Instability of BLE connection due to BLE_HCI_CONNECTION_TIMEOUT

[VTU]

Hello,

may I ask you for help with instability of BLE connection? We use nRF52840 and SD 6.0.0. The issue is that our device is being disconnected with reason BLE_HCI_CONNECTION_TIMEOUT and we do not know why. We suppose to received this reason only when device is disconnected due to out of BLE range but not when it is in the range, e.g. we received this reason when the device is less than 1 m far away from cell phone. Another points is that we are not able to reproduce it, we can observed this issue several times per day....

We connected our device to various cell phone, e.g. iPhone SE iOS 13.6.

Parameters of BLE connection is:

#define REQUESTED_CONN_INTERVAL 180 /**< Connection interval requested by the watch (milliseconds). @hideinitializer */
#define REQUESTED_SLAVE_LATENCY 1 /**< Slave latency requested by the watch. @hideinitializer */
#define REQUESTED_CONN_SUP_TOUT 2000 /**< Connection supervision timeout requested by the watch (milliseconds). @hideinitializer */

and

#define NRF_SDH_CLOCK_LF_ACCURACY 5 /**< @brief External clock accuracy used in the LL to compute timing.*/

Do you have any idea what should be behind? 

Thanks

Vaclav

[Vidar Berg]

Hello Vaclav,

Are you using the crystal oscillator or the internal RC oscillator? Your NRF_SDH_CLOCK_LF_ACCURACY setting is fine if you use the crystal oscillator, but not if you have selected the RC which only has an accuracy of 500 ppm.

Best regards,

Vidar