提到串口編程,就不得不提到JNI,不得不提到JavaAPI中的文件描述符類:FileDescriptor。下面我分別對(duì)JNI、FileDescriptor以及串口的一些知識(shí)點(diǎn)和實(shí)現(xiàn)的源碼進(jìn)行分析說明。這里主要是參考了開源項(xiàng)目android-serialport-api。
串口編程需要了解的基本知識(shí)點(diǎn):對(duì)于串口編程,我們只需對(duì)串口進(jìn)行一系列的設(shè)置,然后打開串口,這些操作我們可以參考串口調(diào)試助手的源碼進(jìn)行學(xué)習(xí)。在Java中如果要實(shí)現(xiàn)串口的讀寫功能只需操作文件設(shè)備類:FileDescriptor即可,其他的事都由驅(qū)動(dòng)來完成不用多管!當(dāng)然,你想了解,那就得看驅(qū)動(dòng)代碼了。這里并不打算對(duì)驅(qū)動(dòng)進(jìn)行說明,只初略闡述應(yīng)用層的實(shí)現(xiàn)方式。
(一)JNI:
關(guān)于JNI的文章網(wǎng)上有很多,不再多做解釋,想詳細(xì)了解的朋友可以查看云中漫步的技術(shù)文章,寫得很好,分析也很全面,那么在這篇拙文中我強(qiáng)調(diào)3點(diǎn):
1、如何將編譯好的SO文件打包到APK中?(方法很簡(jiǎn)單,直接在工程目錄下新建文件夾 libs/armeabi,將SO文件Copy到此目錄即可)
2、命名要注意的地方?(在編譯好的SO文件中,將文件重命名為:libfilename.so即可。其中filename.so是編譯好后生成的文件)
3、MakeFile文件的編寫(不用多說,可以直接參考package/apps目錄下用到JNI的相關(guān)項(xiàng)目寫法)
這是關(guān)鍵的代碼:
- <span style="font-size:18px;"> int fd;
- speed_t speed;
- jobject mFileDescriptor;
-
-
- {
- speed = getBaudrate(baudrate);
- if (speed == -1) {
-
- LOGE("Invalid baudrate");
- return NULL;
- }
- }
-
-
- {
- 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)
- {
-
- LOGE("Cannot open port");
-
- return NULL;
- }
- }
-
-
- {
- struct termios cfg;
- LOGD("Configuring serial port");
- if (tcgetattr(fd, &cfg))
- {
- LOGE("tcgetattr() failed");
- close(fd);
-
- return NULL;
- }
-
- cfmakeraw(&cfg);
- cfsetispeed(&cfg, speed);
- cfsetospeed(&cfg, speed);
-
- if (tcsetattr(fd, TCSANOW, &cfg))
- {
- LOGE("tcsetattr() failed");
- close(fd);
-
- return NULL;
- }
- }
- </span>
(二)FileDescritor:
文件描述符類的實(shí)例用作與基礎(chǔ)機(jī)器有關(guān)的某種結(jié)構(gòu)的不透明句柄,該結(jié)構(gòu)表示開放文件、開放套接字或者字節(jié)的另一個(gè)源或接收者。文件描述符的主要實(shí)際用途是創(chuàng)建一個(gè)包含該結(jié)構(gòu)的FileInputStream
或FileOutputStream
。這是API的描述,不太好理解,其實(shí)可簡(jiǎn)單的理解為:FileDescritor就是對(duì)一個(gè)文件進(jìn)行讀寫。
(三)實(shí)現(xiàn)串口通信細(xì)節(jié)
1) 建工程:SerialDemo包名:org.winplus.serial,并在工程目錄下新建jni和libs兩個(gè)文件夾和一個(gè)org.winplus.serial.utils,如下圖:
2) 新建一個(gè)類:SerialPortFinder,添加如下代碼:
上面這個(gè)類在“android-serialport-api串口工具測(cè)試隨筆”中有詳細(xì)的說明,我就不多說了。
3)新建SerialPort類,這個(gè)類主要用來加載SO文件,通過JNI的方式打開關(guān)閉串口
- <span style="font-size:18px;">package org.winplus.serial.utils;
-
- 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";
-
-
-
-
-
- private FileDescriptor mFd;
- private FileInputStream mFileInputStream;
- private FileOutputStream mFileOutputStream;
-
- public SerialPort(File device, int baudrate, int flags)
- throws SecurityException, IOException {
-
-
- if (!device.canRead() || !device.canWrite()) {
- try {
-
- Process su;
- su = Runtime.getRuntime().exec("/system/bin/su");
- String cmd = "chmod 666 " + 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) {
- Log.e(TAG, "native open returns null");
- throw new IOException();
- }
- mFileInputStream = new FileInputStream(mFd);
- mFileOutputStream = new FileOutputStream(mFd);
- }
-
-
- public InputStream getInputStream() {
- return mFileInputStream;
- }
-
- public OutputStream getOutputStream() {
- return mFileOutputStream;
- }
-
-
- private native static FileDescriptor open(String path, int baudrate,
- int flags);
-
- public native void close();
-
- static {
- System.loadLibrary("serial_port");
- }
- }
- </span>
4) 新建一個(gè)Application 繼承android.app.Application,用來對(duì)串口進(jìn)行初始化和關(guān)閉串口
- <span style="font-size:18px;">package org.winplus.serial;
-
- import java.io.File;
- import java.io.IOException;
- import java.security.InvalidParameterException;
-
- import org.winplus.serial.utils.SerialPort;
- import org.winplus.serial.utils.SerialPortFinder;
-
