ota-updates

name	ota-updates
description	Design over-the-air firmware updates — dual-bank, delta updates, rollback, and secure update verification
allowed-tools	["Read","Write","Grep"]
effort	high

When to activate

• Designing OTA firmware update architecture
• Implementing secure update verification (signatures)
• Building dual-bank flash update mechanisms
• Implementing delta/differential updates
• Designing rollback strategies for failed updates

When NOT to use

• For initial firmware programming (factory flash)
• For wired update mechanisms (USB, JTAG)
• For cloud-side software updates

Instructions

1. Flash layout. Dual-bank (App A + App B) or single-bank + staging area. Dual is safer, single saves flash.
2. Update flow. Download → Verify → Write inactive bank → Verify → Swap boot flag → Reboot → Confirm → Commit.
3. Security. Code signing (ECDSA-P256). Verify signature before writing. Encrypted firmware (AES-256) if IP protection needed.
4. Rollback. If new firmware fails to confirm within N reboots, revert to previous bank. Never brick the device.
5. Delta updates. bsdiff/detools for binary patches. 50-80% bandwidth savings. More complex but critical for large firmware over cellular.
6. Transport. HTTPS for cloud-hosted. CoAP for constrained networks. Chunked download with resume capability.
7. Testing. Test power loss during update. Test corrupt image. Test version downgrade prevention. Test resume after network failure.

Example

OTA Update Flow: Dual-Bank

Flash Layout:
  0x08000000: Bootloader (16KB) — never updated via OTA
  0x08004000: App Bank A (240KB) — currently running
  0x08040000: App Bank B (240KB) — update target
  0x0807C000: Config (16KB) — boot flag, version, attempt counter

Update Sequence:
  1. Download firmware to Bank B (chunked, with CRC per chunk)
  2. Verify Bank B image signature (ECDSA-P256)
  3. Set boot flag = Bank B, attempt counter = 3
  4. Reboot → Bootloader loads Bank B
  5. Bank B firmware confirms: set attempt counter = 0
  6. If not confirmed after 3 reboots → rollback to Bank A