Began skeleton of new UninitializedW5500 struct and Bus trait/impls

src/bus/three_wire.rs

@@ -0,0 +1,24 @@
+use embedded_hal::spi::FullDuplex;
+
+use crate::bus::Bus;
+
+pub struct ThreeWire {}
+
+impl ThreeWire {
+    pub fn new() -> Self {
+        Self { }
+    }
+}
+
+impl<Spi: FullDuplex<u8>> Bus<Spi> for ThreeWire {
+    type Error = Spi::Error;
+    fn transfer_frame<'a, 'b>(
+        spi: &'b mut Spi,
+        address_phase: [u8; 2],
+        control_phase: u8,
+        data_phase: &'a mut [u8],
+    ) -> Result<&'a mut [u8], nb::Error<Self::Error>> {
+        // TODO implement transfer
+        Ok(data_phase)
+    }
+}