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

Are you connecting multiple boards to the central device here? If so, how many? If you have a lot of connected devices, increasing the connection supervision timeout to make sure all devices are able to get back to the central before they time out. Especially if the disconnects happen rarely, I think increasing the timeout should help a lot.

It's difficult to find specific factors to monitor here. The best way to find what the restricting factor is would be a sniffer trace to monitor what's going on on-air, but as you say, that might not be too easy to make happen.

Best regards,

Simon