Thread: Co-processor

The Thread Co-processor sample demonstrates how to implement OpenThread’s Co-processor designs inside the Zephyr environment. Depending on the configuration, the sample uses the Network co-processor (NCP) architecture or Radio co-processor (RCP) architecture.

The sample is based on Zephyr’s OpenThread Co-Processor sample. However, it customizes Zephyr’s sample to the nRF Connect SDK requirements (for example, by increasing the stack size dedicated for the user application), and also extends it with several features:

  • Increased mbedTLS heap size.

  • Lowered main stack size to increase user application space.

  • No obsolete configuration options.

  • Vendor hooks for co-processor architecture allowing users to extend handled properties by their own, customized functionalities.

This sample supports optional Vendor hooks extension and logging extension, which can be turned on or off independently. See Configuration files for details.


The sample demonstrates using a co-processor target on the MCU to communicate with Userspace WPAN Network Daemon (wpantund) on Unix-like operating system. According to the co-processor architecture, the MCU part must cooperate with user higher layer process to establish the complete full stack application. The sample shows how to set up the connection between the co-processor and wpantund.

This sample comes with the full set of OpenThread functionalities enabled (CONFIG_OPENTHREAD_NORDIC_LIBRARY_MASTER).

Vendor hooks extension

The vendor hook feature extension allows you to define your own commands and properties for the Spinel protocol, and extend the standard set used in communication with the co-processor. Thanks to this feature, you can add new custom functionalities and manage them from host device by using serial interface - in the same way as the default functionalities.

For more detailed information about the vendor hooks feature and host device configuration, see Vendor hooks. For information about how to enable the vendor hook feature for this sample, see Activating the vendor hook feature.

Logging extension

This sample by default uses Spinel logging backend, which allows sending log messages to the host device using the Spinel protocol. This feature is very useful, because it does not require having separate interfaces to communicate with the co-processor through the Spinel protocol and collect log messages. Moreover, selecting the Spinel logging backend (by setting CONFIG_LOG_BACKEND_SPINEL) does not exclude using another backend like UART or RTT at the same time.

By default, the log levels for all modules are set to critical to not engage the microprocessor in unnecessary activities. To make the solution flexible, you can change independently the log levels for your modules, for the whole Zephyr system, and for OpenThread. Use the overlay-logging.conf overlay file as reference for this purpose.

FEM support


Software FEM support is not present on nRF53 Series devices yet. For now, it also cannot be combined with multiprotocol operation.

You can add support for the nRF21540 front-end module to the sample. See Radio front-end module (FEM) support for more information.

To add support for the nRF21540 FEM, add the provided dts-nrf21540-fem.overlay devicetree overlay file when building. The file is located in the samples/openthread/common folder. Make sure that the GPIOs in the file correspond to those in which your front-end module is connected.


You must add the provided overlay file if you use the nRF21540 EK. If you use the nRF21540 DK, build your application for the nrf21540dk_nrf52840 board. The devicetree for the nRF21540 DK already contains the required FEM configuration, so you do not need to add the overlay file.

See Set devicetree overlays for different ways of adding the overlay file.

The easiest way to add the file when building is to set it in the DTC_OVERLAY_FILE variable. However, doing so will override the default settings. For some boards, this sample requires additional overlay files, which are automatically included when building with the default settings. When you set the DTC_OVERLAY_FILE variable, you must specify all overlay files that are needed for building. Check the boards folder to see the additional overlay files.

Follow the instructions in Providing CMake options to specify the DTC_OVERLAY_FILE variable. For example, to build the sample from the command line for an nRF52833 DK with an attached nRF21540 EK, invoke the following command within the sample directory:

west build -b nrf52833dk_nrf52833 -- -DDTC_OVERLAY_FILE="boards/nrf52833dk_nrf52833.overlay;../common/dts-nrf21540-fem.overlay"

Alternatively, you can copy the contents of dts-nrf21540-fem.overlay to the board’s overlay file.

To add support for other front-end modules, add the respective overlay files in the same way.


The sample supports the following development kits for testing the network status:

Hardware platforms


Board name

Build target

nRF52840 DK




nRF52833 DK




nRF21540 DK




To test the sample, you need at least one development kit. Additional development kits programmed with the Co-processor sample can be used for the optional testing of network joining.

