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Old 03-09-2007, 08:11 AM   #1
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Another Powersaving idea?

Hi!

I've asked this question before, but then there were no real results since the Cources were not published and iRex was not interested (still thinking to implement proper powersaving).

What I'm looking at is the following:

Give the User a "switch" in the Contentlister or some submenu that reboots the device into "Reading Mode", deactivates all unnecessary Hardware and activates Maximum Powersaving for the Processor.

When reading fiction I don't need the Stylus, WLAN, LAN and Audio. All I need is the screen, the keys, Cardslots and of course the hardware neccessary for running the Linux OS. CPU Powersaving (can you clock the PXA255 to 33Mhz and reduce voltage?) should of course also be a priority, putting the CPU on lowest setting as soon as a book is loaded and the pages have been precached.

Going back to normal mode should be just as easy, simply selecting the entry in the Contentlister and rebooting.

In addition to greatly enhancing the batterylife it should also considerably reduce the booting time since many drivers would not have to be loaded.

any ideas on this from those who can actually read the code? How dangerous would this be (bricking is always an imminent danger when playing witht eh Kernel I guess...)?
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Old 03-09-2007, 08:22 AM   #2
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to change the cpu from a command if you have the command shell is easy, but the problem what i see that are stoping to us to bring a big jump in the developement of the iliad, it's what you say, if you touch the kernel and for example a missing ; or a parameter don't put correctly and "perhaps" you will need to reflash....

this is was is stopping me, yes i know that we have the toolchain and shell (i'm very grateful for that) but i if i have to change the base (the linux) i need to probe the state of mind that if something goes wrong, i can reboot and return to normal....

Please karel says that the iliad will give us a lilo configurable, please....
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Old 03-09-2007, 12:39 PM   #3
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i think RedBoot would be interesting. Or does lilo have telnet access? With the ability to get access through ethernet you wouldn't have to open the case of the iLiad. till now there seems to be no sign that there is a serial console, iirc.

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Old 03-09-2007, 06:53 PM   #4
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Setting CPU frequency

Here is a quick and dirty script which sets the cpu-frequency using /proc/sys/cpu/0/speed.
You can give it the speed in the comment area of the filename in an interval of about 400000 to 33000.
Please remember that the change is non-permanent and is reverted on reboot.

However, the script is very simple and it does not have any checks, it's just a quick hack I use myself for testing.

Have fun and please report how it affects your runtime.

#!chris

20060310/00:34
Of course there is a bug in the script, in the "Give it a userfriendly name" - part, so it only runs once, the contentlister renames the folder after the corresponding property in the manifest.xml. This was new to me.

20060310/00:52
The script should be fixed by now. It's called 'cpufreq' now.

P.S. This is a crossposting. See the other thread at http://forum.irexnet.com/viewtopic.php?t=1061

Last edited by k2r; 03-09-2007 at 07:53 PM.
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Old 03-10-2007, 08:36 AM   #5
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Thanks!

I don't have the time right now to try this, can somebody else perhaps measure the uptime of the Iliad with this hack applied?

I'll see, maybe I'll manage to try it sometime, but i've got my first serious audition coming up next week and another one the week after, so I'm a bit stressed at the moment...
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Old 03-10-2007, 11:38 AM   #6
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Well, I decided to give it a try anway.
I'm not sure whether it worked however.

I set the frequency to 33Mhz. The Iliad did a short screenrefresh and then everything continued working as normal. I'm not sure whether the process really worked...

I loaded a PDF file (took a while, but I think not longer (or not much) than usual. Page-turnings seems to work like normal too. the Battery-meter does not work (was full, now shows empty).

I'll leave the Iliad lying here until it dies. I started the Process around 13:30 German Time, the battery was not freshly loaded but should have been pretty full (battery-meter showed full...).
This will not be a clean and accurate benchmark, but maybe it'll at least give some insight.
Only trouble is that I'll porbably be fast aslweep when the battery dies...
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Old 03-10-2007, 12:50 PM   #7
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Maybe Irex could make an entry in a log file on the iLiad when it shuts off because of low battery (with a time code). Then you could check when it switched of.

But I would start with a full battery, no memory cards and no Wacom digitizer switched on.
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Old 03-10-2007, 05:46 PM   #8
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The Iliad is still running. 9 hours so far. I just powered it down and back up so that i can check the battery indicator. It is now at about 1/3 charge. I then put the device back in low-speed mode and reopened the PDF.

I'm not sure whether the script is really working since I tried a very brieft scribble on PDf earlier on and could not see any speed-difference to normal (as far as I can tell) nor any change in general operating and page-turning speed (from the little I have done to get to the PDf I wanted...).

Can someone check whether this script actually lowers the clock or not?


UPDATE:

I just realized that the script does something strange...is seems to run, then hang (green light constantly on) and only continues when I press the cursor keys. Is this normal? I did not notice this before...if I don't press any keys, the Iliad hangs.
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Old 03-10-2007, 08:28 PM   #9
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Quote:
Originally Posted by CommanderROR
Can someone check whether this script actually lowers the clock or not?
The script tries to set the CPU frequency from the comment, reads back the actual speed afterwards and writes into the comment again. If you try setting setting your iLiad to 33001 it should say 33000 after you ran the script since 33000 MHz is the closest allowed step.
You can try to set your iLiad to 400000 (MHz), and it should report something about 398000 afterwards.

