I2C: tolerate invalid event in idle state.

Do not panic if invalid event occurs in idle
state; instead ignore it.

openemc-firmware/src/i2c_reg_slave.rs

@@ -93,7 +93,7 @@ where
                         self.pos = 0;
                         return Ok(Event::Read { reg: self.reg });
                     }
-                    _ => defmt::unreachable!(),
+                    other => defmt::error!("Invalid I2C event in idle state: {:?}", other),
                 },
                 State::ReceiveReg => match self.i2c_event()? {
                     I2cEvent::Read(value) => {

openemc-firmware/src/i2c_slave.rs

@@ -253,6 +253,19 @@ pub enum Event<'a, I2C, PINS> {
     End,
 }
 
+impl<'a, I2C, PINS> defmt::Format for Event<'a, I2C, PINS> {
+    fn format(&self, fmt: defmt::Formatter) {
+        match self {
+            Self::StartRead => defmt::write!(fmt, "StartRead"),
+            Self::StartWrite => defmt::write!(fmt, "StartWrite"),
+            Self::Read(_) => defmt::write!(fmt, "Read"),
+            Self::Write(_) => defmt::write!(fmt, "Write"),
+            Self::Restart => defmt::write!(fmt, "Restart"),
+            Self::End => defmt::write!(fmt, "End"),
+        }
+    }
+}
+
 /// Transmits a byte to the I2C master.
 pub struct Writer<'a, I2C, PINS>(&'a mut I2cSlave<I2C, PINS>);