ｃ/c++によるシリアル通信の実装について

現在、こちらのサイト(https://gist.github.com/zonque/0ae2dc8cedbcdbd9b933)のコードをもとに自作関数を実装しています。
自作している関数はXMODEMを受け取る関数について自作しています。
名前は xmodem_receiveです。
しかし、main関数内で実行すると送信を待たず、エラーもなくすぐに終了してしまいます。
どうしてなのでしょうか。

static_cast<uint8_t*>"を使ているのでタグはc/c++とさせて頂きます。

実装している自作関数

static int xmodem_receive(int serial_fd, char* filename){
    int skip = 0;
    uint8_t sdACK = X_ACK;
    uint8_t eof = X_EOF;
    uint8_t sdNAK = X_NAK;
    uint8_t recSTX; // receive SOH from chunk
    uint8_t recBlk; // receive blk from chunk
    uint8_t recNegBlk; // receive blk negative from chunk
    uint8_t recData[1024]; // receive data from chunk
    uint16_t recChksum;
    FILE *fp;
    int ret, fd;
    struct stat stat;
    // If we want to receive, We have to send NAK to Sendor.



        /* binary write */
    fp = fopen(filename, "wb");
    //Send NAK still read SOH that header of one data chunks
        while(1){
            printf("Waiting for receiver ping ...");
            fflush(stdout);
            //
            do {
                    // send NAK before read SOH
                    ret = write(serial_fd, &sdNAK, sizeof(sdNAK));
                    // after sending NAK,receiving SOH from chunk
                    ret = read(serial_fd, &recSTX, sizeof(recSTX));
                    if (ret != sizeof(recSTX)) {
                            perror("read");
                            return -errno;
                    }
            } while (recSTX != X_STX);

            //So next, receiving blk
            ret = read(serial_fd, &recBlk, sizeof(recBlk));
            if (ret != sizeof(recBlk)) {
                perror("read");
                return -errno;
            }
            ret = read(serial_fd, &recNegBlk, sizeof(recNegBlk));
            if (ret != sizeof(recNegBlk)) {
                perror("read");
                return -errno;
            }
            ret = read(serial_fd, &recData, sizeof(recData));
            if (ret != sizeof(recData)) {
                perror("read");
                return -errno;
            }
            ret = read(serial_fd, &recChksum, sizeof(recChksum));
            if (ret != sizeof(recChksum)) {
                perror("read");
                return -errno;
            }
            // data block number check
            if(recBlk == 0xff - recNegBlk){
                perror("read");
                return -errno;
            }
            // data integrity check
            if(recChksum == swap16(crc16(recData, sizeof(recData)))){
                perror("read");
                return -errno;
            }
            // check of appended "0xff" from end of data to  end of chunk in chunk
            unsigned char *ptr = recData;
            ptr += sizeof(recData);
            while(*ptr == 0xff){
                ptr--;
            }
            fwrite(recData, (ptr - recData),1,fp); // write Datas bytes from our buffer
            // set skip flag or end connect
            ret = write(serial_fd, &eof, sizeof(uint8_t));
            if (ret != sizeof(eof) || ret != sizeof(X_STX)){
                return -errno;
            }else{
                if(ret == X_STX){
                    skip = 1;
                }else if(ret == EOF){
                    printf("EOF ...");
                    ret = write(serial_fd, &sdACK, sizeof(sdACK));
                    break;
                }else{
                    return -errno;
                }
            }

        }
    printf("done.\n");
    fclose(fp);
    return 0;

}

main関数内での呼び出し

int main(int argc, char **argv)
{
        int a, ret, serial_fd;

        serial_fd = open_serial("/dev/ttyUSB0", 115200);
        if (serial_fd < 0)
                return -errno;


        if(argv[2] == "0" || argv[2] == NULL){
            ret = xymodem_send(serial_fd, argv[1], PROTOCOL_XMODEM, 1);
            if (ret < 0)
                return ret;
        }

        if(argv[2] == "1"){
            ret = xmodem_receive(serial_fd, argv[1]);
            if (ret < 0)
                return ret;
        }


        return 0;
}