Building by FUBs

Below we have a conventional block diagram of the Intel Atom processor:

You'll see nine distinct blocks and in conventional microprocessor design at Intel, this is how the chip would be divided and conquered. You'd have one team working on the L2 cache, one team working on the IO interfaces, etc... Unfortunately the team at Austin was significantly smaller than your conventional microprocessor design group, so things had to be done a little differently.

Intel calls the Atom approach a Sea-of-FUBs chip layout, a more granular approach to chip layout and design. A FUB (Functional Unit Block) is a floor-plannable object, an individual adder is a FUB, a decoder is a FUB, a cache is a FUB, etc... Because the size of each FUB made them more manageable, a single designer could handle multiple FUBs. The FUBs were also treated more modularly so that once a FUB was defined, designers can work on the FUB, chip integraters can give it to the layout guys and the timing guys can work in parallel as well. It allows for much more concurrent design than the conventional, more serial approach to chip design.

Approximately 90% of the fubs are built using standard Intel logic cells, minimizing the amount of custom work that needs to be done and decreasing the time to market on a processor like Atom. Minimizing the amount of custom Intel logic also means that it's easier to produce variants of Atom that may incorporate other important features depending on the target market.

The Sea-of-FUBs approach was also driven by a desire to keep power consumption and feature creep to a minimum. Area budgets were developed for each FUB and cluster of FUBs and Intel forced the designers to stick to these budgets. If a designer needed more die space for their FUB they couldn't just take it. A review board was setup where designers would come in and ask to grow their FUB. They were allowed to grow the FUB only if they were able to find another FUB that would shrink to accommodate it. The same thing applied for power.

An Unbalanced L1 Cache: We Know Why Gridless Clock Distribution


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  • FlakeCannon - Wednesday, April 02, 2008 - link

    This was an absolutely fantastic article as far as I'm concerned. One of the best I've read from AnandTech. I'm truly impressed with the amount of effort and dedication that the engineers at Intel put into the Atom. Thought the consumer may not see its importance today the Atom will continue to develop one throughout the next 2 years and show why this is such a huge step in the right direction. I really think that this article outlines very well the architecture involved and where it intends to lead Intel and others in the future.

    I'm always impressed to see Intel take architecture that was revolutionary in its time 15 years ago in the Pentium and Pentium Pro and resurrect it in modern day fashion with help of the Dothan Pentium M architecture and even things borrowed from the miserable Netburst technology that 15 years later I believe will once again create a product revolutionary in nature. I was never able to appreciate it in the days of the Pentium but certainly can now.

    This is one product I think is deserving of being excited about.
  • fitten - Wednesday, April 02, 2008 - link

    What does an on-die memory controller have to do with ILP? Reply
  • Anand Lal Shimpi - Wednesday, April 02, 2008 - link

    Woops, I've clarified the statement :)

    Take care,
  • erwos - Wednesday, April 02, 2008 - link

    I was thinking that this would be a fantastic platform for making a small, silent HTPC box for doing streaming media, but the lack of 1080p output kills that to a large extent. I know it's not a big priority for the first revision given the UMPC targeting, but I hope the "Atom 2" does try to squeeze that feature in. Reply
  • FITCamaro - Wednesday, April 02, 2008 - link

    It could always be paired with a different, more capable graphics core. Reply
  • ltcommanderdata - Wednesday, April 02, 2008 - link

    It;d be very interesting to see how the 1.86GHz Silverthorne stacks up against a 1.8GHz P4 Northwood, a 1.86GHz Dothan, a 1.8GHz Conroe-L based Celeron, and a 1.8GHz Athlon 64.

    I wonder if Apple is going to refresh AppleTV with Silverthorne since it seems ideal with replace the current 1GHz ULV Dothan in there.
  • yyrkoon - Wednesday, April 02, 2008 - link

    Well at least Intel did not name their Atom CPUs the 'Atom Z80' . . . heh.

    Anyways, this is good for our future, as the mITX, and pITX 'systems' now days are still kind of large-ish, and cost quite a bit of money for what they are. Though, I think that putting a web browser on just any old appliance in the house would be way overkill, and possibly a very serious mistake. A TV with a web browser ? An Oven ? Please . . . this is why we have PCs, and micro mobile devices.

    Recently a friend and myself have been working on an embedded project, and I can see the potential here, but a 'problem' does exist. Some of the things you would want to do with such a processor . . . well lets just say there still would not be enough processing power. That being said, I do not see why these could not help make a TVs/HD-DVD player menu operate faster.

  • pugster - Thursday, April 03, 2008 - link

    It certainly sounds nice, but the atom processor cost alot because some of the higher end models cost more than $100 each. I find it surprising that their Polosbo chipset is manufactured at 130mm. It probably came from one of their foundries that was due to upgrade to 32mm sometime next year anyways. They could've earily manufactured at 65mm.

    Somehow I don't see their product as mature and maybe the next gen product they would have a cpu and the north/south bridge in the same die.
  • lopri - Wednesday, April 02, 2008 - link

    I honestly don't get the excitement. Should I? I mean, I wouldn't feel comfortable with one gigantic company controlling every single electronics in our life. If Intel opens up the X86 and everyone can compete on even end, then maybe. Since that won't happen, the future looks scary enough. Reply
  • clnee55 - Wednesday, April 02, 2008 - link

    NO, how can you get excitement. I am already bored with your conspiracy theory. Let's talk about tecnical issue here. Reply

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