- import android.content.SharedPreferences;
-
- public class Application extends android.app.Application {
- public SerialPortFinder mSerialPortFinder = new SerialPortFinder();
- private SerialPort mSerialPort = null;
-
- public SerialPort getSerialPort() throws SecurityException, IOException, InvalidParameterException {
- if (mSerialPort == null) {
-
- SharedPreferences sp = getSharedPreferences("android_serialport_api.sample_preferences", MODE_PRIVATE);
- String path = sp.getString("DEVICE", "");
- int baudrate = Integer.decode(sp.getString("BAUDRATE", "-1"));
-
-
- if ( (path.length() == 0) || (baudrate == -1)) {
- throw new InvalidParameterException();
- }
-
-
- mSerialPort = new SerialPort(new File(path), baudrate, 0);
- }
- return mSerialPort;
- }
-
- public void closeSerialPort() {
- if (mSerialPort != null) {
- mSerialPort.close();
- mSerialPort = null;
- }
- }
- }
- </span>
5) 新建一個(gè)繼承抽象的Activity類,主要用于讀取串口的信息
- <span style="font-size:18px;">package org.winplus.serial;
-
- import java.io.IOException;
- import java.io.InputStream;
- import java.io.OutputStream;
- import java.security.InvalidParameterException;
-
- import org.winplus.serial.utils.SerialPort;
-
- import android.app.Activity;
- import android.app.AlertDialog;
- import android.content.DialogInterface;
- import android.content.DialogInterface.OnClickListener;
- import android.os.Bundle;
-
- public abstract class SerialPortActivity extends Activity {
- protected Application mApplication;
- protected SerialPort mSerialPort;
- protected OutputStream mOutputStream;
- private InputStream mInputStream;
- private ReadThread mReadThread;
-
- private class ReadThread extends Thread {
-
- @Override
- public void run() {
- super.run();
- while (!isInterrupted()) {
- int size;
- try {
- byte[] buffer = new byte[64];
- if (mInputStream == null)
- return;
-
-
-
-
- size = mInputStream.read(buffer);
- if (size > 0) {
- onDataReceived(buffer, size);
- }
- } catch (IOException e) {
- e.printStackTrace();
- return;
- }
- }
- }
- }
-
- 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);
- mApplication = (Application) getApplication();
- try {
- mSerialPort = mApplication.getSerialPort();
- mOutputStream = mSerialPort.getOutputStream();
- mInputStream = mSerialPort.getInputStream();
-
-
- 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);
- }
- }
-
- protected abstract void onDataReceived(final byte[] buffer, final int size);
-
- @Override
- protected void onDestroy() {
- if (mReadThread != null)
- mReadThread.interrupt();
- mApplication.closeSerialPort();
- mSerialPort = null;
- super.onDestroy();
- }
- }
- </span>
6)編寫string.xml 以及baudrates.xml文件
在string.xml文件中添加:
- <span style="font-size:18px;"> <string name="error_configuration">Please configure your serial port first.</string>
- <string name="error_security">You do not have read/write permission to the serial port.</string>
- <string name="error_unknown">The serial port can not be opened for an unknown reason.</string>
- </span>
在baudrates.xml文件中添加
- <span style="font-size:18px;"><?xml version="1.0" encoding="utf-8"?>
- <resources>
-
- <string-array name="baudrates_name">
- <item>50</item>
- <item>75</item>
- <item>110</item>
- <item>134</item>
- <item>150</item>
- <item>200</item>
- <item>300</item>
- <item>600</item>
- <item>1200</item>
- <item>1800</item>
- <item>2400</item>
- <item>4800</item>
- <item>9600</item>
- <item>19200</item>
- <item>38400</item>
- <item>57600</item>
- <item>115200</item>
- <item>230400</item>
- <item>460800</item>
- <item>500000</item>
- <item>576000</item>
