[hylafax-users] Serial latency

["Tim Allen" <timallen@dcallen.co.uk>]

Thanks for the suggestions Jay.

Breakout box shows no activity on pin 20 during transmission, pulses on
hangup. So it looks as if our hardware handshaking from the Linux end isn't
working. Presumably this is all done by kernel routines called by Hylafax
which should toggle the DTR line when the UART fifo is getting full. Tried
XonXoff for good measure with no improvement, so that may help to pinpoint
the level at which things aren't working.

Tim

> On Wed, Jun 27, 2001 at 09:56:23AM +0100, Tim Allen wrote:
> > I'm running Hylafax 4.1rc2 under RH 7.1 on a 486 100MHz (16550AF UARTS)
with
> > a Multitech MT1932ZDXK Class 2 modem, RTSCTS handshaking (cabling
> > double-checked) and 38400 Baud between PC and modem.
>
> ATTENTION EVERYBODY:  See that?  That's how a problem report *should*
> start.  Thanks, Tim.  :-)
>
> > Clearly the machine isn't exactly cutting edge and once the machine
comes
> > under load when receiving a fax I start losing chunks of the incoming
page.
> > Can anyone advise on the likely success of any of the following ideas:
> >
> > Drop the modem comms speed to 19200 or 9600 Baud.
> >
> > Run setserial at startup with the low_latency option.
> >
> > Modify the UART fifo interrupt threshold. At some point during the
> > installation I recall a message stating this was set to 8 but I don't
know
> > what to do to change this.
>
> If you're running in class 2 and dropping incoming data, the problem is
> almost certainly interrupt latency, and if your 550 is configured
> correctly, I'm shocked; *shocked*, I tell you.  :-)
>
> I would recommend putting a break out box on the cable, and msking sure
> that the handshake lines are actually toggling, and making sure that
> the modem is actually configured for that (&K?).
>
> Yeah, I would try backing the modem rate off to 19.2... and I'd also
> look into increasing memory, if you don't have at *least* 32MB; 64M
> would be better.  Swapping will *kill everything* on a Unix box; if
> you're swapping, you don't have enough RAM.
>
> RAM's cheap.  ;-)
>
> Cheers,
> -- jra




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