HFXO to HFINT switch over and vice versa

[astomi]

Hi,

NRF52805 custom board.

I want to preserve HF clock state in my code (adding custom function to the bootloader) but found datasheet a bit confusing.

My simple question is - when HFCLKSTAT == 0, is HFINT running or not?

And if it is only running when bit 16 (CLOCK_HFCLKSTAT_STATE_Msk) is on, how can I restore HF clocks to this particular state?

There is no TASKS_HFINTSTART available...

Thanks.

[Kazi Afroza Sultana]

Hello,

When HFCLKSTAT = = 0, it means HFCLK is not running at all (neither HFINT nor HFXO).

When the system requests one or more clocks from the HFCLK controller, the HFCLK controller will automatically provide them. If the system does not request any clocks provided by the HFCLK controller, the controller will enter a power saving mode. HFINT is running only when HFCLK is requested and HFXO is not running. 

There is no way to explicitly start HFINT; it is automatically started by the hardware when the system requires a high-frequency clock and HFXO is not running. You cannot manually start HFINT using a task—there is no TASKS_HFINTSTART available.