USB4 v2 enables an asymmetric 3 Tx + 1 Rx configuration

by ddos · September 5, 2022

Recently, the USB Promoter Group announced the upcoming release of the USB4 2.0 specification. Data transfer rates of up to 80 Gbps (10GB/s) can be achieved over USB Type-C cables, and the USB Type-C and USB Power Delivery (USB PD) specifications will also be updated.

According to Angstronomics, the USB Type-C connector was standardized in 2014. In the normal data configuration, it will be configured in a symmetric mode of 2Tx+2Rx. For the new USB4 2.0 specification, the bandwidth of a single channel is 40 Gbps, making the bidirectional bandwidth reach 80 Gbps. However, USB4 2.0 also supports the asymmetric mode of 3Tx+1Rx, which means that the host can output 120 Gbps, and the return from the device to the host is 40 Gbps. This asymmetric mode can carry out complete tunneling protocol transmission, that is, UHBR20, the highest specification of DisplayPort 2.0.

Asymmetric mode isn’t much of a problem for USB Type-C cables, as DisplayPort Alt Mode is already taking advantage of this. The USB4 2.0 specification will move from the current 64b/66b encoding or 128b/132b encoding to the PAM3 encoding, and it is rumored that the next generation of Thunderbolt will do the same. Last year, Gregory Bryant, executive vice president, and general manager of Intel’s client computing group, accidentally posted a photo by mistake, exposing the technical specifications of a new generation of Thunderbolt, which also reaches a speed of 80 Gbps.

It is understood that Intel has long been preparing for the USB4 2.0 specification, and is likely to support USB4 2.0 when Meteor Lake is launched. AMD needs to wait for industry partners to develop ready-made design libraries to integrate into processors, which is expected to be between 1 and 2 years behind Intel, while Apple’s USB4 2.0 support should be between Intel and AMD.

USB4 v2 enables an asymmetric 3 Tx + 1 Rx configuration

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