NDK & JNI（方式讀寫Android系統的Ｄｅｍｏ）

大家都知道Android系統是一種基于Linux的自由及開放源碼的操作系統，所以讀寫GPIO也可以直接用Linux那一套export/unexport方法，本文將介紹如何使用NDK jni方式來讀寫Android系統的GPIO。

1.環境的具體配置參考博客：http://blog.csdn.net/darlingqiang/article/details/79049638

2. Android Studio安裝NDK

打開Android Studio 中的SDK Manager，菜單Tools -> Android -> SDK Manager

查看安裝情況如下，如果沒有安裝完整的話，請選中NDK，點擊OK就可以安裝NDK

3. 創建Android工程

(1) 創建Android工程jnigpio，然后添加一個新的java類GPIOControl.java

代碼如下：

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，會生成 .ｃｌａｓｓ文件

(3) 生成jni的頭文件

Android Studio Terminal中輸入如下命令：cd app/src/main/java/
Ｔｅｒｎｉａｌ執行:?????? javah -d jni com.sun.jnigpio.GPIOControl(前面博客有介紹具體的意思)

生成jni頭文件如下圖： 生成　

(4) jni目錄下創建GPIOControl.c程序
代碼如下：

//
// 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內容：
ndk{moduleName "GPIOControl" //so文件: lib+moduleName+.soldLibs "log", "z", "m" // 添加android日志引用abiFilters "armeabi", "armeabi-v7a", "x86" //cpu的類型}3

(6) Rebuild Project 生成so文件 
so文件在app>build>intermediates>ｍａｋｅ>debug>lib>目錄下，如圖： 

(7) 方法調用
    // 定義GPIO輸入輸出方式和高低電平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();}});
注意事項：該控制GPIO需要su權限，可以試著用adb shell去修改 /sys/class/gpio/export 和 /sys/class/gpio/unexport 的讀寫權限。如：chmod 666 /sys/class/export
參考自博客：http://blog.csdn.net/zjc3909/article/details/78732374?

總結

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