Android 串口开发（二） 支持设置奇偶校验、数据位、停止位

谷歌官网提供的串口库的奇偶校验位数据位停止位都是默认的，如果有项目需要配置固定的参数的时候，很显然谷歌官网提供的是不可行的，但是是可参考的谷歌开源串口库，下面这边文章也仅仅是作为自己的一个踩过的坑的记录，本篇文章主要参考了一位简书上的大哥的文章，Android 串口通信 

 

在上一篇已经讲解了谷歌开源的串口库的一些东西，所以在这篇里面就不过多口舌了

项目结构

看过我上篇文章的笔友会发现其实和上篇的东西大差不差，项目结构以及类的划分基本一致，主要改动还是java向jni文件里传值多了三个参数，这个native方法就是用来和jni里面的C通信的，比谷歌提供的又新增了三个参数

   /**
     * 打开串口
     *
     * @param device   串口设备文件
     * @param baudRate 波特率
     * @param parity   奇偶校验，0 None（默认）； 1 Odd； 2 Even
     * @param dataBits 数据位，5 ~ 8  （默认8）
     * @param stopBit  停止位，1 或 2  （默认 1）
     * @param flags    标记 0（默认）
     * @throws SecurityException
     * @throws IOException
     */
    private native static FileDescriptor open(String path, int baudRate, int parity, int dataBits,
                                              int stopBit, int flags);

同样修改后发现居然运行不起来，百度上找了一大堆文章都没能解决问题，想起来之前一位同事说简书要比csdn上的可靠，所以一大早来到公司就上简书搜索，果然不出所料，才看了两篇就找到想要的答案了，就是上面参考的那位大哥的文章，文章不繁琐，结构清晰，做过硬件开发的Android或者玩过串口的朋友一看就知道怎么回事，好了废话不多说，在这里还有两个文件没有贴出来，下面贴一下serial-port.cpp代码

//
// Created by Administrator on 2019\1\29 0029.
//

#include 
#include 
#include 
#include 
#include 
#include 
#include 



#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;
    }
}

static void throwException(JNIEnv *env, const char *name, const char *msg)
{
    jclass cls = env->FindClass(name);
    /* if cls is NULL, an exception has already been thrown */
    if (cls != NULL) {
        env->ThrowNew(cls, msg);
    }

    /* free the local ref */
    env->DeleteLocalRef(cls);
}

extern "C"
JNIEXPORT jobject JNICALL
Java_com_deemons_serialportlib_SerialPort_open
        (JNIEnv *env, jobject instance, jstring path, jint baudrate,jint parity, jint dataBits, jint stopBit, jint flags)
{
    int fd;
    speed_t speed;
    jobject mFileDescriptor;

    /* Check arguments */
    {
        speed = getBaudrate(baudrate);
        if (speed == -1) {
            throwException(env, "java/lang/IllegalArgumentException", "Invalid baudrate");
            return NULL;
        }
        if (parity <0 || parity>2) {
            throwException(env, "java/lang/IllegalArgumentException", "Invalid parity");
            return NULL;
        }
        if (dataBits <5 || dataBits>8) {
            throwException(env, "java/lang/IllegalArgumentException", "Invalid dataBits");
            return NULL;
        }
        if (stopBit <1 || stopBit>2) {
            throwException(env, "java/lang/IllegalArgumentException", "Invalid stopBit");
            return NULL;
        }
    }

    /* Opening device */
    {
        jboolean iscopy;
        const char *path_utf = env->GetStringUTFChars(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(path, path_utf);
        if (fd == -1)
        {
            throwException(env, "java/io/IOException", "Cannot open port");
            return NULL;
        }
    }

    /* Configure device */
    {
        struct termios cfg;
        LOGD("Configuring serial port");
        if (tcgetattr(fd, &cfg))
        {
            LOGE("tcgetattr() failed");
            close(fd);
            throwException(env, "java/io/IOException", "tcgetattr() failed");
            return NULL;
        }

        cfmakeraw(&cfg);
        cfsetispeed(&cfg, speed);
        cfsetospeed(&cfg, speed);

        /* More attribute set */
        switch (parity) {
            case 0: break;
            case 1: cfg.c_cflag |= PARENB; break;
            case 2: cfg.c_cflag &= ~PARODD; break;
        }
        switch (dataBits) {
            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;
        }
        switch (stopBit) {
            case 1: cfg.c_cflag &= ~CSTOPB; break;
            case 2: cfg.c_cflag |= CSTOPB; break;
        }

        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("java/io/FileDescriptor");
        jmethodID iFileDescriptor = env->GetMethodID(cFileDescriptor, "", "()V");
        jfieldID descriptorID = env->GetFieldID(cFileDescriptor, "descriptor", "I");
        mFileDescriptor = env->NewObject(cFileDescriptor, iFileDescriptor);
        env->SetIntField(mFileDescriptor, descriptorID, (jint)fd);
    }

    return mFileDescriptor;
}


/*
 * Class:     cedric_serial_SerialPort
 * Method:    close
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_deemons_serialportlib_SerialPort_close
        (JNIEnv *env, jobject thiz)
{
    jclass SerialPortClass = env->GetObjectClass( thiz);
    jclass FileDescriptorClass = env->FindClass( "java/io/FileDescriptor");

    jfieldID mFdID = env->GetFieldID(SerialPortClass, "mFd", "Ljava/io/FileDescriptor;");
    jfieldID descriptorID = env->GetFieldID(FileDescriptorClass, "descriptor", "I");

    jobject mFd = env->GetObjectField(thiz, mFdID);
    jint descriptor = env->GetIntField(mFd, descriptorID);

    LOGD("close(fd = %d)", descriptor);
    close(descriptor);
}

完了以后呢，还有一个CMakeLists.txt文件需要配置一下，具体有什么用呢，我也不太清楚，也是第一次看这样配置

# 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.

add_library( # Sets the name of the library.
             serial-port

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/serial-port.cpp

             )


# 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.
                       serial-port

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

最后在build.gradle里面再添加一下配置

 

致辞结束，还是非常感谢这位仁兄，帮助我解决了一大难题

上一篇  Android 串口开发（一） 串口读写操作