Added bus model and InactiveW5500 state

src/bus/three_wire.rs

@@ -1,19 +1,30 @@
 use embedded_hal::spi::FullDuplex;
 
-use crate::bus::Bus;
+use crate::bus::{ActiveBus, Bus};
 
 pub struct ThreeWire {}
 
 impl ThreeWire {
     pub fn new() -> Self {
-        Self { }
+        Self {}
     }
 }
 
-impl<Spi: FullDuplex<u8>> Bus<Spi> for ThreeWire {
+impl Bus for ThreeWire {}
+
+impl ThreeWire {
+    pub fn activate<Spi: FullDuplex<u8>>(self, spi: Spi) -> ActiveThreeWire<Spi> {
+        ActiveThreeWire { spi }
+    }
+}
+
+pub struct ActiveThreeWire<Spi: FullDuplex<u8>> {
+    spi: Spi,
+}
+
+impl<Spi: FullDuplex<u8>> ActiveBus for ActiveThreeWire<Spi> {
     type Error = Spi::Error;
-    fn transfer_frame<'a, 'b>(
-        spi: &'b mut Spi,
+    fn transfer_frame<'a>(
         address_phase: [u8; 2],
         control_phase: u8,
         data_phase: &'a mut [u8],
@@ -22,3 +33,9 @@ impl<Spi: FullDuplex<u8>> Bus<Spi> for ThreeWire {
         Ok(data_phase)
     }
 }
+
+impl<Spi: FullDuplex<u8>> ActiveThreeWire<Spi> {
+    pub fn deactivate(self) -> (ThreeWire, Spi) {
+        (ThreeWire::new(), self.spi)
+    }
+}