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System Design/Creating Gap Analysis and Solutions Documentation/03_OTA_Strategy.md

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+# 3. OTA Strategy
+
+## Overview
+Over-the-Air (OTA) updates are critical for maintaining and improving industrial devices in the field. The ASF strategy focuses on safety, reliability, and automatic recovery from failed updates.
+
+## Partition Layout
+For a device with **8MB of flash**, the following partition layout is recommended to support safe OTA updates:
+
+| Partition | Size | Purpose |
+| :--- | :--- | :--- |
+| **bootloader** | - | Initial boot code |
+| **partition_table** | - | Defines the flash layout |
+| **factory** | - | Optional minimal rescue firmware |
+| **ota_0** | 3.5 MB | Primary application slot |
+| **ota_1** | 3.5 MB | Secondary application slot for updates |
+| **nvs** | 64 KB | Encrypted Non-Volatile Storage for config |
+| **phy_init** | - | Physical layer initialization data |
+| **coredump** | 64 KB | Storage for crash logs and debugging |
+
+## OTA Policy
+A formal policy ensures that updates are downloaded correctly and that the system can roll back if the new firmware is unstable.
+
+| Step | Rule |
+| :--- | :--- |
+| **Download** | Conducted via HTTPS or MQTT in chunks. |
+| **Chunk Size** | 4096 bytes (optimized for flash page size). |
+| **Integrity** | Verified using a full image SHA-256 hash. |
+| **Validation** | System must boot and send a health report. |
+| **Confirmation** | The application must confirm stability within 60 seconds. |
+| **Failure** | Automatic rollback to the previous known-good version. |
+
+### Closing the Gaps
+This strategy directly addresses the following gaps:
+*   **GAP-OTA-001:** Reliable image delivery.
+*   **GAP-OTA-002:** Integrity and authenticity verification.
+*   **GAP-OTA-003:** Safe rollback mechanisms.