Re: Serial port latency

[Geir Thomassen <geirt@powertech.no>]

Trent Jarvi wrote:
> 
> Hi,
> 
> I'm not on the kernel list.  I just ran across your email while looking at the
> weekly archive.
> 
> I think you want to enable software flow control.
> 
>         tcgetattr( fd, &ttyset );
>         ttyset.c_iflag |= IXOFF;
>         tcsetattr( fd, TCSANOW, &ttyset );
> 

Just tested it, it didn't change anything. The response from the controller
can contain ^S/^Q, so it would be a bad idea anyway ....

> Someone reported that the Java CommAPI driver at http://www.rxtx.org got
> 150-200ms latency with (9600,N,8,1,XON/XOFF).  Beyond that you may have to
> look at something like the realtime support.  I guess 2 ms is normal on
> win98.

Win98 is the problem I am trying to solve with my program ...

> Since you have the scope hooked up you may look at hardware flow control too.
> 
>         tcgetattr( fd, &ttyset );
>         ttyset.c_cflag |= HARDWARE_FLOW_CONTROL;
>         tcsetattr( fd, TCSANOW, &ttyset );

Do you mean CRTSCTS ? HARDWARE_FLOW_CONTROL is not defined in my header files.
I use CLOCAL, which should make the driver ignore modem control lines.

> Let me know if you find anything out.  I'm the maintainer of rxtx and would
> be interested in documenting this for others.

sure ...

> --
> Trent Jarvi
> TrentJarvi@yahoo.com

Thanks anyway

Geir