Android应用程序访问硬件驱动（JNI方式）

Java应用程序通过JNI方式访问C库，C库向上给Java程序提供接口，向下调用了硬件驱动，这里以LED的控制为例。

一、LED驱动

leds_4412.c是tiny4412开发板一个简单的LED驱动

#include #include #include #include #include #include #include #include #include #include #include #include #include #include static int led_gpios[] = {    EXYNOS4212_GPM4(0),    EXYNOS4212_GPM4(1),    EXYNOS4212_GPM4(2),    EXYNOS4212_GPM4(3),};static int led_open(struct inode *inode, struct file *file){    /* 配置GPIO为输出引脚 */    int i;    for (i = 0; i < 4; i++)        s3c_gpio_cfgpin(led_gpios[i], S3C_GPIO_OUTPUT);    return 0;}/* app : ioctl(fd, cmd, arg) */static long led_ioctl(struct file *filp, unsigned int cmd,        unsigned long arg){    /* 根据传入的参数设置GPIO */    /* cmd : 0-off, 1-on */    /* arg : 0-3, which led */    if ((cmd != 0) && (cmd != 1))        return -EINVAL;    if (arg > 4)        return -EINVAL;    gpio_set_value(led_gpios[arg], !cmd);    return 0;}static struct file_operations leds_ops = {    .owner  =   THIS_MODULE,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */    .open   =   led_open,         .unlocked_ioctl = led_ioctl,};static int major;static struct class *cls;int leds_init(void){    major = register_chrdev(0, "leds", &leds_ops);    /* 为了让系统udev,mdev给我们创建设备节点 */    /* 创建类, 在类下创建设备 : /sys */    cls = class_create(THIS_MODULE, "leds");    device_create(cls, NULL, MKDEV(major, 0), NULL, "leds"); /* /dev/leds */    return 0;}void leds_exit(void){    device_destroy(cls, MKDEV(major, 0));    class_destroy(cls);    unregister_chrdev(major, "leds");}module_init(leds_init);module_exit(leds_exit);MODULE_LICENSE("GPL");MODULE_AUTHOR("xy");

将驱动程序放入内核编译:
a. 放入Linux内核 drivers/char中
b. 修改 drivers/char/Makefile，添加：

obj-y += leds_4412.o

为避免干扰，将自带的 leds 驱动屏蔽：

config TINY4412_LEDS    tristate "LED Support for FriendlyARM Tiny4412 GPIO LEDs"    depends on MACH_TINY4412    default n

c. 重新编译内核： make zImage
d. 重新烧录zImage，系统起来后会看到/dev/leds设备。

二、JNI文件（C库）

hardcontrl.c用于实现后面的HardContrl.java里面的native方法对应的C函数，C函数分别对应了驱动里面各个接口。

JNI_OnLoad在java程序执行System.loadLibrary的时候被调用，作用：
1. 通过GetEnv获取运行环境
2. 通过FindClass(env, “com/thisway/hardlibrary/HardControl”)找到HardControl这个Java类。
3. 通过RegisterNatives注册下面三个native方法

/* Java方法名，JNI字段描述符，C语言函数名 */static const JNINativeMethod methods[] = {    {"ledOpen", "()I", (void *)ledOpen},    {"ledClose", "()V", (void *)ledClose},    {"ledCtrl", "(II)I", (void *)ledCtrl},};

编译命令：

arm-linux-gcc -fPIC -shared hardcontrol.c -o libhardcontrol.so //编译共享动态库so文件-I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/  //指定jni.h文件路径；-nostdlib /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so// 编译时不会自动使用标准的libc.so.6-I /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/include //指定log.h文件路径/work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/liblog.so//__android_log_print依赖的库

hardcontrol.c完整代码：

#include   /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */#include #include #include #include #include #include #include   /* liblog *///__android_log_print(ANDROID_LOG_DEBUG, "JNIDemo", "native add ...");#if 0typedef struct {    char *name;          /* Java里调用的函数名 */    char *signature;    /* JNI字段描述符, 用来表示Java里调用的函数的参数和返回值类型 */    void *fnPtr;          /* C语言实现的本地函数 */} JNINativeMethod;#endifstatic jint fd;jint ledOpen(JNIEnv *env, jobject cls){    fd = open("/dev/leds", O_RDWR);    __android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledOpen : %d", fd);    if (fd >= 0)        return 0;    else        return -1;}void ledClose(JNIEnv *env, jobject cls){    __android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledClose ...");    close(fd);}jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status){    int ret = ioctl(fd, status, which);    __android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledCtrl : %d, %d, %d", which, status, ret);    return ret;}/* Java方法名，JNI字段描述符，C语言函数名 */static const JNINativeMethod methods[] = {    {"ledOpen", "()I", (void *)ledOpen},    {"ledClose", "()V", (void *)ledClose},    {"ledCtrl", "(II)I", (void *)ledCtrl},};/* System.loadLibrary */JNIEXPORT jint JNICALLJNI_OnLoad(JavaVM *jvm, void *reserved){    JNIEnv *env;    jclass cls;    if ((*jvm)->GetEnv(jvm, (void **)&env, JNI_VERSION_1_4)) {        return JNI_ERR; /* JNI version not supported */    }    cls = (*env)->FindClass(env, "com/thisway/hardlibrary/HardControl");    if (cls == NULL) {        return JNI_ERR;    }    /* 2. map java hello <-->c c_hello */    if ((*env)->RegisterNatives(env, cls, methods, sizeof(methods)/sizeof(methods[0])) < 0)        return JNI_ERR;    return JNI_VERSION_1_4;}

