Android平台读写i2c设备开发笔记三

三、app调用服务接口访问硬件

上主要代码EEPROMActivity.java  

package com.zkgd.eeprom;import android.app.Activity;import android.os.Bundle;import android.os.ServiceManager;import android.os.IIICService;import android.os.RemoteException;import android.util.Log;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;public class EEPROMActivity extends Activity  implements OnClickListener{private final static String LOG_TAG = "com.zkgd.eeprom";          private IIICService iicService = null;        private EditText valueText = null;      private Button readButton = null;      private Button writeButton = null;      private Button clearButton = null;      int len = 1;    /** Called when the activity is first created. */      @Override      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.main);            iicService = IIICService.Stub.asInterface(          ServiceManager.getService("iic"));                    valueText = (EditText)findViewById(R.id.edit_value);          readButton = (Button)findViewById(R.id.button_read);          writeButton = (Button)findViewById(R.id.button_write);          clearButton = (Button)findViewById(R.id.button_clear);        readButton.setOnClickListener(this);      writeButton.setOnClickListener(this);      clearButton.setOnClickListener(this);                    Log.i(LOG_TAG, "Activity Created");      }            public void onClick(View v) {          if(v.equals(readButton)) {          try {  len = 1;                //在从设备中读取数据                String val =  iicService.getVal(0x50,len);                    valueText.setText(val);          } catch (RemoteException e) {              Log.e(LOG_TAG, "Remote Exception while reading value from device.");          }                 }          else if(v.equals(writeButton)) {          try {                  String val = valueText.getText().toString();                  len = val.length();                 //在从设备的子地址处开始写入数据                iicService.setVal(val,0x50,0x10,len);          } catch (RemoteException e) {              Log.e(LOG_TAG, "Remote Exception while writing value to device.");          }          }          else if(v.equals(clearButton)) {              String text = "";              valueText.setText(text);          }      }  }

工程eeprom放置在源码目录package/app/下

编译命令：mmm package/app/eeprom

打包，烧写固件至开发板，启动就可以看到该应用的图标了。

小结：

整个调用流程为：app<---AIDL访问服务<---JNI本地方法实现<---HALso文件<---硬件

一个问题，这种方法改动了android原生api，毕竟是访问了硬件。如果想做通用app又想使用c/c++提高效率，直接进行NDK开发，功能编译成库文件打进app应用的工程中。

另一个问题，硬件访问会遭遇到权限问题。如果做通用app，需要设备root了，然后在代码里添加权限修改操作，例如："chmod 777 "+getPackageCodePath(); "chmod 777 /dev/i2c-1";