Seeing the Future: DisplayPort 1.2

While Barts doesn’t bring a massive overhaul to AMD’s core architecture, it’s a different story for all of the secondary controllers contained within Barts. Compared to Cypress, practically everything involving displays and video decoding has been refreshed, replaced, or overhauled, making these feature upgrades the defining change for the 6800 series.

We’ll start on the display side with DisplayPort. AMD has been a major backer of DisplayPort since it was created in 2006, and in 2009 they went as far as making DisplayPort part of their standard port configuration for most of the 5000 series cards. Furthermore for AMD DisplayPort goes hand-in-hand with their Eyefinity initiative, as AMD relies on the fact that DisplayPort doesn’t require an independent clock generator for each monitor in order to efficiently drive 6 monitors from a single card.

So with AMD’s investment in DisplayPort it should come as no surprise that they’re already ready with support for the next version of DisplayPort, less than a year after the specification was finalized. The Radeon HD 6800 series will be the first products anywhere shipping with DP1.2 support – in fact AMD can’t even call it DP1.2 Compliant because the other devices needed for compliance testing aren’t available yet. Instead they’re calling it DP1.2 Ready for the time being.

So what does DP1.2 bring to the table? On a technical level, the only major change is that DP1.2 doubles DP1.1’s bandwidth, from 10.8Gbps (8.64Gbps video) to 21.6Gbps (17.28Gbps video); or to put this in DVI terms DP1.2 will have roughly twice as much video bandwidth as a dual-link DVI port. It’s by doubling DisplayPort’s bandwidth, along with defining new standards, that enable DP1.2’s new features.

At the moment the feature AMD is touting the most with DP1.2 is its ability to drive multiple monitors from a single port, which relates directly to AMD’s Eyefinity technology. DP1.2’s bandwidth upgrade means that it has more than enough bandwidth to drive even the largest consumer monitor; more specifically a single DP1.2 link has enough bandwidth to drive 2 2560 monitors or 4 1920 monitors at 60Hz. Furthermore because DisplayPort is a packet-based transmission medium, it’s easy to expand its feature set since devices only need to know how to handle packets addressed to them. For these reasons multiple display support was canonized in to the DP1.2 standard under the name Multi-Stream Transport (MST).

MST, as the name implies, takes advantage of DP1.2’s bandwidth and packetized nature by interleaving several display streams in to a single DP1.2 stream, with a completely unique display stream for each monitor. Meanwhile on the receiving end there are two ways to handle MST: daisy-chaining and hubs. Daisy-chaining is rather self-explanatory, with one DP1.2 monitor plugged in to the next one to pass along the signal to each successive monitor. In practice we don’t expect to see daisy-chaining used much except on prefabricated multi-monitor setups, as daisy-chaining requires DP1.2 monitors and can be clumsy to setup.

The alternative method is to use a DP1.2 MST hub. A MST hub splits up the signal between client devices, and in spite of what the name “hub” may imply a MST hub is actually a smart device – it’s closer to a USB hub in that it’s actively processing signals than it is an Ethernet hub that blindly passes things along. The importance of this distinction is that the MST hub does away with the need to have a DP1.2 compliant monitor, as the hub is taking care of separating the display streams and communicating to the host via DP1.2. Furthermore MST hubs are compatible with adaptors, meaning DVI/VGA/HDMI ports can be created off of a MST hub by using the appropriate active adaptor. At the end of the day the MST hub is how AMD and other manufacturers are going to drive multiple displays from devices that don’t have the space for multiple outputs.

For Barts AMD is keeping parity with Cypress’s display controller, giving Barts the ability to drive up to 6 monitors. Unlike Cypress however, the existence of MST hubs mean that AMD doesn’t need to dedicate all the space on a card’s bracket to mini-DP outputs, instead AMD is using 2 mini-DP ports to drive 6 monitors in a 3+3 configuration. This in turn means the Eyefinity6 line as we know it is rendered redundant, as AMD & partners no longer need to produce separate E6 cards now that every Barts card can drive 6 DP monitors. Thus as far as AMD’s Eyefinity initiative is concerned it just became a lot more practical to do a 6 monitor Eyefinity setup on a single card, performance notwithstanding.

For the moment the catch is that AMD is the first company to market with a product supporting DP1.2, putting the company in a chicken & egg position with AMD serving as the chicken. MST hubs and DP1.2 displays aren’t expected to be available until early 2011 (hint: look for them at CES) which means it’s going to be a bit longer before the rest of the hardware ecosystem catches up to what AMD can do with Barts.

