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A closer look at AMD’s Brazos platform

Cyril Kowaliski
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A little over a week ago, I flew down to AMD’s Austin campus for a short visit. Waiting for me there was the hot Texas sun, which provided a welcome reprieve from the cold and rain of Vancouver, as well as a few precious hours of hands-on time with a machine running AMD’s new Zacate accelerated processing unit. On top of that, AMD disclosed some fresh details about the Brazos platform that will catapult Zacate into ultraportables, nettops, and netbooks early next year, allowing me to fly back home with a pretty complete picture of AMD’s next big thing.

Now for the bad news: while I have a spreadsheet bursting at the seams with benchmark data I collected from the development system, AMD won’t lift the press embargo on Zacate benchmarks for another little while. Luckily, pretty much anything beside cold, hard numbers is fair game—and there’s plenty of that to go around. Over the next couple of pages, we’re going to take a look at what makes Brazos tick, what the first Zacate APUs will look and perform like, and how much you can expect to pay for products based on them.

Now, I should point out that this won’t be an exhaustive look at the new Bobcat microarchitecture that powers Zacate’s microprocessor component. Scott already covered Bobcat in detail this summer; if you don’t already know what makes Bobcat different from past AMD architectures, you should read his article.

In short, though, Bobcat was fashioned from the ground up for low-power systems. You can think of it as AMD’s answer to the Intel Atom, except Bobcat emphasizes power-efficient performance more than extreme power efficiency. Fully out-of-order instruction execution, 64-bit extensions, and hardware virtualization are all be on the menu. AMD claims the architecture can deliver performance almost equivalent to that of today’s entry-level desktop offerings, yet dual Bobcat cores can still huddle together with an integrated GPU inside a 9W thermal envelope.

Bobcat, meet Brazos
The first two Bobcat-based designs are accelerated processing units, or APUs for short—essentially microprocessors sharing die space with graphics processing components. AMD code-names those two APUs Zacate and Ontario, having tailored the former for an 18W thermal envelope and the latter for a 9W TDP. Despite the different code names, both parts are actually based on the exact same silicon. They occupy 75 mm² of die area and fit onto 19 x 19-mm, 413-ball BGA packages just like the one pictured above. Both are manufactured using TSMC’s 40-nm fab process.

That 75 mm² die includes not just two Bobcat cores, but also a GPU component with video decoding logic, a single-channel DDR3 memory controller, and a “platform interface” block with PCI Express lanes and display outputs. Together with Hudson, an auxiliary chip that provides additional I/O connectivity, Zacate and Ontario make up the platform code-named Brazos.

Before we delve deeper into Brazos’ I/O capabilities, let’s first talk about its graphics component. The GPU built inside Zacate and Ontario shares the same foundation as AMD’s DirectX 11 Radeons. It includes two SIMD arrays with 40 ALUs each for a grand total of 80 ALUs, or stream processors, per chip. GPU clock speeds range from 280MHz on Ontario to 500MHz on Zacate. AMD complements those resources with a UVD3 block—the same one found in discrete, 6000-series Radeons—which will assist the Bobcat cores with the decoding of H.264, VC1, DivX, and XviD video. Fittingly, the machine I tested detected Zacate’s GPU as a Radeon HD 6310 in the Windows 7 Device Manager.

As one would expect, this GPU component shares memory bandwidth with the CPU cores. There won’t be a whole lot of bandwidth to share, mind you, because the chip’s memory controller only supports up to two DDR3 DIMMs running at 800-1066MHz along a single, 64-bit channel. You’re looking at maximum theoretical memory bandwidth of about 8.3GB/s, and that’s shared across the entire APU.

Zacate and Ontario will also have built-in PCI Express connectivity. There will be four PCIe Gen2 lanes to connect the chip directly to third-party network controllers or a discrete graphics processor, with an additional four Gen1 lanes linking the APU to the Hudson chipset (or “Fusion Controller Hub”). AMD calls the link between the Hudson FCH and Zacate/Ontario the Unified Media Interface (UMI), but from what I’ve been able to gather, that’s fancy-talk for a plain-jane, four-lane PCIe connection.

