Renamed W5500 -> Device, added an Interface struct that should implement the embedded-nal traits, used it to internalize the mutability of the device

src/inactive_device.rs

@@ -0,0 +1,34 @@
+use bus::{ActiveFourWire, ActiveThreeWire, Bus, FourWire, ThreeWire};
+use embedded_hal::digital::v2::OutputPin;
+use embedded_hal::spi::FullDuplex;
+use network::Network;
+use device::Device;
+
+pub struct InactiveDevice<SpiBus: Bus, NetworkImpl: Network> {
+    bus: SpiBus,
+    network: NetworkImpl,
+}
+
+impl<SpiBus: Bus, NetworkImpl: Network> InactiveDevice<SpiBus, NetworkImpl> {
+    pub fn new(bus: SpiBus, network: NetworkImpl) -> Self {
+        Self { bus, network }
+    }
+}
+
+impl<ChipSelect: OutputPin, NetworkImpl: Network> InactiveDevice<FourWire<ChipSelect>, NetworkImpl> {
+    pub fn activate<Spi: FullDuplex<u8>>(
+        self,
+        spi: Spi,
+    ) -> Device<ActiveFourWire<Spi, ChipSelect>, NetworkImpl> {
+        Device::new(self.bus.activate(spi), self.network)
+    }
+}
+
+impl<NetworkImpl: Network> InactiveDevice<ThreeWire, NetworkImpl> {
+    pub fn activate<Spi: FullDuplex<u8>>(
+        self,
+        spi: Spi,
+    ) -> Device<ActiveThreeWire<Spi>, NetworkImpl> {
+        Device::new(self.bus.activate(spi), self.network)
+    }
+}