The DisplayPort 2.1 specifications were officially released by VESA on Monday, and this was followed yesterday by USB-IF’s announcement to release the 80 Gbps USB4 v2 specifications. These have highlighted the significant technical effort that has gone into creating a unified protocol capable of handling the external I/O bandwidth demands of tomorrow’s computing systems. Today, Intel announces early prototype demonstrations for next-generation Thunderbolt based on the USB4 v2 and DisplayPort 2.1 specifications.
Intel’s donation of the Thunderbolt 3 specifications to the USB promoter group to form the basis of USB4 has had its share of pros and cons. On the one hand, the convergence of the Type-C connector ecosystem has theoretically achieved the goal of minimizing end-user confusion, and the royalty-free specification for PCIe tunneling has opened the market to other silicon vendors such as ASMedia. However, it also fueled consumer fears, as most of USB4’s attractive features (like its 40Gbps bandwidth and compatibility with PCIe tunneling) were entirely optional features. However, Intel made it possible for Intel to market Thunderbolt ports as a Type-C that can do anything. Intel’s demonstration of next-gen Thunderbolt also included a sneak peek at the specs, though certain aspects aren’t finalized. Before delving deeper into Intel’s press release, a quick recap of the announcement of the 80Gbps USB4 v2 specifications is required.
USB4 v2 updates
USB4 v2 builds on the multi-protocol tunneling architecture introduced in USB4 by doubling the available bandwidth while maintaining the same port/pin layout and cable structure. This was achieved by moving the physical layer signal encoding to PAM3 (detailed in our 80 Gbps “Thunderbolt 5” coverage last year). This means that existing 40Gbps USB4 cables can also support 80Gbps operation.
The USB4 v2 specifications now allow tunneling of DisplayPort 2.1 signals and up to four PCIe 4.0 lanes. The data and display log updates also make it more efficient as USB data tunneling can exceed 20Gbps.
One of the key updates in the move to support DisplayPort 2.1 tunneling relates to the maximum total bandwidth for four lanes in UHBR 20 transmission mode. This equates to 80 Gbps, leaving essentially nothing on the transmit side for other protocols. To handle this, USB4 v2 introduces the concept of asymmetric links. In general, a USB4 connection uses two connected high-speed differential signaling pairs to transmit and receive data, enabling 40 Gbps duplex operation (40 Gbps transmit and 40 Gbps receive) in the symmetric case. However, the track initialization process can optionally configure the link to have 3 transmitters and one receiver on one side and 3 receivers and one transmitter on the other side. In combination with the higher data rates thanks to PAM3, this allows the host to send 120 Gbit/s while the receive bandwidth is reduced to 40 Gbit/s. High-resolution displays can be reliably driven without sacrificing too much bandwidth available on the transmit side for other purposes (like high-speed storage).
The power supply specifications have also been updated to match the updates made in USB4 v2, and new logo guidelines for consumer-facing devices have been issued.
Thunderbolt has seen incredible momentum over the past few years – driven primarily by the integration of Thunderbolt controllers into the high-volume notebook processors, starting with Ice Lake. The combination of data, video and power in one port/cable makes it beneficial for a variety of use cases. In particular, the increasing popularity of hybrid work/hot-desking (monitors/networks, etc. behind a dock so multiple employees can easily plug in their Thunderbolt-equipped systems at different times) has also given impetus to Thunderbolt adoption in the future business/ office space. Gamers and content creators have an incredible thirst for I/O bandwidth, which Thunderbolt serves well.
As already mentioned, Next Generation Thunderbolt takes the USB4 v2 specifications as a basis and makes all attractive optional features mandatory. Additionally, Intel’s integration of Thunderbolt into notebook processors ensures that the host-side implementation is energy efficient. Making Thunderbolt mandatory for Intel Evo and vPro notebooks further solidifies Intel’s leadership in the USB4 v2 space.
The dynamic bandwidth balancing feature, which allows tunneling of the highest bandwidth DisplayPort 2.1 streams while still allowing the use of high-bandwidth peripherals, is one of the most exciting features of USB4 v2 that is sure to come in systems powered by Thunderbolt equipped with next-generation connections.
Intel’s demonstration included both host and device implementations, with the host configuration shown at the beginning. A discrete GPU’s DisplayPort output feeds into the host controller board, and two Type-C cables branch out, one ostensibly to the display and the other to a dock (device) with an attached SSD.
Aspects such as power delivery limits (Thunderbolt 3/4 support up to 15W by default) for the next-generation Thunderbolt ports will be clarified in the near future. Intel did not provide any information on market availability.
Based on a look at the USB4 v2 specs and Intel’s description of Next-Generation Thunderbolt, it’s clear that Thunderbolt ports will continue to be the Type-C port that can do it all.
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