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";