大家好，又见面了，我是你们的朋友全栈君。

关于Linux串口的一些小知识

1. 串口名称使用 ls -l /dev/ttyS* 一般情况下串口的名称全部在dev下面，如果你没有外插串口卡的话默认是dev下的ttyS*,一般ttyS0对应com1，ttyS1对应com2，当然也不一定是必然的；

2. 记得看一下串口的权限，是不是rw-rw-rw-，不是的话请运行chmod 666 /dev/ttyS\*给予可读写权限。

3. 检查串口是否可用，可以对串口发送数据比如对com1口，echo Hello > /dev/ttyS0。

4. 串口驱动：cat /proc/tty/drivers/sw_serial。

5. 在PC上查看连接到CubieBoard2的串口设备：dmesg | grep ttyS*。
   
dmesg | grep ttyS*
[ 0.000000] console [tty0] enabled
[ 6.246827] systemd[1]: Created slice system-getty.slice.
[ 13.740764] usb 3-4: ch341-uart converter now attached to ttyUSB0


以下内容均在Android Studio中实现

配置环境

配置JAVA

下载并配置好JAVA（JAVA_HOME、CLASSPATH、PATH），CMD中要能使用javah命令。

配置gradle

1. 在gradle目录中找到gradle-wrapper.properties文件。
   修改其中配置为distributionUrl=https://services.gradle.org/distributions/gradle-2.10-all.zip。
   gradle必须高于一定的版本，好像网上说NDK支持是后面加进来的。

   在菜单中File->Project Structure->Project中修改Gradle version为2.10也可以，改完后OK。

2. 项目中的build.gradle

   // Top-level build file where you can add configuration options common to all sub-projects/modules. buildscript { 
        
       repositories {
           jcenter()
       }
       dependencies {
           classpath 'com.android.tools.build:gradle:2.1.2'
   
           // NOTE: Do not place your application dependencies here; they belong
           // in the individual module build.gradle files
       }
   }
   
   allprojects {
       repositories {
           jcenter()
       }
   }
   
   task clean(type: Delete) {
       delete rootProject.buildDir
   }

3. NDK
   在项目中local.properties中配置ndk，ndk应该没什么要求。

   ndk.dir=D:\\Programs\\Androidsdk\\ndk-bundle
   sdk.dir=D:\\Programs\\Androidsdk

   我用的是AS自动下载配置的，版本为android-ndk-r12d。

工程

新建

1. 新建一个类，类名为SerialPort。代码如下：

   package com.bilibili.www.serialporttest;
   
   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;
   
   import android.util.Log;
   
   public class SerialPort { 
        
       private static final String TAG = "SerialPort";
   
       // JNI
       static {
           //指定库名，需要和build.gradle中一致
           try {
               System.loadLibrary("serial_port");
           }
           catch (UnsatisfiedLinkError e) {
               Log.d(TAG, "Unsatisfied Link error: " + e.toString());
           }
       }
   
       private static native FileDescriptor open(String path, int baudrate, int flags);
       public native void close();
   
       /* * 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, int flags) 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/bin/su");//获得root
                   String cmd = "chmod 666 " + device.getAbsolutePath() + "\n"
                           + "exit\n";//全部用户权限为可读写
                   su.getOutputStream().write(cmd.getBytes());
                   if ((su.waitFor() != 0) || !device.canRead()
                           || !device.canWrite()) {
                       throw new SecurityException();
                   }
               } catch (Exception e) {
                   e.printStackTrace();
                   throw new SecurityException();
               }
           }
           Log.d(TAG, "Start！！！！！！！");
           mFd = open(device.getAbsolutePath(), baudrate, flags);
           if (mFd == null) {
               Log.e(TAG, "native open returns null");
               throw new IOException();
           }else {
               mFileInputStream = new FileInputStream(mFd);
               mFileOutputStream = new FileOutputStream(mFd);
           }
       }
   
       // Getters and setters
       public InputStream getInputStream() {
           return mFileInputStream;
       }
   
       public OutputStream getOutputStream() {
           return mFileOutputStream;
       }
   }

   1. 打开terminal，输入cd <你的工程位置>\app\src\main\java；输入javah -jni <你的包名>.<类名>。这里是如javah -jni com.bilibili.www.serialporttest.SerialPort
这样的命令，完成之后如果没有问题，会在java目录下出现一个com_bilibili_www_serialporttest_SerialPort.h的文件。

