Chapter 28 of FreeRTOS: OTA Firmware Upgrade Design

Table of Contents

• 1. Dual Bank Switching Mechanism
• 1.1 Basic Concepts
• 1.2 Implementation Plan
• 1.3 FreeRTOS Integration Points
• 2. Implementation of Security Verification Process
• 2.1 Verification Mechanism Design
• 2.2 Encryption Algorithm Selection
• 2.3 Tamper Protection
• 3. Practical Demonstration
• 3.1 Code Structure
• 3.2 Key Code Snippets
• Best Practice Recommendations

1. Dual Bank Switching Mechanism

1.1 Basic Concepts

1.2 Implementation Plan

Step	Action	FreeRTOS Considerations
1	Divide Flash into Bank0/Bank1	Consider memory alignment and partition size
2	Implement Bootloader Jump Logic	Disable all interrupts and tasks
3	Design State Flag Storage Area	Use NVS or independent Flash sector
4	Power Failure Recovery Handling	Add watchdog timeout protection

1.3 FreeRTOS Integration Points

• Execute jump after <span>vTaskEndScheduler()</span>
• Pause all tasks during upgrade:

  vTaskSuspendAll();
  // Perform Flash operations
  xTaskResumeAll();
  

2. Implementation of Security Verification Process

2.1 Verification Mechanism Design

Triple Verification Mechanism:

1. CRC32 Check (Fast Verification)
2. SHA-256 Digest Check
3. Digital Signature Verification (Optional)

2.2 Encryption Algorithm Selection

Algorithm Type	Recommended Implementation	Resource Consumption
Hash Algorithm	mbedTLS-SHA256	~3KB ROM
Asymmetric Encryption	ECDSA	~8KB ROM
Symmetric Encryption	AES-128	~2KB ROM

2.3 Tamper Protection

• Implementation Plan:

  if(verify_signature(firmware)!= PASS){
  erase_bank(1);// Immediately erase abnormal firmware
  system_reset();
  }
  

3. Practical Demonstration

3.1 Code Structure

ota/
├── bootloader/      # Bootloader with FreeRTOS
├── bank_swap/       # Dual Bank Switching Implementation
├── crypto/          # Security Verification Component
└── ota_task.c       # OTA Background Task

3.2 Key Code Snippets

// OTA Task Example
void vOTATask(void* pvParameters){
while(1){
if(xOTAEventGroup & DOWNLOAD_COMPLETE_BIT){
vPortEnterCritical();
if(verify_firmware()){
set_active_bank(1);
vTaskDelay(pdMS_TO_TICKS(1000));// Wait for UART output to complete
NVIC_SystemReset();
}
vPortExitCritical();
}
vTaskDelay(pdMS_TO_TICKS(100));
}

Best Practice Recommendations

1. Always keep a rollback version
2. Use hardware security modules (e.g., STM32’s HASH peripheral)
3. Implement progress reporting mechanism (via UART/network)
4. Test various exceptional scenarios (power failure, verification failure, etc.)