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 for
621      * solicited and unsolicited signal strength updates
622      *
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 parse
629         // all fields
630 
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: " + ex
239                             + "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 rr
1129                 = 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 happens
2813                 // frequently
2814                 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