Re: Serial port latency

Trent Jarvi
2001-03-22T20:16:47Z

On Thu, 22 Mar 2001, Geir Thomassen wrote:

> 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.
>

Ya.. My bad. I use that to support multiple platforms

#ifdef CRTSCTS
#define HARDWARE_FLOW_CONTROL CRTSCTS
#else

Do you happen to have shared interupts enabled in the kernel?

> > 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
>

--
Trent Jarvi
TrentJarvi@yahoo.com