关于串口编程的总结

96
世外大帝
2019.05.17 17:04 字数 679

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
Android手记
Gupao