -1328,7 +1328,7 @@ pub trait Rx: crate::private::Sealed {
 
     fn start_transfer(&mut self) -> Result<(), DmaError>;
 
-    fn stop_transfer(&mut self);
+    fn reset_state_machine(&mut self);
 
     #[cfg(esp32s3)]
     fn set_ext_mem_block_size(&self, size: DmaExtMemBKSize);
@@ -1407,7 +1407,7 @@ where
         }
     }
 
-    fn stop_transfer(&mut self) {
+    fn reset_state_machine(&mut self) {
         R::reset_in();
     }
 
@@ -1505,8 +1505,8 @@ where
         self.rx_impl.start_transfer()
     }
 
-    fn stop_transfer(&mut self) {
-        self.rx_impl.stop_transfer();
+    fn reset_state_machine(&mut self) {
+        self.rx_impl.reset_state_machine();
     }
 
     #[cfg(esp32s3)]
@@ -1582,7 +1582,7 @@ pub trait Tx: crate::private::Sealed {
 
     fn start_transfer(&mut self) -> Result<(), DmaError>;
 
-    fn stop_transfer(&mut self);
+    fn reset_state_machine(&mut self);
 
     #[cfg(esp32s3)]
     fn set_ext_mem_block_size(&self, size: DmaExtMemBKSize);
@@ -1639,7 +1639,7 @@ where
         }
     }
 
-    fn stop_transfer(&mut self) {
+    fn reset_state_machine(&mut self) {
         R::reset_out();
     }
 
@@ -1749,8 +1749,8 @@ where
         self.tx_impl.start_transfer()
     }
 
-    fn stop_transfer(&mut self) {
-        self.tx_impl.stop_transfer();
+    fn reset_state_machine(&mut self) {
+        self.tx_impl.reset_state_machine();
     }
 
     #[cfg(esp32s3)]

esp-hal/src/spi/master.rs

@@ -1512,19 +1512,23 @@ mod dma {
         }
 
         fn do_cancel(&mut self) {
+            // The SPI peripheral is controlling how much data we transfer, so let's
+            // update its counter.
             // 0 doesn't take effect on ESP32 and cuts the currently transmitted byte
             // immediately.
             // 1 seems to stop after transmitting the current byte which is somewhat less
             // impolite.
             self.spi_dma.spi_mut().configure_datalen(1, 1);
             self.spi_dma.spi_mut().update();
 
+            // We need to reset the DMA state machines for the DMA to also pick up the
+            // change.
             if self.spi_dma.is_tx_in_progress() {
-                self.spi_dma.channel_mut().tx.stop_transfer();
+                self.spi_dma.channel_mut().tx.reset_state_machine();
                 self.spi_dma.set_tx_in_progress(false);
             }
             if self.spi_dma.is_rx_in_progress() {
-                self.spi_dma.channel_mut().rx.stop_transfer();
+                self.spi_dma.channel_mut().rx.reset_state_machine();
                 self.spi_dma.set_rx_in_progress(false);
             }
         }