Moreover, the sample requires a Userspace higher layer process running on user’s device in order to communicate with the MCU co-processor part. This sample uses wpantund as reference.

User interface

All the interactions with the application are handled using serial communication.

You can interact with the sample through wpantund, using wpanctl commands. If you use the RCP architecture (see CONFIG_OPENTHREAD_COPROCESSOR_RCP), you can alternatively use ot-daemon or ot-cli with commands listed in OpenThread CLI Reference. See OpenThread POSIX applications for more information.

Both NCP and RCP support communication with the kit using Pyspinel commands.

You can use your own application instead of the ones listed above, provided that it supports the Spinel communication protocol.


This sample has Hardware Flow Control mechanism enabled by default in serial communication. When enabled, it allows devices to manage transmission by informing each other about their current state, and ensures more reliable connection in high-speed communication scenarios. In addition, the Co-processor sample by default reconfigures the baud rate to 1000000 bit/s.


See Configuring your application for information about how to permanently or temporarily change the configuration.

Check and configure the following library options that are used by the sample:

Configuration files

The sample provides predefined configuration files for typical use cases, and to activate sample extensions. You can find the configuration files in the root directory of the sample.

Specify the corresponding file names in the OVERLAY_CONFIG option when building. See Providing CMake options for instructions on how to add this option. For more information about using configuration overlay files, see Important Build System Variables in the Zephyr documentation.

The following configuration files are available:

  • overlay-vendor_hook.conf - Enables the vendor hooks extension. This file enables the vendor hooks feature and specifies the source file to use. See Activating the vendor hook feature for more information.

  • overlay-logging.conf - Enables the logging extension. This file configures different log levels for the sample, the Zephyr system, and OpenThread.

  • overlay-rcp.conf - Enables the RCP architecture. This file configures the sample to use the RCP architecture instead of the NCP architecture.

  • overlay-minimal_rcp.conf - Enables a minimal configuration that reduces the code size and RAM usage. This file enables the RCP architecture with basic functionality and optimizes stacks and buffer sizes. For more information, see Memory footprint optimization.

Building and running

Make sure to enable the OpenThread stack before building and testing this sample. See Thread for more information.

This sample can be found under samples/openthread/coprocessor in the nRF Connect SDK folder structure.

See Building and programming a sample application for information about how to build and program the application.

Activating the vendor hook feature

Handling of extension commands and properties is done through the vendor hook .cpp file, which is attached to the Co-processor sample during the linking.

To enable the feature:

  1. Provide the implementation of this file.

  2. Insert information about the file location in the CONFIG_OPENTHREAD_COPROCESSOR_VENDOR_HOOK_SOURCE field. This field is located in the overlay configuration file (see overlay-vendor_hook.conf). The inserted path must be relative to the Co-processor sample directory.

The Co-processor sample provides the vendor hook user_vendor_hook.cpp file in the src directory that demonstrates the proposed implementation of handler methods. You can either:

  • Use the provided user_vendor_hook.cpp file.

  • Provide your own implementation and replace the CONFIG_OPENTHREAD_COPROCESSOR_VENDOR_HOOK_SOURCE option value in the overlay file with the path to your file.

For information about how to test the vendor hook feature, see Testing vendor hooks after configuration.


After building the sample and programming it to your development kit, test it by performing the following steps:

  1. Connect the development kit’s SEGGER J-Link USB port to the PC USB port with an USB cable.

  2. Get the kit’s serial port name (for example, /dev/ttyACM0).

  3. Run and configure wpantund and wpanctl as described in Configuring wpantund.

  4. In the wpanctl shell, run the following command to check the kit state:

    wpanctl:leader_if> status

    The output will look similar to the following:

    leader_if => [
      "NCP:State" => "offline"
      "Daemon:Enabled" => true
      "NCP:Version" => "OPENTHREAD/gde3f05d8; NONE; Jul  7 2020 10:04:51"
      "Daemon:Version" => "0.08.00d (0.07.01-343-g3f10844; Jul  2 2020 09:07:40)"
      "Config:NCP:DriverName" => "spinel"
      "NCP:HardwareAddress" => [E8F947748F493141]

    This output means that NCP is offline.

