Android Telephony —— 手机信号实时变化源码分析过程记录

源码版本：4.4

跳过InCallActivity等UI实现。先看service以及底层。

1，在frameworks/opt下面会发现如下文件列表：

./telephony/src/java/com/android/internal/telephony/cdma/CdmaServiceStateTracker.java./telephony/src/java/com/android/internal/telephony/cdma/CdmaLteServiceStateTracker.java./telephony/src/java/com/android/internal/telephony/gsm/GsmServiceStateTracker.java./telephony/src/java/com/android/internal/telephony/gsm/GsmLteServiceStateTracker.java./telephony/src/java/com/android/internal/telephony/ServiceStateTracker.java

2，可以直接进入./telephony/src/java/com/android/internal/telephony/ServiceStateTracker.java 分析，很容易发现类似于如下的代码：

619     /**620      * send signal-strength-changed notification if changed Called both for621      * solicited and unsolicited signal strength updates622      *623      * @return true if the signal strength changed and a notification was sent.624      */625     protected boolean onSignalStrengthResult(AsyncResult ar, boolean isGsm) {626         SignalStrength oldSignalStrength = mSignalStrength;627 628         // This signal is used for both voice and data radio signal so parse629         // all fields630 631         if ((ar.exception == null) && (ar.result != null)) {632             mSignalStrength = (SignalStrength) ar.result;633             mSignalStrength.validateInput();634             mSignalStrength.setGsm(isGsm);635         } else {636             log("onSignalStrengthResult() Exception from RIL : " + ar.exception);637             mSignalStrength = new SignalStrength(isGsm);638         }639 640         return notifySignalStrength();641     }

　　这里主要是结构体的初始化以及上下文环境的简单判断。我们继续追踪notifySignalStrength（）

229     private SignalStrength mLastSignalStrength = null;230     protected boolean notifySignalStrength() {231         boolean notified = false;232         synchronized(mCellInfo) {233             if (!mSignalStrength.equals(mLastSignalStrength)) {234                 try {235                     mPhoneBase.notifySignalStrength();236                     notified = true;237                 } catch (NullPointerException ex) {238                     loge("updateSignalStrength() Phone already destroyed: " + ex239                             + "SignalStrength not notified");240                 }241             }242         }243         return notified;244     }

这里有mSignalStrength 和mLastSignalStrength 两个和信号强度相关的量。算是找到切入点了，信号强度更新的中间点就是这里了。

3，我们先向下分析看有什么可以学习的。onSignalStrengthResult 是被　　frameworks/opt/telephony/src/java/com/android/internal/telephony/gsm/GsmServiceStateTracker.java中handleMessage在Message Type是　　　　EVENT_GET_SIGNAL_STRENGTH的时候调用的：

 424             case EVENT_GET_SIGNAL_STRENGTH: 425                 // This callback is called when signal strength is polled 426                 // all by itself 427  428                 if (!(mCi.getRadioState().isOn())) { 429                     // Polling will continue when radio turns back on 430                     return; 431                 } 432                 ar = (AsyncResult) msg.obj; 433                 onSignalStrengthResult(ar, true); 434                 queueNextSignalStrengthPoll(); 435  436                 break;

4，到这里就需要对RIL有一定的了解才好继续追下去。RIL的event传到上层之后主要通过一个叫做Registrant的机制分发的。

　　我们跳到frameworks/opt/telephony/src/java/com/android/internal/telephony/RIL.java中去。

　　这里有主动去得到signalstrength的方法：

1127     getSignalStrength (Message result) {1128         RILRequest rr1129                 = RILRequest.obtain(RIL_REQUEST_SIGNAL_STRENGTH, result, mIs2ndRil);1130 1131         if (RILJ_LOGD) riljLog(rr.serialString() + "> " + requestToString(rr.mRequest));1132 1133         send(rr);1134     }

　　继续往下看，接受到底层发来的数据后通过Registrant Notification：

2811             case RIL_UNSOL_SIGNAL_STRENGTH:2812                 // Note this is set to "verbose" because it happens2813                 // frequently2814                 if (RILJ_LOGV) unsljLogvRet(response, ret);2815 2816                 if (mSignalStrengthRegistrant != null) {2817                     mSignalStrengthRegistrant.notifyRegistrant(2818                                         new AsyncResult (null, ret, null));2819                 }2820             break;

5，继续追下去，我们看到有主动通过RIL_REQUEST_SIGNAL_STRENGTH去request signal strength的。

　　所以直接在hardware/ril下搜关键字：RIL_REQUEST_SIGNAL_STRENGTH得到结果如下：

./include/telephony/ril.h:1388: * RIL_REQUEST_SIGNAL_STRENGTH./include/telephony/ril.h:1402:#define RIL_REQUEST_SIGNAL_STRENGTH 19./libril/ril.cpp:3758:        case RIL_REQUEST_SIGNAL_STRENGTH: return "SIGNAL_STRENGTH";./libril/ril_commands.h:36:    {RIL_REQUEST_SIGNAL_STRENGTH, dispatchVoid, responseRilSignalStrength},./reference-ril/reference-ril.c:2093:        case RIL_REQUEST_SIGNAL_STRENGTH:./reference-ril/ril.h:1388: * RIL_REQUEST_SIGNAL_STRENGTH./reference-ril/ril.h:1402:#define RIL_REQUEST_SIGNAL_STRENGTH 19

　　很明显是hardware/ril/reference-ril/reference-ril.c里面如下函数被调用去查询信号强度了，调用AT command等一看便知：

 839 static void requestSignalStrength(void *data, size_t datalen, RIL_Token t) 840 { 841     ATResponse *p_response = NULL; 842     int err; 843     char *line; 844     int count =0; 845     int numofElements=sizeof(RIL_SignalStrength_v6)/sizeof(int); 846     int response[numofElements]; 847  848     err = at_send_command_singleline("AT+CSQ", "+CSQ:", &p_response); 849  850     if (err < 0 || p_response->success == 0) { 851         RIL_onRequestComplete(t, RIL_E_GENERIC_FAILURE, NULL, 0); 852         goto error; 853     } 854  855     line = p_response->p_intermediates->line; 856  857     err = at_tok_start(&line); 858     if (err < 0) goto error; 859  860     for (count =0; count < numofElements; count ++) { 861         err = at_tok_nextint(&line, &(response[count])); 862         if (err < 0) goto error; 863     } 864  865     RIL_onRequestComplete(t, RIL_E_SUCCESS, response, sizeof(response)); 866  867     at_response_free(p_response); 868     return;

从上层追到下层基本告一段落，Telephony的其他功能的实现结构都一样，也可以同样通过上述思路去追踪。

涉及到的源码路径基本有：

frameworks/av

frameworks/base

frameworks/opt

packages/apps

hardware/ril

等

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