1. 現象

為什么第一次開機或者格式化后電池顯示上次充滿電是xxx天或者xxx分鐘前，不管之前電池電量數值

實際操作：

充滿電且拔除充電線，則顯示上次充滿電為0分鐘前

新機器第一次開機，不論當前電量大小，拔除充電線，則顯示上次充滿電為0分鐘前

修改系統時間未來時間，則顯示上次充滿電是xxx天或者xxx分鐘前

修改系統時間過去時間，則顯示為0分鐘前

2. 原因

因為上次充滿電接口getStartClockTime中 mStartClockTime = currentTime - (mClocks.elapsedRealtime()/當前自開機后，經過的時間，包括深度休眠的時間/-(mRealtimeStart/1000))決定，其中elapsedRealtime和mRealtimeStart的數值刷新邏輯BatteryStatsImpl->setBatteryStateLocked->setOnBatteryLocked->resetAllStatsLocked->initTimes改變

故這里顯示上次充滿電是xxx天或者xxx分鐘前，是因為沒有實際充電的時刻時，取的上次充滿電時間為系統當前時間.故會有明明沒充滿電，顯示上次充滿電是xxx天或者xxx分鐘前的邏輯顯示。除非充滿電且拔除充電線則為正常顯示了。

Google的這個邏輯確實存在不精確

3. 源碼

3.1 設置->電池

package com.android.settings.fuelgauge;public class PowerUsageSummary extends PowerUsageBase implements OnLongClickListener,BatteryTipPreferenceController.BatteryTipListener {@VisibleForTestingvoid updateLastFullChargePreference() {if (mBatteryInfo != null && mBatteryInfo.averageTimeToDischarge!= Estimate.AVERAGE_TIME_TO_DISCHARGE_UNKNOWN) {// 電池在充滿電后的預估使用時間} else {final long lastFullChargeTime = mBatteryUtils.calculateLastFullChargeTime(mStatsHelper,System.currentTimeMillis());mLastFullChargePref.setTitle(R.string.battery_last_full_charge); // 上次充滿電mLastFullChargePref.setSubtitle(StringUtil.formatRelativeTime(getContext(), lastFullChargeTime,false /* withSeconds */));}}

3.2 BatteryUtils.calculateLastFullChargeTime

package com.android.settings.fuelgauge;/*** Utils for battery operation*/ public class BatteryUtils {/*** Calculate the time since last full charge, including the device off time* 計算上次充電電時間，包含設備關機時間** @param batteryStatsHelper utility class that contains the data 電池信息類* @param currentTimeMs current wall time 當前時間* @return time in millis 返回時長*/public long calculateLastFullChargeTime(BatteryStatsHelper batteryStatsHelper,long currentTimeMs) {return currentTimeMs - batteryStatsHelper.getStats().getStartClockTime();}

3.3 BatteryStatsHelper.getStats().getStartClockTime()

• frameworks/base/core/java/com/android/internal/os/BatteryStatsHelper.java

package com.android.internal.os;public class BatteryStatsHelper {private BatteryStats mStats;public BatteryStats getStats() {if (mStats == null) {load();}return mStats;}private static BatteryStatsImpl getStats(IBatteryStats service) {try {ParcelFileDescriptor pfd = service.getStatisticsStream();if (pfd != null) {try (FileInputStream fis = new ParcelFileDescriptor.AutoCloseInputStream(pfd)) {byte[] data = readFully(fis, MemoryFile.getSize(pfd.getFileDescriptor()));Parcel parcel = Parcel.obtain();parcel.unmarshall(data, 0, data.length);parcel.setDataPosition(0);BatteryStatsImpl stats = com.android.internal.os.BatteryStatsImpl.CREATOR.createFromParcel(parcel);return stats;} catch (IOException e) {Log.w(TAG, "Unable to read statistics stream", e);}}} catch (RemoteException e) {Log.w(TAG, "RemoteException:", e);}return new BatteryStatsImpl();}

3.3.1 BatteryStats.getStartClockTime()

• frameworks/base/core/java/android/os/BatteryStats.java

package android.os;public abstract class BatteryStats implements Parcelable {/*** Return the wall clock time when battery stats data collection started.*/public abstract long getStartClockTime()

3.3.2 BatteryStatsImpl.getStartClockTime()

• frameworks/base/core/java/com/android/internal/os/BatteryStatsImpl.java

package com.android.internal.os;public class BatteryStatsImpl extends BatteryStats {// 獲取上次充滿電時間@Override public long getStartClockTime() {final long currentTime = System.currentTimeMillis();if (ensureStartClockTime(currentTime)) {recordCurrentTimeChangeLocked(currentTime, mClocks.elapsedRealtime(),mClocks.uptimeMillis());}return mStartClockTime;}

