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Cardboy Time Sync Companion

This SwiftUI app connects to the Cardboy device over Bluetooth Low Energy and updates its wall clock using the custom time sync service exposed by the firmware. The sources live inside the existing cardboy-companion/cardboy-companion.xcodeproj so you can open and run them directly in Xcode.

Requirements

  • Xcode 15 or newer
  • iOS 16 or newer deployment target (can be lowered to 15 with minor API tweaks)
  • A Cardboy running firmware that includes the BLE time sync service

How it works

  1. The app scans for peripherals exposing service UUID 00000001-CA7B-4EFD-B5A6-10C3F4D3F230.
  2. Once connected it discovers characteristic 00000002-CA7B-4EFD-B5A6-10C3F4D3F231.
  3. Tapping Sync Now writes a 12‑byte payload containing:
    • 8 bytes Unix epoch seconds (little endian)
    • 2 bytes time zone offset in minutes from UTC (little endian)
    • 1 byte DST flag (1 if daylight saving is active)
    • 1 reserved byte (0)
  4. The firmware applies the timestamp with settimeofday() and updates the TZ environment variable so the clock app renders local time.

Usage

  1. Open cardboy-companion/cardboy-companion.xcodeproj in Xcode.
  2. Ensure the CoreBluetooth capability is enabled for the cardboy-companion target and keep the Uses Bluetooth LE accessories background mode on (preconfigured in this project).
  3. Build & run on a real device (BLE is not available in the simulator).
  4. Allow Bluetooth permissions when prompted. The app keeps scanning in the background, so the Cardboy can request a sync even while the companion is not foregrounded. Tap Sync Now any time you want to trigger a manual refresh.

Optionally bundle this code into your existing app—TimeSyncManager is self‑contained and can be reused.