Besides MST, DP1.2’s bandwidth has three other uses for AMD: higher resolutions/bitdepths, bitstreaming audio, and 3D stereoscopy. As DP1.1’s video bandwidth was only comparable to DL-DVI, the monitor limits were similar: 2560x2048@60Hz with 24bit color. With double the bandwidth for DP1.2, AMD can now drive larger and/or higher bitdepth monitors over DP; 4096x2160@50Hz for the largest monitors, and a number of lower resolutions with 30bit color. When talking to AMD Senior Fellow and company DisplayPort guru David Glen, higher color depths in particular came up a number of times. Although David isn’t necessarily speaking for AMD here, it’s his belief that we’re going to see color depths become important in the consumer space over the next several years as companies look to add new features and functionality to their monitors. And it’s DisplayPort that he wants to use to deliver that functionality.

Along with higher color depths at higher resolutions, DP1.2 also improves on the quality of the audio passed along by DP. DP1.1 was capable of passing along multichannel LPCM audio, but it only had 6.144Mbps available for audio, which ruled out multichannel audio at high bitrates (e.g. 8 channel LPCM 192Khz/24bit) or even compressed lossless audio. With DP1.2 the audio channel has been increased to 48Mbps, giving DP enough bandwidth for unrestricted LPCM along with support for Dolby and DTS lossless audio formats. This brings it up to par with HDMI, which has been able to support these features since 1.3.

Finally, much like how DP1.2 goes hand-in-hand with AMD’s Eyefinity initiative, it also goes hand-in-hand with the company’s new 3D stereoscopy initiative, HD3D. We’ll cover HD3D in depth later, but for now we’ll touch on how it relates to DP1.2. With DP1.2’s additional bandwidth it now has more bandwidth than either HDMI1.4a or DL-DVI, which AMD believes is crucial to enabling better 3D experiences. Case in point, for 3D HDMI 1.4a maxes out at 1080p24 (48Hz total), which is enough for a full resolution movie in 3D but isn’t enough for live action video or 3D gaming, both of which require 120Hz in order to achieve 60Hz in each eye. DP1.2 on the other hand could drive 2560x1600 @ 120Hz, giving 60Hz to each eye at resolutions above full HD.

Ultimately this blurs the line between HDMI and DisplayPort and whether they’re complimentary or competitive interfaces, but you can see where this is going. The most immediate benefit would be that this would make it possible to play Blu-Ray 3D in a window, as it currently has to be played in full screen mode when using HDMI 1.4a in order to make use of 1080p24.

In the meantime however the biggest holdup is still going to be adoption. Support for DisplayPort is steadily improving with most Dell and HP monitors now supporting DisplayPort, but a number of other parties still do not support it, particular among the cheap TN monitors that crowd the market these days. AMD’s DisplayPort ambitions are still reliant on more display manufacturers including DP support on all of their monitors, and retailers like Newegg and Best Buy making it easier to find and identify monitors with DP support. CES 2011 should give us a good indication on how much support there is for DP on the display side of things, as display manufacturers will be showing off their latest wares.

Barts: The Next Evolution of Cypress Seeing the Present: HDMI 1.4a, UVD3, and Display Correction


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  • 529th - Saturday, October 23, 2010 - link

    the marketers wanted to differentiate themselves from Nvidia, that's why they are using their second place cards to be in the same category as nvidias second place cards

    If you are shopping for a top of the line card you should know atleast a little bit about them although the un-educated video-card shopper would think that a 470 and 5870 or 6870 is on the SAME performance level, WHICH ISN'T TOO FAR FROM THE TRUTH, but I think it's here where AMD marketers are trying to make a statement

    i could be wrong, i have had very little sleep last night, cedar point was a blast!
  • SininStyle - Saturday, October 23, 2010 - link

    Can I just say THANK YOU for adding a OC edition of the 460. Don't know why everyone is whining. If you don't want to know how an OC edition compares then ignore the stupid bench for it. Why is such a huge deal?
    I personally am glad they included it and this is why. The 460 1gb stock is 675mhz and can OC "reliably" to 850mhz.. That's 175mhz gain and its noticeable. Stock volt stock fan. And for those that wanna claim heat, mine shows 64c at 75% fan on OCCT. The 6870 get 50hz OC at stock volt/fan. SEE why this is important people? $180 vs $240 with same results.

    Now with volt changes I'm sure they both have room to go I'm not sure how much. I tend to shy away from higher voltages at least for now.

