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tcaddr()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。

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。