How to Implement Fallback Logic for Failed Updates in Your Firmware

Develop a Dual-Bank Firmware Architecture

• Implementing a dual-bank system can help ensure that if a new firmware update fails, the system can roll back to the previous working version. Allocate separate memory banks for the active firmware and the backup version.

 

• Ensure that upon successful update validation, the new firmware is copied to the secondary bank and its integrity is verified.

#define FIRMWARE_BANK_A 0x08000000 // Primary Bank
#define FIRMWARE_BANK_B 0x08100000 // Secondary Bank

void switchToBankB() {
    // Logic to boot from Bank B
}

Implement CRC or Checksum Verification

• Post-update, a verification process should occur to validate the integrity of the updated firmware. Use CRC or checksum hashes for this purpose during the update process.

 

• Pre-calculate the checksum of the newly downloaded firmware image and store it securely. After the update, calculate the checksum of the active firmware and compare it to the stored checksum.

#include <stdint.h>

uint32_t calculateCRC(uint8_t* data, size_t length) {
    uint32_t crc = 0xFFFFFFFF;
    for (size_t i = 0; i < length; i++) {
        crc ^= data[i];
        for (uint8_t j = 0; j < 8; j++) {
            if (crc & 1)
                crc = (crc >> 1) ^ 0xEDB88320;
            else
                crc >>= 1;
        }
    }
    return ~crc;
}

bool verifyFirmware(uint8_t* firmware, size_t length, uint32_t expectedCRC) {
    return calculateCRC(firmware, length) == expectedCRC;
}

Utilize Watchdog Timers for System Recovery

• A Watchdog Timer (WDT) should be employed to reset the system in case the firmware gets stuck due to a bad update. Configure the WDT such that it resets the system if the main loop does not service it regularly.

 

• Ensure that your bootloader or initialization code can detect if the reset was due to a WDT, and accordingly switch to a stable firmware bank if needed.

#include <WatchdogLibrary.h>

void setup() {
    Watchdog.enable(4000); // 4 seconds WDT
}

void loop() {
    // Your main loop code
    Watchdog.reset();  // Reset WDT timer
}

Design a Safe Update Process with Rollback Mechanisms

• During the update process, maintain states to track the progress so that any interruption can be managed gracefully. This includes downloading, verifying, and writing firmware to memory.

 

• If the update process encounters any unforeseen issues, initiate a rollback to the previous firmware version stored in the secondary bank.

enum UpdateState {
    IDLE,
    DOWNLOADING,
    VERIFYING,
    INSTALLING,
    COMPLETE,
    FAILED
};

UpdateState currentState = IDLE;

void handleUpdate() {
    // Logic to perform and track update
    if (updateFails()) {
        rollbackFirmware();
    }
}

Log Update Processes and Errors

• Logging both successful and failed updates, along with the reasons for failure, helps diagnose and improve future updates. Store logs in non-volatile memory if available, ensuring persistence across reboots.

 

• Analyze these logs post-failure to identify patterns or issues in the update process that require addressing.

void logError(char* message) {
    // Logic to store the log internally or send to a server
}

Implement User Feedback and Diagnostics

• Provide clear feedback mechanisms to the user or system administrators regarding the current update status and any errors that arise. This can be through LEDs, serial console, or a networked UI.

 

• Consider implementing a diagnostic mode that outputs detailed error states and allows for manual intervention if needed.

void provideFeedback(bool success) {
    if (success) {
        // Indicate success (e.g., blink LED green)
    } else {
        // Indicate failure (e.g., blink LED red)
    }
}