Poulsbo: An Unusually Revolutionary Chipset

In 2005 work began on the Poulsbo chipset, the ying to the Atom processor's yang. Much like the Atom processor itself, Poulsbo's design goal was simple: the focus was power and how to reduce it, even if it meant a performance hit.

The lead designers on Poulsbo had all worked on Intel's i840 chipset, one of the only desirable RDRAM chipsets of its time.

When Poulsbo was designed all of the available ICH designs were 130nm, and thus Poulsbo became 130nm as well. If you look at the pictures of the Atom processor and its chipset, it now makes sense why the chipset is so very huge.


The Intel Atom processor (left) vs. The Poulsbo chipset (right)

With Poulsbo being a 130nm part, it also helps explain why Atom is reserved for larger-than-iPhone devices today: the pair of chips simply wouldn't fit in anything too small. There are obvious power consumption concerns as well, but physically getting these two into a smartphone-sized device is going to be impossible until the next iteration.

At a high level, Poulsbo looks to be no different than your run of the mill Intel chipset with integrated graphics:

You'll quickly notice that the single chip solution, what Intel is calling a System Controller Hub (SCH) is a bit more unique. Instead of re-using a desktop chipset, Intel architected Poulsbo from scratch. In order to conserve power things like SATA and some of the USB ports were ripped out of the design. The designers chose to move back to PATA mostly because of power and smaller drives. Apparently in an idle state there isn't a power difference between PATA and SATA, but when actively transferring data SATA consumes much higher power due to its serial nature.

The FSB and memory frequencies are locked together which reduces power and PLL count. The chipset features a single channel DDR2-400/533 memory controller.

Poulsbo supports HD audio (Azalia, not the HD audio codecs) but reduced the number of audio engines supported in order to keep power under control. Only 2 channel audio is supported but you can access the audio interface externally, so conceivably you could dock an Atom device (such as a MID) and using an external codec get full 7.1 support.


The parts of Poulsbo

Intel also developed a fairly sophisticated message fabric to send data across the SCH - think of it as an on-chip Ethernet network for carrying things like interrupts and power management signals across the chip in an efficient manner.

Poulsbo introduces a new FSB to memory bridge that's much simpler than conventional designs. In most chipsets you have many different queues for traffic between the FSB and memory subsystem designed to extract the best possible performance from the platform. With Poulsbo the designers simply outfitted the memory controller with a large 8K memory and all FSB/memory traffic must go through that. The single memory storage made validation a lot easier, the chipset itself a lot smaller but could incur a performance hit. The MCH/North Bridge part of the SCH is around 20% of the area of what traditional MCH/North Bridges are thanks to this approach.

The ICH/South Bridge parts of Poulsbo are similarly trimmed. Years of legacy have been stripped out of the chipset, there's no parallel port, no floppy disk controller. In mainstream chipsets as long as someone is using the feature, it must be kept in play - the same wasn't true for Poulsbo. If the target market didn't need it, the feature wasn't going in the chipset.

The benefit of cutting the fat in Poulsbo is that the chipset was physically smaller with fewer gates, meaning lower leakage power.

In a highly atypical move for Intel, Poulsbo also supports non-standard 1.5V DDR2 memory. There's no official JEDEC spec for 1.5V DDR2 memory but many vendors have good enough modules that will work at 1.5V, so if an OEM wants to undervolt its memory the chipset will support it.

Much of the Poulsbo's design couldn't have been done had it not been for the Atom project. There are many revolutionary techniques at work within Poulsbo, it's a more modular design, a more efficient design and potentially holds the key to better chipset design in general - but none of these techniques were ever allowed to surface before.

Intel's chipset business is like a clock, every year a new platform is expected and some of the more revolutionary changes that could potentially interrupt the normal flow of things are generally frowned upon. Poulsbo, at least internally, broke down a lot of these barriers. While it's far from the highest performance chipset Intel has ever produced, Poulsbo requires roughly half the power of mainstream chipsets. Intel has been on an efficiency kick with its CPUs for a few years now, Poulsbo may help ignite a similar trend with chipsets as well.

