NDK & JNI方式读写Android系统的demo(二)

最新推荐文章于 2023-05-07 00:34:11 发布

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最新推荐文章于 2023-05-07 00:34:11 发布

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文章标签： NDK JNI

本文链接：https://blog.youkuaiyun.com/Darlingqiang/article/details/79078704

本文介绍如何使用NDK和JNI技术实现对Android系统的GPIO进行读写操作。通过创建Java类和对应的C/C++代码，实现了GPIO的导出、设置方向、读取状态、写入状态和取消导出等功能。

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NDK & JNI（方式读写Android系统的Ｄｅｍｏ）

大家都知道Android系统是一种基于Linux的自由及开放源码的操作系统，所以读写GPIO也可以直接用Linux那一套export/unexport方法，本文将介绍如何使用NDK jni方式来读写Android系统的GPIO。

1.环境的具体配置参考博客：http://blog.youkuaiyun.com/darlingqiang/article/details/79049638

2. Android Studio安装NDK

打开Android Studio 中的SDK Manager，菜单Tools -> Android -> SDK Manager

查看安装情况如下，如果没有安装完整的话，请选中NDK，点击OK就可以安装NDK

3. 创建Android工程

(1) 创建Android工程jnigpio，然后添加一个新的java类GPIOControl.java

代码如下：


public class GPIOControl {
    static {
        System.loadLibrary("GPIOControl");
    }

    public final static native int exportGpio(int gpio);
    public final static native int setGpioDirection(int gpio, int direction);
    public final static native int readGpioStatus(int gpio);
    public final static native int writeGpioStatus(int gpio, int value);
    public final static native int unexportGpio(int gpio);

}

(2) Build -> Rebuild Project即可，会生成 .ｃｌａｓｓ文件

(3) 生成jni的头文件

Android Studio Terminal中输入如下命令：cd app/src/main/java/
Ｔｅｒｎｉａｌ执行: javah -d jni com.sun.jnigpio.GPIOControl(前面博客有介绍具体的意思)

生成jni头文件如下图：生成　

(4) jni目录下创建GPIOControl.c程序
代码如下：

//
// Created by Gavin Zhuang on 05/12/2017.
//

#include <jni.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <android/log.h>

#include "com_zhuang_jnigpio_GPIOControl.h"

#define TAG "jni_gpio"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,TAG ,__VA_ARGS__)
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,TAG ,__VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG ,__VA_ARGS__)
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,TAG ,__VA_ARGS__)

#define IN              0
#define OUT             1
#define LOW             0
#define HIGH            1

#define BUFFER_MAX    3
#define DIRECTION_MAX 48

/*
 * Class:     com_zhuang_jnigpio_GPIOControl
 * Method:    exportGpio
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_zhuang_jnigpio_GPIOControl_exportGpio(JNIEnv *env, jobject instance, jint gpio)
{
    char buffer[BUFFER_MAX];
    int len;
    int fd;

    fd = open("/sys/class/gpio/export", O_WRONLY);
    if (fd < 0) {
        LOGE("Failed to open export for writing!\n");
        return(0);
    }

    len = snprintf(buffer, BUFFER_MAX, "%d", gpio);
    if (write(fd, buffer, len) < 0) {
        LOGE("Fail to export gpio!\n");
        return 0;
    }

    close(fd);
    return 1;
}

/*
 * Class:     com_zhuang_jnigpio_GPIOControl
 * Method:    setGpioDirection
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zhuang_jnigpio_GPIOControl_setGpioDirection(JNIEnv *env, jobject instance, jint gpio, jint direction)
{
    static const char dir_str[]  = "in\0out";
    char path[DIRECTION_MAX];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/direction", gpio);
    fd = open(path, O_WRONLY);
    if (fd < 0) {
        LOGE("failed to open gpio direction for writing!\n");
        return 0;
    }

    if (write(fd, &dir_str[direction == IN ? 0 : 3], direction == IN ? 2 : 3) < 0) {
        LOGE("failed to set direction!\n");
        return 0;
    }

    close(fd);
    return 1;
}

/*
 * Class:     com_zhuang_jnigpio_GPIOControl
 * Method:    readGpioStatus
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_zhuang_jnigpio_GPIOControl_readGpioStatus(JNIEnv *env, jobject instance, jint gpio)
{
    char path[DIRECTION_MAX];
    char value_str[3];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/value", gpio);
    fd = open(path, O_RDONLY);
    if (fd < 0) {
        LOGE("failed to open gpio value for reading!\n");
        return -1;
    }

    if (read(fd, value_str, 3) < 0) {
        LOGE("failed to read value!\n");
        return -1;
    }

    close(fd);
    return (atoi(value_str));
}

/*
 * Class:     com_zhuang_jnigpio_GPIOControl
 * Method:    writeGpioStatus
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_zhuang_jnigpio_GPIOControl_writeGpioStatus(JNIEnv *env, jobject instance, jint gpio, jint value)
{
    static const char values_str[] = "01";
    char path[DIRECTION_MAX];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/value", gpio);
    fd = open(path, O_WRONLY);
    if (fd < 0) {
        LOGE("failed to open gpio value for writing!\n");
        return 0;
    }

    if (write(fd, &values_str[value == LOW ? 0 : 1], 1) < 0) {
        LOGE("failed to write value!\n");
        return 0;
    }

    close(fd);
    return 1;
}

/*
 * Class:     com_zhuang_jnigpio_GPIOControl
 * Method:    unexportGpio
 * Signature: (I)I
 */
JNIEXPORT jint JNICALL Java_com_zhuang_jnigpio_GPIOControl_unexportGpio(JNIEnv *env, jobject instance, jint gpio)
{
    char buffer[BUFFER_MAX];
    int len;
    int fd;

    fd = open("/sys/class/gpio/unexport", O_WRONLY);
    if (fd < 0) {
        LOGE("Failed to open unexport for writing!\n");
        return 0;
    }

    len = snprintf(buffer, BUFFER_MAX, "%d", gpio);
    if (write(fd, buffer, len) < 0) {
        LOGE("Fail to unexport gpio!");
        return 0;
    }

    close(fd);
    return 1;
}

android.useDeprecatedNdk=true

在defaultConfig中添加ndk内容：
ndk{
        moduleName "GPIOControl" //so文件: lib+moduleName+.so
        ldLibs "log", "z", "m" // 添加android日志引用
        abiFilters "armeabi", "armeabi-v7a", "x86" //cpu的类型
    }3

(6) Rebuild Project 生成so文件 
so文件在app>build>intermediates>ｍａｋｅ>debug>lib>目录下，如图： 

(7) 方法调用
    // 定义GPIO输入输出方式和高低电平
    public final static int GPIO_DIRECTION_IN = 0;
    public final static int GPIO_DIRECTION_OUT = 1;
    public final static int GPIO_VALUE_LOW = 0;
    public final static int GPIO_VALUE_HIGH = 1;
                         Thread.sleep(1000);
                            }
                            GPIOControl.unexportGpio(gpioPin);
                        } catch (Exception ex){

                        }
                    }
                });

                thread.start();
            }
        });
注意事项：该控制GPIO需要su权限，可以试着用adb shell去修改 /sys/class/gpio/export 和 /sys/class/gpio/unexport 的读写权限。如：chmod 666 /sys/class/export
参考自博客：http://blog.youkuaiyun.com/zjc3909/article/details/78732374