ok6410 android driver(12)

　　In this essay, I will talk about how to write the service libraries.

 

　　TIPS :

I won't discuss the name rules about HAL libraries, but it's quite important to our understanding.
You can check the source file :
android_source/hardware/libhardware/hardware.c
Or google with key word :
android hardware.c

　　

　　1、Android.mk

　　In this file, it's important to write the LOCAL_SHARED_LIBRARIES and LOCAL_C_INCLUDE to assign the libraries for the service.

# Android.mk
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)

# [optional, user, eng] 
# eng = required
# optinal = no install on target
LOCAL_MODULE_TAGS := eng

# This is the target being built.
LOCAL_MODULE:= leds_hal_jni

# Target install path.
LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)

# All of the source files that we will compile.
LOCAL_SRC_FILES:= \
    LedHalService.cpp

# All of the shared libraries we link against.
LOCAL_SHARED_LIBRARIES := \
    　　libandroid_runtime \
    　　libcutils \
　　    libhardware \
　　    libhardware_legacy \
　　    libnativehelper \
　　    libsystem_server \
　　    libutils \
　　    libui \
　　    libsurfaceflinger_client
       

# Also need the JNI headers.
LOCAL_C_INCLUDES += \
　　　　$(JNI_H_INCLUDE) \
        　　 hardware/leds_hal

# Don't prelink this library.  For more efficient code, you may want
# to add this library to the prelink map and set this to true.
LOCAL_PRELINK_MODULE := false

include $(BUILD_SHARED_LIBRARY)

 

　　2、LedHalService.cpp

　　Acturely, this file is the JNI file. Load the hal libraries (Use the hw_get_module function in hardware.c) and offer the API to android applications.

　　There are another methods array we should know is JNINativeMethod.

　　According the the native method, we could name the JNI functions ourselves without the long JNI default name.

#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>
#include <jni.h>

#include <leds_hal.h>

struct leds_device_t *leds_device = NULL;

static jboolean leds_setOn(JNIEnv *env, jobject thiz, jint led)
{
    LOGI("Leds HAL JNI : leds_setOn() is invoked.");

    if (leds_device == NULL) {
        LOGI("Leds HAL JNI : leds_device was not fetch correctly.");
        return -1;
    } else {
        return leds_device->set_on(leds_device, led);
    }
}

static jboolean leds_setOff(JNIEnv *env, jobject thiz, jint led)
{
    LOGI("Leds HAL JNI : leds_setOff() is invoked.");

    if (leds_device == NULL) {
        LOGI("Leds HAL JNI : leds_device was not fetch correctly.");
        return -1;
    } else {
        return leds_device->set_off(leds_device, led);
    }
}

static inline int leds_device_open(const struct hw_module_t* module,
        struct leds_device_t** device)
{
    return module->methods->open(module, LED_HARDWARE_MODULE_ID,
            (struct hw_device_t**) device);
}

static jboolean leds_init(JNIEnv *env, jclass clazz)
{
    leds_module_t* module;

    LOGI(" >> finding HAL...");
    LOGI("HAL id :"LED_HARDWARE_MODULE_ID);

    if (hw_get_module(LED_HARDWARE_MODULE_ID, 
        (const hw_module_t**) &module) == 0) {
        LOGI("LedService JNI : Led Stub found.");
        if (leds_device_open(&module->hw_module, 
                &leds_device) == 0) {
            LOGI("LedService JNI : Got Stub operation.");
            return 0;
        }
    }
    LOGE("LedService JNI : Get Stub operation failed.");
    return -1;
}

static const JNINativeMethod methods[] = {
    { "_init", "()Z", (void *) leds_init },
    { "_set_on", "(I)Z", (void *) leds_setOn },
    { "_set_off", "(I)Z", (void *) leds_setOff },
};

int register_leds_hal(JNIEnv *env)
{
    static const char* const kClassName = "mobile/android/leds/hal/service/LedHalService";
    
    jclass clazz;

    clazz = env->FindClass(kClassName);

    if (clazz == NULL) {
        LOGE("Can't find class %s.\n", kClassName);
        return -1;
    }

    if (env->RegisterNatives(clazz, methods, 
        sizeof(methods)/sizeof(methods[0]) != JNI_OK)) {
        LOGE("Failed registing methods for %s.\n", kClassName);
        return -1;
    }

    return 0;
}

jint JNI_OnLoad(JavaVM *vm, void *reserved)
{
    JNIEnv *env = NULL;

    if (vm->GetEnv((void **) &env, JNI_VERSION_1_4) != JNI_OK) {
        LOGE(" GetEnv failed!");
        return -1;
    }

    register_leds_hal(env);

    return JNI_VERSION_1_4;
}

　　The prototype of JNINativeMethod :

typedef struct { 
    const char* name; 
    const char* signature; 
    void*       fnPtr; 
} JNINativeMethod;

