aioble: receiving data from server with indication

[emgema]

I try to use a laser rangefinder (bosh PLR 30 C) via bluetooth from my eps32 with aioble.

With the code below I can successfully send a command (a hex byte code) to the device, which triggers the measurement. But I just cannot receive any response. I know (from investigations with nRF Connect android app) that the device can do indications and when sending the byte code via nRF connect app I am getting response (which is a hex byte code) as expected.

Why is it not working with aioble? Do I miss something? How can I receive data from server to client after a write command with response?
Do I use char.indicated() correct?

import uasyncio as asyncio
import aioble
import bluetooth
import time

BLE_ADDR = "00:13:43:8F:1D:75"
SERVICE_UUID = bluetooth.UUID("00005301-0000-0041-5253-534f46540000")
CHAR_UUID = bluetooth.UUID("00004301-0000-0041-5253-534f46540000")
COMMAND = b"\xC0\x40\x00\xEE"

async def send_and_receive():
    print(" Verbinde mit PLR 30 C.")
    device = aioble.Device(aioble.ADDR_PUBLIC, BLE_ADDR)

    try:
        conn = await device.connect(timeout_ms=5000)
    except asyncio.TimeoutError:
        print("Verbindung fehlgeschlagen: Timeout")
        return
    print("Verbunden!")

    services = []
    async for s in conn.services():
        services.append(s)
    service = None
    for s in services:
        if s.uuid == SERVICE_UUID:
            service = s
            break

    characteristics = []
    async for c in service.characteristics():
        characteristics.append(c)
    char = None
    for c in characteristics:
        if c.uuid == CHAR_UUID:
            char = c
            break

    await char.subscribe(indicate=True)

    await char.write(COMMAND)

    start_time = time.ticks_ms()
    while True:
        try:
            data = await char.indicated(timeout_ms=500)
            print("Indication empfangen:", data)
            break

        except asyncio.TimeoutError:
            print(" Noch keine Antwort...")
            if time.ticks_diff(time.ticks_ms(), start_time) > 5000:
                print("Timeout: Keine Antwort nach 5 Sekunden")
                break

    await conn.disconnect()


asyncio.run(send_and_receive())

Thanks for your help!

[emgema]

The problem was in

char.subscribe(indicate=True)

It will set the value of the descriptor at address bluetooth.UUID(0x2902) to b'\x03\x00'
BUT it should be b'\x02\x00' !!!

My fix:

Instead of char.subscribe(indicate=True):

descriptors = []
async for d in char.descriptors():
    descriptors.append(d)
for desc in descriptors:
    if desc.uuid == bluetooth.UUID(0x2902):
        await desc.write(b'\x02\x00')

then the code works like a charm!

[ekspla]

The default value of notify is True,
in micropython-lib/micropython/bluetooth/aioble/aioble/client.py

async def subscribe(self, notify=True, indicate=False):

In your case, you have to write explicitely as:

char.subscribe(notify=False, indicate=True)