Cellular: SMP Server

This sample is a reference implementation to use MCUboot recovery mode or serial SMP server mode for external image update.


The sample supports the following development kits:

Hardware platforms


Board name

Board target

nRF9160 DK





The sample supports the mcuboot shell commands for checking image information and a new activated image will be confirmed automatically.

Connecting nRF9160 SiP to nRF52840 SoC

On the nRF9160 DK, you can configure the hardware interface between the nRF9160 SiP and nRF52840 SoC to use serial connection. In this sample, the nRF9160 SiP uses UART2 and nRF52840 SoC uses UART1. The reset line is needed for activating MCUboot recovery mode.

   | nRF9160     |                            |    nRF52840    |
   | UART 2      |                            | UART1          |
   | RTS   P0.17 | -- nRF interface line 0 -- | P0.17  CTS     |
   |       P0.18 | -- nRF interface line 1 -- | P0.20          |
   |       P0.19 | -- nRF interface line 2 -- | P0.15          |
   | RX    P0.21 | -- nRF interface line 3 -- | P0.22  TX      |
   | CTS   P0.22 | -- nRF interface line 4 -- | P1.04  RTS     |
   | TX    P0.23 | -- nRF interface line 5 -- | P1.02  RX      |
   |       COEX0 | -- nRF interface line 6 -- | P1.13          |
   |       COEX1 | -- nRF interface line 7 -- | P1.11          |
   |       COEX2 | -- nRF interface line 8 -- | P1.15          |
   |       P0.24 | -- nRF interface line 9 -- | P0.18 (nRESET) | (in v0.14.0 or later)

SMP and MCUmgr protocols are used to communicate over UART.


See Configuring and building an application for information about how to permanently or temporarily change the configuration.

Configuration files

The sample supports UART1 connection for the nRF9160 DK with or without MCUboot recovery mode. The nRF52840 SoC needs to enable UART1 on the devicetree using the following configuration files and recovery mode overlay files:

  • overlay-serial.conf - Defines the MCUmgr server configuration with SMP serial transport for UART1. This requires an additional devicetree overlay file nrf9160dk_nrf52840_mcumgr_srv.overlay.

  • nrf9160dk_nrf52840_recovery.overlay - Devicetree overlay file that enables resetting of the MCUboot recovery mode.

MCUboot configuration

The sample has defined configuration and device tree overlay files for MCUboot that are available in the sample folder:

  • child_image/mcuboot.conf - Defines the MCUboot recovery mode.

  • child_image/mcuboot/boards/nrf9160dk_nrf52840_0_14_0.overlay - Define UART1 for MCUmgr.

The MCUboot configuration is enabled automatically at build.

Partition management

The sample has a static partition management file pm_static_nrf9160dk_nrf52480.yml to enable MCUboot secondary slot usage, which is a requirement.


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

When built as firmware image for a board target with the */ns variant, the sample has Cortex-M Security Extensions (CMSE) enabled and separates the firmware between Non-Secure Processing Environment (NSPE) and Secure Processing Environment (SPE). Because of this, it automatically includes the Trusted Firmware-M (TF-M). To read more about CMSE, see Processing environments.

To build the sample, follow the instructions in Configuring and building an application for your preferred building environment. See also Programming an application for programming steps and Testing and optimization for general information about testing and debugging in the nRF Connect SDK.


In the nRF repositories, building with sysbuild is enabled by default.


Before building the sample, make sure the PROG/DEBUG switch is set to nRF52.

MCUboot recovery mode

west build --pristine -b nrf9160dk/nrf52840 -- -DEXTRA_DTC_OVERLAY_FILE="nrf9160dk_nrf52840_recovery.overlay"

MCUmgr server image management

west build --pristine -b nrf9160dk/nrf52840 -- -DEXTRA_CONF_FILE="overlay-serial.conf" -DEXTRA_DTC_OVERLAY_FILE="nrf9160dk_nrf52840_mcumgr_srv.overlay"


After programming the sample to your development kit, complete the following steps to test it:

  1. Connect the kit to the computer using a USB cable. The kit is assigned a COM port (Windows) or ttyACM device (Linux), which is visible in the Device Manager.

  2. Connect to the kit with a terminal emulator (for example, nRF Connect Serial Terminal). See Testing and optimization for the required settings and steps.

  3. Observe that the sample starts.

  4. Open a terminal connection for the nRF52840 SoC (VCOM1), in Linux /dev/ttyACM1, and call the mcuboot command on the shell. You can see the following output on the terminal:

    uart:~$ mcuboot
    swap type: none
    confirmed: 1
    primary area (2):
       version: 1.0.0+0
       image size: 70136
       magic: unset
       swap type: none
       copy done: unset
       image ok: unset
    failed to read secondary area (5) header: -5


The sample uses the following secure firmware component: