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Handhelds Hardware

Guide To Designing Low Power Handhelds 125

Posted by Hemos from the learning-all-about-it dept.
randomErr writes "iAppliance had a nifty article about designing handhelds. As the state-of-the-art in low-power CPUs races forward, the CPU becomes one of the most critical components in the design of a handheld. New CPUs such as Intel's XScale, Alchemy Semiconductor's Au1000, and Transmeta's Crusoe provide the ability to scale clock frequency and voltage dynamically. As power consumption varies linearly with clock speed and as the square of core voltage, you'll want to have hardware hooks to be able to adjust both clock speed and voltage as necessary, based on device performance."
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Guide To Designing Low Power Handhelds More

Guide To Designing Low Power Handhelds

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  • haldheld like those self-winding watches? Just move it around a little bit.....andit slowl charges it, now that would be awesome!!!

    • Actually you would probably want something like this....

      1) Buy 1 suitably active cat or suitably small dog.

      2) Attach appropiate self-charging generator to faithful pet's collar

      3) Find a way to get the generated power into your PC without using any wires.

      4) Load Quake

      5) Get a another hyper-active pet to run your nearby beer fridge

      6) Enjoy FPS, with a cold beer and low power bills,

    • Re: (Score:3, Interesting)

      by account_deleted ( 4530225 )
      Comment removed based on user account deletion

    • Re:But when can I have a.... (Score:4, Interesting)

      by TH4L35 ( 310071 ) on Monday June 24, 2002 @03:28PM (#3758665)
      Or one that combines such a self-winding pendulum drive with some solar cells and some of those nifty materials that convert thermal energy to electricity?

      Maybe even some antennae that can absorb all the abundant radio/microwave radiation that cell towers, wi-Fi, bluetooth, high-power transmission lines, the sun, etc. etc. are constantly pumping out? Tesla's wireless power dreams finally realized!

      I think that vastly increased use of such passive reclamation systems is about the only way that tomorrows electronic devices can manage to simultaneously get smaller AND significantly more powerful.

      • ---"Maybe even some antennae that can absorb all the abundant radio/microwave radiation that cell towers, wi-Fi, bluetooth, high-power transmission lines, the sun, etc. etc. are constantly pumping out? Tesla's wireless power dreams finally realized!"

        I like tesla too, and I don't mean that "alien supernatural" stuff you see on the web. Look his patents and you'll find a wealth of RF work on his part. However, something you need to remember about his idea of "portable energy" is that teh signal strength is inversly related to the square of the distance. You're talking about piddiling energy. It'd cost more in energy to MAKE the collector than it would ever get in its life.

        I igure this battery life argment will go on ad absurdum. My idea is to use a decent low power chip WITH 2 redundant power cells (9 volt?). If 1 dies, the other one takes over. You would be able to "hot swap" batteries. Just go into a store and buy 1. Or ytou could use LiIon batteries. They're a bit more reliable for correct voltage. But when they die.....
      • I think that vastly increased use of such passive reclamation systems is about the only way that tomorrows electronic devices can manage to simultaneously get smaller AND significantly more powerful.

        I think the near future will be fuel cells instead of batteries. Fuel-cell powered cell phones are already in development; the problem for mass-production is finding cheap enough materials, if I understand correctly.

        In the far future, even absurdly powerful devices will draw very little power. Display and RF (or modulated-light) communication would be the main power drains. You could recharge these adequately by having induction coils scattered about like coffee holders (or coasters), so that your palmtop (or equivalent) would recharge whenever you set it down.

        Ambient RF and environmental heat and motion have little enough capturable power to not be worth the bother. If your device is low enough power to benefit from this, a Li battery will last for weeks and a fuel cell for months.
      • Sorry, this post is merely to cancel the moderation I did (on one of the posts in this thread). There definitely seems to be a bug in the moderation system as this is the second time it's occured for me.

        I chose "interesting" (however the particular posting may have been marked insightful) but after hitting moderate, the post's score was decremented.

        Simon

        PS: Who do you report these sort of bugs to?
    • Why not a magnetic generator inside the mouse or track ball everytime its moved it generates a charge to charge up the battery. It might add 10 minutes of usage time per charge. Ha HA.
    • You can have one of these when your handheld draws MICRO-amps, and you carry it around all the time.

