Fix Serial Write

In order to guarantee the width of the start bit in a serial transfer we
need ot make sure that we are waiting for the correct amount of time.
Since the timer is already started we have no guarantee of the current
count value and therefore should add an initial wait.

Author: Javier-varez

src/serial.rs

@@ -58,6 +58,12 @@ where
     type Error = crate::serial::Error<E>;
 
     fn write(&mut self, byte: u8) -> nb::Result<(), Self::Error> {
+        // WORKAROUND: Since we don't cancel the timer it is possible that the timer has already
+        // overflown, in which case the first call will immediately return, with no guarantees of
+        // being aligned with the start of the count. The second call ensures that we start the
+        // timing at the right moment, since it will for sure block.
+        self.wait_for_timer();
+        self.wait_for_timer();
         let mut data_out = byte;
         self.tx.set_low().map_err(Error::Bus)?; // start bit
         self.wait_for_timer();