时间源优先级

Android 框架使用各种时间源进行时间同步。本页重点介绍网络时间协议 (NTP) 和网络身份和时区 (NITZ) 自动时间源。默认情况下,在 Android 12 或更高版本中,框架将 NTP 作为时间源优先于 NITZ,因为 NTP 比 NITZ 更准确和可靠。在 NTP 不可用的情况下,该框架将使用 NITZ。这是与早期版本平台的默认优先级相反。默认情况下,在 Android 11 及更低版本中,框架优先考虑 NITZ 而非 NTP。

有关此更改的更多详细信息,请参阅以下 AOSP 补丁: 15636781513323

配置时间源优先级

要为特定 Android 版本配置默认优先级的时间源,请在构建时配置frameworks/base/core/res/res/values/config.xml中的config_autoTimeSourcesPriority键。来自列表中较高时间源的时间建议优先于列表中较低的源。

可配置的 Android 时间源位于TimeDetectorStrategy.java中。以下源配置为默认使用:

  • 电话 (NITZ)
  • 网络 (NTP)

测试

要在 NTP 不可用(禁用移动数据和 Wi-Fi 时)验证设备是否使用 NITZ,请执行以下操作:

  1. 确保 DUT 中有工作的 SIM
  2. 关闭移动数据和 Wi-Fi
  3. 将设备置于飞行模式以确保蜂窝无线电已关闭
  4. 关闭自动时间检测
  5. 将来手动将时钟设置为不正确的时间值
  6. 重启设备
  7. 开启自动时间检测
  8. 将设备退出飞行模式

一旦收到 NITZ 信号,这些步骤就会触发对系统时钟的更改。要检查设备时间的设置方式,请运行以下命令:

adb shell dumpsys time_detector

要验证系统时钟是否使用 NITZ,请在命令输出中确认以下内容:

  • mEnvironment.isAutoTimeDetectionEnabled()true
  • mEnvironment.autoOriginPriorities()包含时间源列表,列表中较高的源优先于列表中较低的源。
  • Time change log部分显示系统时钟是使用电话建议设置的。
  • Telephony suggestion history部分包含时间建议。
  • Network suggestion history部分为空。

Telephony suggestion historyNetwork suggestion history部分中的时间建议被认为是时间的真实来源。如果设备已连接到 Internet 并具有 SIM 卡,则会使用 NTP(网络)和 NITZ(电话)生成建议。在这个测试用例中,只有Telephony suggestion history部分包含建议,因为 NTP 被禁用。

Time change log部分记录对设备系统时钟所做的更改以及使用的建议。系统时钟是根据config_autoTimeSourcesPriority键中优先级列表中时间源的顺序设置的。但是,如果建议太旧或无效,则可能会忽略来自更高优先级来源的建议。此外,如果最高优先级的有效建议与设备的当前系统时钟时间匹配在几秒钟内,则时间不会改变。在此测试用例中,只要建议没有过期,系统时钟就会使用Telephony suggestion history中的建议之一设置。

以下是在 NTP 不可用时设备回退使用 NITZ 的输出示例。

TimeDetectorStrategy:
  mLastAutoSystemClockTimeSet=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}
  mEnvironment.isAutoTimeDetectionEnabled()=true
  mEnvironment.elapsedRealtimeMillis()=73059
  mEnvironment.systemClockMillis()=1614186767818
  mEnvironment.systemClockUpdateThresholdMillis()=2000
  mEnvironment.autoTimeLowerBound()=2021-02-24T15:44:15Z(1614181455000)
  mEnvironment.autoOriginPriorities()=[network,telephony]
  Time change log:
    66261 / 2021-02-24T17:12:41.020Z - Set system clock using time=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000} cause=Found good telephony suggestion., bestTelephonySuggestion=TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]}, detectionReason=New telephony time suggested. timeSuggestion=TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]} elapsedRealtimeMillis=66259 newSystemClockMillis=1614186761019
  Telephony suggestion history:
    key idx: 0=0
    val idx: 0=TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]}
      Historic values=[
        0@PT1M6.258S: TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]}
      ]
  Network suggestion history:
    {Empty}
  Gnss suggestion history:
    {Empty}
  External suggestion history:
    {Empty}

为了与测试场景中的输出进行比较作为参考,以下是一个典型输出示例,其中设备从 NTP 和 NITZ 时间源接收时间建议。

TimeDetectorStrategy:
  mLastAutoSystemClockTimeSet=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}
  mEnvironment.isAutoTimeDetectionEnabled()=true
  mEnvironment.elapsedRealtimeMillis()=302926
  mEnvironment.systemClockMillis()=1614186997685
  mEnvironment.systemClockUpdateThresholdMillis()=2000
  mEnvironment.autoTimeLowerBound()=2021-02-24T15:44:15Z(1614181455000)
  mEnvironment.autoOriginPriorities()=[network,telephony]
  Time change log:
    66261 / 2021-02-24T17:12:41.020Z - Set system clock using time=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000} cause=Found good telephony suggestion., bestTelephonySuggestion=TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]}, detectionReason=New telephony time suggested. timeSuggestion=TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]} elapsedRealtimeMillis=66259 newSystemClockMillis=1614186761019
  Telephony suggestion history:
    key idx: 0=0
    val idx: 0=TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]}
      Historic values=[
        0@PT1M6.258S: TelephonyTimeSuggestion{mSlotIndex='0', mUtcTime=TimestampedValue{mReferenceTimeMillis=66240, mValue=1614186761000}, mDebugInfo=[Sending new time suggestion nitzSignal=TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}}, reason=handleNitzReceived(TimestampedValue{mReferenceTimeMillis=66240, mValue=NitzData{mOriginalString=21/02/24,17:12:41+00,00, mZoneOffset=0, mDstOffset=0, mCurrentTimeMillis=1614186761000, mEmulatorHostTimeZone=null}})]}
      ]
  Network suggestion history:
    0@PT4M4.04S: NetworkTimeSuggestion{mUtcTime=TimestampedValue{mReferenceTimeMillis=244038, mValue=1614186939242}, mDebugInfo=[Origin: NetworkTimeUpdateService. event=3]}
  Gnss suggestion history:
    {Empty}
  External suggestion history:
    {Empty}