三、HardControl文件（java类）

用于声明native方法，让其他应用程序的代码调用。

package com.thisway.hardlibrary;public class HardControl {    public static native int ledCtrl(int which, int status);    public static native int ledOpen();    public static native void ledClose();    static {        try {            System.loadLibrary("hardcontrol");        } catch (Exception e) {            e.printStackTrace();        }    }}

当应用程序使用到该HardControl 类的时候，会先通过System.loadLibrary 加载hardcontrol.so库文件；

hardcontrol.c编译生成的hardcontrol.so必须放在应用程序的app/libs/armeabi目录下；

Android studio应用程序的build.gradle还要添加：

sourceSets {          main {              jniLibs.srcDirs = ['libs']          }      }

四、应用程序调用HardControl类方法

通过 import com.thisway.hardlibrary.*; 导入HardControl类；
在MainActivity的onCreate方法中open LED设备：HardControl.ledOpen();
在逻辑判断中操作LED：HardControl.ledCtrl(which, status);

package com.thisway.app_0001_leddemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.widget.Button;import android.view.View;import android.widget.CheckBox;import android.widget.Toast;import com.thisway.hardlibrary.*;public class MainActivity extends AppCompatActivity {    private boolean ledon = false;    private Button button = null;    private CheckBox checkBoxLed1 = null;    private CheckBox checkBoxLed2 = null;    private CheckBox checkBoxLed3 = null;    private CheckBox checkBoxLed4 = null;    class MyButtonListener implements View.OnClickListener {        @Override        public void onClick(View v) {            ledon = !ledon;            if (ledon) {                button.setText("ALL OFF");                checkBoxLed1.setChecked(true);                checkBoxLed2.setChecked(true);                checkBoxLed3.setChecked(true);                checkBoxLed4.setChecked(true);                for (int i = 0; i < 4; i++)                    HardControl.ledCtrl(i, 1);            }            else {                button.setText("ALL ON");                checkBoxLed1.setChecked(false);                checkBoxLed2.setChecked(false);                checkBoxLed3.setChecked(false);                checkBoxLed4.setChecked(false);                for (int i = 0; i < 4; i++)                    HardControl.ledCtrl(i, 0);            }        }    }    public void onCheckboxClicked(View view) {        // Is the view now checked?        boolean checked = ((CheckBox) view).isChecked();        // Check which checkbox was clicked        switch(view.getId()) {            case R.id.LED1:                if (checked) {                    // Put some meat on the sandwich                    Toast.makeText(getApplicationContext(), "LED1 on", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(0, 1);                }                else {                    // Remove the meat                    Toast.makeText(getApplicationContext(), "LED1 off", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(0, 0);                }                break;            case R.id.LED2:                if (checked) {                    // Put some meat on the sandwich                    Toast.makeText(getApplicationContext(), "LED2 on", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(1, 1);                }                else {                    // Remove the meat                    Toast.makeText(getApplicationContext(), "LED2 off", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(1, 0);                }                break;            case R.id.LED3:                if (checked) {                    // Put some meat on the sandwich                    Toast.makeText(getApplicationContext(), "LED3 on", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(2, 1);                }                else {                    // Remove the meat                    Toast.makeText(getApplicationContext(), "LED3 off", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(2, 0);                }                break;            case R.id.LED4:                if (checked) {                    // Put some meat on the sandwich                    Toast.makeText(getApplicationContext(), "LED4 on", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(3, 1);                }                else {                    // Remove the meat                    Toast.makeText(getApplicationContext(), "LED4 off", Toast.LENGTH_SHORT).show();                    HardControl.ledCtrl(3, 0);                }                break;            // TODO: Veggie sandwich        }    }    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        button = (Button) findViewById(R.id.BUTTON);        HardControl.ledOpen();        checkBoxLed1 = (CheckBox) findViewById(R.id.LED1);        checkBoxLed2 = (CheckBox) findViewById(R.id.LED2);        checkBoxLed3 = (CheckBox) findViewById(R.id.LED3);        checkBoxLed4 = (CheckBox) findViewById(R.id.LED4);        button.setOnClickListener(new MyButtonListener());/*        button.setOnClickListener(new View.OnClickListener() {            public void onClick(View v) {                // Perform action on click                ledon = !ledon;                if (ledon)                    button.setText("ALL OFF");                else                    button.setText("ALL ON");            }        });*/    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.menu_main, menu);        return true;    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        // Handle action bar item clicks here. The action bar will        // automatically handle clicks on the Home/Up button, so long        // as you specify a parent activity in AndroidManifest.xml.        int id = item.getItemId();        //noinspection SimplifiableIfStatement        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }}

Android应用程序访问硬件驱动（JNI方式）

Android应用程序访问硬件驱动（JNI方式）

一、LED驱动

二、JNI文件（C库）

三、HardControl文件（java类）

四、应用程序调用HardControl类方法

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