Began skeleton of new UninitializedW5500 struct and Bus trait/impls

src/bus/four_wire.rs

@@ -0,0 +1,39 @@
+use embedded_hal::digital::v2::OutputPin;
+use embedded_hal::spi::FullDuplex;
+
+use crate::bus::Bus;
+
+pub struct FourWire<ChipSelect: OutputPin> {
+    cs: ChipSelect
+}
+
+impl<ChipSelect: OutputPin>
+    FourWire<ChipSelect>
+{
+    pub fn new(cs: ChipSelect) -> Self {
+        Self { cs }
+    }
+    pub fn release(self) -> ChipSelect {
+        self.cs
+    }
+}
+
+impl<Spi: FullDuplex<u8>, ChipSelect: OutputPin> Bus<Spi>
+    for FourWire<ChipSelect>
+{
+    type Error = FourWireError<Spi::Error, ChipSelect::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)
+    }
+}
+
+pub enum FourWireError<SpiError, ChipSelectError> {
+    SpiError(SpiError),
+    ChipSelectError(ChipSelectError),
+}