Hardware & Implementation OTA

OTA Update

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Over-the-Air update -- wirelessly updating BLE device firmware via a GATT service without physical access.

    


    
    
    

      다른 명칭:
      
      OTA
      
      DFU
      
      Over-the-Air Update
      
    

    
  


  




  
  

    
OTA Update (Over-the-Air)


OTA (Over-the-Air) update, also called DFU (Device Firmware Update), is the process of wirelessly updating the firmware of a BLE device through a GATT service or L2CAP channel. OTA capability is essential for deployed IoT products that need security patches, feature additions, or bug fixes without physical access.


Architecture


A typical BLE OTA system consists of three components:


    

  • Bootloader: Runs on the BLE device, validates firmware images, and manages the swap between old and new firmware. Must be robust against power loss during update
    • 

  • DFU ATT">gatt-service/" class="glossary-term-link" data-term="GATT Service" data-definition="Collection of related BLE characteristics." data-category="GATT & ATT">GATT Service: A custom or standardized GATT Service that receives firmware image data from the host device. The service handles image transfer, progress tracking, and validation
    • 

  • Mobile/Gateway application: Sends the firmware image to the target device, manages the transfer protocol, and monitors progress
    • 



Transfer Mechanisms


OTA transfers can use several transport methods:






Method
Throughput
Complexity






GATT Write Without Response
10-50 kBps
Low




GATT Write + DLE + large MTU
30-80 kBps
Medium




L2CAP CoC (Connection-Oriented Channel)
50-150 kBps
High






The choice depends on the firmware image size and acceptable update duration. A 256 KB firmware image takes approximately 5 seconds via L2CAP CoC versus 25 seconds via basic GATT writes.


Security Considerations


OTA updates introduce significant security risks. A compromised update mechanism allows an attacker to install malicious firmware. Essential security measures include:


    

  • Image signing: Firmware images are signed with ECDSA or Ed25519; the bootloader verifies the signature before applying
    • 

  • Encrypted transfer: Use an encrypted BLE link (Pairing + Bonding) or application-layer encryption
    • 

  • Rollback protection: Version counters prevent downgrading to older, vulnerable firmware
    • 

  • Secure boot: Hardware-backed boot chain verification from ROM bootloader to application
    • 



Vendor Implementations


Most BLE SDK vendors provide OTA/DFU solutions:


    

  • Nordic: MCUboot bootloader with nRF Connect SDK, background DFU support
    • 

  • Espressif: ESP-IDF OTA with rollback, A/B partition scheme
    • 

  • TI: OAD (Over-the-Air Download) in SimpleLink SDK
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  • Silicon Labs: Gecko Bootloader with application-level OTA
    • 



When designing an OTA-capable product, allocate sufficient flash for dual image slots (current + candidate), reserve a bootloader partition, and plan for the worst case: a user walking out of BLE range mid-update.

  

  

  
  

  
  

  
  

  
  
  

    
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