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Firmware Over the Air (FOTA) Update for WiFi-Enabled Devices

The software development process for an embedded device is not a one-time action. Even if you have managed to make your code “bug-free”, there are always improvements or new features to add along the way. Look, for example, at Tesla, a car manufacturer that continuously provides new fixes and features to the cars in the field.

Nowadays, firmware over-the-air updates are replacing common manual firmware upgrades, making this process remote, quick, and easier for end users. At Lemberg Solutions, we suggest customers always consider adding FOTA functionality to IoT devices. This article highlights how we do FOTA updates in real Wifi-enabled microcontroller-based products. 

What is FOTA (Firmware Over-the-Air)?

Firmware Over the Air, or FOTA, is a technology integrated into firmware during development that provides wireless and seamless firmware updates from the server. It also makes the upgrade process error-free and safe, as manual firmware updates could lead to hardware malfunction.

What are Firmware Over-the-Air (FOTA) updates?

FOTA updates are regular firmware updates produced, announced, and launched by device manufacturers. They are required to keep the firmware security, power consumption, and stable performance on the appropriate level.

The device downloads FOTA updates and copies them to the firmware. FOTA updates ensure remote firmware upgrades, saving many resources, including time and costs for manufacturers and users. In addition, they help prolong the firmware life, ensuring its compatibility with constantly changing industry standards. Later in this article, we will talk about the FOTA system update process in detail. 

How does firmware Over the Air work?

Before firmware over the air (FOTA) updates became common for electronic devices, users had to deal with updates manually. Fifteen years ago, a common approach to changing firmware for your mp3 player was to connect the device to a PC via USB cable, download a special utility and new binary from the manufacturer's Website, and flash firmware manually. If the update process was interrupted by power loss, for example, one could end up with a hardware brick that would never play music again.

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Nowadays, over-the-air updates provide a secure and reliable way to stay updated with the latest features.

For smart home devices, FOTA updates are usually done either using Bluetooth low energy (BLE) or WiFi technology. BLE-capable devices usually have a corresponding mobile app feature that notifies you when new firmware is available for download. On the other hand, devices with WiFi support can also offer firmware updates using a WEB interface. Such an approach from the user perspective is usually similar; the only difference is that you use a WEB server rather than a mobile app.

Here at Lemberg, we suggest customers always consider adding FOTA functionality to IoT devices. This article highlights how we do FOTA updates in real Wifi-enabled microcontroller-based products. 

Benefits of FOTA updates

FOTA updates improve the firmware's stable performance, ensuring the following benefits. 

  • Minimized risk of human error

FOTA allows users to schedule updates for the period when they won’t use the device instead of just ignoring or rejecting update notifications. Also, tech specialists can debug the system remotely, which saves much time and costs for users and manufacturers. 

  • Flexibility

Once you get a device, there is no need to use the manufacturer`s technical service to upgrade it. Thanks to FOTA, your device will be wirelessly upgraded regularly. You only need to take simple steps to download and install a new version on one device or several devices simultaneously.

  • Power consumption

IoT devices with outdated firmware functionality consume more power than they were expected to. Firmware over-the-air updates help reduce power consumption, which is particularly cost-efficient for large IoT device networks. 

  • Improved security

Regular device updates improve its usability and implement new security measures to protect it from various data threats. Moreover, firmware over-the-air update ensures the firmware complies with the latest industry standards. 

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FOTA implementation approaches

Depending on the WiFi module, the following types of OTA firmware updates are commonly used:

  • native FOTA feature built-in WiFi module;
  • custom FOTA implementation.

The first option is the best for devices whose application code is hosted solely on a WiFi module, as it avoids custom FOTA implementation. However, a custom implementation must be considered when a device consists of a host microcontroller unit (MCU), which runs the application code, and a WiFi module for connectivity support.

The process of FOTA updates

Here, you can find more details about how the process of FOTA software update flows, its specifics, and pitfalls to expect and avoid for seamless regular firmware updates. 

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New firmware download 

As the first step, the device downloads new firmware binary from a remote WEB server. New firmware can be downloaded from a remote server in various ways — for example, using FTP or HTTP/HTTPS protocols.

If possible, it is better to download the firmware as a single file instead of in chunks. The latter allows you to avoid a possible lack of RAM to store the whole file, but it requires careful reassembly of packets if the download is interrupted, for example, due to communication issues.

Persistent memory storage 

After the firmware is retrieved from the server, it must first be stored in some type of persistent memory before flashing to the microcontroller’s internal memory. This is done to ensure firmware integrity, which could be impacted during downloading. Integrity is usually checked by calculating the CRC sum of the downloaded file and comparing it with CRC values appended to the firmware during compilation. External EEPROM or Flash internal MCU memories are usually used as persistent storage. Storing binary to external memory is usually preferred to avoid unintentional corruption of internal flash. However, when external memory is not available, the second option can also be considered. 


When new firmware is downloaded and its CRС is validated, it’s time to involve the bootloader. A bootloader is a special program that usually resides inside internal MCU memory and has a task to substitute the current firmware with the new one. The bootloader can also provide much more functionality, but, for smart home devices, which do not run Linux, it is usually quite simple.

To enter the bootloader, the application code usually performs a CPU reboot followed by launching the bootloader. The bootloader can then check if new firmware exists on persistent memory and copy it to internal memory.

Flashing new firmware

Flashing new firmware is usually straightforward and just requires deleting the current firmware and copying the new one instead. However, it is very important to carefully handle all issues that may arise during programming as this can lead to broken hardware (remember the case with the mp3 player at the beginning?). For example, if the device reboots while copying, internal memory will contain truncated binary, which may not start or can work with undefined behavior.

In our implementations, we always try to foresee such issues and accompany the bootloader with additional safety features, like factory default firmware. In case of an error, the bootloader can always roll back to the factory binary if it can’t program or load existing firmware. When a firmware update is complete, the application code will always send an acknowledgment to the remote server to confirm that FOTA was successful or notify the user that some failure occurred.


During the development of electronic devices, you should always consider adding FOTA functionality to ensure device safety and flexibility. A firmware update option may seem redundant due to time and cost increases, but it will always pay off afterward during support and maintenance.

Check out our firmware development services and how the Lemberg Solutions embedded team might contribute to your project. 

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