ttyATH0 slow interface


While testing a Bluetooth dongle supporting AT Commands, I receive a 400KB file on the GL-AR150 via ttyUSB0 and ttyATH0 using a protocol hand shake .

It takes ~3 min  via cell phone to PC. (This is just a reference test)
It takes ~3 min via the GL-AR150's ttyUSB0.
It takes ~9 min using  GL-AR150's ttyATH0 at 115Kbps wired to uart pins of dongle. At this baud rate it should take less then or ~3min: as tested and verified on other uart products.
Any ideas why the Linux driver for ttyATH0  would be making it slower? 

Serial config:

  tcgetattr(_fd, &options); // Get the current options for the port
  options.c_lflag = 0;
  options.c_iflag = 0;
  options.c_oflag = 0;
  options.c_cflag = 0;

  // ignore modem lines like hangup
  options.c_cflag |= CLOCAL;

  // allow reads from this device
  options.c_cflag |= CREAD;
  options.c_cflag |= B115200;
  options.c_cflag |= CS8;

  options.c_oflag = OPOST;
  //watch hangup line
  options.c_cflag |= HUPCL;

  //no wait between char's
  options.c_cc[VMIN] = 0; //1;
  options.c_cc[VTIME] = 0;

   //set new attributes
  tcsetattr(_fd, TCSANOW, &options);
  sleep(2); //required to make flush work, for some reason
  tcflush(_fd, TCIOFLUSH);


using 115200 it should takes less than 1 minutes, right?

But I have no experience

Yes - should only take about 1 minute, but our protocol and the Bluetooth overhead for LE slows it down. I have been searching on the web and haven’t found anything that talks about an issue like this. Since the firmware is the same all the way down to tty linux drivers read/writes, it would suggest it’s in the configuration of the different tty’s?