The HFINT will be used when HFCLK is requested and HFXO has not been started. The HFXO is started by triggering the HFCLKSTART task and stopped using the HFCLKSTOP task. A HFCLKSTARTED event will be generated when the HFXO has started and its frequency is stable.
You can use driver available in SDK (nrf_drv_clock_hfclk_request), you can use HAL available in SDK( nrf_clock_task_trigger(NRF_CLOCK_TASK_HFCLKSTART) ), you can do it directly on the registers (something like NRF_CLOCK->TASKS_HFCLKSTART = 1) if i remember correctly... ).
You just operate on it like on any other peripherals. There is documentation of SDK available on infocenter, and also there are clock examples available in SDK - you should just check it.
You can use driver available in SDK (nrf_drv_clock_hfclk_request), you can use HAL available in SDK( nrf_clock_task_trigger(NRF_CLOCK_TASK_HFCLKSTART) ), you can do it directly on the registers (something like NRF_CLOCK->TASKS_HFCLKSTART = 1) if i remember correctly... ).
You just operate on it like on any other peripherals. There is documentation of SDK available on infocenter, and also there are clock examples available in SDK - you should just check it.
