[wellylug] Modem upload problems

Lyndsay Mountfort lyndsaym at paradise.net.nz
Sat Jun 4 15:22:27 NZST 2005


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.

Thanks

Lyndsay




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