      It will be about the same time as when your handheld can run for a year off an lithium battery the size of a dime.
      Show me the backlight on one of those "self-powered" watches. Oh? They can't even power a backlight? It will be a while...
  • CPU? most of my drain is caused by the inverter...
    • what inverter?

      Unless you are using an external AC/DC inverter, there usually isn't one in an embedded application. Anything with an LCD the size of a PDA uses a frontlight display. Laptops use inverters to power the CCFL because their screens are simply to large for an effective frontlight to work.
      • The one on the board I'm currently working with that has a battery package with 4 NiMH D cells..

        • er then do you mean regulators?

          I think the term DC-DC inverter is misleading. Anything that does DC-DC conversion is a regulator. Linear regulators consume power like there is no tomorrow. They also produce a sizable amount of heat (imagine that.)
          • Whatever you want to call that big wart transformer looking thingy is that keeps sucking out the power for the display, running my batteries low and then causing the ir sim to do funny things (ringing) while I'm trying to debug my irda implementation.

            >I think the term DC-DC inverter is misleading
            ok.

  • Rechargable packs (Score:1, Insightful)

    by WilliamsDA ( 567274 )
    I know that the ability to have rechargable batteries is out there, but I've always felt it was somewhat funny that while cordless and cellular phones typically run on batteries that you charge when they're not in use, the PDAs don't come with the same option by default. I wonder why this is, and if in the future that rechargable batteries will be the norm.

    • Re:Rechargable packs (Score:2, Informative)

      by restauff ( 168301 )
      Some PDAs have already started moving towards this end. The Visor Edge and some of the other Handspring Visor products have rechargeable batteries built in. My Edge charges in the same cradle as it syncs in, making it quite convenient.
    • That's one of the big things I like about my palm III-c. It charges in it's hotsync cradle. It never made much sense to me to have to replace the batteries in the older model palms and some other PDA's.

      Now if I can just convince myself that I really _need_ one of those palm m515's. Mmm... technolust.

      MoTec

    • Re:Rechargable packs (Score:5, Informative)

      by Dr. Ion ( 169741 ) on Monday June 24, 2002 @03:39PM (#3758743)
      There are some good reasons why devices still use alkaline batteries instead of rechargable:

      - It's cheaper. Making the user buy AAA cells is cheaper than an expensive built-in rechargable. Be angry if you want, but the same shoppers that gripe are the ones that will pick the AAA model because it's $10 cheaper. :)

      - Charger required. more $$$, bigger packaging, more travelling weight, country-specific voltage, UL Listing, the works.

      - Alkalines last longer (per charge) than rechargables. On a device may go weeks without seeing a charger, this counts.

      - Rechargable cells die. What do you do with a PalmV that no longer charges well? LiIon cells only last a year or two before they start to degrade quickly.

      I'm not saying that these are valid reasons to require disposable batteries, but these are factors that manufacturers look at in deciding which way to go.

      • Re:Rechargable packs (Score:2, Informative)

        by swf ( 129638 )
        What is it with this world, people haven't even heard of rechargable batteries!

        There are some good reasons why devices still use alkaline batteries instead of rechargable:
        Are you saying that alkaline and rechargable batteries have a different form factor? They don't. There are rechargable versions of all the common sizes (AA, AAA, etc.)
        - It's cheaper. Making the user buy AAA cells is cheaper than an expensive built-in rechargable. Be angry if you want, but the same shoppers that gripe are the ones that will pick the AAA model because it's $10 cheaper. :)
        That doesn't mean the AAA cell has to be alkaline. You can use rechargable AAAs.

        - Charger required. more $$$, bigger packaging, more travelling weight, country-specific voltage, UL Listing, the works.
        I don't know about you but I've been using rechargable AAAs for my palm and I haven't had a problem with the packaging, and having a recharger means I can also recharge AAs so I don't have to buy a new pack every week.

