nRF5340 drop connection before going to low power

[PabloL]

Hi, 

I´m using a Fanstel BC40M board with a nRF5340 on board as a peripheral device.

Being connected to a central, it triggers some tasks in the peripheral. The peripheral does some task using some peripherals like SPIM, timers, PPI, etc., sends some BLE notifications and then sometimes drops connection before going to low power.

This happens on some devices and not on others (same firmware, same hardware).

The error is: Disconnected from device xx:xx:xx:xx:xx:xx, reason: BLE_HCI_CONNECTION_TIMEOUT

After a while the device reconnects but has the same behaviour.

I'm using Zephyr nRF Connect SDK 2.5.0.

So far, I have tried:

- Increase connection timeout.

- Define different crystal accuracies in prj.conf.

CONFIG_CLOCK_CONTROL_NRF_K32SRC_xxPPM

No success.

any clue?

Thank you!

[PabloL]

Update:

I added in prj.conf:

CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC_CALIBRATION=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_500PPM=y

It uses the internal RC instead of the 32Khz external crystal.

Now things seem to be working on the board that failed.

Do you think this is a board specific problem or there is something wrong with the 32Khz crystal configuration?

[Simonr]

Hi

Glad to hear you were able to make it work as expected with the RC oscillator.

This points to something being wrong with the 32.768kHz crystal on the physical board, as your clock configuration looks correct. Do you see it on multiple BC40M board or just on one specific one? If so a broken or poorly connected 32.768kHz crystal is likely the cause.

Best regards,

Simon

[PabloL]

Thank you Simon,

I tested only a few of them.
I have seen it just on one specific BC40M board so far.
I wonder if Fanstel puts the capacitors to the 32.768Khz crystal or I have to add the internal one to the prj.conf:

CONFIG_SOC_ENABLE_LFXO=y
CONFIG_SOC_LFXO_CAP_INT_7PF=y
CONFIG_BUILD_WITH_TFM=y

Unfortunately, Fanstel doesn't share the internal circuit of the module.
I'm going to ask them.

[PabloL]

From Fanstel:

Some BC40Ms in the distributors' and Fanstel Scottsdale warehouse have incorrect load capacitors for the 32 KHz crystal. Please use the internal RC oscillator.

New production from the factory has the correct load capacitors. Sorry!