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My application only uses Pi very occassionally and only a few seconds each time. It would be ideal if Pi supports suspend to RAM feature to save maximum energy. (I am thinking of the next step of powering Pi with batterries only.)

My question is:

  1. Does Pi support this feature? From what I've researched so far. It doesn't seem so.
  2. If not, is it possible to modify the hardware/kernel a little bit to make suspend to RAM work?

(Edit: The only hardware peripheral my application is using on the Pi is a USB-WiFi adapter.)

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No and No.
The Pi has no way of waking itself up apart from a hardware reset button, which can wake the Pi up from a halt state, i.e. it will reboot the Pi.

You can modify the hardware and use switching regulators rather than the linear regulators that the Pi uses out of the factory for some more energy saving.

Apart from that though, you won't get much more power saving unless you don't use the built in USB hub ( assuming you're using a Model B ), which means no Ethernet and no USB ports...which sort of defeats the purpose of the Pi.

  • Thanks for the comment. I need to use USB WiFi for my application. Can you provide your source of Model B Pi's USB hub cannot be suspended? What if I use Model A? – Penghe Geng Aug 27 '13 at 17:00
  • Will the Pi need to receive data on the USB WiFi adapter to wake up ? Or is this a timer thing ? Model A would save power in this case if all you need is the USB WiFi adapter plugged in. – Lawrence Aug 28 '13 at 3:13
  • I am considering to wake up Pi using GPIO. – Penghe Geng Aug 28 '13 at 3:20
  • raspberrypi.org/phpBB3/… <--- here's one of the threads I could find about powering down the USB/Ethernet chip. According to that if you power down the USB hub, you can't power it back up again. – Lawrence Aug 28 '13 at 3:38
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Both RasPi and USB-WiFi consume quite a lot of power, so unless you're going to power them from car battery or something of similar size, you may forget about running them on batteries.

An usual pack of AA batteries will give you about 1 hour of run time, with very unstable performance after the batteries are half-depleted.

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    I was able to run a Pi (256K original B) all day (over 8 hours) on a 6000 mAh battery pack. I didn't do an exhaustive test but it was used lightly throughout that time and the WiFi ran the full time. – Jerry Gagnon Aug 28 '13 at 15:22

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