CubieBoard2串口

关于Linux串口的一些小知识

串口名称使用

ls -l /dev/ttyS*

一般情况下串口的名称全部在dev下面，如果你没有外插串口卡的话默认是dev下的ttyS*,一般ttyS0对应com1，ttyS1对应com2，当然也不一定是必然的；

记得看一下串口的权限，是不是rw-rw-rw-，不是的话请运行

chmod 666 /dev/ttyS\*

给予可读写权限。

检查串口是否可用，可以对串口发送数据比如对com1口，

echo Hello > /dev/ttyS0

。

串口驱动：

cat /proc/tty/drivers/sw_serial

。

在PC上查看连接到CubieBoard2的串口设备：

dmesg | grep ttyS*

。

dmesg | grep ttyS*

[    0.000000] console [tty0] enabled

[    6.246827] systemd[1]: Created slice system-getty.slice.

[   13.740764] usb 3-4: ch341-uart converter now attached to ttyUSB0

以下内容均在Android Studio中实现

配置环境

配置JAVA

下载并配置好JAVA（JAVA_HOME、CLASSPATH、PATH），CMD中要能使用

javah

命令。

配置gradle

在

gradle

目录中找到

gradle-wrapper.properties

文件。

修改其中配置为

distributionUrl=https://services.gradle.org/distributions/gradle-2.10-all.zip

。

gradle必须高于一定的版本，好像网上说NDK支持是后面加进来的。

在菜单中File->Project Structure->Project中修改Gradle version为2.10也可以，改完后OK。

项目中的

build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:2.1.2'

// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}

allprojects {
repositories {
jcenter()
}
}

task clean(type: Delete) {
delete rootProject.buildDir
}

NDK

在项目中

local.properties

中配置ndk，ndk应该没什么要求。

ndk.dir=D:\\Programs\\Androidsdk\\ndk-bundle
sdk.dir=D:\\Programs\\Androidsdk

我用的是AS自动下载配置的，版本为android-ndk-r12d。

工程

新建

新建一个类，类名为SerialPort。代码如下：

package com.bilibili.www.serialporttest;

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";

// JNI
static {
//指定库名，需要和build.gradle中一致
try {
System.loadLibrary("serial_port");
}
catch (UnsatisfiedLinkError e) {
Log.d(TAG, "Unsatisfied Link error: " + e.toString());
}
}

private static native FileDescriptor open(String path, int baudrate, int flags);
public native void close();

/*
* 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");//获得root
String cmd = "chmod 666 " + device.getAbsolutePath() + "\n"
+ "exit\n";//全部用户权限为可读写
su.getOutputStream().write(cmd.getBytes());
if ((su.waitFor() != 0) || !device.canRead()
|| !device.canWrite()) {
throw new SecurityException();
}
} catch (Exception e) {
e.printStackTrace();
throw new SecurityException();
}
}
Log.d(TAG, "Start！！！！！！！");
mFd = open(device.getAbsolutePath(), baudrate, flags);
if (mFd == null) {
Log.e(TAG, "native open returns null");
throw new IOException();
}else {
mFileInputStream = new FileInputStream(mFd);
mFileOutputStream = new FileOutputStream(mFd);
}
}

// Getters and setters
public InputStream getInputStream() {
return mFileInputStream;
}

public OutputStream getOutputStream() {
return mFileOutputStream;
}
}

打开terminal，输入

cd <你的工程位置>\app\src\main\java

；输入

javah -jni <你的包名>.<类名>

。这里是如

javah -jni com.bilibili.www.serialporttest.SerialPort

这样的命令，完成之后如果没有问题，会在java目录下出现一个com_bilibili_www_serialporttest_SerialPort.h的文件。

在

<你的工程位置>\app\src\main

目录下新建一个

jni

目录。

修改

将com_bilibili_www_serialporttest_SerialPort.h文件放进jni目录。

在

jni

目录下建立一个c文件，内容如下：

/*
* 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 "com_bilibili_www_serialporttest_SerialPort.h"

