Abstract
In the growing landscape of wearable and IoT devices, many rely on Real-Time Operating Systems (RTOS) that are stripped down for performance, size, and energy efficiency. These systems often exclude file system support to reduce resource consumption. However, this presents a significant challenge when implementing reliable Firmware Over-The-Air (FOTA) updates. This whitepaper introduces Redstone OTA’s solution: a robust breakpoint resume and data integrity mechanism that enables resilient FOTA directly on raw Flash memory, ensuring update reliability even in the event of power failure or unexpected shutdowns.
1. Introduction
As devices become smaller and more power-sensitive, especially in sectors like wearables, manufacturers increasingly turn to RTOS platforms. RTOS-based systems are highly efficient but frequently lack the storage abstraction provided by file systems. Firmware updates on such systems face critical reliability issues, especially in environments where network instability or power loss is possible.
Redstone OTA offers a specialized FOTA solution designed for these constraints. By introducing a method to track and verify firmware download progress at the Flash level, our approach enables reliable, resumable firmware updates even in environments with no file system.
2. Problem Definition
Without a file system, firmware must be downloaded and written directly into raw Flash storage (NOR or NAND). Standard download protocols assume the existence of a file system to manage:
- Partial data storage
- Integrity verification
- Resume points after interruption
This leads to several challenges:
- Data loss risk during download due to power failure
- Inability to resume after interruption, requiring full re-download
- No metadata storage to indicate download status
These issues make OTA updates unreliable and costly in terms of time, bandwidth, and user experience.
3. Technical Overview of Redstone OTA’s Solution
3.1 Flash Memory Layout
Redstone OTA partitions the device’s Flash memory into two functional areas:
- Record Area: Used to log the status of each downloaded data block, including hash for verification.
- Data Storage Area: Stores the actual firmware download.
Data storage and download information record process in flash
3.2 Block and Page Mapping
Each data block corresponds to a specific entry (page) in the record area. For example:
- Block 0 → Page 0
- Block 1 → Page 1 …
- Block N → Page N
Each page includes:
- Block index
- Hash of the stored data (e.g., CRC32 or MD5)
- Valid flag (indicating whether the block is complete)
4. Firmware Download & Verification Process
Step-by-Step Download Workflow
- Initiate Download: Device sends request to server for firmware data.
- Write to Data Block: Downloaded chunk is written to the corresponding block in the Data Storage Area.
- Check Completion: Once a block is fully written, its hash is computed.
- Write to Record Area: The hash and valid flag are saved in the corresponding page.
- Repeat Until Done: Process continues for all blocks.
Power Failure Handling
If the device powers off mid-download:
- On restart, the system reads all hash records.
- It recalculates the hash of each data block and compares with the stored hash.
- Match: Block is complete; skip.
- Mismatch or Empty: Block is invalid; re-download.
This ensures only incomplete or corrupted blocks are re-downloaded.
5. Resume Logic and Integrity Assurance
This mechanism provides deterministic, verifiable download state tracking without a file system. Benefits include:
- Efficient bandwidth use by only re-downloading incomplete data
- Instant resume from the last valid block
- Lightweight metadata requiring minimal Flash space
- Protection against data corruption from unexpected shutdowns
6. Advantages of the Redstone OTA Approach
| Feature | Benefit |
|---|---|
| No file system needed | Works in minimal RTOS environments |
| Hash-based validation | Ensures data integrity before firmware is applied |
| Power-failure recovery | Resilient to unexpected interruptions |
| Low memory overhead | Optimized for constrained devices |
| Scalable | Works with compressed/encrypted/delta updates |
7. Implementation Guidelines
- Hash Algorithm: CRC32 recommended for speed vs. reliability balance
- Redundancy: Duplicate the record block for backup in case of Flash wear or bitflips
- Write Protection: Lock record area once complete to prevent unintended changes
- Block Size Tuning: Match block size to Flash erase/write granularity for efficiency
- Location of Record Area: Prefer fixed address space for faster access and system boot checks
8. Use Cases
This solution is ideal for:
- Smart wearables (e.g., fitness trackers, smartwatches)
- True wireless stereo (TWS) earbuds
- Industrial sensors and microcontrollers
- Consumer IoT products with minimal Flash and RAM
9. Conclusion
Redstone OTA’s breakpoint resume mechanism redefines what’s possible for firmware updates in ultra-constrained environments. By managing data and state directly on raw Flash, we ensure reliable OTA performance without needing a file system, making it the ideal choice for the next generation of connected, compact devices.
About Redstone OTA
Redstone OTA provides a highly scalable and secure FOTA (firmware over-the-air) platform for connected devices across 226+ countries and regions. Our technology powers intelligent, reliable firmware updates for embedded systems, from edge devices to global fleets.
Website: www.redstoneota.com
Email: support@redstoneota.com
