Only Discovering the First 7 BLE Bluetooth Characteristics upon Connection

[Dana-AlTaher]

I am trying to use my Raspberry Pi Pico W as w BLE Bluetooth central device and I have around 15 characteristics that I need to be able to update and notify. That is part of a larger program.

I have isolated my issue into not being able to detect/recognize/see more than 7 characteristics when another device (like my phone and others) connects to the Pico W via Bluetooth in a BLE Scanner app for example.

I wrote the below code to demonstrate how I am using Bluetooth. The peripheral device or BLE Scanner app can only see the first 7 characteristics.
On another Raspberry Pi Pico W using the same code, this number was limited to 6.

The BLE Scanner app cannot see and access the rest of the characteristics.

How do I get my Pico W do show all of the characteristics when it is connected?

import time
import aioble
import uasyncio as asyncio
import bluetooth
import struct

# Helper function to convert float to bytes
def float_to_bytes(val):
    return struct.pack('f', val)

# Global variables
connected = False
connection = None
BLE_APPEARANCE_REMOTE = 384
ADV_INTERVAL_US = 250_000

# Define the CCCD UUID
CCCD_UUID = bluetooth.UUID(0x2902)

EDUCATIONAL_CUBESAT_UUID_NUM = "12345678-1234-5678-1234-567812345678"
_EDUCATIONAL_CUBESAT_UUID = bluetooth.UUID(EDUCATIONAL_CUBESAT_UUID_NUM)

''' -----------------------------------------

    GLOBAL

----------------------------------------- '''

# Define the service and characteristic UUIDs
SERVICE_UUID_NUM = "12345678-aaaa-5678-1234-567812345678"
CHARACTERISTIC_UUIDS = [
    "12345678-1234-5678-1234-56781234aaa0",
    "12345678-1234-5678-1234-56781234aaa1",
    "12345678-1234-5678-1234-56781234aaa2",
    "12345678-1234-5678-1234-56781234aaa3",
    "12345678-1234-5678-1234-56781234aaa4",
    "12345678-1234-5678-1234-56781234aaa5",
    "12345678-1234-5678-1234-56781234aaa6",
    "12345678-1234-5678-1234-56781234aaa7",
    "12345678-1234-5678-1234-56781234aaa8",
    "12345678-1234-5678-1234-56781234aaa9",
    "12345678-1234-5678-1234-56781234aaaA",
    "12345678-1234-5678-1234-56781234aaaB",
    "12345678-1234-5678-1234-56781234aaaC",
    "12345678-1234-5678-1234-56781234aaaD",
    "12345678-1234-5678-1234-56781234aaaE",
    "12345678-1234-5678-1234-56781234aaaF",
]

# Initialize Bluetooth UUIDs
SERVICE_UUID = bluetooth.UUID(SERVICE_UUID_NUM)
CHARACTERISTIC_UUIDS = [bluetooth.UUID(uuid) for uuid in CHARACTERISTIC_UUIDS]

# Define the service
service = aioble.Service(SERVICE_UUID)

# Create the characteristics
characteristics = [
    aioble.Characteristic(service, char_uuid, read=True, notify=True, initial=float_to_bytes(0.0))
    for char_uuid in CHARACTERISTIC_UUIDS
]

''' -----------------------------------------

    SIMULATED DATA (FOR TESTING)

----------------------------------------- '''

# Helper function to generate random float values
import random

def generate_float_value():
    return random.uniform(-10.0, 10.0)

# Orientation and notification task with error catching and retries
async def characteristic_update_task():
    global connection
    while True:
        try:
            if connection:  # Ensure the connection is established
                # Simulate updating characteristics with new float values
                for idx, char in enumerate(characteristics):
                    new_value = generate_float_value()
                    char.write(float_to_bytes(new_value))
                    char.notify(connection)  # Only notify if connected
            else:
                pass  # No notification if not connected
        except Exception as e:
            await asyncio.sleep(1)  # Wait before retrying
        await asyncio.sleep_ms(50)


''' -----------------------------------------

    GENERAL BLUETOOTH TASKS

----------------------------------------- '''

# Register services
aioble.register_services(service)

# Bluetooth handling with error catching and retries
async def peripheral_task():
    global connected, connection
    while True:
        try:
            connected = False
            async with await aioble.advertise(
                ADV_INTERVAL_US,
                name="Pico W CubeSat",
                appearance=BLE_APPEARANCE_REMOTE,
                services = [
                    _EDUCATIONAL_CUBESAT_UUID
                ]
            ) as connection:
                connected = True
                await connection.disconnected()
                connected = False
                connection = None
        except Exception as e:
            await asyncio.sleep(1)  # Wait before retrying

# Main function with error catching
async def main():
    try:
        ''' ---------- ADD ALL TASKS HERE ---------- '''
        await asyncio.gather(
            peripheral_task(),
            characteristic_update_task()
        )
    except Exception as e:
        await asyncio.sleep(1)  # Wait before restarting
        asyncio.run(main())  # Restart main loop if error occurs

# Run asyncio loop
asyncio.run(main())

[andrewleech]

I believe btstack has a fixed buffer size used to cache characteristics & services.
I've only hit this limit using it as a device rather than central but this is probably what you're running up against here.

I tried to make this configurable in #6448 but this was replaced with a newer mechanism as described in that last comment on that PR. I haven't used btstack since then so not sure how it works now, but maybe that'll give you a pointer in the right direction.

[Dana-AlTaher]

I will check that out and see if it is easy to implement, thank you!