How to discover a device quickly with BlueZero? - bluetooth

Question

I have an Ubuntu PC that I want to connect to an advertising microcontroller (nrf52840) using python.
They connect just fine when the PC has already discovered the microcontroller using a command line tool like bluetoothctl. The issue is when the devices are interacting for the first time.
According to the Bluezero docs it seems like nearby_discovery() is just the function for the job. The issue is unless I set the timeout to be absurdly long, like ~45 seconds, the Central cannot be created because it hasn't been discovered.
The steps I'm taking now:
from bluezero import adapter, central
dongles = adapter.list_adapters()
dongle = adapter.Adapter(dongles[0])
dongle.nearby_discovery(timeout=45)
myCentral = central.Central(adapter_addr=dongle.address, device_addr="AA:BB:CC:DD:EE:FF")
Is there a more reliable way to discover/connect to new devices?
For what it's worth, bluetoothctl scan on seems to discover devices almost immediately.

Answer 1

The solution turned out to be unrelated to bluezero. I'm using JTAG to grab the MAC address and that function resets the CPU on the board, meaning that it took around 30 seconds to reboot and start advertising again. Thank you for the responses

Answer 2

There shouldn't be any significant time difference between Bluezero and bluetoothctl to discover a device as they are making the same API calls to bluetoothd.
Once a device is in the known list in BlueZ, then because BlueZ ignores "duplicates", it doesn't report a device very frequently in the scan results.
This is what leads to most scripts I've seen not using the nearby_discovery() because once your device is in the known list, you can connect to it without discovery.
In bluetoothctl you can type devices to get the list. In Bluezero there is not a tidy option to do this (Just not something I have thought of providing previously). If you wanted to do a test to see if the device you want to connect to is already in the list then below is my initial thought:
from bluezero import dbus_tools
def known_devices():
"""Get a list of devices Bluez already knows about"""
device_list = []
mng_objs = dbus_tools.get_managed_objects()
for path in mng_objs:
address = mng_objs[path].get('org.bluez.Device1', {}).get('Address')
if address:
device_list.append(str(address))
return device_list
def is_known_device(mac_addr):
"""Is the given Bluetooth address already a known device"""
found_devices = known_devices()
return mac_addr in found_devices
print(f'Device list: {known_devices()}')
look_list = ['DC:DB:16:6B:8C:5F', 'DC:DB:16:6B:8C:xx']
for look_up in look_list:
print(f'{look_up} is known? {is_known_device(look_up)}')
In my testing I got the following output:
Device list: ['DC:DB:16:6B:8C:5F', 'DE:82:35:E7:43:BE']
DC:DB:16:6B:8C:5F is known? True
DC:DB:16:6B:8C:xx is known? False