Atom's FSB and Multi-Core Aspirations Poulsbo's Graphics: Full HD Decode and not Made by Intel
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  • AssBall - Thursday, April 3, 2008 - link

    I was a little surprised at first but when I got thinking... I don't really know if my P35 northbridge is even a 90nm chip.

    - Why would Intel not want to use its old rock solid 130 process that it spent a ton of money on to build simpler parts than it was designed for. As long as their materials and equipment are working fine for a cheap enough 130 part and there is no dire market for lower power chipsets that fit in an ATX standard...

    - Intel's most recent strategy has been to design and manufacture their latest designs on solid existing tech before they shrink it.

    I'm also fairly certain that if this little CPU takes off they will have the 90-65 version of it with some simple refinements out in two shakes of a lamb's tail. I'm really surprised myself that they set it up with ddr2 support... but again its so cheap now, why not?
    Reply
  • rmlarsen - Wednesday, April 2, 2008 - link

    It is articles like this that make me come back to Anandtech. Well written and researched and with the right level of detail. Keep up the good work!
    Reply
  • Woodchuck2000 - Wednesday, April 2, 2008 - link

    One of the best I've seen on Anandtech for quite a while. I've been following this one quite closely and it's great to have such a detailed exposition all in one place.

    Do we have any news on the availability of this as a desktop part? I've been looking to construct an always-on server sitting in a cupboard somewhere, just to act as a file/print server and to do a little light database/web hosting for testing and developement. A 1.6GHz Atom would easily provide enough horsepower to accomplish that and with a notebook HDD, the whole thing should stay well under 10W load power consumption!

    I saw a photo of Silverthorne + Poulsbo on an Intel reference board built to a Mini-ITX form factor but couldn't find any details on whether they were planning to release it to the general public...

    Also any news on when we might expect benchmarks?

    Keep up the good work!
    Reply
  • yyrkoon - Wednesday, April 2, 2008 - link

    You could probably do this now with the VIA pico ITX reference board.

    http://www.logicsupply.com/products/px10000g?refer...">http://www.logicsupply.com/products/px1...=&gc...

    Sorry for the long link . . . but I think power usage is somewhere around ~12W.
    Reply
  • AnnonymousCoward - Friday, April 4, 2008 - link

    Try tinyurl.com

    Thanks for such a high quality article, Anand!
    Reply
  • tfranzese - Wednesday, April 2, 2008 - link

    "These days, Intel manufacturers millions of Core 2 Duo processors each made up of 410 million transistors (over 130 times the transistor count of the original Pentium) in an area around 1/3 the size."

    ...is incorrect. You could nearly fit six Core 2 Duos at 45nm in the same area that the original Pentium occupied or even more impressive, four of them on the die of the original Pentium 4 with room to spare.
    Reply
  • tfranzese - Wednesday, April 2, 2008 - link

    I'm the one with fuzzy logic today and misinterpreted :) Reply
  • Magnus Dredd - Wednesday, April 2, 2008 - link

    It is completely true that there are benefits to having a single platform to support. However, the article is completely off the mark about where the benefits are most realized.

    It's not the HARDWARE.

    It's the API.

    It's all about the API. Unless you're writing drivers or an OS you're not writing to the hardware, with VERY few exceptions. The exceptions to this are for optimizations for seriously intense code like Photoshop filters and video game engines, where 90% or more of the code is to the API. So basically one way or another you're writing to an API. That's Application Programming Interface.

    Since it was mentioned in the article...

    If I'm writing a program that's supposed to run on OSX, the newest version supports TWO hardware platforms (PPC and x86, and not just x86 as the article claimed), and I want to create a "window" using the built in API (named Cocoa) I use the command NSWindow.
    http://developer.apple.com/documentation/Cocoa/Ref...">http://developer.apple.com/documentatio...SWindow_...
    It makes no difference when writing the program whether it's a PPC or Intel based machine that it will be running on with the single exception that in a few places you have to use a small bit of code to make sure that the program uses the byte order appropriate to the processor.