        - Alkalines last longer (per charge) than rechargables. On a device may go weeks without seeing a charger, this counts.
        It barely matters. You can get two rechargable AAAs with 700mAh per charge each. I don't even know what the alkaline AAAs do nowadays because they don't want to show how crappy their batteries actually are against rechargables. On a palm this means that you have to change the batteries about a day earlier, big deal - you save money after the second charge!
        - Rechargable cells die. What do you do with a PalmV that no longer charges well? LiIon cells only last a year or two before they start to degrade quickly.
        You buy another pair of rechargable AAAs. LiIon may only last a year, but NiMH AAAs last by the recharge (around 1000). How long do you think that would last you?

        I'm not saying that these are valid reasons to require disposable batteries, but these are factors that manufacturers look at in deciding which way to go.
        AAA DOES NOT MEAN ALKALINE! Go to your local hardware store and buy some rechargable AAAs. They work, they save you money and help stop the flood of disposable batteries.
        • - Rechargable cells die. What do you do with a PalmV that no longer charges well? LiIon cells only last a year or two before they start to degrade quickly.

          You buy another pair of rechargable AAAs. LiIon may only last a year, but NiMH AAAs last by the recharge (around 1000). How long do you think that would last you?

          I believe what the previous poster was referring to is the non-removability of the Palm V battery. The Handera 330 on the other hand, can use either AAAs or an optional rechargable battery pack.
          • Yes... it seems that most handhelds seem to be using non-removable internal rechargable batteries. I much prefer AAA...they're easy to find, non-proprietary, and inexpensive. I've mostly used alkaline so far, since I get a couple months out of them, and bought a brick of a dozen or so when I bought my Palm Xiii (and haven't run out of 'em yet). I might try rechargable ones eventually, though - if I can find my AAA charger.
          • I did a search [the-gadgeteer.com] and that looks like a really sweet machine. Being able to use CF for storing medical programs and stuff would be really helpful for me, as my IIIxe's 8 megs just isn't enough. Do you own one? Any comments?
    • Well, the easy answer is that you can always buy rechargeable AAA batteries if you want to go that route. This give you the best of both worlds (if you need long lasting batteries you can get alkalines, if you can recharge regularly you can save some money) and getting NiMH (as opposed to NiCd) means your batteries don't develop a memory if you recharge them from half-dead all the time. Get two sets, carry your charger in your luggage if you travel, or just buy regular batteries for the duration of any trip that takes you away from a power outlet.

      Virg
      • I hope that someday rechargable batteries will _really_ work. There are two problems. First of all, people simply don't use them. In my opinion, in many cases, this is just plain stupid. Rechargables are cheaper (because they last longer), and much more environmentally friendly. Any idea how destructive a battery is once disposed? And with many people just dumping their dead batteries, this doesn't give a birght perspective for the future. The second problem with rechargables is that they don't work with many devices. This may have something to do with rechargables providing 1.2 V whereas devices expect 1.5 V. For example: my digital camera works fine with alkaline, but doesn't work with either NiCd or NiMH. I had the same problem with my bike lights, but I traded them for ones that did work. However, as long as we're stuck with devices that don't work with rechargables or rechargables that don't work with devices, and no public awareness of how much better rechargables are, we're stuck.

        As an aside, I don't like the battery packs many mobile devices come with either. They are quite often specific to one type or a limited number of devices. Long live interoperability! Long live standards!

        ---
        Self Test for Paranoia:
        You know you have it when you can't think of anything that's
        your own fault.
  • How does adjusting the clock speed affect timing issues in applications (games)? If it dynamically adjusts the timing, won't this create some bizarre effects?
    • "Basically every game written since 1990 has not run dependent on the clock speed..."

      Yes, but isn't that dependent on a static clock speed? I thought that the clock speed was determined, then applications with timing issues adjusted accordingly.
      • Common misconseption. The processor speed can change while you play the game and all that will change is your frame rate and not your play speed.
        Thats why asynchronous processors are possible.
      • I'm sure they have all have some real-world timer available of a little lower resolution than the clock. You don't need a 0.01 us clock to keep events happening in quake, and they would probably keep a slower timer around for things like asynchronous IO.
    • well this can depend on how the game was written, way back in the day the execution of the realtime engine would be so costly that you wouldn't have enough cpu cycles to calculate anything of significance with what was left. Now since processor speed varies like crazy you can't make a game without a realtime engine. I imagine they'd come up with some way so that the apps know what the cpu is running at and can adjust accordingly, they'll probably also add the ability to force the cpu to a particular speed while a certain app or function (whatever) is running... This would be cool (speaking as a game programmer), the programmer could force the cpu to the exact clock speed he wanted the game to run at and could do away with a realtime engine altogether! let's just hope these new handhelds won't do multitasking as well, that'd throw a monkey wrench into the whole thing :(