  5. In the wpanctl shell, run the following command to set up a Thread network:

    wpanctl:leader_if> form "My_OpenThread_network"

    The output will look similar to the following:

    Forming WPAN "New_network" as node type "router"
    Successfully formed!

    This output means that the network was formed successfully.

  6. In the wpanctl shell, run the status command again to see that “My_OpenThread_network” was formed by NCP:

    wpanctl:leader_if> status

The final output will be similar to the following:

leader_if => [
  "NCP:State" => "associated"
  "Daemon:Enabled" => true
  "NCP:Version" => "OPENTHREAD/gde3f05d8; NONE; Jul  7 2020 10:04:51"
  "Daemon:Version" => "0.08.00d (0.07.01-343-g3f10844; Jul  2 2020 09:07:40)"
  "Config:NCP:DriverName" => "spinel"
  "NCP:HardwareAddress" => [E8F947748F493141]
  "NCP:Channel" => 26
  "Network:NodeType" => "leader"
  "Network:Name" => "My_OpenThread_network"
  "Network:XPANID" => 0x048CA9024CD7D40F
  "Network:PANID" => 0xDB92
  "IPv6:MeshLocalAddress" => "fd04:8ca9:24c:0:ebb8:4ef3:d96:c4bd"
  "IPv6:MeshLocalPrefix" => "fd04:8ca9:24c::/64"
  "com.nestlabs.internal:Network:AllowingJoin" => false

This output means that you have successfully formed the Thread network.

Testing network joining with more kits

Optionally, if you are using more than one kit, you can test the network joining process by completing the following steps:

  1. Connect the second kit’s SEGGER J-Link USB port to the PC USB port with an USB cable.

  2. Get the kit’s serial port name.

  3. Open a shell and run another wpantund process for the second kit as described in Configuring wpantund. Make sure to use the correct serial port name for the second kit (for example, /dev/ACM1) and a different network interface name (for example, joiner_if).

  4. Open another shell and run another wpanctl process for the second kit by using following command:

    wpanctl -I joiner_if
  5. In the wpanctl shell, run the following command to check the kit state:

    wpanctl:joiner_if> status

    The output will look similar to the following:

    joiner_if => [
       "NCP:State" => "offline"
       "Daemon:Enabled" => true
       "NCP:Version" => "OPENTHREAD/gde3f05d8; NONE; Jul  7 2020 10:04:51"
       "Daemon:Version" => "0.08.00d (0.07.01-343-g3f10844; Jul  2 2020 09:07:40)"
       "Config:NCP:DriverName" => "spinel"
       "NCP:HardwareAddress" => [E8F947748F493141]

    This output means that NCP is offline.

  6. In the wpanctl shell of the first kit, run the following command to get the network key from the leader kit:

    wpanctl:leader_if> get Network:Key

    The output will look similar to the following:

    Network:Key = [2429EFAF21421AE3CB30B9204016EDC9]
  7. Copy the network key form the output and set it on the second (joiner) kit by running the following command in the second kit’s wpanctl shell:

    wpanctl:joiner_if> set Network:Key 2429EFAF21421AE3CB30B9204016EDC9
  8. In the second kit’s wpanctl shell, run the following command to scan your neighborhood and find the network formed with the leader kit:

    wpanctl:joiner_if> scan

    The output will look similar to the following:

      | Joinable | NetworkName             | PAN ID | Ch | XPanID           | HWAddr           | RSSI
    1 |       NO | "OpenThread"            | 0xABCD | 11 | DEAD00BEEF00CAFE | 621757E184CEF8E5 |  -82
    2 |       NO | "My_OpenThread_network" | 0xF54B | 13 | 77969855F947758D | 62AAC622CB3ACD9F |  -34

    The first column is the network ID number. For the network formed for this testing procedure, the ID equals 2.

  9. In the second kit’s wpanctl shell, run the following command with the network ID as variable to join your joiner kit to the network:

    wpanctl:joiner_if> join 2

    The output will look similar to the following:

    Joining WPAN "My_OpenThread_network" as node type "end-device", channel:13, panid:0xF54B, xpanid:0x77969855F947758D [scanned network index 2]
    Successfully Joined!

This output means that the joiner kit node has successfully joined the network.


This sample uses the following Zephyr libraries: