Android硬件访问服务学习之（一）Android通过JNI访问硬件

首先来看一下android的系统框图。google后期加入一层HAL层，硬件访问层

https://developer.android.com/guide/platform/index.html

1.1  android访问硬件驱动的两种方式

android如何管理多个应用对硬件的访问：硬件访问服务。

方法1：

java的JNI技术 使得java可以访问C库。那我们就可以写好一个操作硬件的C库，然后加入到应用的工程中去，通过JNI来访问C库，从而实现对硬件的访问，这是操作硬件最简单的方法，但是没有凸显出android的特色。

优点：传统方法，简单易实现

缺点：jni多个设备同时访问，都可以来open吗？显然效率不好。

方法2：

硬件访问服务：发送请求服务—jni。不同硬件对应不同服务。

1.2 LED应用开发

首先我们来写一个应用程序，这个应用程序主要目的是 实现对硬件LED的操作。

1.2.1开发框图

1.2.2编写android应用程序

（1）创建一个android应用程序工程

（2）编写布局代码

（3）添加按键和复选框的监听事件：

代码片段：

button.setOnClickListener(new MyButtonListener());

class MyButtonListener implements View.OnClickListener {    @Override    public void onClick(View v) {        HardControl hardControl = new HardControl();//依赖硬件        led_on = !led_on;        if (led_on) {            button.setText("ALL OFF");            led1.setChecked(true);            led2.setChecked(true);            led3.setChecked(true);            led4.setChecked(true);            for (int i = 0; i < 4; i++)                HardControl.ledCtrl(i, 1);        }
android:onClick="onCheckboxClicked"
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)            {                Toast.makeText(getApplicationContext(),"led1_on",Toast.LENGTH_LONG).show();                HardControl.ledCtrl(1, 1);            }
    else    {        Toast.makeText(getApplicationContext(),"led1_off",Toast.LENGTH_LONG).show();        HardControl.ledCtrl(1, 0);    }    break;case R.id.led2:
（4）申明本地java方法

HardControl.JAVA：

package com.example.yangfei.hardlibrary;public class HardControl {    public static native int ledCtrl(int which, int status);    public static native int ledOpen();    public static native void ledClose();//申明三个本地方法。    static {        try {            System.loadLibrary("hardcontrol");        } catch (Exception e) {            e.printStackTrace();        }    }}

（5）修改build.gradle，告诉系统库在哪里放着

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

（6）在app/libs下建armeabi子目录，放入so文件（so怎么得到看下一节JNI文件的编写）

onCreate： HardControl.ledCtrl(0, 1);

1.3 JNI文件编写hardcontrol.c

（1）基本的JNI访问C库实现hardcontrol.c

#include <jni.h>  /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */#include <stdio.h>#include <stdlib.h>#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;#endifjint ledOpen(JNIEnv *env, jobject cls){return 0;}void ledClose(JNIEnv *env, jobject cls){}jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status){return 0;}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/example/yangfei/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;}

编译hardcontrol.c生成SO文件

arm-linux-gcc -fPIC -shared hardcontrol.c -o libhardcontrol.so -I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/  -nostdlib /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so

-I/usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ ： jni.h的存放目录

-nostdlib  不使用标准库 是android系统源码里的 如下：

/work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so   ： 指定libc.so，因为依赖于这个库

（2）加入打印信息hardcontrol.c

使用：__android_log_print(ANDROID_LOG_DEBUG,"LEDDemo", "native ledOpen ...");

#include <jni.h>  /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */#include <stdio.h>#include <stdlib.h>#include <android/log.h>  /* 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;#endifjint ledOpen(JNIEnv *env, jobject cls){__android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledOpen ...");return 0;}void ledClose(JNIEnv *env, jobject cls){__android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledClose ...");}jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status){__android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledCtrl : %d, %d", which, status);return 0;}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;}

编译

arm-linux-gcc -fPIC -shared hardcontrol.c -o libhardcontrol.so -I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/  -nostdlib /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so -I /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/include /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/liblog.so

（3）hardcontrol.c加入底层控制生成 libhardcontrol.so

#include <jni.h>  /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */#include <stdio.h>#include <stdlib.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <sys/ioctl.h>#include <android/log.h>  /* 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;elsereturn -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;}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/example/yangfei/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;}

编译：

arm-linux-gcc -fPIC -shared hardcontrol.c -o libhardcontrol.so -I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/  -nostdlib /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so -I /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/include /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/liblog.so

1.4 编写驱动程序leds_4412.c（驱动编译进linux内核，并创建设备节点）

（1）驱动程序编写

应用程序的不会看原理图，只会用open read write。

参考内核中的厂家驱动代码：

#include <linux/kernel.h>#include <linux/module.h>#include <linux/miscdevice.h>#include <linux/device.h>#include <linux/fs.h>#include <linux/types.h>#include <linux/moduleparam.h>#include <linux/slab.h>#include <linux/ioctl.h>#include <linux/cdev.h>#include <linux/delay.h> #include <linux/gpio.h>#include <mach/gpio.h>#include <plat/gpio-cfg.h>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 = {/* 结构 */    .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)/* 入口函数 */{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)/* 出口函数 */{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("www.100ask.net");

（2）编译驱动程序

leds_4412.c放入内核 drivers/char

修改drivers/char/Makefile，添加：

obj-y += leds_4412.o

重新编译内核

make zImage

work/linux-3.0.86/arch/boot/zImage

下载内核到开发板

Cat /proc/devices

1.5启动应用 测试程序。

APP,JNI,驱动代码下载地址：

点击打开链接

http://download.csdn.net/detail/fengyuwuzu0519/9755859