Firmware Over-The-Air (FOTA)

Overview

Firmware Over-The-Air (FOTA) updates are critical to modern IoT product lifecycles — enabling remote bug fixes, feature rollouts, and security patches without physical access to deployed devices. The following case studies demonstrate Z-Crossing Solutions’ expertise in designing robust, integrity-verified FOTA systems across multiple hardware platforms, protocols, and connectivity technologies.

 

Case 01 Agricultural IoT Device

BLE-based wireless firmware update via mobile application

Hardware

• STM32F4xx MCU
• BGM220 SoC (Silicon Labs)

Stack & Protocols

• Embedded C
• BLE
• UART
• CRC Verification
• Custom Protocol

Update Flow

1. Mobile application authenticates with the BGM220 BLE SoC before any firmware data is exchanged.
2. Firmware binary is streamed to the BGM220 over BLE in chunks using a custom communication protocol.
3. BGM220 forwards each firmware chunk to the STM32 master MCU via UART.
4. STM32 computes a CRC checksum over all received firmware data and compares it against the CRC value sent by the mobile app.
5. Firmware is written to internal flash only after CRC verification passes — ensuring complete integrity before installation.

 

Key Outcome: End-to-end authenticated and integrity-checked OTA for field-deployed agricultural sensors — no physical access required for firmware maintenance.

Case 02 Production Monitoring System

Secure HTTPS-based cloud FOTA with recovery firmware support

Hardware

• TM4C Tiva-C MCU
• External Flash Memory

Stack & Protocols

• Ti-RTOS
• NDK Stack
• HTTPS
• WolfSSL
• CRC Verification

Update Flow

1. On boot or update check, the device sends its unique MAC ID to the server for device-specific firmware lookup.
2. Server responds with firmware metadata: serial number, firmware size, filename, and a secure download link.
3. Device downloads the firmware securely over HTTPS using WolfSSL, ensuring encrypted transmission.
4. CRC checksum is computed locally and validated against the server-provided checksum before any flash write occurs.
5. Flash is partitioned for Bootloader, Application, Update FW, and Recovery FW — ensuring safe rollback if an update fails.
6. Update process safely resumes after connectivity interruptions, preventing bricked devices in the field.

 

Key Outcome: Production floor devices stay up-to-date via cloud with zero downtime risk — recovery firmware guarantees a safe fallback state.