Not working on the ARM board

char buff[255];
        fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY |O_TRUNC);
        if (fd == -1){
                printf("Can't open port!\n");
                return 1;
        }
        else {

                while (1)
                {
                        send(fd,"NULL");
                        char st[100];
                       memset(st,'\0',sizeof(st));
                         buff[0] = '\0';
                        send(fd, "AT\r\n");
                        sleep(1);
                        size = read(fd,buff,255);
                        printf("GOT:%s",buff);
                        if(buff[0]=='E')
                        {
                                return -1;
                        }
                }

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Continue here:
http://www.linuxquestions.org/questi...rd-4175464834/