sleep / wake-up

sleep / wake-up

[Guennadi Liakhovetski]

Hi all,

This is a complete newbie question - just like I am on powerpc. How does 
one put to sleep / wake up an embedded ppc (mpc8241) system? Notice, I've 
never done it (sleep / suspend) on x86 either, and I only have a VERY 
vague idea of what it's all about... But I'd read if I knew what and where 
- half an hour googleing didn't bring any positive results apart from 
links to pbbuttonsd, which mainly describes ppc / apple notebooks.

What I'd like to know is a bit of theory - kernel-level support and 
user-level utilities, as well as what one does practically to put a ppc to 
sleep / wake it up.

Thanks
Guennadi
---
Guennadi Liakhovetski

Re: sleep / wake-up

[Jon Scully]

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Also, here's an article (just about 4 days old):
http://www.linux.com/article.pl?sid=06/05/24/1716222
(I thought the subject sounded familiar ;-)

On 6/10/06, Guennadi Liakhovetski <g.liakhovetski@gmx.de> wrote:
>
> Hi all,
>
> This is a complete newbie question - just like I am on powerpc. How does
> one put to sleep / wake up an embedded ppc (mpc8241) system? Notice, I've
> never done it (sleep / suspend) on x86 either, and I only have a VERY
> vague idea of what it's all about... But I'd read if I knew what and where
> - half an hour googleing didn't bring any positive results apart from
> links to pbbuttonsd, which mainly describes ppc / apple notebooks.
>
> What I'd like to know is a bit of theory - kernel-level support and
> user-level utilities, as well as what one does practically to put a ppc to
> sleep / wake it up.
>
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski
> _______________________________________________
> Linuxppc-embedded mailing list
> Linuxppc-embedded@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>

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Re: sleep / wake-up

[Guennadi Liakhovetski]

On Sat, 10 Jun 2006, Jon Scully wrote:

> Also, here's an article (just about 4 days old):
> http://www.linux.com/article.pl?sid=06/05/24/1716222
> (I thought the subject sounded familiar ;-)

Ok, thanks for both replies. That's a good start already! But this is all 
about __software__ suspend. But aren't some other "hardware" suspend-modes 
also available on ppc, like suspend-to-RAM? For example, on my system I 
could say quite a bit of power by stopping the HD, switching off 
USB-ports, eth, and then putting the CPU to sleep? Would all this be 
doable by just performing those steps and then clocking the CPU down?

I must admit, I don't understand the whole idea behind suspending at all. 
What happens to all applications that went to sleep for 1 second and wake 
up 2 days later? What about all network connections? timeouts? I have to 
read some basics...

Thanks
Guennadi
---
Guennadi Liakhovetski

Re: sleep / wake-up

[Lee Revell]

On Sun, 2006-06-11 at 00:41 +0200, Guennadi Liakhovetski wrote:
> On Sat, 10 Jun 2006, Jon Scully wrote:
> 
> > Also, here's an article (just about 4 days old):
> > http://www.linux.com/article.pl?sid=06/05/24/1716222
> > (I thought the subject sounded familiar ;-)
> 
> Ok, thanks for both replies. That's a good start already! But this is all 
> about __software__ suspend. But aren't some other "hardware" suspend-modes 
> also available on ppc, like suspend-to-RAM? For example, on my system I 
> could say quite a bit of power by stopping the HD, switching off 
> USB-ports, eth, and then putting the CPU to sleep? Would all this be 
> doable by just performing those steps and then clocking the CPU down?
> 

Did you read the article?

"ACPI state S3 -- also know as Suspend-to-RAM -- is the state where
everything in the system enters a low-power state except for RAM, which
consumes a small amount of power in order to retain its contents, so
that upon resuming, everything is loaded back from the memory and all
running applications are restored immediately."

> I must admit, I don't understand the whole idea behind suspending at all. 
> What happens to all applications that went to sleep for 1 second and wake 
> up 2 days later? What about all network connections? timeouts? I have to 
> read some basics...

It's insanely difficult and complicated.  Every single driver and kernel
subsystem has to be changed.  Zillions of man-hours have gone into
getting suspend to work on Linux and it's still not there...

