How to create custom OpenThread message on OpenThread NCP.

[Vanperdung]

Hello OpenThread Team,
I'm currently working with OpenThread NCP firmware on EFR32. To meet my specific requirement, I need to create a custom Spinel command and also OpenThread message. However, I couldn't find any examples or references related to creating custom messages in OpenThread NCP.
Could you please provide guidance or point me to any resources on how to:

• Create a custom OpenThread message on NCP.
• Modify the NCP to support sending and receiving this custom message.

Thanks.

[abtink]

You can check the OPENTHREAD_ENABLE_NCP_VENDOR_HOOK feature and the related methods and their documentation:

openthread/src/ncp/ncp_base.hpp

Lines 554 to 614 in b42be4c

	#if OPENTHREAD_ENABLE_NCP_VENDOR_HOOK
	/**
	* Defines a vendor "command handler" hook to process vendor-specific spinel commands.
	*
	* @param[in] aHeader The spinel frame header.
	* @param[in] aCommand The spinel command key.
	*
	* @retval OT_ERROR_NONE The response is prepared.
	* @retval OT_ERROR_NO_BUFS Out of buffer while preparing the response.
	*/
	otError VendorCommandHandler(uint8_t aHeader, unsigned int aCommand);
	/**
	* Is a callback which mirrors `NcpBase::HandleFrameRemovedFromNcpBuffer()`. It is called when a
	* spinel frame is sent and removed from NCP buffer.
	*
	* (a) This can be used to track and verify that a vendor spinel frame response is delivered to the host (tracking
	* the frame using its tag).
	*
	* (b) It indicates that NCP buffer space is now available (since a spinel frame is removed). This can be used to
	* implement mechanisms to re-send a failed/pending response or an async spinel frame.
	*
	* @param[in] aFrameTag The tag of the frame removed from NCP buffer.
	*/
	void VendorHandleFrameRemovedFromNcpBuffer(Spinel::Buffer::FrameTag aFrameTag);
	/**
	* Defines a vendor "get property handler" hook to process vendor spinel properties.
	*
	* The vendor handler should return `OT_ERROR_NOT_FOUND` status if it does not support "get" operation for the
	* given property key. Otherwise, the vendor handler should behave like other property get handlers, i.e., it
	* should retrieve the property value and then encode and write the value into the NCP buffer. If the "get"
	* operation itself fails, handler should write a `LAST_STATUS` with the error status into the NCP buffer.
	*
	* @param[in] aPropKey The spinel property key.
	*
	* @retval OT_ERROR_NONE Successfully retrieved the property value and prepared the response.
	* @retval OT_ERROR_NOT_FOUND Does not support the given property key.
	* @retval OT_ERROR_NO_BUFS Out of buffer while preparing the response.
	*/
	otError VendorGetPropertyHandler(spinel_prop_key_t aPropKey);
	/**
	* Defines a vendor "set property handler" hook to process vendor spinel properties.
	*
	* The vendor handler should return `OT_ERROR_NOT_FOUND` status if it does not support "set" operation for the
	* given property key. Otherwise, the vendor handler should behave like other property set handlers, i.e., it
	* should first decode the value from the input spinel frame and then perform the corresponding set operation. The
	* handler should not prepare the spinel response and therefore should not write anything to the NCP buffer. The
	* `otError` returned from handler (other than `OT_ERROR_NOT_FOUND`) indicates the error in either parsing of the
	* input or the error of the set operation. In case of a successful "set", `NcpBase` set command handler will call
	* the `VendorGetPropertyHandler()` for the same property key to prepare the response.
	*
	* @param[in] aPropKey The spinel property key.
	*
	* @returns OT_ERROR_NOT_FOUND if it does not support the given property key, otherwise the error in either parsing
	* of the input or the "set" operation.
	*/
	otError VendorSetPropertyHandler(spinel_prop_key_t aPropKey);
	#endif // OPENTHREAD_ENABLE_NCP_VENDOR_HOOK

You can also check src/ncp/example_vendor_hook.cpp which is an example of how vendor hook can be implemented.

There are allocated ranges for SPINEL_CMD, SPINEL_PROP, SPINEL_STATUS for vendor specific use. You can check spinel.h header.

[Vanperdung]

Hi @abtink,
Thank you for your suggestion! I successfully added a new Spinel command. However, I’m now unsure how to send and receive OpenThread messages between two NCPs in the handler. Could you please provide some suggestions?

[abtink]

how to send and receive OpenThread messages between two NCPs in the handler.

Spinel is a protocol for communication between two components on the same device, such as an NCP and a host through an interface like UART or SPI. It's not designed for communication between two NCPs (i.e., between two devices).

It is not clear to me what your question is.

• If you want to learn how to implement a vendor-specific NCP/spinel commands (send commands, etc), the best place to look and learn from would be the ncp_base_* source files and how different command/get/set handlers are implemented.

• If you want to communicate between two devices, you can use IPv6 messages. Thread is a networking protocol that provides IPv6 support. Check the openthread/ip6.h or the openthread/udp6.h header for IPv6/UDP OpenThread APIs.