      there are some fairly recent games that still have some processor dependant functions... warcraft2 (yes 2, t.w.o.) had processor depend map scrolling... go ahead load it up on your 2Ghz machine and watch that screen scroll!!!! the rest of the game is realtime though.

    • You are assuming that all timing in a system is dependent on the CPU's clock. This usually isn't the case. Most real-time dependant applications rely on another clock to 'keep time' for them. This enables games, for example, to run at any given CPU speeds and have similiar performance. Of course actual game speed would depend on if instructions are executed fast enough. (If your RTC is ticking away at 1ms and it takes a slower processor 3ms to finish its last instruction set, then you are going to see significant slowdowns.)

  • Alchemy Semiconductor (Score:5, Informative)

    by Neon Spiral Injector ( 21234 ) on Monday June 24, 2002 @03:17PM (#3758594)
    Just to point out to anyone who doesn't know, AMD aquired Alchemy Semiconductor.

  • CPU speed is not the biggest factor for me... (Score:3, Insightful)

    by toupsie ( 88295 ) on Monday June 24, 2002 @03:18PM (#3758604) Homepage
    Unless these handheld companies can figure how to improve input into these tiny little computers, it doesn't matter how fast the CPU chip is because my big mitts won't get the data into fast enough for it to matter. To me, they are nothing more than a static data storage and regurgitation device, not an interactive system like my notebook or desktop.

    • I have to agree. While Graffiti is nice, I remember the Newton 2000 (2100? can't remember now) I carried about 4 years ago as part of an R&D project on the campus where I worked then. The thing read my cursive writing - and that's a major feat. Even though I'm good at Graffiti, I still have to focus too much on what my Visor thinks I've written to concentrate on what I need to write next. This inconsistency keeps me from using my Visor to take notes in class.


      I'm wondering now what Apple plans to do with the Ink [apple.com] technology they're planning on building into OS X 10.2. While handwriting technology may be cool for a desktop computer, it would be a major coup for a handheld.


      As for battery life, I generally replace my batteries every six weeks or so. I really don't consider this too frequent.

    • It is only a matter of time. The work on the software for speech and visual pattern recognition is being developed for so many other applications, the only requirement that the handheld device would need to add such features is more computing power. Of course, that is dependent on the overall electric power efficiency of the handheld.

      • The work on the software for speech and visual pattern recognition is being developed for so many other applications, the only requirement that the handheld device would need to add such features is more computing power.

        The problem with speech recognition is that it has to be audible. So far, I am about to slap every Tom, Dick and Mary walking down NYC streets talking on Cell Phones through the little "hands-free" headphone mics. I can't imagine when self important people start walking down the street scheduling appointments and dictating memos on a PDA. When the Cell Phone headphone mic (looks like a walkman headphone) came out at first, I thought that some mental hospital had a clearance sale on schizophrenics with all the people wandering around apparently talking to themselves. Really freaked me out for a bit until I realize that this was a "technological advance".

    • Me thinks the main input for PDAs will be automatic things like GPS, voice, cameras and other data recording devices. With voice and image input--storage capacity and battery life will continue to be the most important issues.

  • Screen real estate (Score:4, Insightful)

    by Myshkin ( 34701 ) on Monday June 24, 2002 @03:20PM (#3758618)
    CPU power is not the issue when it comes to portable computing. The real holy grail will be in acceptable display technology. Whether that be some sort of expanding/folding display technology or a lasar retinal display, something significantly better than our current technology is needed to really make a significant jump in usability and functionality.
    • In the medical area, artificial eyes and hearing implants has made gigant leaps forward in just the last couple of years. From being a SciFi fantasy, we can now project images directly into the optic nerver. Sure it's very low quality, black&white and fuzzy and poor contrast and out of focus and generally lousy.... but that's just an engineering task :)

      Imagine having no displays at all, just sound and video overlayed directly into neural interface chips!

