串口通信

接着上一篇，上一篇写的是产品模块通过usb口连接Android平板，Android平板通过usb host协议和产品模块通信。

实际上产品模块还可以通过串口和模块进行通信，因为我们的平板和模块都连有串口线。当然模块还可以直接和pc通过串口或者usb口通信，如果pc是笔记本的话，可以通过usb转串口的线来和模块通信，usb口的话直接连接就行了。

串口通信其实比较简单，android.serialport包下，有两个类，分别是SerialPort.java 和SerialPortFinder.java。

其中，SerialPort.java，这个类主要用来加载SO文件，通过JNI的方式打开关闭串口。

/* * 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 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 android_serialport_api;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, 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/xbin/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();}}mFd = open(device.getAbsolutePath(), baudrate, flags);if (mFd == null) {throw new IOException();}mFileInputStream = new FileInputStream(mFd);mFileOutputStream = new FileOutputStream(mFd);}// Getters and setterspublic InputStream getInputStream() {return mFileInputStream;}public OutputStream getOutputStream() {return mFileOutputStream;}// JNIprivate native static FileDescriptor open(String path, int baudrate, int flags);public native void close();static {try {          System.loadLibrary("serial_port");      } catch (UnsatisfiedLinkError ule) {          System.err.println("WARNING: Could not load serial_port library!");      } } }

可以看到在构造方法中调用了动态库中的方法open，然后由此open方法返回的FileDescriptor对象构造出输入输出流。此动态库Android也有提供，libserial_port.so，可以在你的工程libs下面创建一个armeabi文件夹，然后把此so文件放入这个文件夹下就可以进行调用了。

SerialPort serialPort = null;try {serialPort = new SerialPort(new File("/dev/ttyS1"),115200,0);} catch (SecurityException e) {} catch (IOException e) {}ins = serialPort.getInputStream();ous = serialPort.getOutputStream();new Thread(new Runnable() {@Overridepublic void run() {// TODO Auto-generated method stubtry {ous.write(sendCommand);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}).start();

这样就可以顺利的和串口进行通信了。

可以看到serialPort的构造参数new File("/dev/ttyS1")，直接可以把串口当做文件来读写就行了。当然前提是必须知道是哪个串口，因为在我们的平板上只有一个串口，而且硬件上已经确定这个串口就是串口1，所以我可以这么写。如果平板上有多个串口，而我不确定模块是和平板的哪个串口连接的，那我就必须先通过类SerialPortFinder.java来寻找连接的串口，找到了之后再进行如上操作。