Information on XO-1 power efficiency

Richard A. Smith richard at
Thu Nov 12 01:22:07 EST 2009

> 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

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