My low-power HD HTPC... how to go even *lower*?

[NeoteriX]

Hi!!! First time posting at SPCR! After a month of reading and buying and tinkering, I've finally got something substantive to ask--

Low Power HTPC Build:

- AMD Athlon 64 LE-1640 (single Orleans core @ 2.6 Ghz)
- Gigabyte GA-MA78GM-S2HP (780G w/ integrated ATI 3200 HD)
- G.Skill 2 GB (2 x 1GB) DDR2 800
- Icy Dock 2.5" to 3.5" SATA HD Cradle
- Western Digital 2.5" SATA 320GB HDD at 5400 RPM
- Samsung SH-S223F 22x SATA DVD+R/RW
- IN WIN Black Steel IW-BT566T.300BL mATX Case


The goal for this build was to have an HTPC powerful enough to play HD content with the lowest idling power consumption possible so that I may leave it idling 24/7. With the 3200 HD (DXVA) acceleration, HD content isn't a problem.

For the processor, I was primarily influenced by this Tom's Hardware article. I went with the single core Athlon LE-1640 for $35. It is similar to the Athlon 2000+ used in the article, though it is 90nm instead of 65nm and has a 1MB L2 cache. I considered the X2 4850e for more performance, but this type of processor's ability to run completely fanless was proven in the article, and I figured, a single core would consume less than a dual core underclocked to the same speed.

Additionally, I went with a 2.5" HDD which was a bit more expensive for less capacity, but the savings was probably a handful of watts. I was considering going without an optical drive, but in my testing, an idle DVD drive consumed negligible power.


Power Consumption: (as measured by Kill-A-Watt)
With included 300W in-win/powerman psu
Underclocked/volted to 1Ghz@ .900V: Idles at ~40W
(oddly, with hard drive activity, the idle didn't change much)

With 150v PicoPSU & 102W AC adapter
Underclocked/volted to 1Ghz@ .900V: Idles at ~30W
w/ hard drive activity: ~31-32W

The biggest unforeseen issue with this low-horsepower setup is that video that cannot be accelerated may run into problems. This includes HD content not encoded properly, or HD content from Youtube or Hulu.

How do I go lower? (with more power?) Suggestions?
I was hoping to hit around the mid-20's at idle with the addition of the PicoPSU.

The AMD setup is supposed to rival that of the Atom, and this guy is pulling 23W at idle with an atom and 2.5" HDD. This person is hitting the mid-20's at idle with a 4450e (though with no HDD). This Tom's hardware article shows an idle of 28W on an Athlon 2000+ setup - with a 3.5" HDD and without a PicoPSU.

It sounds a little crazy, but would I be able to go even lower with a faster processor? If I were to go with a low-power X2 dual core, would I receive the coolnquiet idling benefits (if I could undervolt the idling clock speed) and still come out ahead by having more power when necessary? Or maybe if I were to have an unlocked X2 processor, would I be able to set the multiplier even lower to 4x? (800mhz)

[mattthemuppet]

30W really isn't bad for a full mATX build w/ 2GB RAM! Is the CPU permanently underclocked to 1GHz? If it is, then you can always use CrystalCPUID to dynamically scale clock speed and volts on demand, that way you get the best of both worlds.

Can you undervolt any lower? Most recent AMD chips are perfectly happy with 0.85V or even 0.8V, which'll save you a couple of watts perhaps. You may be able to save another watt or two by changing to a 65nm X2 (any will do, they all seem to undervolt the same), but it's possible that the extra core will cancel out the benefits of the smaller process. That extra core will certainly help in an HTPC though.

The only other option would be to drop one stick of RAM - that's another 3W or so. To be honest, when you're down as low as 30W, you'll have to make some pretty severe compromises to drop even 5W. When you think how little difference losing those few watts makes and how much performance you may lose, what's the point?

[NeoteriX]

Ah yes, I tinkered around with CrystalCPUID and RMclock last night--thanks for the suggestion.

I guess I had assumed that the "Cool'NQuiet" clock scaling wasn't a feature on my Athlon LE-1640, since under CPU-Z the clock multiplier was locked to whatever I set it at; I assumed it would automatically scale like the notebook processors I'm used to. I didn't realize it would require a driver/software to implement!

I have it set up to scale appropriately, and now non-HD Hulu and Youtube content play very well. (HD is still a problem... for obvious reasons )

Also, after doing some digging around here and here, I figured out that I needed to lower the HyperTransport speed/multiplier if I wanted to crack into the CPU's 4x multiplier territory. After some tinkering, I think I'm successful at running the processor at 800 Mhz @ .800v -- I probably gained about a watt reduction from that, maybe a hair less.


