Add example to README

README.md

@@ -4,8 +4,68 @@ usbd-midi
 A simple usb midi device class for [usb-device](https://crates.io/crates/usb-device).
 
 Currently this aims to be a very simple implementation, that allows the micro
-controller to send midi information to the PC.
+controller to send MIDI information to the PC and also receive MIDI information.
 
 This crate requires the use of a hardware driver, that implements the
 usb-device traits.
 
+## Example
+
+### Receive MIDI
+Turn on the integrated LED of a STM32 BluePill board as long as C2 is pressed
+```rust
+fn main() -> ! {
+    let dp = pac::Peripherals::take().unwrap();
+
+    let mut rcc = dp.RCC.constrain();
+
+    let mut gpioa = dp.GPIOA.split(&mut rcc.apb2);
+    let mut gpioc = dp.GPIOC.split(&mut rcc.apb2);
+
+    let mut led = gpioc.pc13.into_push_pull_output(&mut gpioc.crh);
+    led.set_high().unwrap();
+
+    let mut usb_dp = gpioa.pa12.into_push_pull_output(&mut gpioa.crh);
+
+    let usb = Peripheral {
+        usb: dp.USB,
+        pin_dm: gpioa.pa11,
+        pin_dp: usb_dp.into_floating_input(&mut gpioa.crh),
+    };
+
+    let usb_bus = UsbBus::new(usb);
+
+    let mut midi = MidiClass::new(&usb_bus);
+
+    let mut usb_dev = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x5e4))
+        .product("MIDI Test")
+        .device_class(USB_AUDIO_CLASS)
+        .device_sub_class(USB_MIDISTREAMING_SUBCLASS)
+        .build();
+
+    loop {
+        if !usb_dev.poll(&mut [&mut midi]) {
+            continue;
+        }
+
+        let mut buffer = [0; 64];
+
+        if let Ok(size) = midi.read(&mut buffer) {
+            let buffer_reader = MidiPacketBufferReader::new(&buffer, size);
+            for packet in buffer_reader.into_iter() {
+                if let Ok(packet) = packet {
+                    match packet.message {
+                        Message::NoteOn(Channel1, Note::C2, ..) => {
+                            led.set_low().unwrap();
+                        },
+                        Message::NoteOff(Channel1, Note::C2, ..) => {
+                            led.set_high().unwrap();
+                        },
+                        _ => {}
+                    }
+                }
+            }
+        }
+    }
+}
+```