How to configure a secondary clock crystal in Zephyr for NRF52833dk?

[Maneesh N]

Hi all,

I am trying to interface a BLE mikrobus module onto a Yocto based Linux SBC. I need to use Zephyr's hci_uart example to flash it onto the module, the mikrobus BLE module is based on nrf52833dk. But it doesn't have a primary 32.678KHz crystal, so I need to use a secondary crystal. If anyone knows how to configure a secondary crystal in Zephyr for the hci_uart example and flash it onto the module, please help me out on this.

The code works fine when I use the EVK and fails to run on the Module. If anyone can help me on how to configure a second crystal it'll really be helpful to me.

Thanks in advance.

[Sigurd]

Hi,

You need to configure it to use the internal 32.768 kHz RC oscillator (LFRC).

Set these configs:

# 32kHz clock source
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_500PPM=y

[Maneesh N]

Hi Sigurd,

May I know on which file do I set this?

[Sigurd]

Try setting it in prj.conf for the hci_uart sample,

https://github.com/nrfconnect/sdk-zephyr/blob/master/samples/bluetooth/hci_uart/prj.conf

But ideally, it should be set in the board file for the custom board, so that it's applied for all samples/applications that are built.

[Maneesh N]

I tried it on the Hello world example to see if the module is able to print anything onto the console, nothing comes up on the console.

The message that I have received from the vendor of that is said "The module doesn't have 32.678KHz crystal, You need to select the secondary crystal. I mean the Internal RC Circuit".

I couldn't make much out of it. But that's what they said.

[Maneesh N]

These are the changes that the Vendor suggested I do on the nrfSDK.

#ifndef  NRF_SDH_CLOCK_LF_SRC
#define NRF_SDH_CLOCK_LF_SRC 0
#endif

 
#ifndef   NRF_SDH_CLOCK_LF_RC_CTIV
#define  NRF_SDH_CLOCK_LF_RC_CTIV 5
#endif


#ifndef  NRF_SDH_CLOCK_LF_RC_TEMP_CTIV
#define NRF_SDH_CLOCK_LF_RC_TEMP_CTIV 10
#endif


#ifndef  NRF_SDH_CLOCK_LF_ACCURACY
#define NRF_SDH_CLOCK_LF_ACCURACY 1
#endif

 
#ifndef  CLOCK_CONFIG_LF_SRC
#define CLOCK_CONFIG_LF_SRC 0
#endif


#ifndef  NRFX_CLOCK_CONFIG_LF_SRC
#define NRFX_CLOCK_CONFIG_LF_SRC 0
#endif

 
#ifndef  CLOCK_CONFIG_LF_SRC
#define CLOCK_CONFIG_LF_SRC 0
#endif

Since there was no hci_uart example on nrfSDK, I had to switch to Zephyr. The vendor isn't sure about the changes that need to be done on Zephyr.

[Sigurd]

Maneesh N said:

I tried it on the Hello world example to see if the module is able to print anything onto the console, nothing comes up on the console.

 Do you know what pins the module uses for printing? Is there some UART-USB-bridge / virtual COM port via UART on the module?

[Maneesh N]

It is a virtual COM port via UART.

On the Nordic SDK, making the changes mentioned above and flashing this ble_app_uart example is working fine on the module. And

#ifndef  NRF_SDH_CLOCK_LF_SRC
#define NRF_SDH_CLOCK_LF_SRC 0
#endif


#ifndef  NRF_SDH_CLOCK_LF_ACCURACY
#define NRF_SDH_CLOCK_LF_ACCURACY 1
#endif

These 2 macro definitions give me the same meaning as you had sent me before. i.e,

# 32kHz clock source
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_500PPM=y

but the others I'm not quite sure.

[Sigurd]

1) This is the sample you used? https://github.com/nrfconnect/sdk-zephyr/tree/master/samples/hello_world

2) What board did you build for ? nrf52833dk_nrf52833 ?

3) Are you using command-line/ west to build and flash, or SES ?

[Maneesh N]

1. Yes, that's the example I'm trying

2. Yes!

3. Command-Line, I'm using west.

[Sigurd]

Could it be an issue with flow-control?

Try this overlay to turn flow-control on:

&uart0 {
	hw-flow-control;
};

alternatively, to turn it off, try this:

&uart0 {
	/delete-property/ rts-pin;
	/delete-property/ cts-pin;
	/delete-property/ hw-flow-control;
};

7206.nrf52833dk_nrf52833.overlay

[Maneesh N]

This overlay file should be added under samples/hello_world/boards/nrf52833dk_nrf52833.overlay right?

[Sigurd]

Maneesh N said:

This overlay file should be added under samples/hello_world/boards/nrf52833dk_nrf52833.overlay right?

 Yes. Also, if the module don't have DC/DC components for the regulator, then set this in prj.conf:

CONFIG_BOARD_ENABLE_DCDC=n