int open_port(int port_nr) {
    int fd; /* File descriptor for the port */
    switch (port_nr) {
    case 1:
        fd = open("/dev/ttyO1", O_RDWR | O_NOCTTY | O_NDELAY); 
        break;
    case 2:
        fd = open("/dev/ttyO2", O_RDWR | O_NOCTTY | O_NDELAY); 
        break;
    default:
        printf("Invalid Serial port selected\n");
        return (-1);
    }
    if (fd == -1) {
                /* Could not open the port.*/
        perror("open_port Failed - ");
    } else {
        switch (port_nr) {
        case 1:
            sig_act.sa_handler = ttyO1_signal_handler_IO;
            UART_port_ttyO1 = fd;
            ttyO1_TX_list = NULL;
            if (pltfrm_mbx_init(&ttyO1_Mbx, sizeof(sPubMsg), 20) < 0) {
              printf("failed to create mailbox !! \n");
              return (-1);
            }
            break;
        case 2:
            sig_act.sa_handler = ttyO2_signal_handler_IO;
            UART_port_ttyO2 = fd;
            ttyO2_TX_list = NULL;
            if (pltfrm_mbx_init(&ttyO2_Mbx, sizeof(sPubMsg), 20) < 0) {
              printf("failed to create mailbox !! \n");
              return (-1);
            }
            break;
        default:
            printf("Invalid Serial port selected\n");
            return (-1);
        }
        sig_act.sa_flags = 0;
        sig_act.sa_restorer = NULL; 
        sigaction(SIGPOLL, &sig_act, NULL);
        fcntl(fd, F_SETFL, (FNDELAY | FASYNC));
        fcntl(fd, F_SETOWN, getpid());
    }
    return (fd);
}

void setup_port(int port_nr) {
    struct termios  options;
    int             port = port_nr_to_fd(port_nr);
    if (port < 0) {
        printf("Request to set-up invalid port(%d) detected...\n", port_nr);
    }
            /* get the current options */
    tcgetattr(port, &options);
            /* Set the to 57600kbps baud rate 8N1*/
    cfsetispeed(&options, B57600);
    cfsetospeed(&options, B57600);
    options.c_cflag &= ~(PARENB | CSTOPB | CSIZE);
    options.c_cflag |= CS8;    /* Select 8 data bits */
    options.c_cflag     |= (CLOCAL | CREAD);
    options.c_lflag     &= ~(ICANON | ECHO | ECHOE | ISIG);
    options.c_oflag     &= ~OPOST;
    options.c_iflag     &= ~(IXOFF | IXON);
    options.c_cc[VMIN]  = 0;
    options.c_cc[VTIME] = 0;
            /* set the options */
    tcsetattr(port, TCSANOW, &options);
}

static int rd_serial(int port, uint8_t *buff, int len) {
    int res;
    res = read(port, buff, len); 
    if (res == -1) {
        perror("serial_read: Failed to read /dev/ttyO2 - ");
    } 
    return res;
}

static int handle_RX_payload(int port, sMsgData *RX_msg) {
***
    rd_serial(port, pnt, (RX_msg->message_len - rx_len));
***
}

static int handle_RX_header(int port, sMsgData *RX_msg) {
    static uint8_t  header[6];
    uint8_t         byte;
    int             rx_cnt;
    do {
        rx_cnt = rd_serial(port, &byte, 1);
        if (rx_cnt > 0) {
            memcpy(header, &header[1], 5);
            header[5] = byte; 
            RX_msg->mesage_type = check_header(header);
            if (RX_msg->mesage_type != 0xFF) {  //valid header sequence found
                RX_msg->message_len = (header[3] << 8) + header[2] - 4; 
                RX_msg->payload = (uint8_t*)malloc(RX_msg->message_len);
                return STAGE_COMPLETED;
            }
        }
    } while (rx_cnt > 0); 
    return EMPTY_BUFFER;
}

static uint8_t signal_handler_IO (int port, uint8_t *rx_state, sMsgData *RX_msg) {
    uint8_t   *state = rx_state;
    int       res;
***
    res = handle_RX_header(port, RX_msg);
***
    res = handle_RX_payload(port, RX_msg);
***
}

void ttyO1_signal_handler_IO (int status) {
    static uint8_t  state = 2;
    static sMsgData ttyO1_RX_msg;
    signal_handler_IO(UART_port_ttyO1, &state, &ttyO1_RX_msg);
}

void ttyO2_signal_handler_IO (int status) {
    static uint8_t  state = 2;
    static sMsgData ttyO2_RX_msg;
    signal_handler_IO(UART_port_ttyO2, &state, &ttyO2_RX_msg);
}