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Android 串口編程原理和實現(xiàn)方式(附源碼)

日期：2019-08-22 分類：微信刷臉開發(fā)SDK資料下載：14129 瀏覽：19448

參考鏈接2：https://blog.csdn.net/tangcheng_ok/article/details/7021470

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JNI、FileDescriptor以及串口的一些知識點和實現(xiàn)的源碼進行分析說明。這里主要是參考了開源項目android-serialport-api。

串口編程需要了解的基本知識點：對于串口編程，我們只需對串口進行一系列的設(shè)置，然后打開串口，這些操作我們可以參考串口調(diào)試助手的源碼進行學(xué)習(xí)。在Java中如果要實現(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)動來完成不用多管！當(dāng)然，你想了解，那就得看驅(qū)動代碼了。這里并不打算對驅(qū)動進行說明，只初略闡述應(yīng)用層的實現(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調(diào)3點：

1、如何將編譯好的SO文件打包到APK中？（方法很簡單，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)項目寫法）

這是關(guān)鍵的代碼：

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;

}

（二）FileDescritor：

文件描述符類的實例用作與基礎(chǔ)機器有關(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)的另一個源或接收者。文件描述符的主要實際用途是創(chuàng)建一個包含該結(jié)構(gòu)的FileInputStream 或FileOutputStream。這是API的描述，不太好理解，其實可簡單的理解為：FileDescritor就是對一個文件進行讀寫。

（三）實現(xiàn)串口通信細節(jié)

1) 建工程：SerialDemo包名：org.winplus.serial，并在工程目錄下新建jni和libs兩個文件夾和一個org.winplus.serial.utils，如下圖：

2) 新建一個類：SerialPortFinder，添加如下代碼：

package org.winplus.serial.utils;

import java.io.File;

import java.io.FileReader;

import java.io.IOException;

import java.io.LineNumberReader;

import java.util.Iterator;

import java.util.Vector;

import android.util.Log;

public class SerialPortFinder {

private static final String TAG = "SerialPort";

private Vector<Driver> mDrivers = null;

public class Driver {

public Driver(String name, String root) {

mDriverName = name;

mDeviceRoot = root;

}

private String mDriverName;

private String mDeviceRoot;

Vector<File> mDevices = null;

public Vector<File> getDevices() {

if (mDevices == null) {

mDevices = new Vector<File>();

File dev = new File("/dev");

File[] files = dev.listFiles();

int i;

for (i = 0; i < files.length; i++) {

if (files[i].getAbsolutePath().startsWith(mDeviceRoot)) {

Log.d(TAG, "Found new device: " + files[i]);

mDevices.add(files[i]);

}

return mDevices;

}

public String getName() {

return mDriverName;

}

Vector<Driver> getDrivers() throws IOException {

if (mDrivers == null) {

mDrivers = new Vector<Driver>();

LineNumberReader r = new LineNumberReader(new FileReader(

"/proc/tty/drivers"));

String l;

while ((l = r.readLine()) != null) {

// Issue 3:

// Since driver name may contain spaces, we do not extract

// driver name with split()

String drivername = l.substring(0, 0x15).trim();

String[] w = l.split(" +");

if ((w.length >= 5) && (w[w.length - 1].equals("serial"))) {

Log.d(TAG, "Found new driver " + drivername + " on "

+ w[w.length - 4]);

mDrivers.add(new Driver(drivername, w[w.length - 4]));

}

r.close();

}

return mDrivers;

}

public String[] getAllDevices() {

Vector<String> devices = new Vector<String>();

// Parse each driver

Iterator<Driver> itdriv;

try {

itdriv = getDrivers().iterator();

while (itdriv.hasNext()) {

Driver driver = itdriv.next();

Iterator<File> itdev = driver.getDevices().iterator();

while (itdev.hasNext()) {

String device = itdev.next().getName();

String value = String.format("%s (%s)", device,

driver.getName());

devices.add(value);