      This might be a reality 15-30 years down the road...
      • Imagine having no displays at all, just sound and video overlayed directly into neural interface chips!

        Don't forget to make it DRM enabled. If you're walking down the street and see something copyrighted, a payment transaction should be automatically generated.
  • Its gotten to the point where CPU power consumption is so good that the real concerns in designing a low power device reside in the peripherals.

    I was designing a low-power DSP application, and the CPU consumed like 24 mW at 100 mHZ. But, when I added any peripherals to it the power consumption shot up an order of magnitude. The moral of the story is that people should stop worrying so much about CPU power consumption and take a good look at trying to bring up all the things that go with a CPU to the same level.

  • I have experience programming for embeded systems but something that I've wanted to be getting into is designing embeded systems. Ideally what I want is a small hand size device that supports all common hookups, serial, usb, firewire, ethernet, etc. For me this would be unbelievably useful especially if it was combined with a moderatly size hd. If I could get a 5 gig hd, (ipod toshiba hd) packaged with all the connectors I'd be able to test about anything I could need at this time.

  • Cooling? (Score:2, Insightful)

    by Vengie ( 533896 )
    I could be wrong, but don't we need a discussion about cooling somewhere? I thought one of the key points to the Transmeta Carusoe chips was the "lower power consumption and therefore lower temperatures and therefore less power needed for cooling so therefore longer battery life." While the whole "fan" issue is a moot point, dont they have to make serious considerations about heat dissipation in handheld devices? Why isn't it dealt with in the article....

  • Low power - Asynchronous (Score:4, Informative)

    by brejc8 ( 223089 ) on Monday June 24, 2002 @03:25PM (#3758645) Homepage Journal
    If you want low power than asynchronous is the way to go. Amulet [man.ac.uk] processors use much lower power than synchronous processors. They are asynchronous so they will slow down when the voltage drops or you go somewhere hot. When they are not working they don't use any power. There is no messing about with software controled clock control, you just stick it into a branch on spot and it freezes. This is great for things like pagers or handhelds where you dont even need to power the clock nets while you are not doing anything. A large processors clock power consumption can be as high as 80%.

    You might have seen it already but this [man.ac.uk] is me powering an Amulet2 off a mouse wheel. They are very robust.
    • This is great for things like pagers or handhelds where you dont even need to power the clock nets while you are not doing anything.

      but don't most handhelds have little things called calendars, with little events, which can have alarms. thus, the handheld has to have a little loop running (at least once per minute) to check "are there any events scheduled to have an alarm fired at this time". this is why my Palm has to have its batteries replaced every few weeks regardless of whether i turn the damned thing on or not.

      -rp
      • There are two clocks here. One for your calendar at a resolution of 1 sec and the other to drive you processor.
        The second one should be turned off while the processor is not in use (i.e. while you are thinking of the next key to press).
        This doesnt happen in all processors and is costly.
        The calendar clock is there anyway to wake the processor up every sec to check if you have to do something.
        Even worse is when the processor sits there ticking and looking at the clock waiting for a specific time.
      • There's a big difference between powering a small quartz clock which notifies the chip of an event, and powering the clock + entire cpu + other critical components to notify and handle all of these events. That's the difference between asynch and synch.

    • "If you want low power than asynchronous is the way to go. Amulet [man.ac.uk] processors use much lower power than synchronous processors. They are asynchronous so they will slow down when the voltage drops or you go somewhere hot. When they are not working they don't use any power. There is no messing about with software controled clock control, you just stick it into a branch on spot and it freezes. This is great for things like pagers or handhelds where you dont even need to power the clock nets while you are not doing anything."

      True, but non-clocked processors are a pain to design. Sure they have great power consumption and speed characteristics but without a clock, a lot more time/money must be thrown into R&D to prevent the circuit from getting out of synch. (This is what clock cycles are for.) Are you willing to wait longer and pay more for such a device? (Now that I think about it, the answer from many slashdotters would be 'yes' but from the general public 'no')

    • > You might have seen it already but this
      > [man.ac.uk] is me powering an Amulet2 off a mouse
      > wheel.
      Was I the only person who was expecting a scroll-wheel mouse attached to the processor?
    • How about Reconfigurable Computers [elixent.com]? These are basically FPGAs featuring some ALUs and general gates, but instead of configuring these once at "burn-time" they are reconfigured dynamically on the fly, to transform the complete processor core for a specific task.The technique is somewhat young, but the ides is promising both in reducing die-size (or maximizing resource usage) bringing down power consumption.

