Writing and reading data to development board

Question

I'm using sama5d3 development board. I'm trying to read and write data to the device connected to the USB port. 2.i can write the data to the device.

3.How can i read data from the device?

4.How can i know whether the data is writing to the device?`

int main()

{

 char fd1,retval,speed;

 struct termios usb_parm;

 fd1=open("/dev/ttyACM0",O_RDONLY|O_WRONLY|O_NONBLOCK|O_NOCTTY);

  if(fd1>0)
  {
  printf("Device detected\n");        
  }
  else
  {
  printf("Port free\n");
  return -1;
  }

  ioctl(fd1,TCSETS2,&usb_parm);
  usb_parm.c_cflag &=~CBAUD;
  usb_parm.c_iflag=speed;
  usb_parm.c_oflag=speed;
  usb_parm.c_cflag |=BOTHER;                                   
  retval=ioctl(fd1,TCSETS2,&usb_parm);
   printf("retval=%d\n",retval);
  tcflush(fd1,TCIFLUSH);                                      
  tcsetattr(fd1,TCSANOW,&usb_parm);                       
  tcgetattr(fd1,&usb_parm);                                    

 char write_buff[]="q,e";
 int bytes_written=0;

 bytes_written =write(fd1,write_buff,sizeof(write_buff));
 printf("written to ttyUSB0=%s\n",write_buff);
 printf("Bytes written to ttyUSB0=%d\n", bytes_written);

char read_buff[]={"gdfjhtfgjif"};
int  bytes_read=0;
int byteavailable=0;

tcflush(fd1, TCIFLUSH); 
ioctl(fd1,FIONREAD,&byteavailable);
memset(read_buff,0,sizeof(read_buff));
if(byteavailable>0)
{   
bytes_read=read(fd1,read_buff,sizeof(read_buff));
}
else
{
printf("error\n");
return -1;
} 
printf("Read buff=%s\n",read_buff);
printf("Bytes read=%d\n",bytes_read);

}