Over the Air Updates

Over the Air Updates#

Over the Air (OTA) updates are a way to update the firmware of a device remotely. This is a mandatory feature for any IoT device. The device must be able to update its firmware without any physical user intervention.

flownexus implements OTA updates according to the LwM2M protocol. The LwM2M protocol specifies how to update the firmware of a device. The OTA process is implemented by sending a link to a firmware via LwM2M object 5/0/1 - Package URI. This method is called Pull via HTTP(s) and is faster, compared to a transfer via CoAP. Updates via CoAP blockwise transfer to download the firmware are not supported.

A https server is usually be hosted under a subdomain. The default is https://fw.flownexus.org. This makes it easy to use a self-signed certificate for the https server. For details, check chapter Setup a Virtual Server.

More information about a possible firmware implementation can be found in the lwm2m_client firmware sample at flownexus/simulation/lwm2m_client/src/firmware_update.c.

Note

Firmware Updates are implemented in the LwM2M server and the example firmware. A set up a PKI with self-signed certificates is required for the server to communicate with the device via https. This setup will be described in upcoming releases shortly.

Update process of a Firmware#

The update process is described in detail in the LwM2M core specification v1.1.1 Chapter E.6 LwM2M Object: Firmware Update. This chapter summarizes the update process:

  1. flownexus sends a link to the firmware to the device via LwM2M object 5/0/1 - Package URI. It is a relative link to the firmware on the server, e.g. /binaries/v0.1.0.bin. The host https://fw.flownexus.org is fixed in firmware.

  2. The device downloads the firmware from the server via http(s) and sets the state to STATE_DOWNLOADING.

  3. The device sets the state to STATE_DOWNLOADED after the download is complete.

  4. flownexus executes the command 5/0/2 - Update to the device.

  5. The device sets the state to STATE_UPDATING upon receiving the command.

  6. The device updates the firmware, usually by performing a reboot.

  7. The device registers and sends the firwmare version to flownexus via resource Firmware Version - 3/0/3. Depending if the update was successful or not, flownexus sets the result and state of the update in the database accordingly.

This process ensures that errors during the update process are handled and communicated to the backend.

States of a OTA Update#

There are 4 device states during an OTA update. flownexus tracks the state of the device during the update process in the database (FirmwareUpdate table). Once the update is completed (failed or successful), the state is set always set to STATE_IDLE.

Device States during an OTA Update#

State

Description

STATE_IDLE

device is idle

STATE_DOWNLOADING

device is downloading

STATE_DOWNLOADED

download is complete

STATE_UPDATING

device is updating

Result Codes for an OTA Update#

For every OTA update, a result is generated after the update failed or successful. There can be only one active OTA update at a time for each client. An active OTA is indicated by the result RESULT_DEFAULT. The result for each OTA update is stored in the database (FirmwareUpdate table).

Result Codes for an OTA Update#

Result

Description

RESULT_DEFAULT

default state

RESULT_SUCCESS

update was successful

RESULT_NO_STORAGE

no storage available

RESULT_OUT_OF_MEM

out of memory

RESULT_CONNECTION_LOST

connection was lost

RESULT_INTEGRITY_FAILED

integrity check failed

RESULT_UNSUP_FW

unsupported firmware

RESULT_INVALID_URI

invalid uri provided

RESULT_UPDATE_FAILED

update failed

RESULT_UNSUP_PROTO

unsupported protocol