    The 6850 is the better buy between the 2 68xx cards. That has allot of headroom to OC. That would even be a better comparison to the 460 due to the price. And owning the 460 doesn't make me a fanboy and I will say you can flip a coin for value on these 2.

    So again thanks for the added information. Cant see why anyone would complain about more info. If you don't like the info ignore it if it makes you feel better. Feel free to add OCed 6850s and 6870s I look forward to the comparison.
  • Parhel - Saturday, October 23, 2010 - link

    "The 460 1gb stock is 675mhz and can OC "reliably" to 850mhz"

    No, it absolutely cannot. the FTW card is a "golden sample" which is why there are so few available. Stock cooling on a stock card will not get you to 850Mhz with 24/7 reliability. You *might* get to 800Mhz, probably a bit less. That's a great value, IMO. If I were in the market at the moment, I'd pick a base model GTX 460 and OC it. Not arguing that point at all. But presenting this card in the 6870 launch article is a sham and major black eye to Anandtech's credibility.
  • rom0n - Saturday, October 23, 2010 - link

    Is it possible to post the GPUZ of the HD6850. It seems there are numerous cases where HD6850 has 1120 sent out to reviewers. See If this happens to be one of them the results may be a little misleading. If not then it'll reaffirm the results.
  • GullLars - Saturday, October 23, 2010 - link

    This means a 6870 with open-air fan optimized for noise will be my early winter solstice present for myself, togheter with the 4x C300 64GB i just got :D
    I went for a value-upgrade of my old rigg with P2x6 1090T, 8GB kingston value DDR3, and AM3 mobo with SB850, so once i get both the SSD in RAID-0 and the GPU, I'll be a happy camper (or rusher) <3
    It'll tide me over untill i can get Bulldozer or a next gen Intel (high end/workstation) around winter 2011/2012.
  • poohbear - Saturday, October 23, 2010 - link

    "Apparently a small number of the AMD Radeon HD 6850 press samples shipped from AIB partners have a higher-than-expected number of stream processors enabled.

    This is because some AIBs used early engineering ASICs intended for board validation on their press samples. The use of these ASICs results in the incorrect number of stream processors. If you have an HD 6850 board sample from an AIB, please test using a utility such as GPU-z to determine the number of active stream processors. If that number is greater than 960, please contact us and we will work to have your board replaced with a production-level sample.

    All boards available in the market, as well as AMD-supplied media samples, have production-level GPUs with the correct 960 stream processors."

    so which one did Anandtech get? false marketing is such BS, just wanna be sure your benchmarks for the 6850 are reliable and we're not getting overrated benchmarks due to a cherry picked review sample.
  • lakrids - Saturday, October 23, 2010 - link

    The review ended up looking like an advertisement for EVGA at page 7 and beyond. Why EVGA? Why not some other brand?
    Why include that brand at all? Just mark the card "GTX 460 OC'd 850MHz".

    At the very first benchmark: Crysis 2560x1600, you didn't include the reference GTX 460, you pitched the HD6870 against the EVGA overclocked version. EVGA here, EVGA there, EVGA everywhere.

    Would you blame me if I suspect you of being on EVGA's paycheck?
  • Lolimaster - Sunday, October 24, 2010 - link

    When I call you a Intel/Nvidia biased site I'm saying the truth. Are you reviewing the HD6000 or doins an EVGA product reviews.

    This is an insult.

    Nvidia will disappear like the dodo, just a bit more time and at that time all this sh1t will end.
  • SininStyle - Sunday, October 24, 2010 - link

    You do understand if Nvidia vanishes the price of GPUs goes through the roof right? Nvidia isnt going to vanish any earlier then Radeon. Saying either just translates into "Im a fanboy"

    Stop defending a sticker and start shopping price performance. Neither company would hesitate to rape your wallet if the other would allow it. Case in point look at the price of the 57xx and 58xx 2 months ago. Then look at the price of the same cards including the 68xx cards now. Any of these cards perform less then they did 2 months ago? But the price is a whole lot cheaper isnt it? Well you can thank the 460 for that. Competition results in better pricing for the same performance. You should be thanking Nvidia not hating them.
  • Super_Herb - Sunday, October 24, 2010 - link

    I love it - "as a matter of policy we do not include overclocked cards on general reviews"..........but this time nVidia said pretty please so we did. But because our strict ethical policy doesn't allow us to include them we'll just tell you we did it this one special time because a manufacturer specifically sent us a special card and then our integrity is still 100% intact......right? Besides, the "special" card nVidia sent us was so shiny and pretty!

    Back to [H]ard to get the real story.

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