串口收发的怪异有关问题

static int fd;
static SEM_ID dataSemId;
int taskIdOne, taskIdTwo;

char sendBuf[] = "$GPRMC,A*20\r\n";

int tty_receive()
{
    int width;
    struct fd_set readFds;
    char tch = 0;
    int recfd = 0;

    recfd = fd;
    while(1)
    {
        FD_ZERO(&readFds);   
        FD_SET(recfd, &readFds);
        width = recfd + 1;
        
        if(select(width, &readFds,NULL,NULL,NULL) == ERROR)
        {
            logMsg("select() error!\n", 1,2,3,4,5,6);
            return(ERROR);
        }
        if(FD_ISSET(recfd, &readFds))
        {
            if (read(recfd, &tch, 1) == 0)
            {
                 logMsg("read() error!\n", 1,2,3,4,5,6);
                 return(ERROR);
            }
            if ('$' == tch)
            {  
                semGive (dataSemId);  // --> 触发发送
            }
        }
    }
    
    close(recfd);

    return 1;
}

int tty2_send(void)
{
    int bytes_out;
    int writeFd = 0;
    /*writeFd = open("/tyCo/2", O_RDWR, 0);*/    // 注1
    writeFd = fd;                                // 注2
    
    if (writeFd < 0)
    {
        logMsg("open serial error!\n", 1,2,3,4,5,6);
        return(ERROR);
    }
    else
        logMsg("open serial succeed!\n", 1,2,3,4,5,6);
    
    while(1)
    {
        semTake (dataSemId, WAIT_FOREVER);
        
        bytes_out = write(writeFd, sendBuf, strlen(sendBuf));
        if (bytes_out == 0)
        {
            logMsg("write error() - bytes_out = 0.\n", 1,2,3,4,5,6);
            return(ERROR);
        }
        else
        {
            logMsg("output chars total: %d\n", bytes_out,2,3,4,5,6);   // 注3
        }
    }

    return 1;
}

int app()
{
    dataSemId = semBCreate (SEM_Q_FIFO, SEM_EMPTY);
    if (NULL == dataSemId)
    {
        logMsg("create bianry sem error\n", 1,2,3,4,5,6);
        return(ERROR);
    }
    
    fd = open("/tyCo/2", O_RDWR, 0);
    if (fd < 0)
    {
        logMsg("app(): open serial error\n", 1,2,3,4,5,6);
        return(ERROR);
    }
    else
        logMsg("app(): open serial succeed - fd(%d)\n", fd,2,3,4,5,6);

    if (ioctl(fd, FIOSETOPTIONS, OPT_RAW) == ERROR)
    {
        logMsg("ioctl(OPT_RAW) ERROR!\n", 1,2,3,4,5,6);
        return(ERROR);
    }
    if (ioctl(fd, FIOBAUDRATE, 115200) == ERROR)
    {
        logMsg("ioctl(115200) ERROR!\n", 1,2,3,4,5,6);
        return(ERROR);
    }
    if (ioctl(fd, SIO_HW_OPTS_SET, CS8) == ERROR)
    {
        logMsg("ioctl(CS8) ERROR!\n", 1,2,3,4,5,6);
        return(ERROR);
    }
    
    if (taskIdOne = taskSpawn("comrec",90,0x100,2000,(FUNCPTR)tty_receive,
                          0,0,0,0,0,0,0,0,0,0) == ERROR)
    {
        logMsg("Error in spawning task comrec\n", 1,2,3,4,5,6);
        return(ERROR);
    }

    if (taskIdTwo = taskSpawn("comsend",90,0x100,2000,(FUNCPTR)tty2_send,
                          0,0,0,0,0,0,0,0,0,0) == ERROR)
    {
        logMsg("Error in spawning task comsend\n", 1,2,3,4,5,6);
        return(ERROR);
    }
    
    return(OK);
}

void close_com(void)
{
    taskDelete(taskIdOne);
    taskDelete(taskIdTwo);

    semDelete(dataSemId);

    close(fd);
}