pis have no ACPI or PMICs: think hibernate still possible?

[curious4872]

All versions of Linux 2.6 Kernel support hibernation (which means saving the contents of memory to disk, then shutting down the PC completely. The next time the PC is physically powered back on, as part of the boot process the old contents of memory are read from disk, restoring the previous session such as open browser windows, applications, and anything else that was being done. - "[Hibernation] is implemented by swsusp which is built into the 2.6 [Linux kernel] series.")

However, the Raspberry Pis have no ACPI support (Advanced Configuration and Power Interface) nor include a PMIC (Power Management IC, which could be part of a SoC but perhaps isn't for the one in Pis).

So, given this state of affairs, do you think it's still possible to get Pis to hibernate anyway? Why or why not?

I realize it would be pretty pointless, as at the end of the hibernation process you would have ... a running, shut-down pi that is ready to be physically powered down. I'm just curious what prevents this?

Obviously it would only make sense if there were some kind of external chip (maybe powered by Arduino) that waited until the Pi was shut down (maybe gave it 2 minutes to do so), and then physically interrupted its power until it needed it again.

The sleepypi seems to be along these lines, but I'm not sure if it hibernates or actually shuts down:

-> https://www.google.com/search?q=does+sl ... +shut+down

Doesn't answer in the first two pages of results.

The faq seems to imply it does a complete Shutdown (not hibernate): http://spellfoundry.com/sleepy-pi/sleep ... spberry_Pi

So it seems the sleepy pi is along these lines - but for some reason actually shuts down the Pi instead of hibernating it.

So is a proper hibernate command even possible? Why or why not? What is physically preventing it, if the kernel supports it? My understanding is that it's just a special shutdown sequence and a special boot sequence.... I don't see why it wouldn't work on a pi, other than having to interrupt the power manually once it has had time to complete....

(Please do correct any mistakes I made above.)

[ghans]

Nobody has tried it - thats all. Testing such a thing would
certainly involve repeatedly compiling the Kernel and
other parts of Raspbian and original research on
(ARM ? Linux ? Debian ?) powersave modes on Raspberries since
no resources on that topic actually exist. That puts
most people off.

Note when i say original research i mean you could also
fail in finding a solution. Which also puts people off.

I certainly favor a system where an external micro
is involved.


ghans

[curious4872]

Nobody has tried it - thats all. Testing such a thing would
certainly involve repeatedly compiling the Kernel and
other parts of Raspbian and original research on
(ARM ? Linux ? Debian ?) powersave modes on Raspberries since
no resources on that topic actually exist. That puts
most people off.

Note when i say original research i mean you could also
fail in finding a solution. Which also puts people off.

I certainly favor a system where an external micro
is involved.


ghans

an external micro has to be involved as there is no way to interrupt the power - the raspberry pis are always-on when powered. This is a separate question from whether it is only possible to shutdown (still requires an external micro to physically cut power) or whether it is possible to hibernate (still requires an external micro to physically cut power.)

To explain in simple terms. If you run a normal shut down, you have to then unplug it. After plugging it back in you get a reboot.

If hibernation is possible, then after hibernating you have to then unplug it. After plugging it back in you would get a reboot. (But with the effect of waking from a hibernation.)

[fruitoftheloom]

The WittyPi has power down / power up capabilities, so it is not exactly want you want but may be an alternative with limitations:

http://www.uugear.com/witty-pi-realtime ... spberry-pi


It would seem your subject was brooched 4 years ago without resolution: viewtopic.php?f=27&t=7808

[epoch1970]

AFAIK to suspend/hibernate devices have to be able to respond to freeze/thaw commands from the kernel, and the CPU (and RAM) have to accept switching to a specific state too.
Linux took a loooong time until it handled low power states gracefully, so if hardware support is there, adding software support could be quite a project.
I didn't know of the sleepypi hardware. I suppose the guy who designed it knows the ins and outs of the Pi's power management capabilities. Perhaps you could drop him a line, too?

[fruitoftheloom]

AFAIK to suspend/hibernate devices have to be able to respond to freeze/thaw commands from the kernel, and the CPU (and RAM) have to accept switching to a specific state too.
Linux took a loooong time until it handled low power states gracefully, so if hardware support is there, adding software support could be quite a project.
I didn't know of the sleepypi hardware. I suppose the guy who designed it knows the ins and outs of the Pi's power management capabilities. Perhaps you could drop him a line, too?

I believe Linux uses rtcwake for machines with BIOS / ACPI etc...

http://linux.die.net/man/8/rtcwake

[epoch1970]

I don't think rtcwake is the big guy, drivers have to implement some calls sent by the kernel.

Some PC systems can't currently exit sleep states such as mem using only the kernel code accessed by this driver.

I admit I am totally out of my league.

[curious4872]

This page (admittedly from 2011) says GRUB can read hibernated swap file to reload from it:

http://chriseiffel.com/everything-linux ... 4-mint-11/

But is there any way to get GRUB to work? The link (4 years old) says grub doesn't work with an rpi - is this the latest? viewtopic.php?f=24&t=10814

[fruitoftheloom]

This page (admittedly from 2011) says GRUB can read hibernated swap file to reload from it:

http://chriseiffel.com/everything-linux ... 4-mint-11/

But is there any way to get GRUB to work? The link (4 years old) says grub doesn't work with an rpi - is this the latest? viewtopic.php?f=24&t=10814

All RPi and CM boot from the VC4** so no change:

http://wiki.beyondlogic.org/index.php?t ... ot_Process

http://wiki.beyondlogic.org/index.php?t ... aspberryPi


**the RPi 3B is slightly different as also supports USB Boot / PXE as mentioned at end of this podcast, but not yet implemented:

http://thepipodcast.com/the-pi-podcast-22-eben-upton

[curious4872]

This page (admittedly from 2011) says GRUB can read hibernated swap file to reload from it:

http://chriseiffel.com/everything-linux ... 4-mint-11/

But is there any way to get GRUB to work? The link (4 years old) says grub doesn't work with an rpi - is this the latest? viewtopic.php?f=24&t=10814

All RPi and CM boot from the VC4** so no change:

http://wiki.beyondlogic.org/index.php?t ... ot_Process

http://wiki.beyondlogic.org/index.php?t ... aspberryPi


**the RPi 3B is slightly different as also supports USB Boot / PXE as mentioned at end of this podcast, but not yet implemented:

http://thepipodcast.com/the-pi-podcast-22-eben-upton

Thanks. These are fantastic links. Do you know what beyondlogic.org is? The about page on bottom-right is blank.