Clock Control Configuration Confirmation

RE: Clock Control Configuration Confirmation

Bendik Heiskel — Fri, 07 Mar 2025 11:34:09 GMT

Hi,

Apologies for the delay.

0x40004000 is the base address used in non secure. If you are building for bl5340_dvk_nrf5340_cpuapp you need to use 0x50004000 as the base address .

Best regards,

Bendik

RE: Clock Control Configuration Confirmation

blue_dew — Wed, 05 Mar 2025 21:13:13 GMT

I'm dumb. I found the base address and offset for the bypass register within the link you posted. Ty again bendik.

I tried:

#define NRF_XOSC32KI_BYPASS_REG (*(volatile uint32_t *)(0x40004000UL + 0x6C0UL)) // Register for bypassing the LFCLK crystal oscillator, board dependant and needs to be updated to use the board config to determine base address

static int lfclk_bypass_full_swing(void)
{
 NRF_XOSC32KI_BYPASS_REG = 1;
 return 0;
}

SYS_INIT(lfclk_bypass_full_swing, EARLY,0);

Unfortunately, this causes the system to hang and I get no output. I need some more guidance here.

RE: Clock Control Configuration Confirmation

blue_dew — Wed, 05 Mar 2025 19:12:57 GMT

Hey Bendik,

I spoke too soon. That include <nrf.h> file doesn't define any "NRF" struct. I'm attempting to use ncs 2.9.0. I also don't see any NRF struct inside of the zephyr/init.h file. The docs linked are helpful for understanding the registers but don't indicate how I can access or modify them. Please advise.

RE: Clock Control Configuration Confirmation

blue_dew — Wed, 05 Mar 2025 15:18:45 GMT

Thank you so much Bendik! That was very helpful.

RE: Clock Control Configuration Confirmation

Bendik Heiskel — Wed, 05 Mar 2025 14:54:13 GMT

Hi,

The configuration for the HFXO looks correct.

[quote user=""]When I look at the bl5340_dvk defconfig file for example, they have the same settings for the HFXO clock, so I think that is right, but that dev kit also uses an external low frequency oscillator, but I don't see an explicit config for setting the low frequency controller to use the external source. Am I misunderstanding what the "CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y" option does? Is this not required, and does the system automatically know to utilize the external source? [/quote]

CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y is needed to use the external oscillator source. I assume the development kit for the module doesn't set this as default since the module doesn't have the crystal internally.

[quote user=""]Do I need to set "CONFIG_CLOCK_CONTROL_NRF_K32SRC_20PPM=y" as that is the lowest option, my source is rated at 5ppm?[/quote]

Yes, this config is for crystalls/oscillators with 0-20ppm accuracy.

[quote user=""] I'm assuming I don't need to set any of the internal LFXO caps due to our rail to rail clock setu[/quote]

It doesn't hurt to explicitly disable the internal load caps by adding:

CONFIG_SOC_LFXO_CAP_EXTERNAL=y

You also need to set the XOSC32KI.BYPASS register, to bypass the LFCLK crystall oscillator when using a rail-to-rail external source.

This can be done by adding:

#include <zephyr/init.h>
#include <nrf.h>

static int lfclk_bypass_full_swing(void)
{
	NRF->OSCILLATORS.XOSC32KI.BYPASS=1;
	return 0;
}

SYS_INIT(lfclk_bypass_full_swing, EARLY,0);

Best regards,
Bendik