Possible reasons for disconnect reason 8

[wgeeurickx]

Hi,

I have an application with custom boards using nRF54L15 (running ncs 2.9.1) as the peripheral and currently a modified nRF9160DK (running ncs 2.5.1) as the central, which connects to multiple peripherals at a time. I am noticing quite some disconnects happening in (unattended) field tests, and I would like to understand if there is a way to diagnose/fix these. I already started adding more logging of metrics so I have more context, and this is what I have so far.

# Connection parameters
CONFIG_BT_PERIPHERAL_PREF_MIN_INT=400
CONFIG_BT_PERIPHERAL_PREF_MAX_INT=400
CONFIG_BT_PERIPHERAL_PREF_LATENCY=2
CONFIG_BT_PERIPHERAL_PREF_TIMEOUT=1000

There are no resets happening on the peripheral/central side, and the RSSI is pretty stable, with the 10% quantile for the device that is furthest away at a stable -80dBm. I know this is on the low end, but I assume it should still be high enough for a stable connection. In this case, the central has 4 peripherals connected to it. The disconnects occur for all peripherals, but at widely different (random) intervals.

Could you give me any pointers on what could be going wrong and how I can try to identify it? It's hard for me to get a sniffer trace as this field test is happening unattended at a public site, and the occurence of the disconnects is pretty random and can take some time before they start happening.

Best,

Wout

[Simonr]

Hi

Where do you see the disconnects exactly, do you have any logging information you can upload here? Disconnect reason 0x8 points to a BLE HCI CONNECTION TIMEOUT, and that should only be triggered by a connection supervision timeout, meaning there has been no activity in the BLE connection for the supervision timeout. You set the preferred timeout to 1000 (ms), but in the end it's the central application that decides the connection parameters. Please share the connection parameters from the central application, or potentially a sniffer trace so we can see what's happening on the air. You can use another DK and the nRF Sniffer tool + Wireshark for getting sniffer traces for example: https://www.nordicsemi.com/Products/Development-tools/nRF-Sniffer-for-Bluetooth-LE 

Best regards,

Simon