　　TIPS :

In the LedHalService.cpp, we use #include <leds_hal.h> instead of #include "leds_hal.h", because of the Path was loaded in the Android.mk

　　After compiling, we should push the file leds_jni.so to dir /system/lib/ in ok6410.

 

　　Finaly, we write the Java program to call service library.

package mobile.android.leds.hal.service;
public class LedHalService {
    private static LedHalService ledHalService;

    public static LedHalService getInstance() {
        if (ledHalService == null)
            return new LedHalService();
        else 
            return ledHalService;
    }

    private LedHalService() {
        init();
    }

    public boolean init() {
        return _init();
    }

    public boolean setOn(int led) {
        return _set_on(led);
    }

    public boolean setOff(int led) {
        return _set_off(led);
    }

    private native boolean _init();
    private native boolean _set_on(int led);
    private native boolean _set_off(int led);

    static {
        System.load("/system/lib/leds_hal_jni.so");
    }
}

　　What's more, this is a Java file and we can't use it directly. We stiil need to create an apk to call its jar file.

package com.example.leds_haljni;

import mobile.android.leds.hal.service.LedHalService;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.CheckBox;

public class MainActivity extends Activity {
    private CheckBox[] cBox_leds = new CheckBox[4];
    LedHalService ledHalService = LedHalService.getInstance();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        cBox_leds[0] = (CheckBox) findViewById(R.id.checkBox_led1);
        cBox_leds[1] = (CheckBox) findViewById(R.id.checkBox_led2);
        cBox_leds[2] = (CheckBox) findViewById(R.id.checkBox_led3);
        cBox_leds[3] = (CheckBox) findViewById(R.id.checkBox_led4);
    }
    
    public void onClick_switch(View view) {
        
        for (int i = 0; i < 4; i ++) {
            if (cBox_leds[i].isChecked()) {
                ledHalService.setOn(i);
            } else {
                ledHalService.setOff(i);
            }    
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

 　　Ok, here is the activity.xml and strings.xml :

　　(1) activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hal_hello" />

    <CheckBox
        android:id="@+id/checkBox_led1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView1"
        android:layout_below="@+id/textView1"
        android:layout_marginTop="14dp"
        android:text="@string/led1" />

    <Button
        android:id="@+id/button_led"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/checkBox_led4"
        android:layout_alignBottom="@+id/checkBox_led4"
        android:layout_alignParentRight="true"
        android:onClick="onClick_switch"
        android:text="@string/button_led" />

    <CheckBox
        android:id="@+id/checkBox_led2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/checkBox_led1"
        android:layout_alignBottom="@+id/checkBox_led1"
        android:layout_alignRight="@+id/textView1"
        android:layout_marginRight="26dp"
        android:text="@string/led2" />

    <CheckBox
        android:id="@+id/checkBox_led3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/checkBox_led2"
        android:layout_alignBottom="@+id/checkBox_led2"
        android:layout_toRightOf="@+id/checkBox_led2"
        android:text="@string/led3" />

    <CheckBox
        android:id="@+id/checkBox_led4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/checkBox_led3"
        android:layout_alignBottom="@+id/checkBox_led3"
        android:layout_marginLeft="34dp"
        android:layout_toRightOf="@+id/checkBox_led3"
        android:text="@string/led4" />

</RelativeLayout>

　　(2) strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">ledshal</string>
    <string name="action_settings">Settings</string>
    <string name="hal_hello">This is a leds HAL application :</string>
    <string name="led1">Led1</string>
    <string name="led2">Led2</string>
    <string name="led3">Led3</string>
    <string name="led4">Led4</string>
    <string name="button_led">Switch</string>

</resources>

　　That's all about the simple Led Hal.