What does Hudson look like? I don’t have a sexy chip shot with a quarter for reference, but AMD’s spec sheet paints a pretty good picture. The Hudson FCH is built on a 65-nm fab process and has a 23 x 23-mm, 605-ball BGA package—slightly larger than the APU it accompanies. Power consumption ranges from 2.7W to 4.7W for “typical configurations.” Inside Hudson lurk the four PCIe Gen1 lanes required for the UMI interface, an extra four PCIe Gen2 lanes, six 6Gbps Serial ATA connections, 14 USB 2.0 connections, and built-in fan control logic.

The presence of 6Gbps SATA might seem a tad over-the-top, since few netbooks or ultraportables are likely to sport ultra-fast solid-state drives capable of pushing the boundaries of the 3Gbps standard. Still, it’s good to see AMD isn’t cutting too many corners. Folks hoping to build, say, cloud computing clusters out of Brazos systems may find some use for the fast storage ports, too.

Because Brazos supports discrete GPUs, it can arrange all of that I/O connectivity in one of two ways. In the first configuration depicted below, Brazos happily relies on its integrated graphics and hooks up Gigabit Ethernet and 802.11n Wi-Fi straight to the APU, with Hudson handling more menial duties.

The second diagram shows Brazos outfitted with a discrete graphics processor. In this case, the discrete GPU is connected directly to the APU via four Gen2 PCI Express lanes, and Hudson plays host to the networking controllers.

One thing to note is that both Hudson and Zacate/Ontario can run their non-UMI PCI Express lanes at either Gen1 or Gen2 speeds. AMD says it recommends using Gen1 for “the power benefit,” but in the context of a nettop or an ultraportable with discrete graphics, I wouldn’t be surprised to see Gen2 speeds used. (If you’ve lost your computer standards reference manual, PCIe Gen1 lanes can push 250MB/s in each direction, while Gen2 lanes have twice as much bandwidth.) Four PCIe Gen2 lanes may not be optimal for high-end discrete graphics, of course, but they should suffice for low-end notebook GPUs likely to accompany this platform.

That’s Brazos in a nutshell: a low-power, two-chip solution with enough computing, graphics, and I/O resources to keep a lot of folks happy. Intel’s Pine Trail platform is starting to look a tad anemic in comparison. As you’re about to see, though, Brazos and Pine Trail might both be tailor-made for low-power systems, but they’re not quite fighting over the same turf.

 

Parts and positioning
After speaking with the folks at AMD, and after tinkering with a Zacate rig myself, I believe the best way to think about Brazos isn’t so much as an Atom competitor, but as a successor to AMD’s existing Nile ultraportable platform. AMD just had a slightly different set of priorities this time around. CPU performance has gone down a little bit, giving way to greater graphics horsepower and overall power efficiency.

Brazos has double the graphics ALUs of Nile’s IGP, and AMD quotes a 10-50% improvement in raw graphics performance. Nile already had fairly decent gaming chops considering its low-power credentials, so that ain’t nothing to sneeze at. On the power efficiency front, Brazos trims platform TDP from 25W to 21W, with active core power draw tumbling from 10.8W on average to just 6.5W. Consequently, AMD expects to see battery life spiral up to 8.5-9 hours for Zacate laptops with 55Wh batteries. Ontario netbooks will purportedly reach a stratospheric 10.5 hours. Those are official estimates, of course. AMD quoted roughly eight hours of run time for Nile earlier this year, but we got just under five hours of web browsing out of our first Nile notebook using a 61Wh battery.

In any case, AMD will have four Brazos offerings ready for launch. Two Zacate-based models will make up the E series, while two Ontario APUs will materialize as C-series parts. All four chips will support DDR3-1066 memory speeds and feature 512KB of L2 cache per core, UVD3 video decoding logic, and hardware virtualization capabilities.

