SMP Server Sample


This sample application implements a Simple Management Protocol (SMP) server. SMP is a basic transfer encoding for use with the MCUmgr management protocol. For more information about MCUmgr and SMP, please see Device Management.

This sample application supports the following mcumgr transports by default:

  • Shell

  • Bluetooth

  • UDP

smp_svr enables support for the following command groups:

  • fs_mgmt

  • img_mgmt

  • os_mgmt

  • stat_mgmt

  • shell_mgmt


  • The MCUboot bootloader is required for img_mgmt to function properly. More information about the Device Firmware Upgrade subsystem and MCUboot can be found in MCUboot.

  • The mcumgr command-line tool only works with Bluetooth Low Energy (BLE) on Linux and macOS. On Windows there is no support for Device Firmware Upgrade over BLE yet.


Installing the mcumgr cli

To interact remotely with the management subsystem on a device, we need to have the mcumgr installed. Follow the instructions in the Command-line Tool section of the Management subsystem documentation.

Building a BLE Controller


This section is only relevant for Linux users

If you want to try out Device Firmware Upgrade (DFU) over the air using Bluetooth Low Energy (BLE) and do not have a built-in or pluggable BLE radio, you can build one and use it following the instructions in Using the controller with BlueZ.

Building and flashing MCUboot

The below steps describe how to build and run the MCUboot bootloader. Detailed instructions can be found in the MCUboot documentation page.

The Zephyr port of MCUboot is essentially a normal Zephyr application, which means that we can build and flash it like normal using west, like so:

west build -b <board> -d build_mcuboot bootloader/mcuboot/boot/zephyr
west flash -d build_mcuboot

Substitute <board> for one of the boards supported by the sample, see sample.yaml.

Building the sample application

The below steps describe how to build and run the smp_svr sample in Zephyr. The smp_svr sample comes in different flavours.

To build the bluetooth sample:

west build \
   -b nrf52dk_nrf52832 \
   samples/subsys/mgmt/mcumgr/smp_svr \
   -- \

Signing the sample image

A key feature of MCUboot is that images must be signed before they can be successfully uploaded and run on a target. To sign images, the MCUboot tool imgtool can be used.

To sign the sample image we built in a previous step:

west sign -t imgtool -- --key bootloader/mcuboot/root-rsa-2048.pem

The above command creates an image file called zephyr.signed.bin in the build directory.

For more information on image signing and west sign, see the Signing Binaries documentation.

Flashing the sample image

Upload the zephyr.signed.bin file from the previous to image slot-0 of your board. See Flash map for details on flash partitioning.

To upload the initial image file to an empty slot-0, we simply use west flash like normal. west flash will automatically detect slot-0 address and confirm the image.

west flash --bin-file build/zephyr/zephyr.signed.bin

We need to explicitly specify the signed image file, otherwise the non-signed version will be used and the image won’t be runnable.

Sample image: hello world!

The smp_svr app is ready to run. Just reset your board and test the app with the mcumgr command-line tool’s echo functionality, which will send a string to the remote target device and have it echo it back:

sudo mcumgr --conntype ble --connstring ctlr_name=hci0,peer_name='Zephyr' echo hello


The mcumgr command-line tool requires a connection string in order to identify the remote target device. In the BT sample we use a BLE-based connection string, and you might need to modify it depending on the BLE controller you are using.


In the following sections, examples will use <connection string> to represent the --conntype <type> and --connstring=<string> mcumgr parameters.

Device Firmware Upgrade (DFU)

Now that the SMP server is running on your board and you are able to communicate with it using mcumgr, you might want to test what is commonly called “OTA DFU”, or Over-The-Air Device Firmware Upgrade. This works for both BT and UDP.

The general sequence of a DFU process is as follows:

  • Build an MCUboot enabled application, see Building the sample application

  • Sign the application image, see Signing the sample image

  • Upload the signed image using mcumgr

  • Listing the images on the device using mcumgr

  • Mark the uploaded image for testing using mcumgr

  • Reset the device remotely using mcumgr

  • Confirm the uploaded image using mcumgr (optional)

Direct image upload and Image mapping to MCUboot slot

Currently the mcumgr supports, for direct upload, 4 target images, of which first two are mapped into MCUboot primary (slot-0) and secondary (slot-1) respectively.

The mcumgr image upload command may be provided optional -e -n <image> parameter that will select target image for upload; when parameter is no provided, 0 is assumed, which means “default behaviour”, and it performs upload to the “image-1”, the MCUboot secondary slot.

For clarity, here is DTS label to slot to <image> translation table:

DTS label


-n <image>






0, 1






The -e option actually means “no erase”, and is provided to the mcumgr to prevent it from sending erase command to target, before updating image. The options is always needed when -n is used for image selection, as the erase command is hardcoded to erase slot-1 (“image-1”), regardless of which slot is uploaded at the time.

Upload the signed image

To upload the signed image, use the following command:

sudo mcumgr <connection string> image upload build/zephyr/zephyr.signed.bin


At the beginning of the upload process, the target might start erasing the image slot, taking several dozen seconds for some targets. This might cause an NMP timeout in the management protocol tool. Use the -t <timeout-in-seconds option to increase the response timeout for the mcumgr command line tool if this occurs.

List the images

We can now obtain a list of images (slot-0 and slot-1) present in the remote target device by issuing the following command:

sudo mcumgr <connection string> image list

This should print the status and hash values of each of the images present.

Test the image

In order to instruct MCUboot to swap the images we need to test the image first, making sure it boots:

sudo mcumgr <connection string> image test <hash of slot-1 image>

Now MCUBoot will swap the image on the next reset.


There is not yet any way of getting the image hash without actually uploading the image and getting the hash by using the image list command of mcumgr.

Reset remotely

We can reset the device remotely to observe (use the console output) how MCUboot swaps the images:

sudo mcumgr <connection string> reset

Upon reset MCUboot will swap slot-0 and slot-1.

Confirm new image

The new image is now loaded into slot-0, but it will be swapped back into slot-1 on the next reset unless the image is confirmed. To confirm the new image:

sudo mcumgr <connection string> image confirm

Note that if you try to send the very same image that is already flashed in slot-0 then the procedure will not complete successfully since the hash values for both slots will be identical.

Download file from File System

SMP server supports downloading files from File System on device via mcumgr. This is useful with FS log backend, when files are stored in non-volatile memory. Build and flash both MCUboot and smp_svr applications and then use mcumgr with download command, e.g.:

mcumgr --conntype serial --connstring='dev=/dev/ttyACM0,baud=115200' \
fs download /lfs/log.0000 ~/log.txt