Add reliable Android BLE ride recorder

tools/capture_ble.py

@@ -7,12 +7,13 @@ import argparse
 import asyncio
 import csv
 import os
+import secrets
 import signal
 from contextlib import ExitStack
 from datetime import datetime
 from pathlib import Path
 
-from trikke_ble import BleFrameReassembler, encode_ack
+from trikke_ble import BleFrameReassembler, encode_ack, encode_begin_session
 from trikke_protocol import (
     CSV_COLUMNS,
     PACKET_TYPE_METADATA,
@@ -27,6 +28,7 @@ DEVICE_NAME = "TrikkeSensor"
 SERVICE_UUID = "7d2ea000-f75b-4a9b-8fbe-3d4c2a1e9c10"
 DATA_UUID = "7d2ea000-f75b-4a9b-8fbe-3d4c2a1e9c11"
 ACK_UUID = "7d2ea000-f75b-4a9b-8fbe-3d4c2a1e9c12"
+CONTROL_UUID = "7d2ea000-f75b-4a9b-8fbe-3d4c2a1e9c13"
 
 
 def parse_args() -> argparse.Namespace:
@@ -86,6 +88,7 @@ async def capture(args: argparse.Namespace) -> int:
     last_persisted_raw: bytes | None = None
     sample_count = 0
     frame_count = 0
+    session_token = secrets.randbits(64)
 
     with ExitStack() as stack:
         raw_capture = stack.enter_context(output.open("wb"))
@@ -110,6 +113,11 @@ async def capture(args: argparse.Namespace) -> int:
                     reassembler.reset()
                     while not fragments.empty():
                         fragments.get_nowait()
+                    await client.write_gatt_char(
+                        CONTROL_UUID,
+                        encode_begin_session(session_token),
+                        response=True,
+                    )
                     await client.start_notify(DATA_UUID, on_fragment)
                     print("BLE connected and subscribed")
                     while not stop.is_set() and client.is_connected:

tools/trikke_ble.py

@@ -6,6 +6,7 @@ import struct
 
 BLE_FRAGMENT_HEADER = struct.Struct("<IHH")
 BLE_ACK = struct.Struct("<4sI")
+BLE_BEGIN_SESSION = struct.Struct("<4sQ")
 BLE_MIN_FRAME_SIZE = 36
 BLE_MAX_FRAME_SIZE = 196
 
@@ -64,3 +65,7 @@ class BleFrameReassembler:
 
 def encode_ack(packet_sequence: int) -> bytes:
     return BLE_ACK.pack(b"ACK1", packet_sequence & 0xFFFFFFFF)
+
+
+def encode_begin_session(session_token: int) -> bytes:
+    return BLE_BEGIN_SESSION.pack(b"BGN1", session_token & 0xFFFFFFFFFFFFFFFF)