How to change ble_app_uart example to work without LFCLK?

[Sergio T]

I'm using SDK12 and SES.

I compiled my code based on ble_app_uart example for nRF51822_QFAA and I see in Memory usage that RAM is at correct addresses (finishes at 0x20003FFF). The code runs on PCA10028 but it doesn't run on my target board that has no 32.768kHz oscillator.

I can't find how to put the controller working without LFCLK. Can anyone give a hint?

It is frustrating that I loose 90% of time looking for solutions to put things running rather than coding... very poor documentation about examples cause this!

[Einar Thorsrud]

Hi,

The clock is configured in the ble_stack_init() function in main.c of the ble_app_uart example, by this code:

    nrf_clock_lf_cfg_t clock_lf_cfg = NRF_CLOCK_LFCLKSRC;

    // Initialize SoftDevice.
    SOFTDEVICE_HANDLER_INIT(&clock_lf_cfg, NULL);

The NRF_CLOCK_LFCLKSRC is defined in the board file so to use the RC oscillator instead of the LFXC, you should either update that, or simply skip it and do like this:

    nrf_clock_lf_cfg_t clock_lf_cfg = {.source        = NRF_CLOCK_LF_SRC_RC,                \
																			 .rc_ctiv       = 16,                                 \
                                       .rc_temp_ctiv  = 1,                                  \
                                       .xtal_accuracy = NRF_CLOCK_LF_XTAL_ACCURACY_250_PPM};

    // Initialize SoftDevice.
    SOFTDEVICE_HANDLER_INIT(&clock_lf_cfg, NULL);

[Sergio T]

In the example on the link below, the values are different. What is correct?

https://devzone.nordicsemi.com/f/nordic-q-a/43321/nrf51822-use-without-external-oscillator/169337#169337

[Einar Thorsrud]

Hi,

Neither are right or wrong, it depends on which configuration you want. Using ctiv=2 instead of 4 means that it will calibrate the RC oscillator more often, leading to a slightly higher average current consumption than if you used 4, but it is insignificant. You can refer to the documentation for nrf_clock_lf_cfg_t for details.

[Sergio T]

Hi again: I'll continue on this ticket then.

I cut SB1 on the DK board meaning that the 32.768kHz crystal is removed from the circuit. Well, the code runs on the DK. Also, the code was compiled for nRF51822-QFAA and I can verify on the Memory usage that the settings are correct. I checked the HW and there are no short-circuits. If there were, then it would not be possible to flash the controller because it has to start for the programming to be possible. Therefore I am out of ideas...

Here is the schematic and a picture of the layout. Anyone can help?

Sorry, file upload just doesn't work...!