Source of HFCLK

[Christoffer Brask]

Hi,

We have a custom PCB with external crystal for HFCLK. Can you tell whether the external crystal is used by default for HFCLK or it has to be selected in the HFCLKSTAT register?

How do you select HFCLK source in zephyr?

CONFIG_APP_ENABLE_HFXO does not seems to be an option anymore.

[Bendik Heiskel]

Hi,

The external crystal oscillator is used when a higher accuracy clock is needed. In order to lower the power usage the crystal oscillator is only running when needed, and otherwise the RC oscillator is used. If you don't care about the current consumption and always want the external crystal oscillator running, you can start the crystal oscillator at startup and leave it running. The Clock Driver API can be used for this.

 

Best regards,

Bendik

[Christoffer Brask]

Hi Bendik,

From what i'm reading, as i'm using BLE, some lowlevel library code will select the use of an external oscillator instead of the internal rc?

[Bendik Heiskel]

Yes, the Bluetooth LE Controller will use the external oscillator as the accuracy is needed for the radio.