Is there a way to reduce the latency in start_notify()?

• bleak version: 0.14.2
• Python version: 3.7.11
• Operating System: Windows 10
• BlueZ version (bluetoothctl -v) in case of Linux: N/A

Description

Hi,

I am running Bleak on Windows 10 (central) reading 9DOF IMU data (packed into 1 GATT characteristic) from Arduino Nano 33 BLE. I have noticed that there is an average of 180ms -200ms latency between when the IMU characteristic is updated and when the python program is notified in the start_notify() callback. I measured this latency by comparing the Arduino Serial Monitor time stamp (connected to the same Windows 10 machine) and the time stamp in the start_notify() callback for the corresponding record. When I switched to polling the characteristic in a while loop with asyncio.sleep(0), the latency drops to an average of 20-25ms. Is polling the best practice in minimizing the latency of reading characteristic value updates?

[datoslabs]

Thank you very much @dlech!

Based on the Bluetooth traffic captured in Wireshark, the polling version, as expected, can only poll every ~110ms due to the extra “handshakes” around read requests whereas notify version continuously receives data packets from the peripheral. After I performed optional driver updates on my Windows 10, the latency for the notify version is at a more acceptable 25-30ms level. One thing to note is that my Bluetooth driver appeared to be the same version after the updates so I am not sure if the latency was fixed due to the restart or updated shared DLLs.

[dlech]

is there a system log I can check for more details on what’s happening at the pocket levels?

Yes, see https://bleak.readthedocs.io/en/latest/troubleshooting.html#capture-bluetooth-traffic