Pull out the unsafe code.

Author: Jonathan Pallant (42 Technology)

src/serial.rs

@@ -319,21 +319,24 @@ macro_rules! hal {
                     // NOTE(unsafe) atomic read with no side effects
                     let isr = unsafe { (*$USARTX::ptr()).isr.read() };
 
+                    // NOTE(unsafe) write accessor for atomic writes with no side effects
+                    let icr = unsafe { &(*$USARTX::ptr()).icr };
+
                     Err(if isr.pe().bit_is_set() {
                         // Clear the bit by writing 1 to the clear register
-                        unsafe { (*$USARTX::ptr()).icr.write(|w| { w.pecf().set_bit() }) };
+                        icr.write(|w| { w.pecf().set_bit() });
                         nb::Error::Other(Error::Parity)
                     } else if isr.fe().bit_is_set() {
                         // Clear the bit by writing 1 to the clear register
-                        unsafe { (*$USARTX::ptr()).icr.write(|w| { w.fecf().set_bit() }) };
+                        icr.write(|w| { w.fecf().set_bit() });
                         nb::Error::Other(Error::Framing)
                     } else if isr.nf().bit_is_set() {
                         // Clear the bit by writing 1 to the clear register
-                        unsafe { (*$USARTX::ptr()).icr.write(|w| { w.ncf().set_bit() }) };
+                        icr.write(|w| { w.ncf().set_bit() });
                         nb::Error::Other(Error::Noise)
                     } else if isr.ore().bit_is_set() {
                         // Clear the bit by writing 1 to the clear register
-                        unsafe { (*$USARTX::ptr()).icr.write(|w| { w.orecf().set_bit() }) };
+                        icr.write(|w| { w.orecf().set_bit() });
                         nb::Error::Other(Error::Overrun)
                     } else if isr.rxne().bit_is_set() {
                         // NOTE(read_volatile) see `write_volatile` below