DisplayPort 2.0 will be Great for 8K, But When is it Coming?
The DisplayPort 2.0 spec increases the video data rates up to 20 Gbps times four lanes, which is fast enough for up to 8K/120p, 16-bit, 4:4:4 transfers. Video transport can be implemented natively in DP connectors or using an Alt Mode in USB-C or Thunderbolt connectors. The spec was issued over 2 years ago and so far, only MacBooks have offered a USB-C connector supporting DP 2.0 per the carriage mandate in the USB-4 specification. So, what’s the holdup?
According to Craig Wiley, a VESA Rep driving DP 2.0 as a technical contributor from Parade Technologies, the plan was to launch products with DP 2.0 functionality in the market by the end of 2020. COVID-19 got in the way, however. This limited the time in the lab needed by engineers to develop products. And just as importantly, it slowed VESA efforts in the development of testing protocols and validation compliance testing. “We finally had our first correlation testing in Portland, Oregon last July and we are hoping to organize a plugfest for this fall,” said Wiley. “The Delta variant may put an end to that plan, however.”
Such plug fests typically bring together the chip makers, monitor or docking station makers as well as PC makers to do interoperability testing and debugging.
Nevertheless, Wiley says that companies continue to build products and the first products are now expected in 2022.
DisplayPort and Thunderbolt were dominant connectors in the PC market, but HDMI is now on almost all devices as well. Meanwhile, USB-C has quietly gobbled up the functionality of other connectors that used to be dedicated for audio, printing, keyboards and mice, including video. In fact, for some system formats USB-C is becoming the connector that replaces everything.
The evolution of DisplayPort, Thunderbolt and USB is a tangled and complicated story. Fortunately, the USB-C connector seems to be emerging as the preferred hardware interface that can allow many types of protocols to run and operate over it.
USB-4 is a beast as it enables high-speed video, fast file transfer via PCI-Express and USB protocols, power charging and connection of many peripherals. USB-4 essentially adds a networking capability to route audio and video to various devices using IP addressing. In USB-4, the bandwidth can also be allocated between video devices and data devices offering lots of flexibility – something previous USB versions did not offer. Since this bandwidth can be dynamically adjusted, it will prioritize video over data, especially if connected to a 4K or 8K monitor.
DP 1.4 supports HBR3 data rates at 8.1 Gbps per lane with four lanes. Encoding using an 8-bit/10-bit scheme means a 25% overhead so only about 25.9 Gbps is available for video. That means support for
- 8K/30p 8-bit 4:2:0
- 8K/30p 8-bit 4:4:4
- 8K/24p 16-bit 4:2:2
DP 1.4 also includes Display Stream Compression (DSC) to increase the effective data rate by three times thus enabling all the way up to 8K/90p 16-bit 4:4:4. DP 2.0 triples the capacity thus dropping the need for DSC for 8K, but with DSC, you can now transfer 16K video. The DP 2.0 standard also implements 128-bit/132-bit encoding to significantly reduce overhead allowing for a full 77 Gbps video payload capability if all 4 lanes are used.
Video timing and supported configurations for Display Port versions are shown below.
DP 2.0 also supports multi-stream which means multiple monitor support, so potentially two 8K monitors via a docking station or daisy chain configuration from a single USB-C connector on a PC.
Multi-stream can also support VR in unique ways by allowing full resolution left and right eye images and/or foveated and background images transmitted at full resolution.
But if your monitor or docking station does not have a USB-C connector and only has HDMI, not to worry. DP 2.0 can convert the video from DP 2.0 format to HDMI 2.1. In fact, Parade just started sampling silicon that does exactly that. The Parade PS195 and PS196 chips are said to be fully compliant with the VESA DP2.0 and HDMI 2.1 specifications and are aimed at makers of motherboards, docking stations, and video dongles.
While the device supports DP 2.0 specifications, it does not support the highest 20 Gbps link rate. Instead, it caps out at 8.1 Gbps over each of the 4 lanes. It is backward compatible with older HDMI versions so supports both TMDS and FRL signaling. Parade’s chip takes advantage of the DP 2.0 “DSC pass-through” function, which enables the use of DSC to deliver 8K video at 60 frames per second using full 4:4:4 color resolution, which is important for crisp computer monitor graphics.
If your monitor has a native DP input, then a USB-C to DP conversion cable can be used, which mostly just provides the plug format conversion since USB-C carries the native DP signal in the DP Alt Mode format.
Historically, DisplayPort has led in terms of speed and features compared to HDMI. But HDMI 2.1 is now more closely aligned with DisplayPort although DP 2.0 will have more speed and has multi-stream support. But the use of DisplayPort over USB-C opens up its use beyond the monitor and gaming segments to phones and tablets as well.
Can DisplayPort, perhaps in USB-4 clothing, make any headway in the TV market? According to Wiley, the DP to HDMI protocol conversion support in DP 2.0 allows support for the CEC back channel which is very useful for allowing a remote to control connected devices like Blu-ray players. “So far I am not aware of much utilization of this so I would say this is more of a lack of implementation vs. capability.”
But a lot of confusion will continue around DisplayPort, Thunderbolt, HDMI, and USB. HDMI, USB, and DP all allow implementors to add functionality al-a-carte meaning it will be difficult to know exactly what the source and sink devices actually support. And we suspect manufacturers are not going to be very forthcoming with this information. Plus, cables will need to be matched to capabilities as well. Look for a new Certified cable standard for DP 2.0.
DP 2.0, especially when used with USB-4, looks like a really great solution for the increasing bandwidths and complexities of desktops. We just need to start seeing more products in the market.