RE: How does the nRF52840 indicate when HFXO is stable?

Kenneth — Tue, 20 Feb 2018 15:59:15 GMT

Hi,

The simplest may be something like shown below, you may also check that HFCLKSTAT register if external crystal is running:
http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/clock.html?cp=2_1_0_18_2_3#register.HFCLKSTAT

Kenneth

    // Stop external HFCLK if it's already running
    NRF_CLOCK->TASKS_HFCLKSTOP = 1;        
    nrf_delay_us(1000); // Just some random delay to ensure it's stopped    
    
    // Start HFCLK 
    // Note: The BLE softdevice require that the startup time is <1.5ms   
    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_HFCLKSTART = 1;    
    while(NRF_CLOCK->EVENTS_HFCLKSTARTED == 0)
        ;    
    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    
    // External HFCLK is now running