android网络时间同步总结
最近看了下网络时间同步，总结一下。
整体描述：
android网络时间同步使用NITZ（Network identity and Time Zone）运营商可选服务。
由Ril层主动上报RIL_UNSOL_NITZ_TIME_RECEIVED消息；通知(notify)给CdmaServiceStateTracker和GsmServiceStateTracker；CdmaServiceStateTracker获得网络同步时间，根据DateTimeSetting中自动同步设置，决定是否同步和发送（ACTION_NETWORK_SET_TIMEZONE、ACTION_NETWORK_SET_TIME）广播。
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);
决定同步的时间间隔，如果网络主动上报间隔小于此时间间隔，则忽略该次消息
/** 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);
上报的NITZ同步时间与当前处理时间的默认间隔，如果实际间隔大于此间隔，则同步该次时间。
同步判断条件
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，上层Setting App中，DateTimeSetting设置了AutoTime is True，则CdmaServiceStateTracker和GsmServiceStateTracker的监听,根据当前
if (mSavedTimeZone != null && mSavedTime != 0 && mSavedAtTime != 0) {
setAndBroadcastNetworkSetTimeZone(mSavedTimeZone);
setAndBroadcastNetworkSetTime(mSavedTime
+ (SystemClock.elapsedRealtime() - mSavedAtTime));
}
广播时间和Time Zone