创建Android Application工程：使用Eclipse的Android插件ADT创建Android工程，工程名称为Gpio，创建完成后将工程目录拷贝到packages/apps/文件夹下，并删除工程目录下的gen文件夹，不删除的话会造成类重复的错误。

src/com/android/gpio/Gpio.java：

package com.android.gpio;  
import com.android.gpio.R;  
import android.app.Activity;  
import android.os.ServiceManager;  
import android.os.Bundle;  
import android.os.IGpioService;  
import android.os.RemoteException;  
import android.util.Log;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  

public class Gpio extends Activity implements OnClickListener {  
private final static String LOG_TAG = "com.android.Gpio";  
private IGpioService gpioService = null;  

private Button setButton = null;  
private Button clearButton = null;  
  
/** Called when the activity is first created. */  
@Override  
public void onCreate(Bundle savedInstanceState) {  
	super.onCreate(savedInstanceState);  
	setContentView(R.layout.main);  

	gpioService = IGpioService.Stub.asInterface(  
	ServiceManager.getService("gpio"));  

	setButton = (Button)findViewById(R.id.button_set);  
	clearButton = (Button)findViewById(R.id.button_clear);  

	setButton.setOnClickListener(this);  
	clearButton.setOnClickListener(this);  
}  
  
@Override  
public void onClick(View v) {  
	if(v.equals(setButton)) {   
	try{
		int val='1';
		gpioService.setVal(val);
	} catch (RemoteException e){
		Log.e(LOG_TAG,"setting value");	
	}	
	} 
	else if(v.equals(clearButton)) {
	try{
		int val='0';
		gpioService.setVal(val);
	   } catch (RemoteException e){
		Log.e(LOG_TAG,"setting value");	
	   }	
	   }  
	}  
}  

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
   android:orientation="vertical"  
   android:layout_width="fill_parent"  
   android:layout_height="fill_parent">  

   <Button
       android:id="@+id/button_clear"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:text="@string/clear"
       android:textStyle="bold"
       android:layout_marginTop="140dp"/>
   <Button
       android:id="@+id/button_set"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:text="@string/set"
       android:textStyle="bold" 
       android:layout_marginTop="0dp"/>
</LinearLayout>  

<?xml version="1.0" encoding="utf-8"?>  
<resources>  
   <string name="app_name">GPIO</string>  
   <string name="set">Set</string>  
   <string name="clear">Clear</string>  
</resources>  

<?xml version="1.0" encoding="utf-8"?>  
<manifest xmlns:android="http://schemas.android.com/apk/res/android"  
  package="com.android.gpio"  
  android:versionCode="1"  
  android:versionName="1.0">  
  <application android:icon="@drawable/ic_launcher" android:label="@string/app_name">  
    <activity android:name=".Gpio"  
              android:label="@string/app_name">  
        <intent-filter>  
            <action android:name="android.intent.action.MAIN" />  
            <category android:name="android.intent.category.LAUNCHER" />  
        </intent-filter>  
    </activity>  
  </application>  
</manifest>   

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE_TAGS := optional
LOCAL_SRC_FILES := $(call all-subdir-java-files)
LOCAL_PACKAGE_NAME := Gpio
LOCAL_CERTIFICATE := platform
include $(BUILD_PACKAGE)
include $(call all-makefiles-under,$(LOCAL_PATH))

在PRODUCT_PACKAGES := \ 后加入Gpio \

编译工程会生成Gpio.apk

make TARGET_PRODUCT=am335xevm_sk -j8 OMAPES=4.x 

out/target/product/am335xevm_sk/system/app/Gpio.apk                 ==>   rootfs/

out/target/product/am335xevm_sk/system/framework/services.jar       ==>   rootfs/system/framework/

out/target/product/am335xevm_sk/system/framework/framework.jar      ==>   rootfs/system/framework/

out/target/product/am335xevm_sk/obj/lib/libandroid_servers.so       ==>   rootfs/system/lib/

out/target/product/am335xevm_sk/obj/lib/gpio.default.so             ==>   rootfs/system/lib/hw/

确保rootfs下 ueventd.rc 已经添加：(Android 从硬件到应用：一步一步向上爬 3 -- 硬件抽象层访问硬件驱动  提到)

/dev/AdrIO                0666   root       root

现象：

点击"Set"按钮：     D1灯亮    

点击"Clear"按钮：   D1灯灭

可见编写的APP通过调用硬件服务已经成功操作了AM335寄存器，改变AM335X_GPIO_LED4的电平，通过N沟MOS器件控制LED D1的亮灭。

Android 从硬件到应用：一步一步向上爬 6 -- 编写APP测试框架层硬件服务(完)