   2. 在<你的工程位置>\app\src\main目录下新建一个jni目录。

修改

1. 将com_bilibili_www_serialporttest_SerialPort.h文件放进jni目录。

2. 在jni目录下建立一个c文件，内容如下：

   /* * 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. */
   #include "com_bilibili_www_serialporttest_SerialPort.h"
   #include <termios.h>
   #include <unistd.h>
   #include <sys/types.h>
   #include <sys/stat.h>
   #include <fcntl.h>
   #include <string.h>
   #include <jni.h>
   //#include "android/log.h"
   #include <android/log.h>
   #ifdef __cplusplus
   extern "C" {
   #endif
   static const char *TAG="serial_port";
   /* 这三个函数是为了打印信息而存在 */
   #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;
   case 1000000: return B1000000;
   case 1152000: return B1152000;
   case 1500000: return B1500000;
   case 2000000: return B2000000;
   case 2500000: return B2500000;
   case 3000000: return B3000000;
   case 3500000: return B3500000;
   case 4000000: return B4000000;
   default: return -1;
   }
   }
   /* * Class: com_bilibili_www_serialporttest_SerialPort * Method: open * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor; */
   JNIEXPORT jobject JNICALL Java_com_bilibili_www_serialporttest_SerialPort_open
   (JNIEnv *env, jclass thiz, jstring path, jint baudrate, jint flags)
   {
   int fd;
   speed_t speed;
   jobject mFileDescriptor;
   /* Check arguments */
   {
   speed = getBaudrate(baudrate);
   if (speed == -1) {
   /* TODO: throw an exception */
   LOGE("Invalid baudrate");
   return NULL;
   }
   }
   /* Opening device */
   {
   jboolean iscopy;
   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);
   (*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, "<init>", "()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: com_bilibili_www_serialporttest_SerialPort * Method: close * Signature: ()V */
   JNIEXPORT void JNICALL Java_com_bilibili_www_serialporttest_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);
   }
   #ifdef __cplusplus
   }
   #endif
   

3. module里面的build.gradle

   import com.android.build.gradle.api.AndroidSourceSet
   apply plugin: 'com.android.application'
   android {
   compileSdkVersion 24
   buildToolsVersion "24.0.0"
   defaultConfig {
   applicationId "com.bilibili.www.serialporttest"
   minSdkVersion 16
   targetSdkVersion 19
   versionCode 1
   versionName "1.0"
   ndk {
   moduleName = "serial_port"
   ldLibs "log", "z", "m", "jnigraphics", "android"
   }
   }
   buildTypes {
   release {
   minifyEnabled false
   proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
   ndk {
   moduleName = "serial_port"//模块名，要和类SerialPort中的System.loadLibrary();一致
   ldLibs "log", "z", "m", "jnigraphics", "android"//所要链接的库
   abiFilters "armeabi", "armeabi-v7a", "x86" //输出指定三种abi体系结构下的so库，目前可有可无。没有的话就生成NDK能生成的所有平台，比如mips
   }
   }
   debug {
   ndk {
   moduleName = "serial_port"
   ldLibs "log", "z", "m", "jnigraphics", "android"
   abiFilters "armeabi", "armeabi-v7a", "x86"
   }
   }
   }
   productFlavors {
   }
   }
   dependencies {
   compile fileTree(include: ['*.jar'], dir: 'libs')
   testCompile 'junit:junit:4.12'
   compile 'com.android.support:appcompat-v7:24.0.0'
   }
   

4. MainActivity
   没有任何布局上的改变，要用控制台查看串口接受信息。这里我使用了接收，需要的话，可以自行添加发送代码。

   package com.bilibili.www.serialporttest;
   import android.support.v7.app.AppCompatActivity;
   import android.os.Bundle;
   import android.os.Handler;
   import java.io.File;
   import java.io.FileInputStream;
   import java.io.IOException;
   import java.util.Arrays;
   import android.util.Log;
   import android.os.Message;
   public class MainActivity extends AppCompatActivity { 
   
   private static final String TAG = "MainActivity";
   private static final int msgKey = 2;
   private File mFile;
   private FileInputStream mInputStream;
   private SerialPort mSerialPort;
   private ReadThread mThread;
   //private StringBuffer mSb;
   private String mSb;
   private boolean flag = true;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   try {
   mFile=new File("/dev/ttySAC0");
   mSerialPort = new SerialPort(mFile, 115200, 0);
   } catch (SecurityException e) {
   e.printStackTrace();
   } catch (IOException e) {
   e.printStackTrace();
   }
   mInputStream = (FileInputStream) mSerialPort.getInputStream();
   //启动线程
   mThread = new ReadThread();
   mThread.start();
   }
   public  static int searchByte(byte[] data, byte value) {
   int size = data.length;
   for (int i = 0; i < size; ++i) {
   if (data[i] == value) {
   return i;
   }
   }
   return -1;
   }
   public class ReadThread extends Thread { 
   
