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Exercise 6 – FOTA over Bluetooth LE via nRF Cloud

Introduction

In the previous exercise, you delivered a firmware update over Bluetooth LE from a local file copied manually from the development machine to your phone. In this exercise, you source it from the cloud using nRF Cloud powered by Memfault instead: you upload a signed release to the cloud, activate it for your fleet, and the device pulls it over the existing Bluetooth LE connection. The workflow you would use to fix an issue in the field without physical access to the device.

For product makers, this is what keeps a shipped product maintainable and future-proof. You can fix a bug or ship a new feature to devices already in the field over the Bluetooth LE link your companion app already uses. Because each device reports its version and update history back to nRF Cloud, you can stage a release to one or more cohorts, confirm it landed, and expand from there. And since the flow builds on open-source iOS and Android libraries, it can live inside your own branded app, rather than using nRF Connect Device Manager mobile app.

The image is transferred from a smartphone to the device using the Simple Management Protocol (SMP); MCUboot installs it after reboot. For the device to appear in the nRF Cloud fleet with its version and update history, it also runs the Memfault Diagnostic Service (MDS), which carries Memfault data to the cloud over the same connection.

Architecture diagram of Exercise 6 – FOTA over Bluetooth LE via nRF Cloud (How a firmware update reaches a device in the field over Bluetooth LE via nRF Cloud)

For this exercise, you can use any development kit that supports Bluetooth LE.

	nRF91XX DKs	nRF54L Series DK	nRF5340 DK	nRF52 Series DK (nRF52840 DK/ nRF52833 DK / …)	nRF7002 DK
Bluetooth LE	❌	✅	✅	✅	✅

Exercise steps

This exercise is available in v3.4.0 and above. The base code of this exercise l9/l9_e6 starts from the previous Exercise 5 (Exercise 5 – FOTA over Bluetooth LE), the LED Button Service (LBS) firmware, which already has MCUboot enabled in sysbuild.conf and FOTA over Bluetooth LE enabled in prj.conf (CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU).

In this exercise, you will add the nRF Cloud release loop on top.

1. Add the cloud configuration in prj.conf

1.1 Preserve Bluetooth bonds across the upgrade.

 CONFIG_MCUMGR_GRP_ZBASIC_STORAGE_ERASE=n

Copy

 CONFIG_MCUMGR_GRP_ZBASIC_STORAGE_ERASE=n

Kconfig

Because the device stores settings in ZMS/NVS, the OTA DFU sample would otherwise let the Device Manager app erase the settings partition (your bonds) during an update.

1.2 Enable the Memfault SDK, project key, and software type.

CONFIG_MEMFAULT=y
CONFIG_MEMFAULT_NCS_PROJECT_KEY="your-project-key-here"
CONFIG_MEMFAULT_LOG_LEVEL_INF=y
CONFIG_MEMFAULT_NCS_FW_TYPE="main"

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CONFIG_MEMFAULT=y
CONFIG_MEMFAULT_NCS_PROJECT_KEY="your-project-key-here"
CONFIG_MEMFAULT_LOG_LEVEL_INF=y
CONFIG_MEMFAULT_NCS_FW_TYPE="main"

Kconfig

Keep in mind that the CONFIG_MEMFAULT_NCS_FW_TYPE="main" must match the release’s Software Type set in step 7.

Note

For the project key, you need to have an nRF Cloud account and create a new project.

If you don’t have an nRF Cloud, navigate to nRF Cloud and create a free account, with this developer account, you can connect up to 10 devices. Once you have an account, create a new project and copy the project key. You will need it for step 1.2. The project key must be 32 characters and written as a string in prj.conf, enclosed in double quotes.

1.3 Enable MDS so the device’s data reaches the cloud over Bluetooth LE.

CONFIG_BT_MDS=y
CONFIG_BT_PRIVACY=y

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CONFIG_BT_MDS=y
CONFIG_BT_PRIVACY=y

Kconfig

1.4 Provide the device serial from the hardware UID.

CONFIG_HW_ID_LIBRARY=y
CONFIG_HW_ID_LIBRARY_SOURCE_DEVICE_ID=y

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CONFIG_HW_ID_LIBRARY=y
CONFIG_HW_ID_LIBRARY_SOURCE_DEVICE_ID=y

Kconfig

1.5 Set the firmware version to 0.0.1

CONFIG_MEMFAULT_NCS_FW_VERSION_STATIC=y
CONFIG_MEMFAULT_NCS_FW_VERSION="0.0.1"
CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION="0.0.1"

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CONFIG_MEMFAULT_NCS_FW_VERSION_STATIC=y
CONFIG_MEMFAULT_NCS_FW_VERSION="0.0.1"
CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION="0.0.1"

Kconfig

CONFIG_MEMFAULT_NCS_FW_VERSION and CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION must match.