#include <termios.h>

#include <unistd.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <string.h>

#include <jni.h>

//#include "android/log.h"

#include <android/log.h>

#ifdef __cplusplus

extern "C" {

#endif

static const char *TAG="serial_port";

/* 这三个函数是为了打印信息而存在 */

#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:     com_bilibili_www_serialporttest_SerialPort
* Method:    open
* Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
*/
JNIEXPORT jobject JNICALL Java_com_bilibili_www_serialporttest_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:     com_bilibili_www_serialporttest_SerialPort
* Method:    close
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_com_bilibili_www_serialporttest_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);
}

#ifdef __cplusplus

}

#endif

module里面的build.gradle

import com.android.build.gradle.api.AndroidSourceSet

apply plugin: 'com.android.application'

android {
compileSdkVersion 24
buildToolsVersion "24.0.0"
defaultConfig {
applicationId "com.bilibili.www.serialporttest"
minSdkVersion 16
targetSdkVersion 19
versionCode 1
versionName "1.0"
ndk {
moduleName = "serial_port"
ldLibs "log", "z", "m", "jnigraphics", "android"
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
ndk {
moduleName = "serial_port"//模块名，要和类SerialPort中的System.loadLibrary();一致
ldLibs "log", "z", "m", "jnigraphics", "android"//所要链接的库
abiFilters "armeabi", "armeabi-v7a", "x86" //输出指定三种abi体系结构下的so库，目前可有可无。没有的话就生成NDK能生成的所有平台，比如mips
}
}
debug {
ndk {
moduleName = "serial_port"
ldLibs "log", "z", "m", "jnigraphics", "android"
abiFilters "armeabi", "armeabi-v7a", "x86"
}
}
}
productFlavors {
}
}

dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:24.0.0'
}

MainActivity

没有任何布局上的改变，要用控制台查看串口接受信息。这里我使用了接收，需要的话，可以自行添加发送代码。

package com.bilibili.www.serialporttest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.os.Handler;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Arrays;

import android.util.Log;
import android.os.Message;

public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";

private static final int msgKey = 2;
private File mFile;
private FileInputStream mInputStream;
private SerialPort mSerialPort;
private ReadThread mThread;
//private StringBuffer mSb;
private String mSb;
private boolean flag = true;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

try {
mFile=new File("/dev/ttySAC0");
mSerialPort = new SerialPort(mFile, 115200, 0);
} catch (SecurityException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

mInputStream = (FileInputStream) mSerialPort.getInputStream();
//启动线程
mThread = new ReadThread();
mThread.start();
}

public  static int searchByte(byte[] data, byte value) {
int size = data.length;
for (int i = 0; i < size; ++i) {
if (data[i] == value) {
return i;
}
}
return -1;
}

public class ReadThread extends Thread {
@Override
public void run() {
// TODO Auto-generated method stub
super.run();
while (!isInterrupted()) {
int size,couth = 128;
try {

Log.d(TAG, "----ReadThread start----");
if (mInputStream == null) {
return;
}

/* 获取可以读取的数据长度 */
/*for(int coutq1 = mInputStream.available();
coutq1 != couth;
coutq1 = mInputStream.available())
{
try {
sleep(10L);
couth = mInputStream.available();
sleep(10L);
} catch (InterruptedException e) {
e.printStackTrace();
}
}*/

byte[] buffer = new byte[couth];

Log.d(TAG, "----read(buffer)----");
size = mInputStream.read(buffer);
Log.d(TAG, "----size----" + String.valueOf(size));
if (size > 0) {
Log.d(TAG, "----ReadThread size>0----");
/*mSb = new StringBuffer();
for (int i = 0; i < buffer.length; i++) {
mSb.append(buffer[i]);
}
Log.d(TAG, "Data=" + mSb.toString());*/
mSb=new String(Arrays.copyOfRange(buffer,0,size));
Log.d(TAG, "Data=" + mSb);

