online

# Example: online

Demonstrates `time_service` with **SNTP synchronization over WiFi**.

The component initializes from the build timestamp, connects to WiFi using the ESP-IDF `protocol_examples_common` helper, then requests an SNTP sync explicitly. The sync result is delivered via a callback showing the exact time correction applied. A logging loop runs continuously, printing a human-readable timestamp every two seconds.

---

## What This Example Shows

- Standard initialization sequence: NVS → netif → event loop → WiFi → `time_service_init()`
- Using `time_service_sync_async()` to request SNTP sync after network is ready
- Handling the sync callback — inspecting `success`, `delta_sec`, old and new timestamps
- Continuous timestamp logging with `time_service_now_str()` before and after sync

---

## Expected Output

```
I (4121) online_example: WiFi connected
I (4131) online_example: Initialized, origin=2 (build time baseline)
I (6141) online_example: Time: 2026-04-14 16:21:17 +0500
I (8141) online_example: Time: 2026-04-14 16:21:19 +0500
I (14141) online_example: Time synced — jump: 3 sec (old=1776087799 new=1776087802)
I (14141) online_example: Time: 2026-04-14 16:21:21 +0500
I (16141) online_example: Time: 2026-04-14 16:21:23 +0500
```

The log shows timestamps running from build time before sync completes, then the jump notification, then corrected timestamps continuing seamlessly.

---

## Build and Flash

```bash
cd examples/online
idf.py build flash monitor
```

Configure your WiFi credentials before building:

```bash
idf.py menuconfig   # → Example Connection Configuration → WiFi SSID / Password
```

---

## Configuration

**Timezone offset** — defined at the top of `main.c`:

```c
#define TIMEZONE_OFFSET_SEC  (5 * 3600)  // UTC+5 Pakistan Standard Time
```

**SNTP servers** — configurable via menuconfig:

```bash
idf.py menuconfig   # → Time Service Configuration → SNTP Server 0 / 1 / 2
```

**SNTP timeout** — if sync fails consistently, increase the timeout:

```bash
idf.py menuconfig   # → Time Service Configuration → SNTP sync timeout
```

---

## Why the 2-Second Delay Before Sync

`example_connect()` returns as soon as an IP address is acquired, but DNS resolution may not be fully stable at that exact moment. The 2-second delay before `sync_async()` gives the network stack time to settle. If you see sync failures on first attempt, try increasing this delay or implement a retry.

---

## Dependencies

This example uses `protocol_examples_common` from the ESP-IDF examples directory. It is available automatically when building within the ESP-IDF environment.