2. Add the MDS code in main.c

Now we will move from prj.conf to main.c and make the necessary changes to add the MDS, which includes bluetooth/services/mds.h, track the encrypted connection, request BT_SECURITY_L2 on connect (and clear it on disconnect), record the connection once encrypted, define the MDS access gate, and register the MDS callback before bt_enable(). The pairing used here is Just Works (no PIN) for simplicity.

2.1 Include the Memfault Diagnostic Service header

#include <bluetooth/services/mds.h>

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#include <bluetooth/services/mds.h>

2.2 Track the connection that is allowed to access MDS

#if defined(CONFIG_BT_MDS)
static struct bt_conn *mds_conn;
#endif

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#if defined(CONFIG_BT_MDS)
static struct bt_conn *mds_conn;
#endif

2.3 Request an encrypted link. MDS data may only be accessed over an encrypted (and, here, bonded) connection. Request an encrypted link when a central connects (in connected())

#if defined(CONFIG_BT_MDS)
	bt_conn_set_security(conn, BT_SECURITY_L2);
#endif

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#if defined(CONFIG_BT_MDS)
	bt_conn_set_security(conn, BT_SECURITY_L2);
#endif

,and clear the tracked connection when it closes (in disconnected()):

#if defined(CONFIG_BT_MDS)
	if (conn == mds_conn) {
		mds_conn = NULL;
	}
#endif

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#if defined(CONFIG_BT_MDS)
	if (conn == mds_conn) {
		mds_conn = NULL;
	}
#endif

2.4 Once the link is encrypted, allow this connection to access MDS.

#if defined(CONFIG_BT_MDS)
	if (!err && level >= BT_SECURITY_L2 && !mds_conn) {
		mds_conn = conn;
	}
#endif

Copy

#if defined(CONFIG_BT_MDS)
	if (!err && level >= BT_SECURITY_L2 && !mds_conn) {
		mds_conn = conn;
	}
#endif

2.5 Only allow the paired/encrypted connection to access MDS

#if defined(CONFIG_BT_MDS)
static bool mds_access_enable(struct bt_conn *conn)
{
	if (mds_conn && (conn == mds_conn)) {
		return true;
	}

	return false;
}

static const struct bt_mds_cb mds_cb = {
	.access_enable = mds_access_enable,
};
#endif

Copy

#if defined(CONFIG_BT_MDS)
static bool mds_access_enable(struct bt_conn *conn)
{
	if (mds_conn && (conn == mds_conn)) {
		return true;
	}

	return false;
}

static const struct bt_mds_cb mds_cb = {
	.access_enable = mds_access_enable,
};
#endif

2.6 Register the MDS access callback before enabling Bluetooth LE

#if defined(CONFIG_BT_MDS)
	err = bt_mds_cb_register(&mds_cb);
	if (err) {
		printk("Memfault Diagnostic service callback registration failed (err %d)\n", err);
		return 0;
	}
#endif

Copy

#if defined(CONFIG_BT_MDS)
	err = bt_mds_cb_register(&mds_cb);
	if (err) {
		printk("Memfault Diagnostic service callback registration failed (err %d)\n", err);
		return 0;
	}
#endif

3. Build and flash the initial firmware (0.0.1). Add a build configuration with Use sysbuild enabled, Build, then Flash (programs MCUboot + the app). Reset and confirm advertising.

4. Upload the symbol file for 0.0.1. Open the web portal of nRF Cloud → Software → Symbol Files → upload build/<app_name>/zephyr/zephyr.elf so crash data from this version can be symbolicated.

5. Connect and verify data is flowing.

First, open nRF Connect Device Manager app (which will act as a Bluetooth LE gateway) and connect to the Nordic_LBS device to allow the device to connect to nRF Cloud via the gateway and report it’s current firmware version.

Then, open nRF Cloud web portal ,In nRF Cloud check Data Ingestion → Processing Log and that the device now appears in Fleet → Devices running 0.0.1.

