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


View All Comments

  • campbbri - Friday, October 22, 2010 - link

    Thanks for the great review. I don't know why everyone is complaining about mixing OC and Non-OC cards when you were extremely explicit in pointing it out. Reply
  • krumme - Friday, October 22, 2010 - link

    I dont think you dont know why everyone is complaining.

    First. To be fair its far from everyone :), unfortunately because Anand is surrounded by far to many yes sayers. All positve. Great in many ways. But it does not develop the site as it could. There is a great huge community, and there is plenty of ressources to get ideas to new methology.

    Its good - if not vital - that Kyle is explicit about it. Otherwise it wouldnt be worth critizicing, then it would just look like a payed job, and nobody would care. Its not. But beeing explicit is not enough even if its most important and a huge quality. You need to have a good case. And Anand does have a very bad case.

    Read what Kyle wrote againg. Do you think this is his best and most sound decicion in his life? do he feel comfortable about it?

    He did betray himself a little bit. And he shouldnt do it. He should lissen to his own doubt.
  • snarfbot - Friday, October 22, 2010 - link

    yes i understand that, but i cant see how you can call a direct replacement that fails to outperform its predecessor as a success.

    especially when you consider that the prices have increased after launch as opposed to decrease as is normal. and have remained artificially high since, due to limitations at tsmc, which renders the cost argument pretty much moot.

    how about an analogy.

    6870 is to 5870 as 4770 is to 4870.

    and its on the same process which makes it even worse, although you cant really blame amd for that.

    you can very much blame their marketing department for making such a terrible decision though.

    its a terrible name, thats the whole point, at whatever price you cant call it a 6870 if it cant beat a 5870.
  • Trefugl - Friday, October 22, 2010 - link

    yes i understand that, but i cant see how you can call a direct replacement that fails to outperform its predecessor as a success.

    But the issue is that the 68xx series alone aren't really replacing the 58xx series. I think they are really splitting what the direct replacement to that market would have been into two - the 69xx (high-end enthusiast) and the 68xx (high-end mid-range).

    I agree that the naming scheme isn't the best, but I think a lot of that could have been mitigated (and maybe even made a non-issue) if the 68xx's weren't the first to launch. If the 69xx came out first people would have accepted them and been happy, but instead we have b*tching because of naming confusion...
  • Targon - Sunday, October 24, 2010 - link

    I missed this too until someone pointed out what I missed. The Radeon 6900 series will replace the 5800 series at the high end, and IS the proper high end part you are looking for.

    Back when DirectX 9 first came out, ATI only had DirectX 9 support in the old Radeon 9500 and 9700. When the X300, X600, and X800 came out, notice that AMD took the cards and started at 600 and 800, rather than 500 and 700 for the mid ranged and high end cards. This has continued a bit. In the HD 2000 series, you even had the HD 2900XT on the high end of the series, but then they went to the 3800, 4800, and 5800 series to mark the high end cards.

    So, AMD/ATI has been tweaking the names a fair bit. What initially threw me off is that the next generation high end cards are not the first cards to show up, and we have the mid-ranged cards showing up first.

    If the article said clearly, "We are reviewing the next generation mid range cards with the high generation 6900 due out next month" right up front in the article instead of buried in the text somewhere on page 2(or was it 3), there would have been less confusion.

    I don't mind the change in numbers if all parts come out at the same time, but for now, there is ONLY confusion because we have yet to see the 6970.
  • GaMEChld - Friday, October 14, 2011 - link

    I love how people are arguing over this naming change. As if people who buy discrete cards or look at video card specs don't know what their doing. If you don't know what you're buying, it serves you right.

    I don't know why this was so hard for people to understand. The 5700 was incredibly successful. AMD wanted to preserve that card for its performance and value. Thus, the 6700 name was taken. The 6800 model is a new model that sits BETWEEN where the 5700 and 5800 line had. If you recall, there was a MASSIVE performance gap between those lines, and AMD felt they should have something to bridge that gap.

    The new 6800 line bridges that gap. It offers NEAR 5800 power at a significant price reduction.

    And now ALL of the top tier cards are housed under the 6900 bracket, with the 6990 taking the dual GPU slot. If I had anything to complain about its the abandonment of the X2 designation on dual GPU cards.

    In fact, the only thing people should be angry about is the fact that the 6700 is virtually identical to the 5700 and offers little performance advantage. THAT is what is reminiscent of the 8800GT -> 9800GT transition. However, since the 5700 was a midrange product, maybe it received less attention than it should have.
  • DanaG - Friday, October 22, 2010 - link

    Now, if the 6870 is what should've been a 6770, and a 6970 is what should've been a 6870... then what'll they call what should've been a 6970? 6-10-70 / 6ten70? 6X70? 6999? Or will they go to 6970 X2? Reply
  • spigzone - Saturday, October 23, 2010 - link

    6990 ... yhat wasn't so hard now, was it? Reply
  • AMD_Pitbull - Saturday, October 23, 2010 - link

    Gotta say, I agree 100%. I really don't understand why everyone is getting so bloody upset with this. New product, new line. You couldn't predict what was going to happen? Sorry. Companies like to keep people guessing.

    Also, if you really want to get technical, this 6870 DOES beat the 5870 if a few things as well. Overall greater effective product AND cheaper? Win in my books. Sorry QQ'ers.
  • dvijaydev46 - Saturday, October 23, 2010 - link

    I tried converting a video file using my 5770 Hawk with MediaEspresso 6 (with hardware acceleration enabled of course), I wasn't impressed but Mediashow 5 properly utilized the GPU power and the speed difference in converting was clear. I'm not sure if there was a problem in the installation of my copy of MediaEspresso 6, but I think you guys can use Mediashow 5 to see if there is any difference in video conversion time with an AMD GPU as I don't have any other card. Reply

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