/************************************************************************************

  *

  *                    android_serialport_api hacking

  *

  *  声明:

  *      1. 这是android_serialport_api的jni源代码解读;

  *      2. 源代码url: https://code.google.com/p/android-serialport-api/

  *      3. 可以从中知道JNI是如何查找类，创建对象，访问对象的属性等等内容;

  *

  *

  * Copyright 2009-2011 Cedric Priscal

  *

  * Licensed under the Apache License, Version 2.0 (the "License");

  * you may not use this file except in compliance with the License.

  * You may obtain a copy of the License at

  *

  * http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  *

  *

  *

  * 相关参考：

  *    1. 访问JAVA中的字段(jfieldID): http://www.cnblogs.com/lijunamneg/archive/2012/12/22/2829023.html

  *    2. JNIEnv解析: http://blog.csdn.net/freechao/article/details/7692239

  *    3. The Java™ Native Interface Programmer’s Guide and Specification

  *

  *****************************************************************************/

 #include <termios.h>

 #include <unistd.h>

 #include <sys/types.h>

 #include <sys/stat.h>

 #include <fcntl.h>

 #include <string.h>

 #include <jni.h>

 #include "SerialPort.h"

 #include "android/log.h"

 /**

  * 定义一些宏，方便写调试代码

  */

 static const char *TAG="serial_port";

 #define LOGI(fmt, args...) __android_log_print(ANDROID_LOG_INFO,  TAG, fmt, ##args)

 #define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, TAG, fmt, ##args)

 #define LOGE(fmt, args...) __android_log_print(ANDROID_LOG_ERROR, TAG, fmt, ##args)

 static speed_t getBaudrate(jint baudrate)

 {

     switch(baudrate) {

     case : return B0;

     case : return B50;

     case : return B75;

     case : return B110;

     case : return B134;

     case : return B150;

     case : return B200;

     case : return B300;

     case : return B600;

     case : return B1200;

     case : return B1800;

     case : return B2400;

     case : return B4800;

     case : return B9600;

     case : return B19200;

     case : return B38400;

     case : return B57600;

     case : return B115200;

     case : return B230400;

     case : return B460800;

     case : return B500000;

     case : return B576000;

     case : return B921600;

     case : return B1000000;

     case : return B1152000;

     case : return B1500000;

     case : return B2000000;

     case : return B2500000;

     case : return B3000000;

     case : return B3500000;

     case : return B4000000;

     default: return -;

     }

 }

 /*

  * Class:     com_android_aplex_SerialPort

  * Method:    open

  * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;

  */

 JNIEXPORT jobject JNICALL Java_com_android_aplex_SerialPort_open

   (JNIEnv *env, jclass thiz, jstring path, jint baudrate, jint flags)

 {

     int fd;

     speed_t speed;

     jobject mFileDescriptor;    //保存文件描述符的对象引用

     // Check arguments

     {

         speed = getBaudrate(baudrate);

         if (speed == -) {

             // TODO: throw an exception

             LOGE("Invalid baudrate");

             return NULL;

         }

     }

     // Opening device

     {

         jboolean iscopy;

         /**

          * 将Java的字符串转换成C中的字符串

          */

         const char *path_utf = (*env)->GetStringUTFChars(env, path, &iscopy);

         LOGD("Opening serial port %s with flags 0x%x", path_utf, O_RDWR | flags);

         fd = open(path_utf, O_RDWR | flags);

         LOGD("open() fd = %d", fd);

         /**

          * 和前面的GetStringUTFChars一对用法，相当于malloc和free

          */

         (*env)->ReleaseStringUTFChars(env, path, path_utf);

         if (fd == -)

         {

             // Throw an exception

             LOGE("Cannot open port");

             // TODO: throw an exception

             return NULL;

         }

     }

     // Configure device

     {

         struct termios cfg;

         LOGD("Configuring serial port");

         if (tcgetattr(fd, &cfg))

         {

             LOGE("tcgetattr() failed");

             close(fd);

             // TODO: throw an exception

             return NULL;

         }

         cfmakeraw(&cfg);

         cfsetispeed(&cfg, speed);

         cfsetospeed(&cfg, speed);

         if (tcsetattr(fd, TCSANOW, &cfg))

         {

             LOGE("tcsetattr() failed");

             close(fd);

             // TODO: throw an exception

             return NULL;

         }

     }

     // Create a corresponding file descriptor

     {

         /**

          * Returns a reference to the named class or interface.

          * 这个相当于在当前虚拟机加载的所有的类中找这个类：java/io/FileDescriptor

          */

         jclass cFileDescriptor = (*env)->FindClass(env, "java/io/FileDescriptor");

         /**

          * To obtain the method ID of a constructor, supply "<init>" as the method name and “V” as the return type.

          * 获取类中的无参构造函数

          */

         jmethodID iFileDescriptor = (*env)->GetMethodID(env, cFileDescriptor, "<init>", "()V");

         jfieldID descriptorID = (*env)->GetFieldID(env, cFileDescriptor, "descriptor", "I");

         /**

          * Constructs a new object. The method ID indicates which constructor method to invoke. This ID may be obtained by calling

          * GetMethodID with "<init>" as the method name and “V” as the return type. The constructor must be defined in the class

          * referred to by clazz, not one of its superclasses.

          * 生成一个类对象

          */

         mFileDescriptor = (*env)->NewObject(env, cFileDescriptor, iFileDescriptor);

         /**

          * Sets the value of an instance field of an object. The obj reference must not be NULL.

          * 设置对象的值

          */

         (*env)->SetIntField(env, mFileDescriptor, descriptorID, (jint)fd);

     }

     return mFileDescriptor;

 }

 /*

  * Class:     com_android_aplex_SerialPort

  * Method:    close

  * Signature: ()V

  */

 JNIEXPORT void JNICALL Java_com_android_aplex_SerialPort_close

   (JNIEnv *env, jobject thiz)

 {

     /**

      * Returns the class of an object. The obj reference must not be NULL.

      * thiz为java层传入的对象，GetObjectClass相当于获得这个对象的类，名字取得不错

      */

     jclass SerialPortClass = (*env)->GetObjectClass(env, thiz);

     /**

      * FindClass initializes the class or interface it returns.

      * 这个相当于在当前虚拟机加载的所有的类中找这个类：java/io/FileDescriptor

      */

     jclass FileDescriptorClass = (*env)->FindClass(env, "java/io/FileDescriptor");

     /**

      * Returns the field ID for an instance field of a class

      * 通过域名、域类型获取类对应的域ID号

      */

     jfieldID mFdID = (*env)->GetFieldID(env, SerialPortClass, "mFd", "Ljava/io/FileDescriptor;");

     jfieldID descriptorID = (*env)->GetFieldID(env, FileDescriptorClass, "descriptor", "I");

     /**

      * Returns the value of a field of an instance. The field to access is specified by a field ID.

      * 通过对象对应域的ID号获取域对象，或者值

      */

     jobject mFd = (*env)->GetObjectField(env, thiz, mFdID);

     jint descriptor = (*env)->GetIntField(env, mFd, descriptorID);

     LOGD("close(fd = %d)", descriptor);

     close(descriptor);

 }