   @Override
   public void run() {
   // TODO Auto-generated method stub
   super.run();
   while (!isInterrupted()) {
   int size,couth = 128;
   try {
   Log.d(TAG, "----ReadThread start----");
   if (mInputStream == null) {
   return;
   }
   /* 获取可以读取的数据长度 */
   /*for(int coutq1 = mInputStream.available(); coutq1 != couth; coutq1 = mInputStream.available()) { try { sleep(10L); couth = mInputStream.available(); sleep(10L); } catch (InterruptedException e) { e.printStackTrace(); } }*/
   byte[] buffer = new byte[couth];
   Log.d(TAG, "----read(buffer)----");
   size = mInputStream.read(buffer);
   Log.d(TAG, "----size----" + String.valueOf(size));
   if (size > 0) {
   Log.d(TAG, "----ReadThread size>0----");
   /*mSb = new StringBuffer(); for (int i = 0; i < buffer.length; i++) { mSb.append(buffer[i]); } Log.d(TAG, "Data=" + mSb.toString());*/
   mSb=new String(Arrays.copyOfRange(buffer,0,size));
   Log.d(TAG, "Data=" + mSb);
   Message msg = new Message();
   msg.what = msgKey;
   mHandler.sendMessage(msg);
   }
   else {
   Log.d(TAG, "----ReadThread DataisNull----");
   }
   } catch (IOException e) {
   Log.d(TAG, "----ReadThread printStackTrace----");
   e.printStackTrace();
   return;
   }
   }
   }
   }
   private Handler mHandler = new Handler() {
   @Override
   public void handleMessage(Message msg) {
   super.handleMessage(msg);
   switch (msg.what) {
   case msgKey:
   //Log.e(TAG, mSb.toString());
   Log.e(TAG, mSb);
   break;
   default:
   break;
   }
   }
   };
   }

编译

1. Make Project(Ctrl + F9)
2. 在<你的工程位置>\app\build\intermediates\ndk\debug\lib目录中，你会发现”armeabi”, “armeabi-v7a”, “x86”三个目录，将他们复制到<你的工程位置>\app\libs中。

运行

GLHF!

问题与经验

1. 编译没有问题，运行时提示tcgetaddr()函数出现错误，找不到该函数。
   没有把”armeabi”, “armeabi-v7a”, “x86”文件夹放进<你的工程位置>\app\libs中，所以apk不包含这几个文件夹中的so二进制文件，所以出现找不到函数的情况。
   另外一种情况是由于api 19 之后的 termios.h 里面的函数有调整，因此调试过程中，出现

   java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol “tcgetattr” referenced by libserialport.so

   解决方法：

   将api 19 的 termios.h 拷贝到 jni 目录下

   termios.h

    /* * Copyright (C) 2008 The Android Open Source Project * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */
   #ifndef _TERMIOS_H_
   #define _TERMIOS_H_
   #include <sys/cdefs.h>
   #include <sys/ioctl.h>
   #include <sys/types.h>
   #include <stdint.h>
   #include <linux/termios.h>
   __BEGIN_DECLS
   /* Redefine these to match their ioctl number */
   #undef TCSANOW
   #define TCSANOW TCSETS
   #undef TCSADRAIN
   #define TCSADRAIN TCSETSW
   #undef TCSAFLUSH
   #define TCSAFLUSH TCSETSF
   static __inline__ int tcgetattr(int fd, struct termios *s)
   {
   return ioctl(fd, TCGETS, s);
   }
   static __inline__ int tcsetattr(int fd, int __opt, const struct termios *s)
   {
   return ioctl(fd, __opt, (void *)s);
   }
   static __inline__ int tcflow(int fd, int action)
   {
   return ioctl(fd, TCXONC, (void *)(intptr_t)action);
   }
   static __inline__ int tcflush(int fd, int __queue)
   {
   return ioctl(fd, TCFLSH, (void *)(intptr_t)__queue);
   }
   static __inline__ pid_t tcgetsid(int fd)
   {
   pid_t _pid;
   return ioctl(fd, TIOCGSID, &_pid) ? (pid_t)-1 : _pid;
   }
   static __inline__ int tcsendbreak(int fd, int __duration)
   {
   return ioctl(fd, TCSBRKP, (void *)(uintptr_t)__duration);
   }
   static __inline__ speed_t cfgetospeed(const struct termios *s)
   {
   return (speed_t)(s->c_cflag & CBAUD);
   }
   static __inline__ int cfsetospeed(struct termios *s, speed_t  speed)
   {
   s->c_cflag = (s->c_cflag & ~CBAUD) | (speed & CBAUD);
   return 0;
   }
   static __inline__ speed_t cfgetispeed(const struct termios *s)
   {
   return (speed_t)(s->c_cflag & CBAUD);
   }
   static __inline__ int cfsetispeed(struct termios *s, speed_t  speed)
   {
   s->c_cflag = (s->c_cflag & ~CBAUD) | (speed & CBAUD);
   return 0;
   }
   static __inline__ void cfmakeraw(struct termios *s)
   {
   s->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL|IXON);
   s->c_oflag &= ~OPOST;
   s->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
   s->c_cflag &= ~(CSIZE|PARENB);
   s->c_cflag |= CS8;
   }
   __END_DECLS
   #endif /* _TERMIOS_H_ */
   

   然后在c文件中，将#include <termios.h>改为#include "termios.h"。

2. 能运行，但是串口没有反应。
   请检查串口权限，要求other是可读可写的。