Unusually high BLE connection latency

RE: Unusually high BLE connection latency

Ziyao Zhou — Mon, 28 Jul 2025 09:08:29 GMT

Thank you so much for your kind reply! Wish you all the best!!!

RE: Unusually high BLE connection latency

blitz0145 — Sun, 27 Jul 2025 10:04:28 GMT

Hi!
You may use Wireshark USBPCap (https://wiki.wireshark.org/CaptureSetup/USB)
Once you connect a BLE device (let's say a mouse); the BLE packet will show up.

BLE HID Mouse. You can see that a packet is received every 7.5ms approx. Cheers :)

RE: Unusually high BLE connection latency

Ziyao Zhou — Sat, 26 Jul 2025 08:25:26 GMT

Hi,

Thank you so much for your suggestion, could you kindly advise how to measure the latency after connection using wireshark:)

RE: Unusually high BLE connection latency

blitz0145 — Sat, 08 Mar 2025 15:26:59 GMT

This has been resolved.

My method of measuring latency was a high speed camera. I was comparing the time between DK LED lighting up and a screen flash on Windows 11 through an app I programmed.

Turns out that this massive latency is a result of how Windows handles HID over BLE. Nothing to do with the actual BLE connection interval.

Similar behaviour was observed with a high end gaming mouse that supports BLE.

To everyone who comes across this post. Please measure connection related parameters with a Bluetooth sniffer- the nrf52840 dongle can be easily programmed to work like a sniffer. Other methods will never be as accurate.

RE: Unusually high BLE connection latency

blitz0145 — Fri, 07 Mar 2025 17:54:49 GMT

One possible theory could be that some part of my code is starving the Soft Device Controller.

But that is not the case either- reason being that in later tests- I decided to make the device run as a BLE HID Peripheral and a BT Central at the same time.
The central code just responds to another DK's latency service messages- the tested latency was a blazing fast 1.5 ms average (LLPM enabled)

While the BT Peripheral continued to give the same average high latency functioning the same way as mentioned in my previous message. (Note: the peripheral connects to a Windows 11 host)

This definitely means that my code is not starving out the SDC- since central works perfectly fine.

Any ideas why peripheral has such a huge latency?

RE: Unusually high BLE connection latency

blitz0145 — Fri, 07 Mar 2025 17:33:23 GMT

Hello!

Yes, the performance critical modules such as mouse sensor input, HID service etc. are all based on nRF Desktop.

I measured internal latencies- the delay between a button getting clicked and right before bt_hids_inp_rep_send() is called is negligible.

I know that internally bt_hids_inp_rep_send() calls bt_gatt_notify_cb()

a GATT notification is sent at the next connection event- so this must mean that the connection is somehow just not able to maintain 7.5 ms and the fact that connection drops when the timeout is set to 100ms means that latency is definitely spiking to 100ms +

RE: Unusually high BLE connection latency

Lorenzo Amicucci — Fri, 07 Mar 2025 13:05:59 GMT

Is this based on nRF Desktop? or you started from scratch?
https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/applications/nrf_desktop/README.html

you can easily build a BLE mouse using nRF Desktop on the nRF52832DK and compare with your results: simply create a configuration folder for your DK here
https://github.com/nrfconnect/sdk-nrf/tree/main/applications/nrf_desktop/configuration