关于串口编程的总结

这部分源码一直没变过,不过现在Android Studio已经支持Cmake方式了,所以不需要单独编译动态链接库了,可以直接修改Cmake文件和C文件

说明

开源库: https://github.com/cepr/android-serialport-api

  1. 参照AS的带C方式创建cpp文件夹,记得把配置也加上。
  2. 把开源库中的 SerialPort.cSerialPort.h 拷贝下来,放入cpp文件夹中
  3. 创建CMake文件,我这里直接拷贝的AS的 CMakeLists.txt

经过以上3步,基本工作就做完了,这时候你的cpp库有3个文件: CMakeLists.txt 文件, c文件和头文件。

然后剩下的就是定义调用串口的文件了

修改代码

修改SerialPort头文件和C代码

以下是 SerialPort.c 文件,除了输出的 JNICALL 基本没啥要改的

  • 格式是Java_包名_类名_方法名 ,用下划线隔开
  • 下面要创建的java类及方法一定要严格对应
  • 头文件和C代码的 JNICALL 保持同名
  /*
   * 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 <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"
  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;
    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:     android_serialport_SerialPort
   * Method:    open
   * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
   */
  JNIEXPORT jobject JNICALL Java_com_jiataoyuan_serialport_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:     cedric_serial_SerialPort
   * Method:    close
   * Signature: ()V
   */
  JNIEXPORT void JNICALL Java_com_jiataoyuan_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);
  }

修改CMake文件

  • add_library

  • 1参设置库名(你要在java中加载的库名称),

  • 2参设置共享(基本都是SHARE),
  • 3参设置源文件的相对路径(因为在同一目录下,直接写文件名即可)

  • find_library

这个东西我也没搞明白,看说明是用来搜索库路径的,但是因为有默认值,所以只需要指定NDK就行了,而且删了也不影响什么

  • target_link_libraries

  • 1参指定目标库,就是上面设置的库

  • 2参用来连接到日志库,已经包含在nkd中了,如果你的 find_library 默认的话,这里也默认就行了,如果 find_library 删掉的话,这里也删掉
  # 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.
          SerialPort
          # 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.
          SerialPort
          # Links the target library to the log library
          # included in the NDK.
          ${log-lib})

创建SerialPort

这个文件我改了一点,变化不大,你也可以直接用开源库中的,主要内容如下:

  • 获取串口:改动部分为将可读写改为可读写可执行
  • 获取读写流
  • 设置jni方法 ,打开和关闭,其中打开方法是私有方法
  /*
   * 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.
   */

  package com.jiataoyuan.serialport;

  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";

      static {
          System.loadLibrary("SerialPort");
      }

      /*
       * Do not remove or rename the field mFd: it is used by native method close();
       */
      private FileDescriptor mFd; //文件描述
      private FileInputStream mFileInputStream;  // 输入流
      private FileOutputStream mFileOutputStream;  // 输出流

      /**
       * 获取串口
       *
       * @param device   设备
       * @param baudrate 波特率
       * @param flags    标志符
       * @throws SecurityException
       * @throws IOException
       */
      public SerialPort(File device, int baudrate, int flags) throws SecurityException, IOException {

          /* 检查访问权限 */
          if (!device.canRead() || !device.canWrite()) {
              try {
                  /* Missing read/write permission, trying to chmod the file */
                  Process su;
                  su = Runtime.getRuntime().exec("/system/bin/su");
                  String cmd = "chmod 777 " + device.getAbsolutePath() + "\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();
              }
          }

          // 如果打不开返回null
          mFd = open(device.getAbsolutePath(), baudrate, flags);
          if (mFd == null) {
              Log.e(TAG, "native open returns null");
              throw new IOException();
          }
          mFileInputStream = new FileInputStream(mFd);
          mFileOutputStream = new FileOutputStream(mFd);
      }

      // Getters and setters
      public InputStream getInputStream() {
          return mFileInputStream;
      }

      public OutputStream getOutputStream() {
          return mFileOutputStream;
      }

      // JNI
      private native static FileDescriptor open(String path, int baudrate, int flags);

      public native void close();


  }

封装SerialPortActivity

为啥封装成这样子,因为我的串口调试助手,所以最后改成这样子了,通俗易懂

/*
 * 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.
 */

package com.jiataoyuan.serialport;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;

import com.jiataoyuan.dronetrack.R;
import com.jiataoyuan.dronetrack.utils.MyConstantUtils;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.InvalidParameterException;


public abstract class SerialPortActivity extends Activity {

    protected SerialPort mSerialPort;
    protected OutputStream mOutputStream;
    private InputStream mInputStream;
    private ReadThread mReadThread;

    // 根据需要修改线程
    private class ReadThread extends Thread {

        @Override
        public void run() {
            super.run();
            int size;
            byte[] buffer = new byte[64];
            StringBuilder sb = new StringBuilder();
            while (!isInterrupted()) {

                try {

                    if ((size = mInputStream.read(buffer)) != -1) {
                        sb.append(new String(buffer, 0, size));
                        onDataReceived(sb.toString());
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                    return;
                }
            }

        }
    }

    // 打印错误消息弹框
    private void DisplayError(int resourceId) {
        AlertDialog.Builder b = new AlertDialog.Builder(this);
        b.setTitle("Error");
        b.setMessage(resourceId);
        b.setPositiveButton("OK", new OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                SerialPortActivity.this.finish();
            }
        });
        b.show();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        try {
            if (null == mSerialPort) {
                // 1参 串口 根据你的串口情况填入,如"/dev/ttyS4" , "/dev/ttyS1"
                // 2参 波特率 根据约定填入,如19200 ,115200
                // 3参 标志位 根据约定填入,没有填0
                mSerialPort = new SerialPort(new File(MyConstantUtils.SerialPortPath), MyConstantUtils.baudrate, 0);
            }
            mOutputStream = mSerialPort.getOutputStream();
            mInputStream = mSerialPort.getInputStream();

            /* Create a receiving thread */
            mReadThread = new ReadThread();
            mReadThread.start();
        } catch (SecurityException e) {
            DisplayError(R.string.error_security);
        } catch (IOException e) {
            DisplayError(R.string.error_unknown);
        } catch (InvalidParameterException e) {
            DisplayError(R.string.error_configuration);
        }
    }

    // 定义接收的抽象方法
    protected abstract void onDataReceived(String buffer);

    // 发送消息
    public void sendMsg(byte[] msg) {
        try {
            mOutputStream = mSerialPort.getOutputStream();
            if (msg.length > 0) {
                mOutputStream.write(msg);
                mOutputStream.flush();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 关闭端口
    public void closeSerialPort() {
        if (mSerialPort != null) {
            mSerialPort.close();
            mSerialPort = null;
        }
    }

    @Override
    protected void onDestroy() {
        if (mReadThread != null)
            mReadThread.interrupt();
        closeSerialPort();
        mSerialPort = null;
        super.onDestroy();
    }
}

调用

要调用的Activity需要继承 SerialPortActivity ,并实现 onDataReceived 方法

    @Override
    protected void onDataReceived(String buffer) {
        mBuffer = buffer;
        Handler handler = new Handler(Looper.getMainLooper());
        handler.postDelayed(runnable, 100);

    }
    private void send(String msg) {
        sendMsg(msg.getBytes());
    }

    private void send(byte[] msg) {
        sendMsg(msg);
        L.e(new String(msg));
    }
  • 开关串口都在 SerialPortActivity 的create和destroy方法中调用了,应用逻辑无需管理

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