}

} catch (IOException e) {

e.printStackTrace();

}

return devices.toArray(new String[devices.size()]);

}

public String[] getAllDevicesPath() {

Vector<String> devices = new Vector<String>();

// Parse each driver

Iterator<Driver> itdriv;

try {

itdriv = getDrivers().iterator();

while (itdriv.hasNext()) {

Driver driver = itdriv.next();

Iterator<File> itdev = driver.getDevices().iterator();

while (itdev.hasNext()) {

String device = itdev.next().getAbsolutePath();

devices.add(device);

}

} catch (IOException e) {

e.printStackTrace();

}

return devices.toArray(new String[devices.size()]);

}

上面這個類在“android-serialport-api串口工具測試隨筆”中有詳細的說明，我就不多說了。

3）新建SerialPort類，這個類主要用來加載SO文件，通過JNI的方式打開關(guān)閉串口

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";

* 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");

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);

}

// 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();

static {

System.loadLibrary("serial_port");

}

4）新建一個MyApplication 繼承android.app.Application，用來對串口進行初始化和關(guān)閉串口

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 MyApplication extends android.app.Application {

public SerialPortFinder mSerialPortFinder = new SerialPortFinder();

private SerialPort mSerialPort = null;

public SerialPort getSerialPort() throws SecurityException, IOException, InvalidParameterException {

if (mSerialPort == null) {

/* Read serial port parameters */

SharedPreferences sp = getSharedPreferences("android_serialport_api.sample_preferences", MODE_PRIVATE);

String path = sp.getString("DEVICE", "");

int baudrate = Integer.decode(sp.getString("BAUDRATE", "-1"));

/* Check parameters */

if ( (path.length() == 0) || (baudrate == -1)) {

throw new InvalidParameterException();

}

/* Open the serial port */

mSerialPort = new SerialPort(new File(path), baudrate, 0);

}

return mSerialPort;

}

public void closeSerialPort() {

if (mSerialPort != null) {

mSerialPort.close();

mSerialPort = null;

}

5）新建一個繼承抽象的Activity類，主要用于讀取串口的信息

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 MyApplication 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;

/**

* 這里的read要尤其注意，它會一直等待數(shù)據(jù)，等到天荒地老，?？菔癄€。如果要判斷是否接受完成，只有設(shè)置結(jié)束標(biāo)識，或作其他特殊的處理。

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 = (MyApplication) getApplication();

try {

mSerialPort = mApplication.getSerialPort();

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);

}

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();

}

6）編寫string.xml 以及baudrates.xml文件

在string.xml文件中添加：

<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>

在baudrates.xml文件中添加

<?xml version="1.0" encoding="utf-8"?>

<string-array name="baudrates_name">

</string-array>

<string-array name="baudrates_value">

</string-array>

</resources>

7）開始編寫界面了：在main.xml布局文件中添加兩個編輯框，一個用來發(fā)送命令，一個用來接收命令：

<?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>

8） SerialDemoActivity類的實現(xiàn)：

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);

// setTitle("Loopback test");

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));

}

});

}

寫到這里，代碼基本上寫完了。下面就是要實現(xiàn)JNI層的功能了，要實現(xiàn)JNI，必須首先生成頭文件，頭文件的生成方式也很簡單，我們編譯工程，在終端輸入 javah org.winplus.serial.utils.SerialPort 則會生成頭文件：org_winplus_serial_utils_SerialPort.h,這個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，可實現(xiàn)掃描頭，指紋識別等外圍USB轉(zhuǎn)串口的特色應(yīng)用。

————————————————

版權(quán)聲明：本文為CSDN博主「tangcheng_ok」的原創(chuàng)文章，遵循CC 4.0 by-sa版權(quán)協(xié)議，轉(zhuǎn)載請附上原文出處鏈接及本聲明。

原文鏈接：https://blog.csdn.net/tangcheng_ok/article/details/7021470

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