      How would this combine with asynchronous computing?

  • Seems to me (Score:5, Interesting)

    by The_Shadows ( 255371 ) <thelureofshadows ... minus physicist> on Monday June 24, 2002 @03:26PM (#3758651) Homepage
    Palm systems are curently on top. They may only be B&W, but they get great battery life and do what most users need. Once you start entering the realm of music, that can be scaled over to an MP3 player instead of a Palm device.

    However, once you start deciding to run higher end applications, give the machines net connects, etc. everything gets more complicated. Full color, integrated (or even unintegrated) 802.11b, sound and so on all drain batteries at an increased rate. My keyboard for my palmtop drains when it's plugged in, which is, obviously, why it's not plugged in all the time.

    Battery life and functionality are both the keys. Is there a potential way to implement a self charging feature? Maybe harness the kinetic energy of movement to assist in charging the device? Most people with handhelds carry them everywhere. It wouldn't work well with high drain / low charge devices, like the Ipaq, Jornada, etc. which have charges of under 10 hours (at best) but maybe a system like this could achieve a few days or a week in a low drain device like a Palm m100.

    I have no idea. Just a decidedly random thought that I had. Later.
    • Uhhhh.... color Palm's have been around for quite some time.

      As for charging, why not hook up one of those units that the wearable computer guys use? You could charge your PDA as you walk from your cubicle to the meeting, and back again! The perfect technology for the drones!

      If only there was some way to convert white noise (drones talking) into a viable power source...
    • Kinetic charging is a good idea, but this is the wrong application. Unlike the Seiko Kinetic watch that uses this technology, it wouldn't work AFAIC for a PDA. The watch is attached to your arm, and you're not looking at it all day long. For the most part, if your arm's moving, the watch is charging.

      A PDA, on the other hand, most often involves looking at it in order to use it for anything. This implies holding it steady in your hand, or otherwise not shaking it around. See where I'm going with this?

      What it all boils down to is that for people who actually *use* their PDAs a lot, this wouldn't work, simply because it's being used more than it's being charged. And you can't realistically use the PDA while simultaneously swinging it back and forth i norder to charge it. But for those who buy the PDA, and instead of actually *using* it, stuff it in their pocket/beckpack/briefcase/whatever all day, this would probably work.
      • The thought that I honestly had was one of when walking around the office, city, home, etc.

        I know I'm not the absolute most coordinated person in the world, but if I'm walking around somewhere, I generally don't have my palmtop out. I had the image of the Palm being charged while moving back and forth inside a pocket. I know it doesn't move as much as a watch (BTW, the standard self-winding and kinetic watches are what made me think of this whole idea) but what I'm thinking of is the amount and force of the movement.

        Sure, the watch may move 2 feet back and forth compared to the 3-6 inches a Palm would move in a pocket, but when you consider the weight of a palm, 6-8 oz., it might just take in some of a charge.

        Also, consider people who use their palms and carry them in purses/bags/briefcases. They move a lot, relatively speaking.

        I think that, for some people, it would work fairly well. The biggest issue would be cost and size. I know that since they have the devices in watches they aren't that large, but I don't know how that would scale up. I also don't have any idea how much they would cost to add in, or even what the potential gain would be.

        Would a 25% gain in battery life, which is just a guesstimate, be worth it to anyone here if you have to pay 10-20% more, but could count on an extra few hours life for an Ipaq, or having to buy or charge batteries a week later for lower end Palms? I certainly wouldn't mind a few extra hours of life on mine, but I don't know if it would be worth $20-100, based on individual machines.