Lee

Re: sleep / wake-up

[Guennadi Liakhovetski]

On Sat, 10 Jun 2006, Lee Revell wrote:

> On Sun, 2006-06-11 at 00:41 +0200, Guennadi Liakhovetski wrote:
> > On Sat, 10 Jun 2006, Jon Scully wrote:
> > 
> > > Also, here's an article (just about 4 days old):
> > > http://www.linux.com/article.pl?sid=06/05/24/1716222
> > > (I thought the subject sounded familiar ;-)
> > 
> > Ok, thanks for both replies. That's a good start already! But this is all 
> > about __software__ suspend. But aren't some other "hardware" suspend-modes 
> > also available on ppc, like suspend-to-RAM? For example, on my system I 
> > could say quite a bit of power by stopping the HD, switching off 
> > USB-ports, eth, and then putting the CPU to sleep? Would all this be 
> > doable by just performing those steps and then clocking the CPU down?
> > 
> 
> Did you read the article?
> 
> "ACPI state S3 -- also know as Suspend-to-RAM -- is the state where
> everything in the system enters a low-power state except for RAM, which
> consumes a small amount of power in order to retain its contents, so
> that upon resuming, everything is loaded back from the memory and all
> running applications are restored immediately."

Yes: "ACPI" - we are talking about a (embedded) PPC... But I thought you 
could "simulate" that without ACPI too. AFAIU, ACPI is the way hardware 
(motherboard / laptop) manufacturers tell you about system's 
configuration, including how to enter S3. In its absence suspending every 
(e.g., embedded) system you have to _know_ the hardware. E.g., what do 
they do on Apple ppc laptops? You don't have ACPI there. Is there any 
generic system there or did they just study every new ppc-mac and handled 
it specially?

> > I must admit, I don't understand the whole idea behind suspending at all. 
> > What happens to all applications that went to sleep for 1 second and wake 
> > up 2 days later? What about all network connections? timeouts? I have to 
> > read some basics...
> 
> It's insanely difficult and complicated.  Every single driver and kernel
> subsystem has to be changed.  Zillions of man-hours have gone into
> getting suspend to work on Linux and it's still not there...

I guess, I really wanted to ask about IO operations in the fly... 
probably, you only use automatic suspend if you know your system is not 
supposed to do any long IO-operations, and "short" ones will be completed? 
Even if you monitor loadavg - it might stay quite low during a long 
transfer. And if you do long IOs you have to decide when it is safe to 
suspend yourself... So that the kernel just has to flush current IO 
queues... Yeah, doesn't sound very easy.

Thanks
Guennadi
---
Guennadi Liakhovetski

Re: sleep / wake-up

[Lee Revell]

On Sun, 2006-06-11 at 01:38 +0200, Guennadi Liakhovetski wrote:
> 
> Yes: "ACPI" - we are talking about a (embedded) PPC... But I thought
> you could "simulate" that without ACPI too. AFAIU, ACPI is the way
> hardware (motherboard / laptop) manufacturers tell you about system's 
> configuration, including how to enter S3. In its absence suspending
> every (e.g., embedded) system you have to _know_ the hardware. E.g.,
> what do they do on Apple ppc laptops? You don't have ACPI there. Is
> there any generic system there or did they just study every new
> ppc-mac and handled it specially? 

It seems that PPC Macs have a hardware PMU:

http://www.resexcellence.com/linux_icebox/01-31-02.shtml

And that some embedded devices handle this at the hardware level with no
OS support needed:

http://ozlabs.org/pipermail/linuxppc-dev/2001-February/010179.html

So AFAICT there's no standard like ACPI - each board does it
differently.

Lee

Re: sleep / wake-up

[Guennadi Liakhovetski]

On Sat, 10 Jun 2006, Lee Revell wrote:

> It seems that PPC Macs have a hardware PMU:
> 
> http://www.resexcellence.com/linux_icebox/01-31-02.shtml
> 
> And that some embedded devices handle this at the hardware level with no
> OS support needed:
> 
> http://ozlabs.org/pipermail/linuxppc-dev/2001-February/010179.html
> 
> So AFAICT there's no standard like ACPI - each board does it
> differently.

Right, so, without such support in the hardware or without the appropriate 
information all you can do is software suspend-to-disk, I think. That's 
for sleep-states. And just for power-saving you can switch various parts 
off in subsystem-specific ways (e.g., spin down a IDE hd), clock the CPU 
down, but still keep your system __running__, i.e. all processes run just 
as usual only slower.

Thanks
Guennadi
---
Guennadi Liakhovetski