android網路時間同步總結

最近看了下網路時間同步，總結一下。

整體描述：

android網路時間同步使用NITZ（Network identity and Time Zone）電訊廠商可選服務。

由Ril層主動上報RIL_UNSOL_NITZ_TIME_RECEIVED訊息；通知(notify)給CdmaServiceStateTracker和GsmServiceStateTracker；CdmaServiceStateTracker獲得網路同步時間，根據DateTimeSetting中自動同步設定，決定是否同步和發送（ACTION_NETWORK_SET_TIMEZONE、ACTION_NETWORK_SET_TIME）廣播。

 

其中

/** if time between NITZ updates is less than mNitzUpdateSpacing the update may be ignored. */

private static final int NITZ_UPDATE_SPACING_DEFAULT = 1000 * 60 * 10;
    private int mNitzUpdateSpacing = SystemProperties.getInt("ro.nitz_update_spacing",
            NITZ_UPDATE_SPACING_DEFAULT);

決定同步的時間間隔，如果網路主動上報間隔小於此時間間隔，則忽略該次訊息

 

/** If mNitzUpdateSpacing hasn't been exceeded but update is > mNitzUpdate do the update */
    private static final int NITZ_UPDATE_DIFF_DEFAULT = 2000;
    private int mNitzUpdateDiff = SystemProperties.getInt("ro.nitz_update_diff",
            NITZ_UPDATE_DIFF_DEFAULT);

上報的NITZ同步時間與當前處理時間的預設間隔，如果實際間隔大於此間隔，則同步該次時間。

 

同步判斷條件

if ((mSavedAtTime == 0) || (timeSinceLastUpdate > nitzUpdateSpacing)
                            || (Math.abs(gained) > nitzUpdateDiff)) {
                        Log.i(LOG_TAG, "NITZ: Auto updating time of day to " + c.getTime()
                                + " NITZ receive delay=" + millisSinceNitzReceived
                                + "ms gained=" + gained + "ms from " + nitz);

                        setAndBroadcastNetworkSetTime(c.getTimeInMillis());

} else {
                        Log.i(LOG_TAG, "NITZ: ignore, a previous update was "
                                + timeSinceLastUpdate + "ms ago and gained=" + gained + "ms");
                        return;
}

 

另，上層Setting App中，DateTimeSetting設定了AutoTime is True，則CdmaServiceStateTracker和GsmServiceStateTracker的監聽,根據當前

if (mSavedTimeZone != null && mSavedTime != 0 && mSavedAtTime != 0) {
            setAndBroadcastNetworkSetTimeZone(mSavedTimeZone);
            setAndBroadcastNetworkSetTime(mSavedTime
                    + (SystemClock.elapsedRealtime() - mSavedAtTime));
}

廣播時間和Time Zone