android 项目串口通信（serialPort）开发遇到的炕

android 项目开发中使用到串口通信功能，在过程中遇到了一些炕。
一、首先要安装Cmake以及 ndk工具。

二、在跟main 目录下创建cpp 文件夹，以及CMakeLists.text 、SerialPort.c 文件

三、在CMakeLists.text 文件中编写生成动态so库

# For more information about using CMake with Android Studio, read the# documentation: https://d.android.com/studio/projects/add-native-code.html# Sets the minimum version of CMake required to build the native library.cmake_minimum_required(VERSION 3.4.1)# Creates and names a library, sets it as either STATIC# or SHARED, and provides the relative paths to its source code.# You can define multiple libraries, and CMake builds them for you.# Gradle automatically packages shared libraries with your APK.add_library( # Sets the name of the library.        native-lib        # Sets the library as a shared library.        SHARED        # Provides a relative path to your source file(s).        SerialPort.c        )# Searches for a specified prebuilt library and stores the path as a# variable. Because CMake includes system libraries in the search path by# default, you only need to specify the name of the public NDK library# you want to add. CMake verifies that the library exists before# completing its build.find_library( # Sets the name of the path variable.        log-lib        # Specifies the name of the NDK library that        # you want CMake to locate.        log)# Specifies libraries CMake should link to your target library. You# can link multiple libraries, such as libraries you define in this# build script, prebuilt third-party libraries, or system libraries.target_link_libraries( # Specifies the target library.        native-lib        # Links the target library to the log library        # included in the NDK.        ${log-lib})

四、在SerialPort.c 文件中写调用jni 接口，一般都是使用android 标准串口。

/* * Copyright 2009 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 o0r 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. */#include #include #include #include #include #include #include #include "android/log.h"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 0: return B0;case 50: return B50;case 75: return B75;case 110: return B110;case 134: return B134;case 150: return B150;case 200: return B200;case 300: return B300;case 600: return B600;case 1200: return B1200;case 1800: return B1800;case 2400: return B2400;case 4800: return B4800;case 9600: return B9600;case 19200: return B19200;case 38400: return B38400;case 57600: return B57600;case 115200: return B115200;case 230400: return B230400;case 460800: return B460800;case 500000: return B500000;case 576000: return B576000;case 921600: return B921600;default: return -1;}}/* * Class:     cedric_serial_SerialPort * Method:    open * Signature: (Ljava/lang/String;)V */JNIEXPORT jobject JNICALL Java_com_serialPort_SerialPort_open  (JNIEnv *env, jobject thiz, jstring path, jint baudrate){int fd;speed_t speed;jobject mFileDescriptor;/* Check arguments */{speed = getBaudrate(baudrate);if (speed == -1) {return NULL;}}/* Opening device */{jboolean iscopy;const char *path_utf = (*env)->GetStringUTFChars(env, path, &iscopy);LOGD("Opening serial port %s", path_utf);fd = open(path_utf, O_RDWR | O_SYNC);LOGD("open() fd = %d", fd);(*env)->ReleaseStringUTFChars(env, path, path_utf);if (fd == -1){/* 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 */{jclass cFileDescriptor = (*env)->FindClass(env, "java/io/FileDescriptor");jmethodID iFileDescriptor = (*env)->GetMethodID(env, cFileDescriptor, "", "()V");jfieldID descriptorID = (*env)->GetFieldID(env, cFileDescriptor, "descriptor", "I");mFileDescriptor = (*env)->NewObject(env, cFileDescriptor, iFileDescriptor);(*env)->SetIntField(env, mFileDescriptor, descriptorID, (jint)fd);}return mFileDescriptor;}/* * Class:     cedric_serial_SerialPort * Method:    close * Signature: ()V */JNIEXPORT void JNICALL Java_com_serialPort_SerialPort_close  (JNIEnv *env, jobject thiz){jclass SerialPortClass = (*env)->GetObjectClass(env, thiz);jclass FileDescriptorClass = (*env)->FindClass(env, "java/io/FileDescriptor");jfieldID mFdID = (*env)->GetFieldID(env, SerialPortClass, "mFd", "Ljava/io/FileDescriptor;");jfieldID descriptorID = (*env)->GetFieldID(env, FileDescriptorClass, "descriptor", "I");jobject mFd = (*env)->GetObjectField(env, thiz, mFdID);jint descriptor = (*env)->GetIntField(env, mFd, descriptorID);LOGD("close(fd = %d)", descriptor);close(descriptor);}

五、创建Serialport文件：

 * Copyright 2009 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. */import android.util.Log;import java.io.File;import java.io.FileDescriptor;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;public class SerialPort {    private static final String TAG = "SerialPort";    /*     * Do not remove or rename the field mFd: it is used by native method close();     */    private FileDescriptor mFd;    private FileInputStream mFileInputStream;    private FileOutputStream mFileOutputStream;    public SerialPort(File device, int baudrate) throws SecurityException, IOException {        /* Check access permission *///if (!device.canRead() || !device.canWrite()) {//try {///* Missing read/write permission, trying to chmod the file *///Process su;//su = Runtime.getRuntime().exec("/system/xbin/su");///*String cmd = "chmod 777 " + device.getAbsolutePath() + "\n"//+ "exit\n";*///String cmd = "chmod 777 /dev/ttyS4" + "\n"//+ "exit\n";//su.getOutputStream().write(cmd.getBytes());//if ((su.waitFor() != 0) || !device.canRead()//|| !device.canWrite()) {//throw new SecurityException();//}//} catch (Exception e) {//e.printStackTrace();//throw new SecurityException();//}//}        //        mFd = open(device.getAbsolutePath(), baudrate, 0);        if (mFd == null) {            Log.e(TAG, "native open returns null");            throw new IOException();        }        mFileInputStream = new FileInputStream(mFd);        mFileOutputStream = new FileOutputStream(mFd);    }        public InputStream getInputStream() {        return mFileInputStream;    }    public OutputStream getOutputStream() {        return mFileOutputStream;    }        private native static FileDescriptor open(String path, int baudrate);    public native void close();    public native static FileDescriptor open(String path, int baudrate, int flags);  }

要注意文件路径创建要跟jni调用路径一直否则调用不到，出现找不到方法的异常，特别是编译好so库之后，给第三方使用要注明
六、读取线程

  class ReadThread extends Thread{        @Override        public void run() {            super.run();            byte[] bytes = new byte[1024];            while (!isInterrupted()){                int size = 0;                    try {                      if (mInputStream != null) {                          if (mInputStream.available() > 0 ) {                              SystemClock.sleep(2);                            try {                                size = mInputStream.read(bytes);                                if (size > 0) {                                     Log.i("SerialPort_test","==== " + bytes );                                }                            } catch (IOException e) {                                e.printStackTrace();                            }                        }                      }                    } catch (Exception e) {                        e.printStackTrace();                    }            }        }    }

**在通信过程中如数据比较大，可以会遇到数据读取不完整，感觉有掉帧一样，执行mInputStream.available()，这时可以在读取之前先延时一段时间，再一次文件流读取数据，
避免数据的错乱，接着过滤协议数据。
**读线程所在的类实例最好是一个单列模式，以避免多线程操作创建不同的对象，否则会读取到数据也跟掉帧一样，多线程并发还是要注意的！！！

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