Quote:
Originally Posted by CommanderROR
I just realized that the script does something strange...is seems to run, then hang (green light constantly on) and only continues when I press the cursor keys.
Running the script might take a few seconds because switching speed sometimes does, maybe the effect you describe is pure coincidence?

Quote:
Originally Posted by CommanderROR
Is this normal? I did not notice this before...
No, the script should terminate itself without the need to press any buttons.
Maybe you should try a new copy and see if the effect lasts?
And I only used the script from SD-Card so far.

And yes, speeding down the iLiad helps: Mine did 14.25h at 100Mhz today.

And of course: all the best whishes for your auditions!

Last edited by k2r; 03-10-2007 at 08:32 PM.
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Old 03-10-2007, 08:46 PM   #10
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Thanks for your elaboration.

I'll try it again, but I think the Iliad just hangs if I don't press anything after starting the script. It's been trying to apply for a couple of minutes now, still showing no progress and the green LED is on constantly.
I hope it's not something stupid like iRex forgot to reapply my Shell Hach or something...I have not tried anything that requires it for a while now...could be that...

Does your battery-indicator stop working after you start the CPUfreq?
Maybe you can find the switch that governs the CPU voltage as well, then the energy-saving effect would be even bigger...


UPDATE:

While I was typing this my Iliad was still trying to apply the speed-adjustment.
After more than 5 minutes nothing had happened and the device was not responing to any input. Reset was the way out. I guess something is not working for me. I'll try to find out what...

Thanks for the great work so far and please continue you efforts on this front. Maybe you can do the measurements at 33Mhz?

UPDATE:

I just recopied the files and changed the value to 30020. If I run the script, the Iliad hangs just like before. If I run and press the key again (like I did before) it appears to do something and the value changes to "30000".

Strange.
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Old 03-10-2007, 09:13 PM   #11
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I'm going to bed now, tomorrow I have a free day, maybe I'll manage to do some testing then.
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Old 03-11-2007, 10:18 AM   #12
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Quote:
Originally Posted by CommanderROR
Does your battery-indicator stop working after you start the CPUfreq?
If I set my iLiad to 100MHz the battery indicator works intermittendly during use, if I set the iLiad to 33MHz it's greyed out. Maybe some timeout problem?

Quote:
Originally Posted by CommanderROR
Maybe you can find the switch that governs the CPU voltage as well
I don't think so.

Quote:
Originally Posted by CommanderROR
I just recopied the files and changed the value to 30020. If I run the script, the Iliad hangs just like before. If I run and press the key again (like I did before) it appears to do something and the value changes to "30000".
When the value displayed is changed, the iLiad's speed was changed, definitely. For the problem of non responsiveness: I have no clue yet. Do run the script from internal memory from SD-Card or from CF-Card? Did you place it in a folder or on the top-level directory?

070311/14:25
I copied the script into my documents folder and had the same effect that you decribed. I only ran it from SD-Card yet. Well, so much for releasing untested quick-and-dirty stuff. I'll track it down this afternoon...

070311/14:35
You might try speeding down to 100MHz only.

Last edited by k2r; 03-11-2007 at 10:36 AM.
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Old 03-11-2007, 10:59 AM   #13
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I ran it from SD card most of the time...put the "cpufreq" folder in the root of the card.


UPDATE:

The script seems to work with my little "workaround", so no problems there...and it seems to be improving the uptime as well. I started the experimtent with a fresh charge at 2:18AM and now it's still responding. I'll see how long it'll be until it finally gives up.
I only did one short scribble and turned pages from time to time, so i'm measuring the "standby time" here.

I guess we'll beat the 15 hours iRex is aiming at, or at least reach it...with a pretty simple little hack...well that Is interesting. Now, what could we manage with reduced voltag as well?
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Old 03-11-2007, 01:21 PM   #14
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Hi CommanderROR,

Please report to us how much you got eventually. I will only try today evening, but I am very interested to see what you get.
Other question: so you use 30000 (30MHz) or 100MHz?
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Old 03-11-2007, 01:48 PM   #15
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I use 30Mhz

Seems to work fine and I can hardly feel the difference in performance so far...but i'm not actively using the device, so I only have a very limited picture. Paging is OK however.

I'm now well past the 15hours mark and the Iliad is still running...^^

UPDATE:

The Iliad just stopped responing. It must have lost power sometime in the last 5 minutes. That makes the total uptime around 15:30 hours. Not really great, but a nice improvement over the standard configuration.

The next steps now would be to add voltage scaling and of course link the script into the iPDF launch. Turning pages at 30Mhz is absolutely OK, no need to scale the processor up again. I could really live with the Iliad running at 30Mhz all the time actually since it does not seem to make that much of a difference in laoding times for iPDF either...but somebody will have to look into that more closely...

UPDATE:

I don't know anything about programming, but there seem to be lots of websites with information about implementing powersaving for PXA255 under Linux, like here:
http://www.applieddata.net/forums/to...?TOPIC_ID=2082
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