3.4 BatteryStatsImpl.getStartClockTime

3.4.1 BatteryStatsImpl.getStartClockTime.ensureStartClockTime

package com.android.internal.os;public class BatteryStatsImpl extends BatteryStats {long mStartClockTime;void initTimes(long uptime, long realtime) {...mStartClockTime = System.currentTimeMillis();...}// 從電池詳情數據庫中 batterystats.bin 更新StartClockTimepublic void readSummaryFromParcel(Parcel in) throws ParcelFormatException {...// 從 batterystats.bin 獲取上次充滿電時間mStartClockTime = in.readLong();mRealtimeStart = in.readLong();...}public void writeSummaryToParcel(Parcel out, boolean inclHistory) {...// Pull the clock time. This may update the time and make a new history entry// if we had originally pulled a time before the RTC was set.long startClockTime = getStartClockTime();out.writeLong(startClockTime);out.writeLong(mRealtimeStart);...}// 是否需要重新校準上次充滿電時間boolean ensureStartClockTime(final long currentTime) {final long ABOUT_ONE_YEAR = 365*24*60*60*1000L; // 1 年時間 31536000000// 是否滿足以下條件// 1. 當前時間毫秒值 大于 1年，例如這里是100%滿足，2018-12-22 10:41:46，即當前時間毫秒值 1545446651000// 2. 上次充滿電時間StartClockTime 小于 當前時間毫秒值與1年的差， 即這里即記錄最長上次充滿電1年內，即我手動調整時間，最長只能記錄上次充滿電365天內// 或者滿足下面條件// 1. 上次充滿電時間StartClockTime 大于 當前時間毫秒值，這個條件可以將系統時間調整為過去的時間if ((currentTime > ABOUT_ONE_YEAR && mStartClockTime < (currentTime-ABOUT_ONE_YEAR))|| (mStartClockTime > currentTime)) {// If the start clock time has changed by more than a year, then presumably// the previous time was completely bogus. So we are going to figure out a// new time based on how much time has elapsed since we started counting.mStartClockTime = currentTime - (mClocks.elapsedRealtime()/*獲取從設備boot后經歷的時間值*/-(mRealtimeStart/1000));return true;}return false;}

3.4.2 查看 mStartClockTime 的賦值情況

BatteryStatsImpl 初始化時間

private BatteryStatsImpl(Clocks clocks, File systemDir, Handler handler,PlatformIdleStateCallback cb,UserInfoProvider userInfoProvider) {...long uptime = mClocks.uptimeMillis() * 1000;long realtime = mClocks.elapsedRealtime() * 1000;initTimes(uptime, realtime)

resetAllStatsLocked 初始化時間

private void resetAllStatsLocked() {final long uptimeMillis = mClocks.uptimeMillis();final long elapsedRealtimeMillis = mClocks.elapsedRealtime();initTimes(uptimeMillis * 1000, elapsedRealtimeMillis * 1000);

initTimes 函數

public interface Clocks {public long elapsedRealtime();public long uptimeMillis();}public static class SystemClocks implements Clocks {public long elapsedRealtime() {return SystemClock.elapsedRealtime(); // 自開機后，經過的時間，包括深度休眠的時間}public long uptimeMillis() {return SystemClock.uptimeMillis(); // 自開機后，經過的時間，不包括深度休眠的時間}}void initTimes(long uptime, long realtime) {mStartClockTime = System.currentTimeMillis(); // 系統當前時間，即日期時間，可以被系統設置修改，如果設置系統時間，時間值會發生跳變。mOnBatteryTimeBase.init(uptime, realtime);mOnBatteryScreenOffTimeBase.init(uptime, realtime);mRealtimeStart = realtime;}

3.5 BatteryStatsImpl.setBatteryStateLocked.setOnBatteryLocked.resetAllStatsLocked

@GuardedBy("this")public void setBatteryStateLocked(final int status, final int health, final int plugType,final int level, /* not final */ int temp, final int volt, final int chargeUAh,final int chargeFullUAh) {if (onBattery != mOnBattery) {...setOnBatteryLocked(elapsedRealtime, uptime, onBattery, oldStatus, level, chargeUAh);@GuardedBy("this")protected void setOnBatteryLocked(final long mSecRealtime, final long mSecUptime,final boolean onBattery, final int oldStatus, final int level, final int chargeUAh) {if (onBattery) {// We will reset our status if we are unplugging after the// battery was last full, or the level is at 100, or// we have gone through a significant charge (from a very low// level to a now very high level).boolean reset = false;if (!mNoAutoReset && (oldStatus == BatteryManager.BATTERY_STATUS_FULL|| level >= 90|| (mDischargeCurrentLevel < 20 && level >= 80)|| (getHighDischargeAmountSinceCharge() >= 200&& mHistoryBuffer.dataSize() >= MAX_HISTORY_BUFFER))) {...resetAllStatsLocked();

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