From Firmware to Field: The Complete OTA Update Journey

What is OTA Update in IoT? 
OTA (Over-the-Air) update is a remote firmware or software upgrade process where new updates are delivered to IoT devices through wireless communication networks such as Wi-Fi, Cellular, or LPWAN technologies.
OTA updates may include:

• Firmware version upgrades
• Bug fixes
• Feature enhancements
• Configuration changes
• Performance optimization

Why Are OTA Updates Important ? 

• Security Improvements: OTA updates help patch vulnerabilities and protect devices from cyber threats.
• Remote Maintenance: Devices deployed in remote areas can be updated without onsite service visits.
• Feature Expansion: New functionalities can be added even after product deployment.
• Bug Fixing: Critical software issues can be resolved quickly across all deployed devices.
• Cost Reduction: Remote updates reduce operational and maintenance expenses significantly.
• Product Lifecycle Management: OTA enables long-term device support and continuous performance improvements.

Challenges in OTA Updates

OTA Update Workflow in IoT 

Step : 1 Firmware Preparation & Validation

• The OTA process begins with preparing the new firmware version. The firmware is tested, validated, and checked for stability, compatibility, and security before deployment to ensure reliable device performance.
• The generated firmware binary (.bin) also includes CRC data appended at the end of the file  for integrity verification during the update process. 
• Firmware optimization and testing under different scenarios are also performed before release.

Step 4: Secure Firmware Download 

• The device securely downloads the firmware package in chunks using encrypted communication protocols such as HTTPS or TLS to prevent unauthorized access or data tampering during transmission.

Step 5: Storing the firmware into the Flash memory.

• Once the firmware package has been successfully downloaded and verified, it is stored in the designated flash memory region without affecting the currently running firmware.
• Depending on the device architecture, the firmware may be stored in either internal flash memory or external flash memory.

Internal Flash Memory Partition Layout for OTA Update

• In devices with sufficient internal flash memory, the bootloader uses a dual-partition (A/B) architecture. The currently running firmware remains active in one partition while the new firmware is downloaded into the inactive partition.
• After successful validation, the bootloader switches execution to the updated firmware during reboot. If the update fails, the device can automatically roll back to the previous working firmware, ensuring safe and reliable OTA updates.

OTA with External Flash Memory

• In memory-constrained devices, the new firmware is downloaded and stored in external flash memory instead of internal application memory.
• After the firmware is fully downloaded and validated, the bootloader copies the verified image into the internal application region and activates it during the next reboot. 
• This approach allows OTA updates even when internal flash memory is insufficient for dual-bank firmware storage.

Step 7: Device Reboot

• After all firmware chunks have been successfully downloaded and stored in the designated flash memory region, the OTA update flag is set to indicate that a new firmware image is ready for activation.
• The device then performs a controlled reboot.
• During startup, execution is transferred to the bootloader, which initiates the firmware validation process and determines whether the newly downloaded firmware should be activated or the existing firmware should continue running.

Step 8: Bootloader

• Bootloader is responsible for controlling and managing the complete firmware upgrade operation. 
• When sufficient internal flash memory is available and the firmware size is relatively small, the bootloader can use an internal dual-bank architecture for OTA updates. 
• For larger firmware images or memory-constrained devices, external flash memory is commonly used to store and manage the firmware update process.

• The device powers up or undergoes a system reset. Control is first transferred to the bootloader before the main application firmware is executed.
• The bootloader initializes essential hardware resources, memory interfaces, and boot configurations. It prepares the system for firmware validation and determines the appropriate boot sequence.
• The bootloader checks for an OTA update flag, pending firmware image, or firmware activation request stored in flash memory. If no update is detected, the bootloader proceeds with the currently active firmware.
• The bootloader validates the firmware image by performing integrity and authenticity checks such as CRC verification, checksum validation, digital signature verification, or cryptographic hash validation. This ensures that only trusted and uncorrupted firmware is executed. 
• Based on the validation results, the bootloader selects the firmware image to boot. 
• In dual-bank architectures, this may involve choosing between the existing firmware image and the newly updated firmware image stored in the alternate memory bank.
• In external flash-based OTA systems, the bootloader copies the validated firmware from external flash to internal application memory before activating it. 
• After successful validation and image selection, the bootloader transfers execution control to the selected application firmware by jumping to its reset vector and application entry point. 
• The application firmware starts executing normally, initializing system peripherals, communication interfaces, and application-specific functions. The device then resumes its intended operation using the selected firmware image.

Step 9: Updated Firmware

• If the reboot and validation process are successful, the device starts operating with the updated firmware and newly added features, improvement.