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Modem Firmware Update (FOTA)

Nordic Semiconductor's cellular SoCs contain two independently-updateable firmware components. To update them with Memfault, we use a separate Memfault Project for the modem firmware:

ComponentUpdated viaMemfault Project
Application firmwareMCUboot swapYour app project
Modem firmwarenRF modem bootloaderA dedicated modem project
Prerequisites

Step 1: Create a Modem Firmware Project​

  1. Log in to app.memfault.com.
  2. Create a new project (e.g. my-product-modem).
  3. Copy the Project Key from Settings → Project Keys. You will need this in your firmware's prj.conf.

Step 2: Configure Modem Project Key​

Add the following to your prj.conf:

prj.conf
# Enable built-in modem FOTA support (Memfault SDK ≥ 1.39.0)
CONFIG_MEMFAULT_FOTA_MODEM_UPDATE=y

# Project key for the dedicated modem Memfault project
CONFIG_MEMFAULT_FOTA_MODEM_PROJECT_KEY="your-modem-project-key-here"

The optional CONFIG_MEMFAULT_FOTA_MODEM_SOFTWARE_TYPE (default "mfw") can be set if you used a different --software-type when uploading.

info

If you are using nRF Cloud CoAP support (CONFIG_MEMFAULT_USE_NRF_CLOUD_COAP=y) and are on NCS >v3.4.0, CONFIG_MEMFAULT_FOTA_MODEM_PROJECT_KEY is optional, and you can instead set the modem Project Key at runtime via the Device Shadow with the memfaultModemKey field. When set via the following JSON, this value will override the value of CONFIG_MEMFAULT_FOTA_MODEM_PROJECT_KEY:

{ "desired": { "control": { "memfaultModemKey": "your-modem-project-key" } } }

See the Device Shadow page for more details on configuring the shadow.

Additionally, see the nRF Cloud CoAP FOTA sample in NCS for an example of reading the shadow from the device and reporting the updated state to nRF Cloud.

Step 3: Integrate into Your FOTA Loop​

Choose the integration path that fits your application.

Option A: Automatic (via existing periodic FOTA check)​

For automatic modem FOTA, set CONFIG_MEMFAULT_PERIODIC_FOTA_CHECK=y. The periodic upload handler will call memfault_zephyr_fota_start() and memfault_zephyr_fota_modem_start() on a regular interval, performing app and modem updates when deployed.

Option B: Manual​

Call the FOTA functions directly at a time of your choosing:

// Check for app update first; if none pending, also checks for modem update:
int rv = memfault_zephyr_fota_start();

// Or check for a modem update only:
rv = memfault_zephyr_fota_modem_start();

Step 4: Upload Modem Firmware to Memfault​

Nordic ships modem firmware as delta packages - a binary that upgrades from one specific version to the next. Download the modem firmware package for your target device:

The delta update filename contains the source and target versions, e.g. mfw_nrf91x1_update_from_2.0.3_to_2.0.4.bin will update from mfw_nrf91x1_2.0.3 to mfw_nrf91x1_2.0.4. This file will be uploaded directly to Memfault without modification.

Full vs. delta updates​

Delta packages are smaller and faster to download, but each one only updates between two specific versions, so devices that fall behind (or that skip a release) may need several delta updates applied in sequence to reach the latest version. Full modem firmware packages (~2.1 MB) can update a device from any version in one step, at the cost of a larger download and requiring external flash storage on the device to stage the image. Use full updates when devices may be several versions behind, or when you'd rather not maintain a chain of delta releases; use delta updates to minimize download size for devices that update on a regular cadence.

To support full modem updates, add the following to your prj.conf:

prj.conf
# Enable full modem update support, in addition to CONFIG_MEMFAULT_FOTA_MODEM_UPDATE
CONFIG_MEMFAULT_FOTA_FULL_MODEM_UPDATE=y

# Required by CONFIG_MEMFAULT_FOTA_FULL_MODEM_UPDATE
CONFIG_NRF_CLOUD_FOTA_FULL_MODEM_UPDATE=y

CONFIG_MEMFAULT_FOTA_FULL_MODEM_UPDATE is only available on nRF91-series devices, and requires CONFIG_MEMFAULT_FOTA_MODEM_UPDATE=y (Step 2, above) and CONFIG_LTE_LINK_CONTROL=y to also be enabled. CONFIG_NRF_CLOUD_FOTA_FULL_MODEM_UPDATE requires external flash of at least 4MB, configured as the FMFU storage partition in your board's devicetree. See Nordic's full modem firmware update documentation for details on setting up the storage partition.

