Which HF clock will be chosen by BLE stack?

[nordicdev]

Hi, In my code, I have not started the HF clock. I call the ble_stack_init where "SOFTDEVICE_HANDLER_INIT(NRF_CLOCK_LFCLKSRC_XTAL_20_PPM, NULL);" is called. Which HF clock will be chosen at what PPM by the micro if I don't deliberately start the HF clock like this:

	NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

	NRF_CLOCK->TASKS_HFCLKSTART = 1;


     while(NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);

[Stian Røed Hafskjold]

The code in your question does not really start the HF clock. It starts the HF crystal. The HF clock is started automatically whenever it is requested by a peripheral (e.g. radio). If the crystal is not running, the internal RC will provide the clock source.

The Softdevice requires an external crystal because the internal RC is not accurate enough for the BLE spec. infocenter.nordicsemi.com/.../ext_reqs.html

The Softdevice starts the crystal automatically and makes sure that it's stable before any radio transmission.

You can see a plot of the SD advertising here: devzone.nordicsemi.com/.../ The second field "ramp" is when the crystal is starting up. And the standby after this is to make sure that it is completely stable.

The maximum PPM allowed for the HF crystal is given here, infocenter.nordicsemi.com/.../clock.html, and is 40 ppm for BLE.

[nordicdev]

Hi Stian, Thanks for the reply. I need to generate pulses as low as 30usec(on time = 30usec and off time = 70 usec) width in my project. I calculate 1 second = 10000 cycles (1 cycle = 30usec on and 70usec off). I use gpiote+ppi to output the pulses. I have used driver apis (not directly register write) for all the functions used. Since they all use softdevice for the driver, I thought the HF Xtal clock started by softdevice would be used for all those driver functions.