Android通過jni讀寫串口

Android讀寫串口的時候需要jni調用c代碼來實現，在開始之前需要下載ndk並配置好環境變量，也就是path裏面加上ndk的bin路徑。下面是具體的步驟
1、建一個包含jni方法的串口操作類：

package com.luoye.frigo.device;

public class SerialPortReaderWriter {

    protected native int open(String path, int baudrate, int parity,int stopBites,int dataBites);
    protected native void close(int fd);
    protected native int read(int fd,byte[] bytes,int len);
    protected native int write(int fd,byte[] bytes,int len);

}

2、在java目錄下編譯SerialPortReaderWriter這個類：

D:\myprojects\android\LibTestApp\device\src\main\java>javac -d ../jni com/luoye/frigo/device/SerialPortReaderWriter.java

3、在jni目錄下生成c頭文件SerialPortReaderWriter.h:

D:\myprojects\android\LibTestApp\device\src\main\jni>javah -o SerialPortReaderWriter.h -jni com.luoye.frigo.device.SerialPortReaderWriter

4、在jni目錄下添加c文件SerialPortReaderWriter.c，在這個文件中實現串口操作的邏輯：

//
// Created by dave on 2020/4/28.
//
#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <jni.h>

#include "SerialPortReaderWriter.h"

#include "android/log.h"
static const char *TAG="serial_port_reader_writer";
#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_tricent_frigo_device_SerialPortReaderWriter
 * Method:    open
 * Signature: (Ljava/lang/String;IIII)I
 */
JNIEXPORT jint JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_open
  (JNIEnv *env, jobject thiz, jstring path, jint baudrate, jint parity, jint stop_bites, jint data_bites){
        int fd=0;
    	speed_t speed;
    	jobject mFileDescriptor;

    	/* Check arguments */
    	{
    		speed = getBaudrate(baudrate);
    		if (speed == -1) {
    			/* TODO: throw an exception */
    			LOGE("Invalid baudrate");
    			return -1;
    		}
    		if(parity>5||parity<1){
    		    LOGE("Invalid parity");
                return -2;
    		}
    		if(stop_bites>3||stop_bites<1){
                LOGE("Invalid stop_bites");
                return -3;
            }
            if(data_bites>8||data_bites<5){
                LOGE("Invalid data_bites");
                return -4;
            }
    	}

    	/* 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 | O_NOCTTY | O_NDELAY);
    		fd = open(path_utf, O_RDWR | O_NOCTTY | O_NDELAY);
    		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 -5;
    		}
    	}

    	/* Configure device */
    	{
    		struct termios cfg;
    		LOGD("Configuring serial port");
    		if (tcgetattr(fd, &cfg))
    		{
    			LOGE("tcgetattr() failed");
    			close(fd);
    			/* TODO: throw an exception */
    			return -6;
    		}

    		//cfmakeraw(&cfg);

            /*設置波特率*/
            //tcflush(fd,TCIOFLUSH);
            cfsetispeed(&cfg,speed);

            /*設置數據位*/
            cfg.c_cflag &= ~CSIZE;
            switch (data_bites) /*設置數據位數*/
            {
                case 5:
                    cfg.c_cflag |= CS5;
                    break;
                case 6:
                    cfg.c_cflag |= CS6;
                    break;
                case 7:
                    cfg.c_cflag |= CS7;
                    break;
                case 8:
                    cfg.c_cflag |= CS8;
                    break;
            }

            /*設置奇偶校驗率*/
            switch (parity)
            {
                case 1:
                    cfg.c_cflag &= ~PARENB;   /* Clear parity enable */
                    cfg.c_iflag &= ~INPCK;     /* Enable parity checking */
                    break;
                case 2:
                    cfg.c_cflag |= (PARODD | PARENB); /* 設置爲奇效驗*/
                    cfg.c_iflag |= INPCK;             /* Disnable parity checking */
                    break;
                case 3:
                    cfg.c_cflag |= PARENB;     /* Enable parity */
                    cfg.c_cflag &= ~PARODD;   /* 轉換爲偶效驗*/
                    cfg.c_iflag |= INPCK;       /* Disnable parity checking */
                    break;
                case 4:  /*as no parity*/
                    cfg.c_cflag &= ~PARENB;
                    cfg.c_cflag &= ~CSTOPB;
                    break;
                case 5:
                    cfg.c_cflag &= ~PARENB;
                    cfg.c_cflag &= CSTOPB;
                    break;
            }
            /* 設置停止位*/
            switch (stop_bites)
            {
                case 1:
                    cfg.c_cflag &= ~CSTOPB;
                    break;
                case 2:
                    cfg.c_cflag |= CSTOPB;
                    break;
            }
            cfg.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
            //屏蔽軟件流控，讓X-ON X-OFF可以發送出去
            cfg.c_iflag &= ~ (IXON | IXOFF | IXANY | ICRNL);
            cfg.c_oflag &= ~OPOST;
            cfg.c_cc[VTIME] = 150; /* 設置超時15 seconds*/
            cfg.c_cc[VMIN] = 0;
            tcflush(fd,TCIFLUSH);/* Update the cfg and do it NOW */
            //立即將新屬性賦予串口
            if (tcsetattr(fd, TCSANOW, &cfg))
            {
                LOGE("tcsetattr() failed");
                close(fd);
                /* TODO: throw an exception */
                return -7;
            }
    	}
        return fd;
  }

