Power down USB when suspending

Matías Poloni mpoloni at ieee.org
Thu Oct 7 20:41:50 EDT 2010

Dear John,

We are working with biologists in our grade thesis. They need to take
pictures of wild animals in a protected native area so our goal is to make
the equipment for this. In addition, there is an ONG involved working with
people who live near this protected area, in particular children (there are
two schools in the area). So the idea is to make an equipment controlled by
the XO and teach the children and teachers how to use it.
Mariana, one of the biologists, alrready worked with commercial "tramping
photo" equipment and she said that the most crucial issue is the time delay
(time between the animal is detected and the photo is taken).
As you guess we suspend the XO to save power (so we can have a small battery
and small solar panels), but we have a long delay in the first picture.
We thought about taking the first picture with the built-in XO-1 camera but
first we wanted to consider other possibilities. Another idea that we came
up with was to use an infrared sensor (or two if needed) with a very wide
sensed area (wider than the camera itself) to have more possibilities
to caught the animal passing by.
With the information that you give us we can decide how to go on, so thank
you very much for your time.


PD: any idea will be very welcome.

2010/10/5 John Gilmore <gnu at toad.com>

> It would be better if you could explain WHY you need to take a photo
> quickly after resuming.  Is the idea that the laptop will save power?
> It could remain suspended for a long time, wake and take a picture,
> then suspend again until the next picture is needed.  In that case,
> you can wake it a bit early, and it can still take the picture on
> time.  If suspend in the OS was working properly, you could just
> sleep() as long as you require, and the OS would automatically suspend
> and resume at the right times.  (Though if you have a USB peripheral
> plugged in, it shouldn't be suspending at all, since that cuts the power
> to the peripheral, which might not be able to deal with that.)
> Is there some other reason why you need the laptop to suspend?
> (Even if it could power the USB bus during suspend -- or if you use
> an external USB hub with power -- the camera will burn power constantly
> rather than saving power while suspended.)
> The built-in XO-1 camera is not connected via USB, so it should be
> available more quickly after resuming from a suspend, if you can use it
> instead of a USB webcam.
>        John

Matías Poloni
+598 98867573
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