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！！！