6. Create a new firmware version (0.0.2).

6.1 Bump both version strings to 0.0.2 (this is where a real fix would go). In our simple exercise we will just bump up the version number in prj.conf

CONFIG_MEMFAULT_NCS_FW_VERSION="0.0.2"
CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION="0.0.2"

Copy

CONFIG_MEMFAULT_NCS_FW_VERSION="0.0.2"
CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION="0.0.2"

Kconfig

6.2 Build but do not flash — the build produces the signed dfu_application.zip, which can be found in the build/ directory

6.3 Upload the new zephyr.elf for 0.0.2 to Software → Symbol Files. same as we did in step 4.

7. Create and activate an OTA release in nRF Cloud.

7.1 Create 0.0.2 release in nRF Cloud by heading to Software → OTA Releases → Create Release . In the Create Release window, set the Version to 0.0.2 relase and click on Create

7.2 Inside the newly created release, click on “Add an OTA payload to Release”

In the Add OTA Payload window:

Specify your DK’s Hardware Version: E.g. nrf54l15dk, nrf5340dk , etc..

Software Type: main, which must match CONFIG_MEMFAULT_NCS_FW_TYPE in prj.conf; nRF Cloud ties the DK hardware types to main, and a mismatch makes the device report “up to date” .

upload dfu_application.zip found in the build/ directory, and click Add.

7.3 Activate release. Click on Activate → Cohort default, rollout Normal.

8. Install the update over Bluetooth LE

Android

8.1 On your Android phone, Open nRF Connect Device Manager (no login/account needed — the device’s project key drives the cloud association) and connect to the device.

8.2 On first connection your phone shows a pairing prompt; with Just Works pairing you simply acknowledge/accept it (there is no PIN to enter)

Once paired, observe the nRF Cloud status, which should indicate that the OTA status is SUPPORTED and the Observability status is STREAMING.

8.3 Switch to the Image tab

Image tab → Check for Updates → Download . This will download the new firmware image from nRF Cloud and prepare to be sent to the device

The release notes are empty simply because we didn’t fill them in step 7.1.

Once the new firmware image is downloaded, press Start and select Confirm Only. The transfer will take some time to finish . On “UPLOAD COMPLETE” the device reboots and MCUboot installs the image.

iOS

9. Verification.

9.1 Reconnect to the DK using nRF Connect Device Manager(Press back to go to the scan tab, then press on Nordi_LBS to reconnect). You should observe now that the SW Version of the firmware running on the DK is 0.0.2.

9.2 Switch to the Image tab and press on Check for Update. Since 0.0.2 is the latest release created in nRF Cloud, the app will report that the device is up to date.

9.3 In nRF Cloud Fleet → Devices confirm 0.0.2; the device Timeline shows the reboot and the 0.0.1 → 0.0.2 change.

Wrap-up

The OTA transfer reused the same Bluetooth LE connection as the diagnostics service; its throughput depends on the connection parameters (interval, DLE, MTU). You have practiced the full field-update loop — observe → diagnose → fix → deploy — without physical access to the device.

Because you set CONFIG_MCUMGR_GRP_ZBASIC_STORAGE_ERASE=n, the bond survived the upgrade — after the device rebooted into 0.0.2, your phone reconnected and re-encrypted without re-pairing.

Troubleshooting

“Check for Updates” says the device is already up to date. The release’s Software Type must match CONFIG_MEMFAULT_NCS_FW_TYPE (main) and the Hardware version must match what the device reports (CONFIG_MEMFAULT_NCS_HW_VERSION, e.g. nrf54l15dk / nrf5340dk), and the device must be in the activated release’s cohort (default). Check Fleet → Devices to see exactly what the device reports.
Connection fails right after re-flashing (Security failed ... err 2 in the log). Flashing with mass-erase wipes the device’s bonds, but your phone still has the old bond. Forget the device in your phone’s Bluetooth settings (and toggle Bluetooth off/on), then reconnect to re-pair. (A normal OTA upgrade does not need this — bonds persist, see step 1.1.)
No serial output. On the nRF54L15 and nRF5340 DKs the application console is on VCOM1, the second of the two J-Link serial ports.

The full solution is available in the course repository in the directory l9/l9_e6_sol. Note that you still need to update the CONFIG_MEMFAULT_NCS_PROJECT_KEY in prj.conf with your own project key for the solution to work.

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nRF Connect SDK Intermediate

Exercise 6 – FOTA over Bluetooth LE via nRF Cloud

Introduction

Exercise steps

Note

Wrap-up

Troubleshooting

Switch language?

Change summary

What's new in the latest version

General updates for nRF Connect SDK v3.4.0

General updates

Bluetooth LE updates

MCUboot & Partition Manager