Android 串口通信

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串口通信SerialPort

生成so文件

首先确保已经安装了NDK和CMake


然后创建一个SerialPort.java文件
主要用来处理so文件
注意包名一旦写好不要更改位置,具体代码:

import android.util.Log;

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;
/**
 * Created by abc on 2021/1/23.
 */

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 

        if (device == null) 
            System.out.println("device is null");
            return;
        


        /* 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 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) 
            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");
    




然后clean project 再rebuild project 生成class文件,
这时候打开如下图的文件夹看是否生成了classes文件夹,没有生成请重新再试一遍。

当然你也不一定会生成compileDebugJavaWithJavac 只要javac->debug下存在classes就可以

再打开Terminal输入指令
cd app/build/intermediates/javac/debug/classes(具体位置定位到classes)
然后再输入指令
javah -jni 包名.SerialPort
注意 这里javah -jni后面跟的是 SerialPort.java 的全路径,如果javah报不存在之类的,是你的Java环境没有配置好。

这时候打开 debug/classes下面的文件发现多了一个以 .h 结尾文件

编写处理C文件

在main下创建一个jni包 将生成的.h文件复制进去

然后创建SerialPort.c文件


#include <stdlib.h>
#include <stdio.h>
#include <jni.h>
#include <assert.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 这里是生成.h文件全称(com_***_***_serialport_SerialPort.h)



#include "android/log.h"
static const char *TAG = "serial_port";
#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:     android_serialport_SerialPort
 * Method:    open
 * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
 */
 //这里同样是生成.h文件全称
JNIEXPORT jobject JNICALL Java_com_***_***_serialport_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:     cedric_serial_SerialPort
 * Method:    close
 * Signature: ()V
 */
  //这里同样是生成.h文件全称
JNIEXPORT void JNICALL Java_com_***_***_serialport_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);


termios.h 具体代码:

#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_ */


生成so文件

首先,在项目(app)的build.gradel中的defaultConfig下添加:

externalNativeBuild 
            cmake 
                cppFlags ""
               // abiFilters "armeabi-v7a", "x86", "arm64-v8a"
            
        

然后再在项目(app)的build.gradel 的 android 闭包下添加:

  externalNativeBuild 
        cmake 
            path "CMakeLists.txt" 
        
    

在app下创建一个CMakeLists.txt

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

#设置生成的so动态库最后输出的路径
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY $PROJECT_SOURCE_DIR/../jniLibs/$ANDROID_ABI)

add_library( # Sets the name of the library.
        #此处填入library名称,就是生成so文件的名称
        serial_port

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s). c文件或cpp文件的相对路径
        src/main/jni/SerialPort.c
        )
# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.
find_library( # Sets the name of the path variable.
        log-lib
        # Specifies the name of the NDK library that
        # you want CMake to locate.
        log)
# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.
target_link_libraries( # Specifies the target library.
        #此处填入library名称,就是生成so文件的名称
        serial_port
        # Links the target library to the log library
        # included in the NDK.
        $log-lib)

你现在就可以Make Project 或者 Rebuild Project 一下 ,之后会在这里会生成so库:

把生成的so文件复制到libs下或者jniLibs下
这时so文件我们生成了就需要把build的注释掉不然下次运行还会生成

externalNativeBuild 
            cmake 
                cppFlags ""
               // abiFilters "armeabi-v7a", "x86", "arm64-v8a"
            
        


 externalNativeBuild 
        cmake 
            path "CMakeLists.txt" 
        
    

然后我们封装一个SerialPortUtils


import android.util.Log;
import android.widget.Toast;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * @author renquan
 */

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