Android開(kāi)發(fā)之串口編程原理和實(shí)現(xiàn)方式
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(kāi)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(xiě)功能只需操作文件設(shè)備類(lèi):FileDescriptor即可,其他的事都由驅(qū)動(dòng)來(lái)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(shuō)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?zhuān)朐敿?xì)了解的朋友可以查看云中漫步的技術(shù)文章,寫(xiě)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(xiě)(不用多說(shuō),可以直接參考package/apps目錄下用到JNI的相關(guān)項(xiàng)目寫(xiě)法)
這是關(guān)鍵的代碼:
<span style="font-size:18px;"> 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;
}
}
</span>
(二)FileDescritor:
文件描述符類(lèi)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(kāi)放文件、開(kāi)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(xiě)。
(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(lèi):SerialPortFinder,添加如下代碼:
<span style="font-size:18px;">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()]);
}
}
</span>
上面這個(gè)類(lèi)在“android-serialport-api串口工具測(cè)試隨筆”中有詳細(xì)的說(shuō)明,我就不多說(shuō)了。
3)新建SerialPort類(lèi),這個(gè)類(lèi)主要用來(lái)加載SO文件,通過(guò)JNI的方式打開(kāi)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";
/*
* 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");
}
}
</span>
4) 新建一個(gè)MyApplication 繼承android.app.Application,用來(lái)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 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;
}
}
}
</span>
5) 新建一個(gè)繼承抽象的Activity類(lèi),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 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(huì)一直等待數(shù)據(jù),等到天荒地老,海枯石爛。如果要判斷是否接受完成,只有設(shè)置結(jié)束標(biāo)識(shí),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();
}
}
</span>
6)編寫(xiě)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(kāi)始編寫(xiě)界面了:在main.xml布局文件中添加兩個(gè)編輯框,一個(gè)用來(lái)發(fā)送命令,一個(gè)用來(lái)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(lèi)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);
// 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));
}
}
});
}
}
</span>
寫(xiě)到這里,代碼基本上寫(xiě)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(lái)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(kāi)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(jiàn)周公去!
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