[wellylug] Modem upload problems - solved

[Lyndsay Mountfort]

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.

Lyndsay