[wellylug] Modem upload problems - solved

[Jethro Carr]

On Sun, 2005-06-05 at 12:26, Lyndsay Mountfort wrote:
> Jethro Carr wrote:
> 
> >On Sat, 2005-06-04 at 15:22, Lyndsay Mountfort wrote:
> >  
> >
> >>I recently gave up on the onboard modem on my laptop, and bought a
> >>PCMCIA modem from Dick Smith. Using Mepis 3.3 and kernel 2.4.29 it was
> >>detected and seemed to work ok. Turned out the standard 2.6.10 build for
> >>Mepis 3.3 was missing the relevant driver (serial_cs), but having
> >>compiled and installed the driver it appeared to work fine also.
> >>
> >>Until I tried to send a reasonably large attachment to someone. It turns
> >>out that all uploads of significant size choke to a crawl, with long
> >>periods of inactivity showing in the KPPP statistics graph. A couple of
> >>hundred kb can take hours. Doesn't matter what software is uploading -
> >>email, browser (webmail), or scp from the Konsole. Downloads of any size
> >>work very well.
> >>
> >>Looking at the PCMCIA HowTo, it suggested that slow performance might be
> >>related to an interrupt conflict, so I followed the instructions and
> >>used setserial to set it to polled mode (irq 0), and hey presto, uploads
> >>worked reasonably well (at least about 2kb/s, a considerable
> >>inprovement. The rating for the modem is 56k down, 33k up).  So from
> >>there I played around with various other interrupts, but none of them
> >>worked satisfactorily.
> >>
> >>So I take it from that there is not necessarily a conflict, but it likes
> >>polled mode better, at least for uploads. Unfortunately, downloads are
> >>excellent (for a modem) using interrupts (>5kb/s), but using irq 0 they
> >>reduce to about 2k as for uploads.
> >>
> >>Has anyone struck this before? Anyone got any ideas what I could try to
> >>get usable upload speeds, but keep good download performance?
> >>Initialisation strings or anything? It's all well outside my very
> >>limited hardware knowledge.
> >>    
> >>
> >
> >I've had simular problems (with a pcmcia modem & a serial modem). The
> >pcmcia modem was fixed when I recompiled pcmcia-cs to autodetect the
> >IRQ. The serial modem had a problem with flow control.
> >
> >It sounds like you've tried all the irq's, so it could be a issue with
> >flow control.
> >
> >
> >I'm not very knowledgeable in this area, but I had a problem with a DSE
> >serial modem once like this which was caused by flow control.
> >
> >Flow control is needed when uploading files, as the modem is slower than
> >the pc at transmitting data. If the pc sends data to it at full speed,
> >the modem gets 'overloaded' and drops all the data it can't fit into
> >it's small buffer.
> >
> >Flow control tells the computer to slow down the sending of the data, to
> >match the upload speed of the modem.
> >
> >I'mm not sure about kppp (I don't use it), but there might be some
> >settings in kppp, and see what the flow control is set to. There is
> >usually 3 options:
> >- none
> >- xon/xoff
> >- crt/crts
> >
> >Try them and see if it works. Certain modems also need extra AT commands
> >passed to them to enable flow control. See your modem's manual.
> >
> >hope this helps,
> >
> Thanks Jethro
> 
> Seems I was looking too hard, without noticing the simpe stuff. I found
> the command supposed to turn on hardware flow control, and it just
> caused a complete hang of the modem. Sofware control did nothing. So I
> turned it all off, and whaddaya know, it works perfectly.
> 
> So I guess that's one more device that gets a big Linux tick. BTW I also
> have their PCMCIA 802.11g wireless card, which also works out-of-the box
> PnP with Mepis. Even in that other OS I had to install drivers.
> 
> Thanks again for pointing me in the right direction.

no worries.

it's always once you solve a problem, it's so simple you can't belive
you missed it! :-)

I do it all the time. :-(


-- 
-- Jethro Carr

jethro.carr at jedolinux.com

http://jethrocarr.jedolinux.com
http://jethrocarr.jedolinux.com/index.php?page=cv/cv.php

http://www.jedolinux.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
Url : http://lists.wellylug.org.nz/pipermail/wellylug/attachments/20050605/a3fb4d1e/attachment.pgp