Processor CPU cores CPU clock GPU ALUs GPU clock TDP
AMD E-350 with Radeon HD 6310 graphics 2 1.6 GHz 80 500 MHz 18W
AMD E-240 with Radeon HD 6310 graphics 1 1.5 GHz 80 500 MHz 18W
AMD C-50 with Radeon HD 6250 graphics 2 1.0 GHz 80 280 MHz 9W
AMD C-30 with Radeon HD 6250 graphics 1 1.2 GHz 80 280 MHz 9W

AMD is targeting the E-350 and E-240 specifically at nettops and ultraportable notebooks with list prices in the $399-449 range. The C-50 and C-30 will populate cheaper, lower-specced systems, which some might be tempted to call netbooks. I doubt we’ll see Ontario sparring with Pineview Atoms in $250, 10-inch machines, though, if only because of the product positioning chart AMD showed me:

See how the Atom is at the bottom of the pack, shoved under the C-series offerings? That pretty much says it all. Admittedly, AMD said this slide reflects its aim on the pricing front, not performance. I wouldn’t necessarily expect APUs like the C-30 to run circles around the Atom N450 in raw CPU performance benchmarks, but AMD will surely have a leg up on the graphics and video decoding side of things. That could justify a small price premium over your typical netbook.

Incidentally, sharp-eyed readers might have noticed the new HD Internet badge in the slide above. AMD says this label signals that Ontario is suitable for “HD Internet browsing,” watching “HD videos online,” and tasks like “email, chat and social networking.” Meanwhile, the plain Vision umbrella, which Zacate falls under, means users can “run mainstream software applications,” enjoy “fast HD Internet browsing” and “casual games,” and watch “DVDs and online HD videos.” I suppose Ontario laptops will catch on fire if you try to plug-in a DVD drive or play Bejeweled, then.

Performance impressions
The question on everyone’s lips must now be: how does Brazos fare against the competition from Intel? Some folks might also be wondering how it compares to Nile, its most direct predecessor. As I said earlier, AMD has slapped a momentary embargo on benchmark numbers obtained last week, but it doesn’t mind us discussing performance in more general terms, without raw numbers.

So, that’s exactly what I’m going to do.

Let’s first tackle the elephant in the room. Yes, Zacate gives Intel’s Atom processors a whupping—even the dual-core N550. In the CPU performance tests we ran, the AMD E-350 test rig didn’t stray too far from either our Nile-based Toshiba Satellite T235D notebook or Zotac’s Zbox HD-ND22, which contains a Celeron SU2300. AMD did have the test rig set up with a 128GB Crucial RealSSD C300, so applications loaded quicker than they would have on a real consumer ultraportable, but the E-350 system still felt pleasantly snappy in web surfing and other, non-storage-bound tasks. That tracks pretty well with AMD’s goal of delivering “good enough” CPU performance.

What about the graphics side of things? I won’t spoil the numbers here, but I will say that, when AMD talks of Brazos beating Nile’s graphics performance by up to 50%, it’s not singling out a best-case scenario. I wouldn’t recommend making a Brazos laptop your primary gaming rig, of course—integrated graphics are what they are—but I think it’s fair to say this platform sets a new high-water mark for mobile AMD IGPs. And thanks to UVD3, high-definition video playback isn’t a problem. All of a sudden, the future of Atom-based netbooks with next-gen Nvidia Ion graphics is looking grim. Very grim.

More detailed analysis will have to wait for our performance article with the full results, but in broad terms, I was impressed by what Brazos had to offer. Not only is it an engineering achievement in itself, being the first AMD processor to feature the Bobcat microarchitecture, the first AMD processor to feature an integrated GPU on the same die as the CPU, and the first AMD processor based on TSMC’s 40-nm bulk silicon fab process. But it also packs quite a punch, delivering solid CPU performance and great graphics performance for its segment.

The only remaining mystery—for me, at least, since you folks still haven’t seen the benchmark data—is battery life. Considering Brazos’ spartan power requirements, AMD might just be able to turn the tables and offer longer run times than Intel CULV systems. That would be a really big deal. However, AMD did make bold claims about Nile’s battery life without completely delivering, so I’ll reserve judgment on that point until we get our hands on our first Brazos notebook.

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