Alternative power/recharging source?
Richard A. Smith
richard at laptop.org
Mon Feb 25 23:23:30 EST 2008
david at lang.hm wrote:
>> And the EC, the memory, various pull up/down resistors, and few other
>> suspend voltage regulators. All these add up to a non-trivial amount.
> you are not nessasarily going to be powering the system memory
In the current setup powering the memory is not optional during suspend
it is placed into self-refresh.
> Jespin at Usenix last year. however I can't just cite my memory, so I
> went looking on the website and found that snippet of information.
> however, it almost doesn't matter which of us is right. the mere fact
> that we are having this disagreement indicates a need for better
> documentation of this sort of info.
It may not matter to you but it matters quite a bit to me since its part
of my job. :) I'm part of the OLPC hardware team. The accurate
measurement and reporting of the XO power draw is our responsibility.
So when I see numbers flying about that I know are inaccurate I've been
trying to correct them and find the source so it can get corrected as well.
Unfortunately, as you and John Gilmore are pointing out, OLPC has
previously made verbal and published statements with wattage numbers
prior to mass production hardware. These statements, while not false,
are only really useful when you know the context under which they were
measured or extrapolated. In many cases this context did not make it
into the statement or publication.
So on that note here's some measurements I took this weekend with the
context of the measurement: Consider these authoritative as of 2008-2-24.
Sleep (No WLAN Firmware, Lid closed) .25W
Ebook (No WLAN Firmware, Mono display, No backlight) .71W
Mesh (Lid closed, WLAN) 1.1W
Suspend (WLAN, Color display, backlight dimmed by ohm) 1.9W
Suspend (WLAN, Color display, backlight minimum) 1.7W
Idle (WLAN, Backlight full, CPU on, no load) 3.9W 4.9 Peak
Camera (WLAN, Backlight full, CPU on, high load) 6.5W 8.7 Peak
These were measured and processed via my battery power logging script
and a python hack I wrote (So I could quit using openoffice). See
http://wiki.laptop.org/go/XO_Power_Draw#XO_power_draw for the code and a
lot of gory details.
No WLAN Firmware != 'olpc-control-panel -s radio off' since it does nto
appear to turn every thing off. With radio-off Ebook mode drew 1.3W
Richard Smith <richard at laptop.org>
One Laptop Per Child
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