Message msg = new Message();
msg.what = msgKey;
mHandler.sendMessage(msg);
}
else {
Log.d(TAG, "----ReadThread DataisNull----");
}
} catch (IOException e) {
Log.d(TAG, "----ReadThread printStackTrace----");
e.printStackTrace();
return;
}
}
}
}

private Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch (msg.what) {
case msgKey:
//Log.e(TAG, mSb.toString());
Log.e(TAG, mSb);
break;
default:
break;
}
}
};
}

编译

Make Project(Ctrl + F9)

在

<你的工程位置>\app\build\intermediates\ndk\debug\lib

目录中，你会发现”armeabi”, “armeabi-v7a”, “x86”三个目录，将他们复制到

<你的工程位置>\app\libs

中。

运行

GLHF!

问题与经验

编译没有问题，运行时提示tcgetaddr()函数出现错误，找不到该函数。

没有把”armeabi”, “armeabi-v7a”, “x86”文件夹放进

<你的工程位置>\app\libs

中，所以apk不包含这几个文件夹中的so二进制文件，所以出现找不到函数的情况。

另外一种情况是由于api 19 之后的 termios.h 里面的函数有调整，因此调试过程中，出现

java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol “tcgetattr” referenced by libserialport.so

解决方法：

将api 19 的 termios.h 拷贝到 jni 目录下

termios.h

/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*  * Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
*  * Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in
*    the documentation and/or other materials provided with the
*    distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/

#ifndef _TERMIOS_H_

#define _TERMIOS_H_

#include <sys/cdefs.h>

#include <sys/ioctl.h>

#include <sys/types.h>

#include <stdint.h>

#include <linux/termios.h>

__BEGIN_DECLS

/* Redefine these to match their ioctl number */

#undef  TCSANOW

#define TCSANOW    TCSETS

#undef  TCSADRAIN

#define TCSADRAIN  TCSETSW

#undef  TCSAFLUSH

#define TCSAFLUSH  TCSETSF

static __inline__ int tcgetattr(int fd, struct termios *s)
{
return ioctl(fd, TCGETS, s);
}

static __inline__ int tcsetattr(int fd, int __opt, const struct termios *s)
{
return ioctl(fd, __opt, (void *)s);
}

static __inline__ int tcflow(int fd, int action)
{
return ioctl(fd, TCXONC, (void *)(intptr_t)action);
}

static __inline__ int tcflush(int fd, int __queue)
{
return ioctl(fd, TCFLSH, (void *)(intptr_t)__queue);
}

static __inline__ pid_t tcgetsid(int fd)
{
pid_t _pid;
return ioctl(fd, TIOCGSID, &_pid) ? (pid_t)-1 : _pid;
}

static __inline__ int tcsendbreak(int fd, int __duration)
{
return ioctl(fd, TCSBRKP, (void *)(uintptr_t)__duration);
}

static __inline__ speed_t cfgetospeed(const struct termios *s)
{
return (speed_t)(s->c_cflag & CBAUD);
}

static __inline__ int cfsetospeed(struct termios *s, speed_t  speed)
{
s->c_cflag = (s->c_cflag & ~CBAUD) | (speed & CBAUD);
return 0;
}

static __inline__ speed_t cfgetispeed(const struct termios *s)
{
return (speed_t)(s->c_cflag & CBAUD);
}

static __inline__ int cfsetispeed(struct termios *s, speed_t  speed)
{
s->c_cflag = (s->c_cflag & ~CBAUD) | (speed & CBAUD);
return 0;
}

static __inline__ void cfmakeraw(struct termios *s)
{
s->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL|IXON);
s->c_oflag &= ~OPOST;
s->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
s->c_cflag &= ~(CSIZE|PARENB);
s->c_cflag |= CS8;
}

__END_DECLS

#endif /* _TERMIOS_H_ */

然后在c文件中，将

#include <termios.h>

改为

#include "termios.h"

。

能运行，但是串口没有反应。

请检查串口权限，要求other是可读可写的。