Information on XO-1 power efficiency

Christoph Derndorfer christoph.derndorfer at
Thu Nov 12 08:06:19 EST 2009

Paul, Richard,

thanks a lot for your extensive replies, much appreciated! :-)

I probably won't be able to finish my slides before Sunday but I'll try and
send you a draft if I can find an Internet connection during my
Munich-Copenhagen-Stockholm train adventure...


On Thu, Nov 12, 2009 at 7:22 AM, Richard A. Smith <richard at>wrote:

> > Now while the original goal of getting the XO-1's power consumption down
> to
> > 2W wasn't achieved it's still a pretty lean and efficient machine.
> In my power talks I give during country meetings I mention that if you see
> reference to a number for XO power usage that does not _specifically_
> indicate the usage during the measurement period then its wrong.
> There are several usage modes where the XO-1's power draw is < 2W and even
> less than 1W.
> 5 of the 7 modes I describe in the link below draw less than 2W.
> What I suspect you mean here is the average power consumption for a average
> user with aggressive power saving mode disabled.  Which yes is above 2W.
>  Its 4W-7W.
> If I seem a bit anal about that its intentional.  The reason is that in the
> past its not been clear that these power numbers discussed were for the low
> power modes and not the holistic average power draw.  I've had to deal with
> several deployments (small and larger) or test sites that have budgeted for
> 2W (or some other odd number) of power and then get all cranky when I
> mention that charging the battery pulls 17W.
> Granted they should have checked but after its gone through 3 people
> speculation seems to turn into fact.
> So I try to very clear and specific when I talk about power usage to help
> try stop that from happening in the future.
> > obviously plan to talk about the choice of hardware components and MLJ's
> > display design. Another topic I'll touch upon is the wide-range voltage
> > input which allows for a variety of power sources to be used without
> > requiring further external regulation.
> 18V max. [1]  Gen 1-5 opens that up to 24V.
> [1] Empirically you can get between 20-22V  but allowing for the tolerances
> of the parts the guaranteed minimum is 18V
> > One thing I'm less sure about is the DCON because I'm don't know how
> > aggressively it is currently being used (maybe someone can shine a light
> on
> > this, I didn't find anything about it on the wiki or the mailing
> By DCON do you mean DCON mode or frozen.  Where the screen holds its last
> value the cpu gets turned off?  If so then its available in the latest XO-1
> build.  Right click on the center XO guy and select control panel then
> select power.  There is an option for enabling "Automatic power management"
> and its listed as experimental.  If you set that your system auto suspend
> when and activity timer expires.
> The knobs for the activity timer can be found in
> /etc/ohm/plugins.d/timeouts.ini  One of them controls when the backlight is
> dimmed the the other when suspend happens.  Units are ms.  If you set them
> really low you will roughly get the "in between keystrokes" behavior.
>  Except that resume with WLAN takes around 900ms.  The drawbacks are that
> some of your networking apps won't work 100% like they did with the system
> up all the time and sometimes the WLAN device refuses to talk on the USB bus
> any more (USB 3 strikes error).
> > list). Another question I'm interested in is what the efficiency of the
> > AC-DC adapters shipped with the XO-1 is?
> The ultimate eff% depends on the line voltage, line frequency, load, and
> ambient temperature.  Its expressed as a series of curves.  See my statement
> above about referring to power with single-across-the-board numbers.  Unless
> you are in the lab you are guaranteed to be wrong.
> That said Energy Star attempts to reduce all that down to a class number by
> taking the average of 4 points spread on the curves. [2] Our class rating is
> IV which says that the adapter has an average efficiency of >= 75%.
> [2] We are on an older energy star spec.  The latest energy star spec rev
> 5.0 (Active July 1, 2009 ) has higher requirements.
> > I'm also wondering whether it makes sense to talk about some of the ideas
> > discussed in the early stages of the project (e.g. suspend inbetween
> > key-strokes which IIRC ended up not being implemented).
> Certainly.  Please do.  These are very much still goals.  Right now the
> focus is on XO-1.5 where we hope to have bypassed some of the issues that
> gave us trouble in XO-1.  Then we can start work on making the networking
> apps and the timer subsystems play nice with turning off a CPU.  When thats
> all done then someone can look at if it makes sense to try and back port
> stuff to XO-1.
> Turning off CPU+Companion chip (or dropping it into non-functional but
> really low power mode) but still having a system that functions normally has
> the potential for large amounts of power savings.
> Consider my laptop where I run my IRC client. I leave it running so that
> people can ping me on IRC. There are many periods when I'm not actively
> using it. During that time its basically just wasting power.  If 90% of the
> devices could be turned off yet wake back up briefly to catch IRC messages
> it would save _lots_ of power.   My AC power meter tells me that my laptop
> sitting here with my various apps open but me not typing draws 17-19W from
> the grid.  That could be reduced to 2W.
> > As I said it's only a short talk (10min max.) but there's anything else
> > significant when it comes to the power consumption and underlying design
> > that I've left out above then please give me a shout.
> I think OLPC's philosophy is significant.  The XO is the lowest power
> laptop of its class.  But its still off by about a factor of 10 from whats
> needed in places with no power infrastructure.
> Designing for low power seems to still be a foreign concept to the PC
> world.  The current method of getting longer battery life appears to be add
> a larger battery.  Quoting Ed McNierney "How big does your battery have to
> be when there's nowhere to plug it in?"
> Hope this helps.
> --
> Richard A. Smith  <richard at>
> One Laptop per Child

Christoph Derndorfer
co-editor, olpcnews
e-mail: christoph at
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