As a final note, while 30W is pretty good, I guess I was expecting more given the results of others hitting the mid 20W range. The old Pentium 4 rig I using as an HTPC/File Server idled at around 80W, it would have been nice to cut power consumption by a 1/4th [/url]

[Tobias]

Nice find Neoterix, that would explain why I can't use the 4x multiplier:) Other than that I think you are about as low as you can go. You can change the RAM from 2*1GB to 1*2GB, which will save you a 2-3 watts, and use an SSD if you have storage somewhere else (for another 2-3watts, but you'd need that storage as well)

Greenfrank manages the numbers he does because he only has 1 or 2 phases on his mainboard. I don't know why, but adding more phases increase the power draw. For some reason I have not found any AMD board with less than 3 phases.

[jessekopelman]

I don't know why, but adding more phases increase the power draw.

For pretty much the same reason that it is hard to make an AC-DC PSU efficient at <<20% load. Adding phases makes the VRM more efficient at higher loads at the expense of efficiency at lower loads. This is generally a good trade off considering that 10% better efficiency at 100WDC is 10W while 25% worse efficiency at 20WDC is is only 5W. Of course, if you consider what percentage of up time is spent at or near idle for the components, the equation changes quite a bit. Still, I think the multiphase VRM may be more a concession to heat (where all we care about is the worst case), rather than power efficiency. This is especially the case where you have a single socket standard that accommodates processors that range quite significantly in TDP (and thus potential draw). It is much safer to use few phases on a MoDT or Atom or Via board since you know a priori that a low draw processor will be used.

[peter_cheat]

For some reason I have not found any AMD board with less than 3 phases.

Some motherboards have dynamic phase switching to reduce power consumption. If you are desperate to go under 30W idle, you will have to look at motherboards like the Asrock K10N78FullHD-hSLI which drops down to 2-phases under low load (Intelligent Energy Saver). Gigabyte have their DES (Dynamic Energy Saver) and ASUS have their EPU technologies. All these technologies are about the same, but I have heard that the Asrock is the best for low power computing.

Unfortunately the GA-MA78GM-S2H doesn't have DES. Dropping 2 phases will drop power consumption by nearly 10W. The reason for 4 or more phases is for more power hungry CPU's, like the 140W Phenom's.

[NeoteriX]

Ah shoot... good points all around.

I have a vague memory of the one DIMM energy saving aspect, but got fooled into the whole "buying in pairs" thing.

In my weeks of research, this was the first time I've come across the motherboard power phase as a component of power conservation, but it makes sense now. It looks like ASrock is the only mfr to offer dynamic phase control for AMD processors (Gigabyte and Asus are both Intel only).

**SIGH**

The major irony of this learning process is that had I known then what I know now, my HTPC build would have been even cheaper -- with a cheaper ASrock mobo, 1 DIMM of 2GB DDR2, and a Sparta Sempron or Lima Athlon... Probably would have shaved off $40-50. Nuts.

[jessekopelman]

**SIGH**

The major irony of this learning process is that had I known then what I know now, my HTPC build would have been even cheaper -- with a cheaper ASrock mobo, 1 DIMM of 2GB DDR2, and a Sparta Sempron or Lima Athlon... Probably would have shaved off $40-50. Nuts.

Don't feel bad. It's hard to really appreciate all the discussion until you have built something of your own and seen its limitations. Unless you are one of those guys who's churning out a new system every year, it's impossible to have a practical grasp of the relative merits of every component in this constantly changing scene.

[mattthemuppet]

sounds like you have a good HTPC there with an enviably low power draw, so I shouldn't feel too bad

As for the 2x1GB vs. 1x2GB debate, don't forget that 2 matched sticks will be faster as they'll be working in dual channel mode, something you won't get with 1 stick. Given that you're working with a single core processor, that little bit of performance may be crucial.

I haven't been all that convinced by various power phase switching schemes - they never seem to make all that much difference either way, though admittedly I haven't seen any tests with very low power PCs (<40W). I certainly wouldn't worry about replacing the MB on that basis.

Are you going to be capturing TV/ video at all?

[NeoteriX]

I've seen that video/capture or PVR is an important part of an HTPC solution for many, but I've been content to rely on uh... rhymes with "Hit-Foreigns" so I haven't had the need to figure that out. Plus I have digital cable... which I think only partially works with any HTPC video capture? Bc of the encoding?

From what I understand I would need a TV capture card, but I'm not sure how much more processing power I would need. I'm assuming more is required than for your typical lowly playback.

If I eventually want to upgrade to PVR, is there anything I should be aware of?

BTW -- thanks for the reassurance guys. I just had this burning desire to beat the Atom at it's own game by putting together a computer that rivalled its low power consumption, but that was much more flexible and powerful enough to play HD content. I *almost* got there

[mattthemuppet]

fair enough, there aren't enough decent films/ shows on the box here in Oz to bother, so I pretty much the same route.

