[mythtv-users] Waking a sleeping system

migmog migmog at gmail.com
Sun May 13 21:12:11 UTC 2007

Hi Chad

I have the EXACT same situation, and I have been trying to get
something going for months... I have given up on getting WOL to work
from the suspended state. I have a suspicion that when the network
driver suspends, it disables wake-up functionality. If I were more
experienced in driver and kernel hacking, I might try to get this
going, but I don't really know where to start. I have also not had
much luck with waking on a timer.

The approach I'm going with now, is to wire up a circuit which will
effectively press the power button by remote control. I've not built
it yet, but I have proved the concept and it should work OK.

On the always-on box, hook up a serial port to the power button header
on the motherboard of the remove machine. My system uses an MSS, which
doesn't have a serial port. However, I have tested the following
solution with a USB->Serial adapter and it does work.

There are two pins on the RS232 serial port that you can control
easily via software: DTR and RTS. Each of these can be switch from +9v
to -9v (the exact voltage will vary from one serial port to another).
You can then take this signal, put in a diode, a resistor and a
transistor to make it into a switch. Connect this circuit to the
power-on button header on your motherboard

Take a look at this page: astrophotographers need to do something very
similar to what we need:


There's some other pages around if you do some googling with example
source code. It's a simple C program to open the device and send an
RTS or DTR ioctl. I've also done it with python - very easy.

I probably won't have time to do this myself for a few weeks. Let me
know if you decide to give it a go. Likewise I will let you know if I
can get it working.


On 13/05/07, Chad <masterclc at gmail.com> wrote:
> Hello!
> I've recently been playing with putting a system to sleep:
> echo -n mem > /sys/power/state
> And the system goes to sleep.  Pressing the power button (I don't have
> a keyboard or any input devices attached) wakes the system and it
> returns to normal activity.  Totally sweet.
> I'm curious though, is there a way to wake a system from sleeping
> using WOL or possibly even a BIOS alarm?  I can shut my system down
> after a period of inactivity through MythTV and using the ACPI
> functionality I can have it wake X amount of time before my next
> scheduled recording.  Great!  But I would like to see if I could sleep
> the system instead of shutting it down?  This means I can't use the
> BIOS alarm to wake the system as the BIOS is not used when resuming
> from a sleep state.  But I do have another always on system that could
> wake the system using WOL but I can't seem to get WOL to wake a
> 'sleeping' system; only a fully shutdown system.  My network card
> supports wake on 'pumbg' so it definitely supports the physical
> activity bit as well as WOL; which I would assume means it would also
> support WOL from sleeping.
> Any hints?  Anyone else tried this, and had success?
> Thanks!
> -Chad
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