VirtualLink

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VirtualLink was a proposed USB-C alternate mode that allowed the power, video, and data required to power virtual reality headsets to be delivered over a single USB-C cable and connector instead of set of three different cables as it was in older headsets.[1][2] The standard was supported by Nvidia, AMD, HTC Vive, Oculus VR, Valve, and Microsoft.[3] The VirtualLink Consortium is chaired by Rambod Jacoby representing NVIDIA.

In VirtualLink mode there are six high-speed lanes active in the USB-C connector and cable: four lanes transmit four DisplayPort HBR 3 video streams from the PC to the headset while two lanes implement a bidirectional USB 3.1 Gen 2 channel between the PC and the headset. Unlike the classic DisplayPort USB-C alternate mode, VirtualLink has no USB 2.0 channels active, instead providing a higher speed USB 3.1 Gen 2 (SuperSpeed+) over the same A6, A7, B7, B6 pins. VirtualLink also requires the PC to provide 15 to 27 watts of power.[3][4] No information pertaining to VirtualLink alternate mode compatibility with USB4 (and so Thunderbolt 3 alternate mode) has been published, as of April 2019.

To achieve six high-speed lanes over USB-C, VirtualLink requires special cables that conform to version 1.3 of the USB-C standard and uses shielded differential pairs for both USB 2.0 pairs.[3][5]

The available bandwidth is estimated to be equivalent to DisplayPort 1.4 (32.4 Gbit/s, up to 4K @ 120 Hz with 8 bpc color) for video and 10 Gbit/s of USB 3.1 Gen 2 data.[3]

Nvidia GeForce 20 series cards, initially released in 2018, implement a single VirtualLink port in all RTX Founders Edition (FE) cards (2060, 2070, 2080, 2080 Ti).[6] This port is also available on Quadro RTX cards.[7]

As of August 2020, the VirtualLink standard failed to propagate into the virtual reality headset market. The Valve Index had initially developed a VirtualLink accessory, but it was canceled due to technical signaling and reliability issues.[8]

As of the Nvidia GeForce 30 Series cards announcement, the VirtualLink Port has been all but officially killed off. All three of Nvidia's new Founders Edition GPUs, alongside the partner boards announced so far, lack a VirtualLink Port.[9]

VirtualLink cable[edit]

The virtuallink cable consists of

  • DisplayPort:
    • 4x DisplayPort balanced pair data path
    • DisplayPort HPD (hot-plug detection pin) as a single wire.
    • DisplayPort AUX signal as a balanced pair
  • USB 3.1 signals
    • A USB TX balanced pair for USB 3.0 data
    • A USB RX balanced pair for USB 3.0 data
  • I2C wire to control the USB Billboard interface, in case the cable is plugged into an unsupported interface.
  • VBUS carrying power to HMD visor
  • GND ground

The USB-C plugs pinout is (According to section 6.1. of VirtualLink Advance Overview):

A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1
GND DP[0]+ DP[0]− VBUS CC1 USBTX+ USBTX− DP[AUX]+ VBUS DP[3]− DP[3]+ GND
GND DP[1]+ DP[1]− VBUS DP[AUX]− USBRX− USBRX+ VCONN VBUS DP[4]− DP[4]+ GND
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12

Unlike most alt-mode; this will also remap A7, A6, B6, B7 to carry USB 3.0 signal, instead of the usual passive USB 2.0 signal. This means that one will not be able to extend the cable using a standard USB-C 3.0 cable, which has these pins mapped only for unshielded USB 2.0 signals. Also this will require the VirtualLink port to also detect the correct orientation of the USB-C plug to ensure that the USB 3.0 TX and RX lanes are correctly connected.

References[edit]

  1. ^ "The next generation of VR headsets will connect over a single USB-C cable". The Verge.
  2. ^ "VirtualLink: Everything USB Type-C Is Supposed To Be". Forbes. 2018-08-17.
  3. ^ a b c d Smith, Ryan (July 17, 2018). "VirtualLink USB-C Alt Mode Announced: Standardized Connector for VR Headsets". AnandTech. Retrieved 2018-08-21.
  4. ^ "Virtual reality giants unveil VirtualLink as a standardized cable that may simplify VR rigs". PCWorld.
  5. ^ "VirtualLink Removes Tangles from VR Goggles". EEJournal. 7 August 2018.
  6. ^ Lang, Ben (20 August 2018). "GeForce RTX Cards Announced with VirtualLink VR Connector". Road to VR.
  7. ^ "NVIDIA Unveils Quadro RTX, World's First Ray-Tracing GPU". NVIDIA.
  8. ^ "Valve Cancels VirtualLink Adapter Accessory for Index, Cites Technical Issues & Laptop Adoption". RoadtoVR.
  9. ^ Smith, Ryan. "NVIDIA Announces the GeForce RTX 30 Series: Ampere For Gaming, Starting With RTX 3080 & RTX 3090". www.anandtech.com. Retrieved 2020-09-03.

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