Power modes

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Revision as of 11:07, 31 August 2010 by Tsh (talk | contribs) (Times)
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Power Modes

Without switching the device entirely off, it may be placed into low power mode or regular power mode; simply pressing the power button will toggle modes. Note that as of hotfix3, opening the lid in low power mode has no effect.

Normal Mode

This is the normal operating mode, screen on, WiFi and Bluetooth on if requested. CPU speed can be selected by the user, and has a small impact on battery life. Screen brightness will also have a significant effect on battery life. The CPU should automatically self-regulate to the current task, and 10-14 hours battery life is possible depending on usage. This is mostly independent of the set CPU speed for any given task. At any time, the battery gauge will show the remaining battery life if the usage remains the same as over the past some seconds.

Lid Closed

The only change with the lid closed is to turn off the LCD backlight. This improves battery life, allowing music playback and streaming to continue. As of Hotfix2, the screen remains on if the device is powered up with the screen closed. It is also possible to set xfce to blank the screen after a period of inactivity, which helps with battery.

Low Power

Low power mode is toggled by a short press of the power switch to the right. The screen is off, the radios are disabled, the CPU max speed is set to 14 MHz. The device is still silently on, allowing for alarms to go off or it to be turned on again instantly. The power LED will be dimmed, and may appear to be off if you are outside.

Low power mode is probably going to be used as the normal "off" for most people, with true off (device powered down entirely, unable to respond to alarms or wake up quickly) available to conserve battery power. Turning the Pandora off completely is the best option if you don't plan on using it for few days or longer.

Since the Pandora has to be powered whilst it is charging, low power mode is best for fastest charging, and will even allow a full charge to be achieved from USB. It is also the best way to use the Pandora as a USB charger for other devices.

Opening the screen whilst in low power mode has no effect (screen stays off, clocks stay low), and you will need to use the power switch to resume.

At the moment, there is no clear advantage in slowing the clocks (other than being an effective pause button when playing MP3). The only saving is through disabling the radios. This is likely to be improved in due course since there are features in the omap processor for power saving which are being added to the linux kernel.

Power Off

Select Logout then Shutdown from the window manager to power off. If a charger is connected, the device will re-boot immediately. It is possible to get into a state where you believe it is powered off, but in fact it is using power at the normal screen off rate - so after 12 hours, 50% of your battery is gone. The Power green LED ought to be a tell-tail. It is possible that some bugs exist in this area, but nothing has been clearly identified[1]

A common problem seems to be that if you switch off before unplugging, your Pandora will re-boot even though it is now left unplugged. This problem is compounded by the low battery shutdown script being called repeatedly (and actually preventing shutdown).


The events which control power can be customised [2]. Lid switch, Power Switch, battery threshold and Window Manager shutdown commands. Note that the battery manager in xfce will also take action when the battery is low, by default forcing a shutdown at 5% (so you may observe a full boot process, the window manager appears, then immediately shuts down)


UK charger and adapter
UK charger and adapter

It is possible to charge from the mains charger (use the supplied one or a GENUINE PSP adaptor only) or USB cable. While a charger is connected, remaining battery level is displayed, but the time displays 00:00. If charging from USB, it is possible that the battery will still discharge slowly, since the Pandora takes more current (in normal mode) than the USB can supply. Mains charge is configured to draw 1000mA, USB charge is more like 500mA.

It is not possible to charge the Pandora without turning it on - the charging circuits rely on the CPU for configuration. In practice, this has minimal impact on usage, except that after charging, you might wish to explicitly turn off (and maybe there is a easy way to automate this by adding a charger event to call a script)

Opperating Point

The OPP is a TI term which reflects the fact that low clock speeds can be achieved with lower supply voltage than the higher clock speeds. Increasing OPP will reduce the lifetime of the device significantly (from 10 years to 5 years of continuous use.) OPP3 is the default as shipped by OpenPandora. As of Hotfix4, it is possible to set a maximum OPP in the range 1-5 (for example, to 5):

echo 5 | sudo tee -a /proc/pandora/cpu_opp_max

This will then increase OPP to suit the requested CPU max, as pre-determined by a table built in to the kernel. These thresholds use OPP1 for below 125 MHz, and OPP5 for above 720 MHz. It is possible to set the limiter and maybe run at 500 MHz in OPP2 (depending on your specific chip). See this forum thread for actual results.

Using anything above OPP3 WILL shorten the lifetime of your Pandora, although it should still outlive the 1 year warranty. Using anything above OPP5 will void your warranty.

Tweaking scripts to make this tuning easier are in the works.


The kernel provides some information about battery state through the filesystem. See Data_provided_by_Battery_and_Power_driver. This may help with diagnosing problems.


(These are my estimates, mostly from HotFix3. Please add to the data section in the talk page, and be clear about the conditions you use)

Charge/Discharge times
Mode Time
Normal Operating 10-14 hours
MP3 play, screen off 17 hours (May improve)
Lid Closed 16-23 hours (est, depends on wifi)
Low Power 23 hours (maybe 30 with Hotfix4)
Power off less than 5% per day charge loss (sometimes more?[3])
Mains charge, operating 20 hours (est)
Mains charge (low power) 8 hours (est)
USB Charge, operating 20 hours (inactive, screen+wifi on), may charge or discharge depending on load
USB Charge, low power 20 hours (est)

Battery Care

  • You can charge your battery to full charge, the charging circuits will then reduce the current to avoid overheating
  • If you won't use the battery for more than a week, it is best to leave it at about 40% charged (as opposed to full)
  • Don't worry about running it down too low, there are protection circuits to avoid a damagingly low discharge.
    • Avoid leaving the battery completely discharged though.
    • When the power runs out, th system will be unable to shutdown cleanly, and might corrupt your files or the system.
  • No harm will come if you only partially recharge it. If you've only got 10 free minutes to charge before leaving, go ahead. You'll put an hour of usage back into the battery, and you can always charge it more later.
  • For best accuracy, the battery meter relies on watching the battery discharge over most of it's range (down to say 10%).
    • This will only affect the 'time to run' indication
  • If you're not going to be using your battery for a very long time, the extremely best thing you can do for it is to discharge to 40%, seal it in an airtight bag, and put it in the fridge. Even years later, you pull it out, and it will be almost as good as when you put it in.