The 2 choices with TV tuner cards are broadly software based and hardware based. SOftware based cards (usually the cheaper ones) draw less power but rely on the CPU for encoding/ decoding, so a single core will be fine for recording OR playback, but not usually both. Hardware based cards (decent Hauppage ones etc) are more expensive, draw between 10-25W (mostly towards the lower end of that) but completely off-load the CPU. They also often have 2 tuners or hybrid digital/ analogue tuners. Most digital cable doesn't need much doing to it as I think (not an expert) it already comes encoded as MPEG4, which I think is supposed to be the best compromise between size and quality.

Other than that, playback software is worth a thought. most cards come with a software bundle which varies from good to useless. Some OSs, like Windows Media Centre, Vista Premium and MythBuntu are designed for HTPCs, but that's a whole other thread and I don't know an awful lot about the details/ pros and cons.

So, if you're happy with it as it is, I'd leave it as it is. If you start wishing you could record some of your favourite shows, then might be worth considering.

[lowpowercomputing]

I have the following

– LE-1640 2.7 GHz 65nm (Lima) @ 1 GHz 0.76V
– Abit AN-M2 (GeForce 7025)
– Kingston 1 GB DDR2-667 (1 stick)
– Fujitsu 2.5" 40GB SATA HDD (5400 rpm) (one platter)
– 3.5" floppy / DVD-RW drive (will retest without them)
– Antec EA380 PSU <---- anyone done a fan swap to make that inaudible?

idling at 25W. I suppose the 65nm Sempron I had before that did 0.8 GHz @ 0.672V would idle at even less.

Lowering the HT link to 4x allowed me to run the CPU at 800MHz using CrystalCPUID but it doesn't go any lower than 0.775V (after editing its ini file). RMClock, on the other hand, offers 0.5V IIRC but doesn't go lower than 5x. Is there a way I can go <5x and <0.775V, perhaps using a combination of both tools?

I just had this burning desire to beat the Atom at it's own game by putting together a computer that rivalled its low power consumption, but that was much more flexible and powerful enough to play HD content. I *almost* got there

Amazing – I built the system above after a disappointing early-adopter's experience with the Intel D945GCLF as well (power draw was much higher than hoped).

[jessekopelman]

Most digital cable doesn't need much doing to it as I think (not an expert) it already comes encoded as MPEG4, which I think is supposed to be the best compromise between size and quality.

In the US, you can't receive Digital Cable without a set-top box (STB) or a capture card that accepts a CableCARD (kind of like a mobile phone SIM, but for a TV), because the signals are encrypted. The exception to this is HD version of your local broadcast channels, which are usually carried on the cable connection in the clear (this means QAM modulated MPEG2 encoded). However, if you only care about local channels, you don't even need cable unless you really live in the boonies. Anyway, since you are going to have a STB between the cable feed and your capture card, the only thing the capture card needs to be able to do is capture NTSC video (at 1080i if you want HD capture). The STB will handle both the demodulating from QAM and the decoding from MPEG2 or MPEG4 into an analog NTSC signal.

Now the big problem is that since you will be relying on the cable box to change the channel, you need some way to have your PC-based PVR control the cable box. In theory it should be able to do this over the Firewire interface that all such boxes must have by FCC mandate. Unfortunately the cable companies like to disable this interface, by default, and are often unwilling to enable it for you even if you threaten to complain to the FCC. Even with it enabled you still need this method of control to be supported by your PVR software. As you might imagine this whole deal is pretty much a huge pain in the ass and doesn't make sense when dual-tuner DVR functionality in your cable company supplied STB only costs ~$16/month. Some company came out with a tuner card that accepted a CableCARD a few years ago, but it didn't work for shit!

The next evolution of CableCARD is completely software based. It will also support video-on demand, which CableCARD cannot. Once the specification is finally ratified (of course, the cable companies are dragging their feet) I'm sure Microsoft will support it in some future version of Windows. Basically, at that point, you will be able to turn any Windows PC with one or more QAM capture cards into a full STB, including PVR functionality. Why Microsoft isn't pressuring the cable companies to hurry up and get this done, since it would seem like a killer feature for getting people to upgrade to that new version of Windows, is probably a good indication of how small a niche HTPC is right now. What amazes me is how Microsoft advertises the PVR functionality of Windows as ready right now, even though it really isn't there for anything but local and analog channels. Millions of people still do only have analog cable, but these aren't the people who want to build HTPCs.

[psiu]

Generally you can just control the boxes via IR Blaster.

[jessekopelman]

Generally you can just control the boxes via IR Blaster.

Maybe even more of a pain in the ass, as you still need the right support in your PVR software and since you are using IR you now have to deal with the horrible UI of the STB. If you are going to have to deal with that horrible UI anyway, what have you gained by rolling your own PVR? Given that there will always be reason enough to upgrade every 2 years, you might as well pay for the cable company solution until the PC version is fully baked.

[mattthemuppet]

ah okay, bit more complicated than I've experienced in the UK and NZ - there it was a simple case of plugging the output of the STB into the input of the TV card (SD only though).