To upload the modem firmware to Memfault, create a new Delta Release (for delta updates) or Release (for full updates) in your modem firmware project. Match the Hardware Version field to the hw_version you use when uploading device data to Memfault (e.g. nrf9160), and see note below about the Software Type field.

Delta release​

Set the From Version and To Version fields to match the source and target versions in the modem firmware filename, and upload the .bin file as the release payload.

You'll likely need to create a new Hardware Version in the modem project before uploading the release artifact. Navigate to Settings → Hardware Versions:

Creating a new hardware version for the modem project

Preferably, you can upload the release payload using the Memfault CLI, using --delta-from and --delta-to to record the source and target versions and create a delta release:

memfault --org-token YOUR_ORG_TOKEN \
  --org YOUR_ORG --project YOUR_MODEM_PROJECT \
  upload-ota-payload \
  --hardware-version YOUR_HW_VERSION \
  --software-type mfw \
  --delta-from mfw_nrf91x1_2.0.3 \
  --delta-to mfw_nrf91x1_2.0.4 \
  mfw_nrf91x1_update_from_2.0.3_to_2.0.4.bin

This both creates the new Delta Release, and uploads the payload to the Release.

Full release​

Extract firmware.update.image.cbor from the modem firmware ZIP file, and upload it as a Full Release payload, passing --software-version with the target version (this is the same version reported by the device in AT+CGMR):

memfault --org-token YOUR_ORG_TOKEN \
  --org YOUR_ORG --project YOUR_MODEM_PROJECT \
  upload-ota-payload \
  --hardware-version YOUR_HW_VERSION \
  --software-type mfw \
  --software-version mfw_nrf9160_1.3.7 \
  firmware.update.image.cbor
Choose your software_type string once and use it consistently

mfw is the recommended convention and matches the SDK default. The value you upload must match CONFIG_MEMFAULT_FOTA_MODEM_SOFTWARE_TYPE on the device (which defaults to "mfw").

Activate the release on the default cohort to begin rolling it out.

Verification/Testing​

You can trigger a manual modem-only FOTA from the shell with the mflt fota_modem command:

uart:~$ mflt fota_modem
[00:01:06.124,755] <inf> mflt: Checking modem FOTA (current version: mfw_nrf91x1_2.0.3)
[00:01:06.524,902] <dbg> mflt: memfault_platform_log: DNS lookup for device-nrf.memfault.com = 44.206.80.55
[00:01:10.440,551] <dbg> mflt: memfault_platform_log: OTA check w/ device info: serial=xxx, hardware=nrf9151dk, software_type=mfw, software_version=mfw_nrf91x1_2.0.3
[00:01:13.656,463] <inf> mflt: FOTA Update Available. Starting Download with URL: https://...
[00:01:13.657,348] <inf> mflt: FOTA In Progress
...
# device will reboot and apply modem firmware update, which takes about 2 minutes to complete

After reboot, confirm the new modem version:

uart:~$ at AT+CGMR
mfw_nrf91x1_2.0.4
OK

If modem firmware is up to date, the logs will indicate it:

uart:~$ mflt fota_modem
[00:07:30.581,787] <inf> mflt: Checking modem FOTA (current version: mfw_nrf91x1_2.0.4)
[00:07:31.053,741] <dbg> mflt: memfault_platform_log: DNS lookup for device-nrf.memfault.com = 54.172.47.91
[00:07:34.266,632] <dbg> mflt: memfault_platform_log: OTA check w/ device info: serial=xxx, hardware=nrf9151dk, software_type=mfw, software_version=mfw_nrf91x1_2.0.4
[00:07:36.568,054] <inf> mflt: Modem firmware is up to date
Modem firmware downgrades

While possible, downgrading modem firmware via Memfault OTA is not recommended. Nordic does not publish reverse-direction delta packages: downgrades are only possible over-the-air via full modem update.

To revert to a previous modem version for testing, download the previous modem firmware package, and flash it appropriately. You can use either the nRF Connect for Desktop app, or nrfutil command line app like so:

# install the "91" nrfutil command if not already installed
❯ nrfutil install 91
# perform the modem downgrade
❯ nrfutil 91 modem-firmware-upgrade --firmware ~/Downloads/mfw_nrf91x1_2.0.3.zip --verify --serial-number 1051243117

Troubleshooting​

SymptomLikely cause
modem_info_string_get returns errorLTE not yet attached when the FOTA check runs
OTA check returns 0 (no update) but release is activatedVerify software_type and software_version reported by the device match what was uploaded; check the Processing Log
fota_download_any returns -ENOTSUPCONFIG_DFU_TARGET_MODEM_DELTA not selected (defaults y on nRF91X; check west build -t menuconfig)
Download starts but device reports wrong version after rebootFor delta updates: the source version in the filename must match the modem firmware currently installed on the device
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