    While I have yet to read info on it, I'd bet that NSWindow is also used by the iPhone which uses a MIPS cpu (yet a third architecture).

    I've written code in ANSI C for Linux that runs without making any changes on PPC, x86(32 bit and 64 bit), and Sparc. If I wanted to go to the trouble I could also compile it on my MIPS based SGI, a Motorola 68000 series Mac, and a HP PA-RISC (if I can ever figure out how to get the damned thing running). That's because nearly all modern applications are compiled.
    ---
    Now if by PC, Anand meant Windows, we're talking a different story, but one with similar flaws.

    So I'm writing an application for Windows and I want to create a "window". I use the win32 command CreateWindow.
    http://msdn2.microsoft.com/en-us/library/ms632679(...">http://msdn2.microsoft.com/en-us/library/ms632679(...

    So lets just say that I want it to run on an Itanium under Windows... I use the win32 command CreateWindow.

    So let's just say that I want to make it run on a WindowsCE based set-top box or internet tablet powered by a MIPS CPU...
    I use the win32 command CreateWindow.
    http://msdn2.microsoft.com/en-us/library/ms908192....">http://msdn2.microsoft.com/en-us/library/ms908192....
    Quoting Wikipedia: "It is supported on Intel x86 and compatibles, MIPS, ARM, and Hitachi SuperH processors."
    http://en.wikipedia.org/w/index.php?title=Windows_...">http://en.wikipedia.org/w/index.php?title=Windows_...
    ---
    I'm actually somewhat saddened to write this post, mostly due to the the amount of respect I have for Anand and many of the great articles he's written over the years. However, I suppose that it goes that way sometimes.

    I just want to make sure that people aren't misled about what makes it hard to port/move a program to another platform like a phone or a BlueRay player. And it's sure as hell not the CPU's instruction set. The CPU may not be fast enough or it's that programs are written for these APIs that may or may not support the hardware. And the fault for this lies with Microsoft, or Apple, or the GTK guys, or Trolltech, or whomever the API belongs to.

    Also simply dropping an x86 CPU into a machine does not mean that it can run Windows. With the sales of XP to cease, your only option for the new batch of supercheap x86 laptops like the ASUS EEE, or the cloudbook may be Linux, regardless of the fact that it's x86 based.

    The bottom line is, if Microsoft doesn't care about your platform, they won't support it and you won't be able to get it with Windows regardless of what the CPU is.

    While I do personally agree that x86 moving "downwards" is a great thing. I just see it taking over for completely different reasons, like Intel's manufacturing prowess.
    Reply
  • yyrkoon - Wednesday, April 2, 2008 - link

    Windows XP Embedded, and the compact .NET framework while you're talking about 'APIs', and platforms. XPe, and Win2003 Embedded are not going away any time soon, and basically have barely been available on a non beta basis. Although CE Builder could probably do the same thing, and as a matter of a fact I've seen some fairly nifty things done with it(eg: a boot-able image that fits on a floppy with all the functionality of your standard NAS, including User Groups and permission policies).

    While sometimes having an OS on an Embedded device may be a hindrance, there are times it can be quite handy. Bank KIOSKs, and Cash registers are only two such examples, and I have worked on/with both that use WinXPe.
    Reply
  • Anand Lal Shimpi - Wednesday, April 2, 2008 - link

    Agreed - the API also plays a large part, but for a company like Apple the pain of maintaining both PPC and x86 codepaths is significant. Perhaps the Firefox reference wasn't the best one, especially as I really see the strengths here for software companies like Apple (not to mention what other conventional hardware companies may start looking more like software companies as their devices get more complex).

    I think you've also hit on a major issue going forward: Microsoft is going to have to focus on these not-PCs a lot more seriously in the future. Instead of trying to scale Windows down, it needs a MCE-esque approach to these "fast enough" devices. Apple made the right first step with the iPhone OS, Microsoft can't stand by idle for too long without a good alternative. And MS does love x86... :)

    Take care,
    Anand
    Reply

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