USB to NVIDIA GPU
Information about VirtualLink, which appeared last year in Anand (and in part was also duplicated on Habré ), did not allow to fully add the impression of one of the important innovations. The presentation of the ASUS Zephyrus S gaming laptop, where the VirtualLink technology has already been implemented , has recently made it possible to become more familiar with the features of the new interface.
So, VirtualLink is just another implementation of a USB bus in a Type-C construct. What is the feature? In contrast to the classic implementation, where two USB 3.x ports and one USB 2.0 ports are connected to the USB-C connector, the bus option customized by NVIDIA uses three USB 3.x ports. Alternative functionality (and if it is simpler - the ability of the system logic to conduct USB bus conductors to transmit signals that are not related to USB management, such as digital video signals) is inherent in both the classic Type-C implementation and the advanced VirtualLink solution.
')
Consider the pin assignment of the USB-C connector — the basic construct for the VirtualLink interface from NVIDIA:
The green color shows the differential pairs of two USB3 ports defined in the classic Type-C variant. The abbreviation DP (Display Port) means that in this context these lines can be used not as USB SSTx, SSRx signals, but as Display Port lines. This means that the signal multiplexers serving the port are switched for video transmission — the port is used in alternative functionality mode.
The red signals in the center of the connector show the four signals that have been the subject of customization of VirtualLink. In the classic Type-C, these are the USB2 lines of a single port, the preservation of which is working when the connector is turned over is achieved by switching.
In a customized version of the port that supports the VirtualLink interface specification, these 4 lines are used to implement another USB 3.x port . Thus, we get a total of three USB 3.x ports instead of two - six differential pairs instead of four . At the same time, we lose the USB2 port. The cable is now required to transfer signals on these lines in a bandwidth of 10 Gbps, against 480 Mbps as it was before. Older cables will not work.
Why did you need another SuperSpeed port? NVIDIA claims it for servicing a motion sensor: link to the headset for motion tracking . It is clear that such a solution has better prospects compared to the USB 2.0 legacy port, for which it is difficult to find worthy use today.
Also, the classical approach to the implementation of alternative functionality turned out to be insufficient for the needs of virtual reality. VirtualLink suggests two options for using USB 3.x green lines. We consider the variant in which both USB3 ports (all 4 differential pairs) operate in the alternate functionality mode ( four lanes of HBR3 DisplayPort ) or one port in the alternate functionality mode, and the second in USB3 port mode ( two lanes of HBR3 DisplayPort + two lanes SuperSpeed USB 3 ). In any case, the video limit mode will support an 8K display with a 60 Hz scanning frequency.
And about the main thing. The USB ports used in VirtualLink are not formed by the Intel processor, not by the system logic of the platform, but are located directly in the graphics processor. Which is quite justified in terms of using USB bus lines as an alternative for transferring video to VR devices. Do not forget that this functionality will require additional costs - the NVIDIA Turing TU104 graphics card node, capable of providing power to the connected peripherals, will consume 35 watts more. You have to pay for everything.
So, VirtualLink is just another implementation of a USB bus in a Type-C construct. What is the feature? In contrast to the classic implementation, where two USB 3.x ports and one USB 2.0 ports are connected to the USB-C connector, the bus option customized by NVIDIA uses three USB 3.x ports. Alternative functionality (and if it is simpler - the ability of the system logic to conduct USB bus conductors to transmit signals that are not related to USB management, such as digital video signals) is inherent in both the classic Type-C implementation and the advanced VirtualLink solution.
')
Consider the pin assignment of the USB-C connector — the basic construct for the VirtualLink interface from NVIDIA:
The green color shows the differential pairs of two USB3 ports defined in the classic Type-C variant. The abbreviation DP (Display Port) means that in this context these lines can be used not as USB SSTx, SSRx signals, but as Display Port lines. This means that the signal multiplexers serving the port are switched for video transmission — the port is used in alternative functionality mode.
The red signals in the center of the connector show the four signals that have been the subject of customization of VirtualLink. In the classic Type-C, these are the USB2 lines of a single port, the preservation of which is working when the connector is turned over is achieved by switching.
In a customized version of the port that supports the VirtualLink interface specification, these 4 lines are used to implement another USB 3.x port . Thus, we get a total of three USB 3.x ports instead of two - six differential pairs instead of four . At the same time, we lose the USB2 port. The cable is now required to transfer signals on these lines in a bandwidth of 10 Gbps, against 480 Mbps as it was before. Older cables will not work.
Why did you need another SuperSpeed port? NVIDIA claims it for servicing a motion sensor: link to the headset for motion tracking . It is clear that such a solution has better prospects compared to the USB 2.0 legacy port, for which it is difficult to find worthy use today.
Also, the classical approach to the implementation of alternative functionality turned out to be insufficient for the needs of virtual reality. VirtualLink suggests two options for using USB 3.x green lines. We consider the variant in which both USB3 ports (all 4 differential pairs) operate in the alternate functionality mode ( four lanes of HBR3 DisplayPort ) or one port in the alternate functionality mode, and the second in USB3 port mode ( two lanes of HBR3 DisplayPort + two lanes SuperSpeed USB 3 ). In any case, the video limit mode will support an 8K display with a 60 Hz scanning frequency.
And about the main thing. The USB ports used in VirtualLink are not formed by the Intel processor, not by the system logic of the platform, but are located directly in the graphics processor. Which is quite justified in terms of using USB bus lines as an alternative for transferring video to VR devices. Do not forget that this functionality will require additional costs - the NVIDIA Turing TU104 graphics card node, capable of providing power to the connected peripherals, will consume 35 watts more. You have to pay for everything.
Source: https://habr.com/ru/post/448452/
All Articles