        Later.
  • There is a good reason for increasing the processor speed of PDAs. I agree that keyboard is completely worthless on these little things. I think companies need to start focusing more on voice recognition to do tasks.
    The day i can get around half-well with voice commands on a PDA, and not have to worry about weilding a wand or typing on a keyboard that will give me carpel-tunnel.
    My friend Rob has a PDA that can do somethings like say the time but there's not much more it can do yet.

    • Re:Keyboard Alternatives (Score:2, Insightful)

      by Anonymous Coward
      I see a problem with voice recognition. It is not the technology itself, but more of where you can use this method. Imagine yourself in a classroom, where all of the students are talking to their PDA, to take class note.
      I think a quiet (less dirturbance to the environment) input method is required. Voice is just not the one.
      • True, but in cases like that, a laptop is better anyways because it has a real keypad as opposed to a thumbpad. Granted you could go spend $100 for one of those nice foldable pocket keyboards. Laptops are just cooler. You can't play mp3s while watchin pr0n on a pda :P

  • Heat prevention for silent PCs (Score:3, Insightful)

    by Anonymous Coward on Monday June 24, 2002 @03:32PM (#3758698)
    The matter is applicable on heat prevention on laptops: Those out that having a laptop with dynamically activated cpu-fan know the problem. Constantly running processes will activate the fan and increase the noise polution- it doesn't matter if the process is nice or not.

    To gain a silent PC we would only need a daemon which constantly checks the CPU-temperature and slows down the system (starting or only from processes with lower priority) to prevent heat and noise.

    Not to mention that this would even increase battery-power if only less important jobs are slowed down and thus fan activation is decreased to a minimum.

    This really sounds like a neat feature, not complicated to implement- or is there already a project out there dealing with this?
  • As power consumption varies linearly with clock speed and as the square of core voltage, ....
    Interesting. Anyone have instructions on how to underclock my IPaq? I'm sick of the low battery warning half the time I think about turning it on.
    • Dunno about the ARM specifically, but on some processors the operating frequency is derived indirectly from the crystal via a PLL (phase locked loop) which can be programmatically set to a multiplier. At full speed the multiplier will be something like 4x but it can be set lower.

      The trick is usually to put the CPU in standby mode while the PLL stabilises to the new frequency, after which it can be started up again. One problem is that the stabilisation time is relatively long - tens of milliseconds - so the CPU speed can't be changed during any time-sensitive operations. Another problem is that any code which relies on the CPU speed for time calculations will break (although code like that is, IMO, broken in the first place).

      In summary, it can probably be done but it's not trivial and might have unexpected consequences.

  • FastCPU (Score:4, Interesting)

    by imuffin ( 196159 ) on Monday June 24, 2002 @03:53PM (#3758803)
    I really like FastCPU for PalmOS. [palmgear.com] I run it on my Treo. Its great to be able to overclock slow apps from 33 MHz to 66 - it makes a helluva difference, and, it doesn't lock up all that often.

    The other cool thing about it is that I can underclock things like notepad or "to-do list" so they use less battery power while running.

    • Re:FastCPU (Score:3, Interesting)

      by karnal ( 22275 )
      There is a hackmaster hack out there called "Afterburner" which will allow you to do this as well (although it doesn't have as much eye candy, I'll admit....)

      It does allow you to specify clock speeds for individual applications (for instance, from what I've heard of the architecture, you do not want to clock up IR applications... something about how the processor actually is used for the IR timings???)

      I've used it, and it does work, but expect significantly reduced battery life. Nowadays, I just use it with some of the extra options turned on (if your memory is good in the unit, there is a no-wait checkbox that speeds up memory accesses) etc....
  • The speculation used in modern processors can be controled. For example the fetch unit fetching instructions after it fetched a conditional branch. These instructions are thrown away if the branch is mispredicted.

    By controling the speculation you can decrease power without hitting your performance as much as lowering the clock rate would. One of the members of my group is working on this with positive results.
  • you have to realize that an out-of-context power consumption specification for a component or a board is about as meaningful as an interrupt latency specification is for a real-time operating system.

    This is the first time i've ever seen an analogy more complex than the original statement.

  • ...the CPU becomes one of the most critical components in the design...

    Isn't this a basic truism for all computer design? After all, no amount of support circuit wizardry is going make an old 4004 run any modern OS at acceptable performance levels...

