Calibrating the internal LF RC oscillator for the ble_dtm example

[Olly_OB]

We have created a custom board using the nRF52832 (as part of the uBlox ANNA-B112 module), and are using the internal LF RC oscillator.

We are about to go through some pre-compliance & spurious emissions testing, for which we are intending to use the ble_dtm example from the nRF5 SDK V16 S132 (along with the nRF Connect app). The spec states that the LF RC needs to be recalibrated every 8s, in order to achieve 250 ppm clock accuracy. However I'm unable to find any details on the clock configuration or how to enable clock calibration for the ble_dtm example.

Are you able to provide any more information about either the ble_dtm clock configuration?

Thanks,

Olly

[Jørgen Holmefjord]

Hi Olly,

The DTM libraries does not use the LFCLK at all, it only uses the HFCLK. This HFCLK is started in timer_init() in ble_dtm.c (this is from SDK 17.0.2):

// Use 16MHz from external crystal
// This could be customized for RC/Xtal, or even to use a 32 kHz crystal
NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
NRF_CLOCK->TASKS_HFCLKSTART    = 1;

while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0)
{
    // Do nothing while waiting for the clock to start
}

See the nRF52832 Product specifications for details about Calibrating the 32.768 kHz RC oscillator.

Best regards,
Jørgen