/*
 * Class:     com_tricent_frigo_device_SerialPortReaderWriter
 * Method:    close
 * Signature: (I)V
 */
JNIEXPORT void JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_close
  (JNIEnv *env, jobject thiz, jint fd){
    LOGD("close(fd = %d)", fd);
    close(fd);
  }

/*
 * Class:     com_tricent_frigo_device_SerialPortReaderWriter
 * Method:    read
 * Signature: (I[BI)I
 */
JNIEXPORT jint JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_read
  (JNIEnv *env, jobject thiz, jint fd, jbyteArray byteArray, jint len){
        //方式1
        jbyte* byte = (*env)->GetByteArrayElements(env,byteArray, 0);
        int nRet = read(fd,byte,len);
        LOGD("read(nRet = %d)", nRet);
        //方式2
        //char chTmp[len];
        //memset(chTmp, 0, len);
        //int nRet = read(fd,chTmp,len);
        //LOGD("read(nRet = %d)", nRet);
        //(*env)->SetByteArrayRegion(env,byteArray, 0, len, chTmp);
        return nRet;
  }

/*
 * Class:     com_tricent_frigo_device_SerialPortReaderWriter
 * Method:    write
 * Signature: (I[BI)I
 */
JNIEXPORT jint JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_write
  (JNIEnv *env, jobject thiz, jint fd, jbyteArray byteArray, jint len){
        jbyte* byte = (*env)->GetByteArrayElements(env,byteArray, 0);
        int nRet = write(fd,byte,len);
        LOGD("write(nRet = %d)", nRet);
        (*env)->ReleaseByteArrayElements(env, byteArray, byte, 0);
        return nRet;
  }

5、在jni目錄下添加makefile文件Android.mk:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := dev-jni
LOCAL_SRC_FILES := SerialPortReaderWriter.c
LOCAL_LDLIBS    := -llog
include $(BUILD_SHARED_LIBRARY)

6、在jni目錄下執行ndk-build命令：

D:\myprojects\android\LibTestApp\device\src\main\jni>ndk-build

7、將生成的libs目錄拷貝到項目根目錄
8、在Java類SerialPortReaderWriter中添加：

static {
        System.loadLibrary("dev-jni");
    }

完善後的完整代碼：

package com.luoye.frigo.device;

public class SerialPortReaderWriter {
	static {
	        System.loadLibrary("dev-jni");
	}
    protected native int open(String path, int baudrate, int parity,int stopBites,int dataBites);
    protected native void close(int fd);
    protected native int read(int fd,byte[] bytes,int len);
    protected native int write(int fd,byte[] bytes,int len);

    private int fd=-1;
    public void openSerialPort(String path, int baudrate, int parity,int stopBites,int dataBites){
        fd=open(path,baudrate,parity,stopBites,dataBites);
    }
    public void openSerialPort(String path, int baudrate){
        openSerialPort(path,baudrate,1,1,8);
    }
    public void closeSerialPort(){
        close(fd);
        fd=-1;
    }
    public int read(byte[] bytes){
        if(bytes==null||fd==-1){
            return 0;
        }
        int len=bytes.length;
        return read(fd,bytes,len);
    }
    public int write(byte[] bytes){
        if(bytes==null||fd==-1){
            return 0;
        }
        int len=bytes.length;
        return write(fd,bytes,len);
    }
}

9、使用示例：

SerialPortReaderWriter serialPortReaderWriter=new SerialPortReaderWriter();
serialPortReaderWriter.openSerialPort("/dev/ttymxc3",9600);
serialPortReaderWriter.write("hello world".getBytes());
byte bs[]=new byte[32];
int r=serialPortReaderWriter.read(bs);
etr.setText(r+":"+new String(bs));
serialPortReaderWriter.closeSerialPort();