- <item>921600</item>
- <item>1000000</item>
- <item>1152000</item>
- <item>1500000</item>
- <item>2000000</item>
- <item>2500000</item>
- <item>3000000</item>
- <item>3500000</item>
- <item>4000000</item>
- </string-array>
- <string-array name="baudrates_value">
- <item>50</item>
- <item>75</item>
- <item>110</item>
- <item>134</item>
- <item>150</item>
- <item>200</item>
- <item>300</item>
- <item>600</item>
- <item>1200</item>
- <item>1800</item>
- <item>2400</item>
- <item>4800</item>
- <item>9600</item>
- <item>19200</item>
- <item>38400</item>
- <item>57600</item>
- <item>115200</item>
- <item>230400</item>
- <item>460800</item>
- <item>500000</item>
- <item>576000</item>
- <item>921600</item>
- <item>1000000</item>
- <item>1152000</item>
- <item>1500000</item>
- <item>2000000</item>
- <item>2500000</item>
- <item>3000000</item>
- <item>3500000</item>
- <item>4000000</item>
- </string-array>
-
- </resources>
- </span>
7)開始編寫界面了:在main.xml布局文件中添加兩個(gè)編輯框,一個(gè)用來發(fā)送命令,一個(gè)用來接收命令:
- <span style="font-size:18px;"><?xml version="1.0" encoding="utf-8"?>
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent"
- android:orientation="vertical" >
-
- <EditText
- android:id="@+id/EditTextReception"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent"
- android:layout_weight="1"
- android:gravity="top"
- android:hint="Reception"
- android:isScrollContainer="true"
- android:scrollbarStyle="insideOverlay" >
- </EditText>
-
- <EditText
- android:id="@+id/EditTextEmission"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:hint="Emission"
- android:lines="1" >
- </EditText>
-
- </LinearLayout>
- </span>
8) SerialDemoActivity類的實(shí)現(xiàn):
- <span style="font-size:18px;">package org.winplus.serial;
-
- import java.io.IOException;
-
- import android.os.Bundle;
- import android.view.KeyEvent;
- import android.widget.EditText;
- import android.widget.TextView;
- import android.widget.TextView.OnEditorActionListener;
-
- public class SerialDemoActivity extends SerialPortActivity{
- EditText mReception;
-
- @Override
- protected void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
-
-
- mReception = (EditText) findViewById(R.id.EditTextReception);
-
- EditText Emission = (EditText) findViewById(R.id.EditTextEmission);
- Emission.setOnEditorActionListener(new OnEditorActionListener() {
- public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
- int i;
- CharSequence t = v.getText();
- char[] text = new char[t.length()];
- for (i=0; i<t.length(); i++) {
- text[i] = t.charAt(i);
- }
- try {
- mOutputStream.write(new String(text).getBytes());
- mOutputStream.write('\n');
- } catch (IOException e) {
- e.printStackTrace();
- }
- return false;
- }
- });
- }
-
- @Override
- protected void onDataReceived(final byte[] buffer, final int size) {
- runOnUiThread(new Runnable() {
- public void run() {
- if (mReception != null) {
- mReception.append(new String(buffer, 0, size));
- }
- }
- });
- }
- }
- </span>
寫到這里,代碼基本上寫完了。下面就是要實(shí)現(xiàn)JNI層的功能了,要實(shí)現(xiàn)JNI,必須首先生成頭文件,頭文件的生成方式也很簡(jiǎn)單, 我們編譯工程,在終端輸入 javah org.winplus.serial.utils.SerialPort 則會(huì)生成頭文件:org_winplus_serial_utils_SerialPort.h,這個(gè)頭文件的名字可以隨意命名。我們將它命名為:SerialPort.h拷貝到新建的目錄jni中,新建SerialPort.c 文件,這兩個(gè)文件的代碼就不貼出來了。直接到上傳的代碼中看吧。
(四)串口的應(yīng)用,可實(shí)現(xiàn)掃描頭,指紋識(shí)別等外圍USB轉(zhuǎn)串口的特色應(yīng)用。
還蠻繁瑣的,以上只是對(duì)開源項(xiàng)目android-serialport-api 進(jìn)行精簡(jiǎn)想了解此項(xiàng)目請(qǐng)點(diǎn)擊此處!就這樣吧,晚了準(zhǔn)備見周公去!
源碼下載地址==》
精心準(zhǔn)備的串口編程資料,歡迎下載==》
原創(chuàng)文章,轉(zhuǎn)載請(qǐng)注明出處:http://www.blog.csdn.net/tangcheng_ok