Jannis
5cee4bd543
- Use write_gatt_char with response=True (Write With Response) — many BMS firmwares ignore Write Without Response packets - Add 0.5s delay after start_notify before sending first command to avoid race where BMS hasn't registered the notification subscription yet Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
201 lines
7.7 KiB
Python
201 lines
7.7 KiB
Python
"""BLE GATT communication handler for the Xiaoxiang Smart BMS."""
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from __future__ import annotations
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import asyncio
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import logging
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import struct
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from bleak import BleakClient, BleakError
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from bleak.backends.device import BLEDevice
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from .const import (
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FRAME_END,
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FRAME_START,
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RX_CHAR_UUID,
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TX_CHAR_UUID,
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)
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_LOGGER = logging.getLogger(__name__)
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# Full frame layout:
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# [0xDD] [CMD] [STATUS] [PAYLOAD_LEN] [PAYLOAD...] [CHK_HI] [CHK_LO] [0x77]
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# Header = 4 bytes, trailer = 3 bytes (checksum × 2 + end marker)
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_HEADER_LEN = 4
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_TRAILER_LEN = 3
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class BmsBluetoothHandler:
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"""Manages BLE connection and protocol framing for a Xiaoxiang BMS device."""
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def __init__(self, address: str) -> None:
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self._address = address
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self._client: BleakClient | None = None
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self._buffer = bytearray()
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self._response_event = asyncio.Event()
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self._response_data: bytes | None = None
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self._lock = asyncio.Lock()
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# ------------------------------------------------------------------
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# Connection management
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# ------------------------------------------------------------------
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@property
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def is_connected(self) -> bool:
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return self._client is not None and self._client.is_connected
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async def connect(self, ble_device: BLEDevice) -> None:
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"""Open BLE connection and start notifications.
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Accepts a BLEDevice resolved by HA's Bluetooth subsystem so that
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ESPHome BLE proxies are used transparently alongside local adapters.
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"""
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if self.is_connected:
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return
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_LOGGER.debug("Connecting to BMS at %s (via %s)", self._address, ble_device.name)
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self._client = BleakClient(
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ble_device,
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disconnected_callback=self._on_disconnect,
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)
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await self._client.connect()
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await self._client.start_notify(RX_CHAR_UUID, self._on_notify)
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# Give the BMS a moment to register the notification subscription
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# before we start sending commands — avoids dropped first response
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await asyncio.sleep(0.5)
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_LOGGER.debug("Connected to BMS at %s", self._address)
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async def disconnect(self) -> None:
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"""Close the BLE connection cleanly."""
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if self._client:
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try:
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await self._client.disconnect()
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except Exception:
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pass
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self._client = None
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def _on_disconnect(self, _client: BleakClient) -> None:
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_LOGGER.debug("BMS at %s disconnected", self._address)
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self._client = None
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# ------------------------------------------------------------------
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# Frame reception
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# ------------------------------------------------------------------
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def _on_notify(self, _char, data: bytearray) -> None:
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"""Accumulate BLE notification chunks into complete protocol frames.
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BLE max payload is 20 bytes (default MTU), so a single BMS frame
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(up to ~50 bytes for 16 cells) arrives across several notifications.
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We buffer until we can calculate and verify the expected frame length.
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"""
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self._buffer.extend(data)
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# Discard leading garbage until we see a frame start byte
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while self._buffer and self._buffer[0] != FRAME_START:
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self._buffer.pop(0)
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# Need at least the 4-byte header to know payload length
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if len(self._buffer) < _HEADER_LEN:
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return
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payload_len = self._buffer[3]
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expected_total = _HEADER_LEN + payload_len + _TRAILER_LEN
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if len(self._buffer) < expected_total:
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return # still waiting for more chunks
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frame = bytes(self._buffer[:expected_total])
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del self._buffer[:expected_total]
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if frame[-1] != FRAME_END:
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_LOGGER.warning("BMS frame missing end marker, discarding: %s", frame.hex())
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return
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if frame[2] != 0x00:
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_LOGGER.warning("BMS returned error status 0x%02X for cmd 0x%02X",
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frame[2], frame[1])
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return
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_LOGGER.debug("BMS frame received (cmd=0x%02X, len=%d)", frame[1], payload_len)
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self._response_data = frame
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self._response_event.set()
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# ------------------------------------------------------------------
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# Request / response
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# ------------------------------------------------------------------
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async def request(self, command: bytes, timeout: float = 5.0) -> bytes | None:
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"""Send a command frame and wait for the corresponding response frame."""
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async with self._lock:
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self._response_event.clear()
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self._response_data = None
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try:
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await self._client.write_gatt_char(TX_CHAR_UUID, command, response=True)
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except BleakError as exc:
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_LOGGER.error("BLE write failed: %s", exc)
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return None
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try:
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await asyncio.wait_for(self._response_event.wait(), timeout)
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return self._response_data
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except asyncio.TimeoutError:
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_LOGGER.warning("BMS response timeout (cmd=%s)", command.hex())
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return None
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# ------------------------------------------------------------------
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# Frame parsers
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# ------------------------------------------------------------------
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@staticmethod
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def parse_general_info(frame: bytes) -> dict:
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"""Parse a 0x03 general info response frame.
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Payload byte offsets (frame[4] is payload[0]):
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0-1 Total voltage uint16 BE ÷100 → V
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2-3 Current int16 BE ÷100 → A (positive = charging, negative = discharging)
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4-5 Residual capacity uint16 BE ÷100 → Ah
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6-7 Nominal capacity uint16 BE ÷100 → Ah
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8-9 Cycle count uint16 BE
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10-11 Production date (ignored)
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12-15 Balance status (ignored)
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16-17 Protection status (ignored)
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18 Software version (ignored)
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19 State of charge uint8 %
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20 MOS status uint8
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21 Cell count uint8
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22 Temp probe count uint8
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23+ Temperatures uint16 BE each (raw − 2731) ÷ 10 → °C
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"""
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p = frame[_HEADER_LEN:-_TRAILER_LEN]
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temp_count = p[22]
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temperatures: list[float] = []
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for i in range(temp_count):
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raw = struct.unpack_from(">H", p, 23 + i * 2)[0]
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temperatures.append(round((raw - 2731) / 10.0, 1))
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return {
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"voltage": round(struct.unpack_from(">H", p, 0)[0] / 100.0, 2),
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"current": round(struct.unpack_from(">h", p, 2)[0] / 100.0, 2),
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"residual_capacity": round(struct.unpack_from(">H", p, 4)[0] / 100.0, 2),
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"nominal_capacity": round(struct.unpack_from(">H", p, 6)[0] / 100.0, 2),
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"cycle_count": struct.unpack_from(">H", p, 8)[0],
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"state_of_charge": p[19],
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"cell_count": p[21],
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"temperatures": temperatures,
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}
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@staticmethod
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def parse_cell_info(frame: bytes) -> dict:
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"""Parse a 0x04 cell voltage response frame.
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Per spec: frame[3] (the header length byte) = cell_count × 2.
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The payload contains ONLY the voltage bytes — no count byte.
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0+ Cell voltages uint16 BE each unit mV ÷1000 → V
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"""
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count = frame[3] // 2 # header length byte = N_cells × 2
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p = frame[_HEADER_LEN:-_TRAILER_LEN]
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voltages: list[float] = []
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for i in range(count):
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raw = struct.unpack_from(">H", p, i * 2)[0]
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voltages.append(round(raw / 1000.0, 3))
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return {"cell_voltages": voltages}
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