SMP Server sample drops connection with custom board - crystal config issue?

[zigenz]

Hi there,

I am running a custom board based on the nRF5340-DK.  It's a minimal board, notably with both oscillators

It seems to behave itself with low-rate BLE use-cases (eg. HRS, example), but I am struggling to perform a DFU using the Zephyr SMP Server sample - it may start (or not), but will fail quickly with a 0x08 GATT_CONN_TIMEOUT although it seems to work fine on the DK. Using NCS 1.4.2.

RSSI on my board is better than the DK, so I'm comfortable I've tuned the antenna sufficiently well.  I am however using the same Golledge crystals with no external caps.  I was wondering if I need to do anything special with the UICR registers to make sure they're engaged correctly?

Thanks in advance - Z

[ketiljo]

Have you set the load cap values for the crystal in UICR? The value will be dependent on the CL value of the crystal as Ccap = CL * 2 - Cpin, where Cpin = 4 pF. For a crystal with CL = 8 pF, set the load caps to 12 pF.