examples/bluetooth: Add basic BLE peripheral examples.

Consisting of:
- ble_advertising.py -- helper to generate advertising payload.
- ble_temperature.py -- simple temperature device.
- ble_uart_periperhal.py -- BLE UART wrapper.
- ble_uart_repl.py -- dupterm-compatible uart.

examples/bluetooth/ble_advertising.py

@@ -0,0 +1,37 @@
+# Helpers for generating BLE advertising payloads.
+
+from micropython import const
+import struct
+
+# Advertising payloads are repeated packets of the following form:
+#   1 byte data length (N + 1)
+#   1 byte type (see constants below)
+#   N bytes type-specific data
+
+_ADV_TYPE_FLAGS = const(0x01)
+_ADV_TYPE_NAME = const(0x09)
+_ADV_TYPE_UUID16_COMPLETE = const(0x3)
+_ADV_TYPE_APPEARANCE = const(0x19)
+
+# Generate a payload to be passed to gap_advertise(adv_data=...).
+def advertising_payload(limited_disc=False, br_edr=False, name=None, services=None, appearance=0):
+    payload = bytearray()
+
+    def _append(adv_type, value):
+        nonlocal payload
+        payload += struct.pack('BB', len(value) + 1, adv_type) + value
+
+    _append(_ADV_TYPE_FLAGS, struct.pack('B', (0x01 if limited_disc else 0x02) + (0x00 if br_edr else 0x04)))
+
+    if name:
+        _append(_ADV_TYPE_NAME, name)
+
+    if services:
+        for uuid in services:
+            # TODO: Support bluetooth.UUID class.
+            _append(_ADV_TYPE_UUID16_COMPLETE, struct.pack('<h', uuid))
+
+    # See org.bluetooth.characteristic.gap.appearance.xml
+    _append(_ADV_TYPE_APPEARANCE, struct.pack('<h', appearance))
+
+    return payload