nRF51 RF channel center frequency in BLE mode

[phlb]

Hello,

I developed a firmware on nrf51422 with nrf51. I use a development board PCA10028. With this firmware I control the directly the radio registers (Soft Device is disabled). My code is inspired from "radio test" available in SDK 10.0 (nRF51_SDK_10.0.0_dc26b5e\examples\peripheral\radio_test).

I'm in RADIO_MODE_MODE_Ble_1Mbit mode.

I call radio_tx_carrier(radio_x_power, radio_x_mode, radio_x_channel);

The radio_tx_carrier() code from nRF51_SDK_10.0.0_dc26b5e\examples\peripheral\radio_test\radio_test.c

With RF analyser I have this results:

channel 1 mesure: 2.41140, channel 2 mesure: 2.41248, channel 3 mesure: 2.41340, channel 4 mesure: 2.41443, channel 5 mesure: 2.41548,
channel 6 mesure: 2.41647, channel 7 mesure: 2.41735, channel 8 mesure: 2.41838, channel 9 mesure: 2.41957, channel 10 mesure: 2.42053,

Channel center frequency is shifted.

How I can set correctly the center frequency? I read that there was a register FICR:BLE_1MBIT[n]. Where is the description of the value that I can write? Frequency offset? unit? ...

Thanks for your help.

Regards.

phlb

[Kenneth]

The radio override register does not apply here, as it will have an effect on the deviation, not the center frequency. The radio_test example should already do what you describe, but what you might have overlooked is:

static void init(void)
{
    NRF_RNG->TASKS_START = 1;
    
    // Start 16 MHz crystal oscillator
    NRF_CLOCK->EVENTS_HFCLKSTARTED  = 0;
    NRF_CLOCK->TASKS_HFCLKSTART     = 1;

    // Wait for the external oscillator to start up
    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0)
    {
        // Do nothing.
    }  
}

[phlb]

ok, thanks! I forgot this initialization.

The radio override register has an effect on the deviation. This parameter it is obtained by a calibration procedure for each device?

[Kenneth]

Yes, these calibration values are measured and written in our production, and ensure that the product meet the requirements set in the BLE specifications.

[phlb]

Ok. what is the unit of this parameter (Hz,kHz,%,..)? where can I find information about this parameter and the calibration procedure?

[Kenneth]

The details is described in PCN-083 : Calibration of Radio Deviation

It's not intended for anyone to modify these values, the calibration is done by Nordic Semiconductor as part of production test of each individual nRF IC.