[maemo-users] Power consumption and WLAN APs

From: Frederic Crozat fred at crozat.net
Date: Sun Jul 20 23:46:14 EEST 2008
On Sun, Jul 20, 2008 at 10:27 PM, Andrew Daviel <advax at triumf.ca> wrote:
> On Mon, Apr 21, 2008 at 4:58 PM, Eero Tamminen <eero.tamminen at nokia.com>
> wrote:
>>  One possibility is a WLAN AP with broken power management
> I recently noticed that my tablet battery runs down faster at work than
> at home, with the WiFi enabled but otherwise sitting idle (12%/hour vs
> 1%/hour).
> I thought the issue might be that there's more broadcast/multicast
> traffic at work, which would get through the filters in the ethernet chip
> and into the kernel, but then I found a reference to your post on the
> list.
> At home I have a Linksys WRT54; at work I think Orinoco-AP2000 where I
> may be able to change some settings (writing this at home I can't login
> to check).
> What power-management issues have you seen affecting battery life ?

I think it is usually caused by interoperability deficiency between
770/n8x0 and some routers wifi chipset regarding PSM (Power Saving
Management) part of wifi specification.

I'm seeing this kind of issue between my work AP (Linksys) which have
working PSM and my home AP (Freebox, a set-top-box provided by my
ISP), where PSM is not working properly with a maximum uptime of 8h
when wifi is on.

I've been in contact with one of my ISP engineers who is taking care
of writing wifi driver in their set-top-box. From the first
investigation, it seems Conexant chip (used on Nokia tablets) was
known to be problematic (Freebox is using Ralink chipset). A first bug
was found in ralink proprietary driver which was losing AP association
after some time in PSM mode, which was fixed by Ralink.

Unfortunately, this fix was not sufficient to fix the power
consumption issue and we are kind of stuck now :(

If Eero or another Nokia hackers have some information which might
help Freebox engineers to track the issue, I'll be happy to serve as a

> Would it affect other laptops as well or just the tablets ?

I guess it will depend on laptop wifi chipset. And compared to Nokia
tablets, entire laptop power consumption is way more important than a
tablet, so if wifi is too important, it is probably hidden by other
component consumption.

Frederic Crozat

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