  • Comment removed (Score:3, Insightful)

    by account_deleted ( 4530225 ) on Monday June 24, 2002 @05:47PM (#3759409)
    Comment removed based on user account deletion
    • Indeed, there are some people who will gladly shell out several hundred dollars in order to avoid buying a cheap daytimer. However, and this is the important part, there are also people who want something more. My main problem with Palm is that they subscribe to this philosophy -- that they know what their users want better than their users do.

      So while you may just want all of the functions of a IIxe, there are people (and this is borne out by the fact that Compaq can still sell iPaqs) who want something more from their PDAs.

      Think about what you say first.

    • I agree that high-powered hand-helds (especially linux hand-helds) have development going in the directions that really doesn't fit the needs of most mobile users. If I had a dime for every idiot that screwed up a mobile device UI by ignorantly trying to carbon-copy a desktop UI, I'd have a lot of dimes I could use to start my own hand-held company that did things right. However, I do think that in the hands of a developer who truly understands the human computer interaction consequences of 240x320 screen, lots of RAM and CPU allow that developer to make a far better organizer. Two examples of how RAM + CPU can make for a better mobile computing experience
      1. Hand Writing Recognition. A lot of non-geeks are turned off by having to learn a different style of writing (a la grafitti). More CPU cycles would allow for more complex and powerful HWR algorithms while maintaining a real-time feel. Which allows for HWR that is better tailored to a person's natural style of hand-writing. Even if you still stick with grafitti, more CPU cycles would allow for fewer grafitti mistakes. As a side note, one of my biggest grievances with Palm is that they have made their devices have color screens and wireless capability, but Grafitti now is still as inaccurate and makes just as many mistakes as it did four years ago.
      2. Second example: I'm trying to lose weight, so I wrote a stupid little program for my Sharp Zaurus that I can use to record everything I eat and how many calories it is. I needed to get the program done quickly because my ass was getting too fat for it's own good. I really wanted to save information about my eating habits in an XML format so it would be open, portable, and easily manipulatable and parsable on a desktop system. My need for quick application development time and XML capability was met by writing the program in python and making use of python's XML capability as well as the Qt bindings for python (which allow me to create a decent UI for the program). Python + XML + UI capability would tax the living hell out of a Palm. A 33mhz Dragonball processor, 8MB of RAM, and a 4k limit on stack size does not facilitate a python interpreter, a large XML DOM tree, and a responsive user interface. While an end user wouldn't care about any of that technical jargon, they do care about having lots of simple, useful, and usable programs that don't do a lot but get the job done. A setup like the kind I used that allows people who are not embedded-development gurus to quickly create such programs, which is A Good Thing.
  • This was a very good article. I've worked with battery powered systems where battery life was importatant, and every point in the article was on target.

    I would like to make a point about clocking. Sleep mode involves turning off the clock (unlike Idle mode, where the clock continues to run). When the clock is turned back on it will take a certain amount of time - usually measured in milliseconds - for the clock to stabilize. This period of time will not matter if you are responding to the on/off switch, but means you can't service a high speed device out of Sleep mode.

  • The old rule of thumb was that power consumption in a digital CMOS chip was proportional to C*f*V^2, or total capacitance times frequency times voltage squared. Halve the size or clock speed, halve the power (and heat). Halve the voltage, cut the power by one fourth! Problem is that model becomes less realistic as you go down in geometries. As you get down to these ultra deep sub micron circuits (say .1 micron) leakage current becomes a big issue. This means that a section of the chip may draw an unacceptable amount of current even when the clock is turned off! Ugh. Makes me glad I got out of back end chip design.
  • Kyocera's best PDA, and strangely, the last machine for which Bill Gates ever wrote a BASIC interpreter/ operating system, was marketed in the early eighties by Radio Shack as the TRS-80 Model 100. I still use it; runs 22 hours off of AA batteries. It's lightweight, has a great keyboard, built in word processor and terminal software, and you can even today buy a ROM for it so you can do 8085 assembly programming when you are bored on the bus.

    If only it had a bit more RAM. I snagged some off of an ethernet card; it exceeds the power draw expected a bit, but it works. If it had a bit more, it could probably run UZI, the Unix that ran on Z80s, with a little work.

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