|PDAs have always been "battery challenged".
Back at the dawn of PDAs, their 16 Mhz processors were barely powerful enough to drive their screens and perform the minimal processing chores required to search an address book and maintain a calendar. And they could generally run for five or six hours on a set of batteries. If the device was used as a "quick reference" for brief periods of time, those batteries could last for weeks or even months.
As battery technology advanced from replaceable carbon-zinc through nickel-cadmium, nickel-metal-hydride, lithium-ion and finally to today's high-performacne lithium polymer, PDA processor speed/power and display quality advanced just quickly. As a result, despite the fact that battery technology has advanced tremendously, after continuous-use PDA battery life still falls into the 3 to 5 hours range.
If you're just looking stuff up . . .
Today's large screen, high-resolution (480x320) high-performance (400+ Mhz) PDAs are entirely useful for watching movies, listening to music, and reading books . . .
Reading books and watching movies on my Palm
So eBooks are the highest density form of entertainment in terms of hours of entertainment per byte of storage. But like any form of media, they require that my Palm stays on more or less continuously, consuming precious battery power minute by minute.
No matter what form of media you want your PDA to deliver, movies, music or books, using any of these means that instead of turning your PDA on, looking something up, and turning it off again, you are inherently leaving it on and running it as long as its batteries will last. So total battery life becomes much more important when our PDAs are operating in "media delivery mode" over the span of a few hours than when they are operating in "quick lookup mode" over the span of many weeks.
What's a "milliamp hour" ??
|Palm Model||Battery Capacity|
|T T2 T3||900 mAh|
|The motivation for this research was to determine exactly how much power our Palm Tungsten LCD backlights consume. I wanted to know what the actual measured power consumption difference was from full brightness to minimum. And what about processor speed? Just how much power can be saved by deliberately "underclocking" the Palm all the way down to 52 Mhz?
consumption from 245 milliamps, down to just
105 milliamps . . . for a total battery lifetime
increase of 233% or more than 2.33 times.
Before long, "overclocking" utilites were available for virtually all handheld PDA-style devices. While the overclocking utility authors were at it, they added "underclocking" capabilities to their applications to make them more complete. Unfortunately, as the years have gone by, PDAs have become so much more powerful, faster, and capable, that the need to overclock them has largely disappeared. So there is no longer a wide range of clock rate setting utilities to choose among. For some reason the idea of "underclocking" PDAs to extend their battery life hasn't caught on (yet) enough for people to create underclocking utilities for their own sake. So people who want to underclock their Palm devices are currently stuck using older and less heavily supported overclocking utilities that also happen to offer underclocking support.
"LightSpeed" and "PXAClocker"
The very nice and clean "Lightspeed" Palm clocking utility.
|What's worse (much worse) is that many of these options are extremely dangerous and WILL lockup your Palm totally and permanently, rendering it completely non-functional for days as the battery slowly drains. No form of soft or hard reset will bring it back everything is ignored.
During my early experiments with PXAClocker on my T5 it locked up totally. After waiting for days for the battery to drain, it never did sufficiently. So I was forced to crack open the unit and unsolder the battery to finally regain the use of the Palm. The gadeteer side of me would love the idea of all those bells and whistles if they were useful for anything at all. But since I have absolutely determined that they do not reduce the Palm's power consumption by even the slightest amount, they are just "booby traps" in the purest sense of the word, and the PXAClocker utility is FAR more dangerous to use than it should be or needs to be. (Especially on Palm devices without user-removeable batteries!)
Still, I'm using PXAClocker . . .
The good news about PXAClocker, is that as long as you steer clear of its pitfalls and landmines, it works well and reliably. The screen above was taken from my T5. It shows that while the system default processor speed is 416 megahertz, the processor clock rate will be reduced to just 26 megahertz whenever the Palm's calculator (Calc) or electronic book reader (eReader) are running in the foreground. PXAClocker automatically changes the Palm's processor speed on a "per-application" basis, allowing a high degree of performance and battery life tuning and customization.
As mentioned above, since battery drain equals "rate x time", any applications where you spend a great deal of time, such as book reading, music listening, or movie watching, will yield large cumulative battery life benefits if the system's processor runs as slowly as possible while it's in each of those high-usage applications.
The chart above may not be surprising. Brigther backlighting consumes more current from the Palm's battery. But I wanted to know exactly how much more, and what percentage of the Palm's total power usage was backlighting compared with the rest of the Palm. I was also wondering whether the current versus brightness relationship might be non-linear and perhaps have a "sweet spot" where it was possible to get some more brightness at less current cost. But as you can see, the experimental results are just about as linear as you could ask from laboratory measurements.
One important fact I was also curious to learn, and determined with certainty, was that the backlight's current consumption is independent of processor speed. The current readings shown in the chart above were taken with the processor running at its minimum stable speed of 52 Mhz. But the difference in backlight current consumption, from maximum to minimum brightness, is always approximately 60 milliamps (0.060 amps) and is completely independent of processor speed.
When the processor is running as slowly as possible, the difference in the Palm's overall battery consumption, between minimum and maximum brightness, is significant. This can be seen clearly in the chart above which is "zero-based" to give a true sense for the proportion of current being consumed by the Palm T5.
The clock rate power consumption chart also has no surprise. Higher processor speed results in greater power consumption. But, again, knowing the relative amount of power consumption is the whole point behind taking precise measurements.
One coincidental fact is that the range of power consumption from minimum to maximum processor clock speed is almost exactly the same as for minimum to maximum display backlight brightness.
And, again, the power consumption due to processor speed is independent of any due to display brightness. The difference from running the processor at 52 Mhz and drawing 100 milliamps and running it at its normal "full speed" of 416 Mhz and drawing 170 milliamps is 70 milliamps, or 0.070 amps.
Important Note: The slowest clock speed shown in the chart above 26 megahertz and the three black clock speeds shown in the middle, are not usefully available. The Palm crashes badly when set to any of those speeds. (An example of why PXAClocker is dangerous without instructions.)
The following chart assembles this raw data into a simple chart showing the various current consumptions and total theoretical running times for the four combinations of maximum and minimum clock speed and brightness. Since the scales and relationships are all highly linear, you can easily compute the performance of any mid-point between:
|Running Time|| %
|Max||Max||245 mA||5.31 hrs.||100%|
|Min||Max||185 mA||7.03 hrs.||132%|
|Max||Min||175 mA||7.43 hrs.||140%|
|Min||Min||105 mA||12.38 hrs.||233%|
As the chart above makes clear, running high-usage applications at the minimum speed they require, rather than always at the Palm's default maximum, can deliver significant saves of up to 400% or 2.12 hours.|
And similarly, running the Palm's display as low as possible is always a good idea. When indoors, if any application will be used for a long time, turning the screen's brightness all the way to minimum can result in a savings of 320r 1.72 hours.
And finally, since the savings from clock rate and backlight brightness are additive, the combined savings of minimum clock rate and minimum backlight intensity can result in an overall savings of 133% for a total running time of 12.38 hours . . . more than SEVEN HOURS longer battery life from the Palm T5's standard internal battery.
Gibson Research Corporation is owned and operated by Steve Gibson. The contents
of this page are Copyright (c) 2014 Gibson Research Corporation. SpinRite, ShieldsUP,
NanoProbe, and any other indicated trademarks are registered trademarks of Gibson
|Last Edit: Mar 28, 2013 at 11:39 (733.77 days ago)||Viewed 23 times per day|