System Design and Verification Blogs

Verification of a USB4 router design is not just about USB4 but also about the inclusion of the three other major protocols namely, USB3, DisplayPort (DP), and PCI Express (PCIe). These protocols can be simultaneously tunneled through a USB4 router. Put in simple terms, such tunneling involves the conversion of the respective native USB3, DP, or PCIe protocol traffic into the USB4 transport layer packets, which are tunneled through a USB4 fabric, and converted back into the respective original native protocol traffic.

It may sound simple but is perhaps not.

There are several aspects in a router that come into picture to carry out this task of conversion of native protocol traffic, route it to the intended destination, and then convert it back to the original form. Some of those are the USB3, DP and PCIe protocol adapters, transport mechanism using routing, flow control, paths, path set-up and teardown, control and configuration, configuration spaces.

That is not all. There are core USB4 specific logical layer intricacies as well, which carry out the tasks of ensuring that all the USB4 ports and links are working as desired to provide up to 40Gbps speed and that the USB4 traffic flows through out the fabric in the intended way. These bring on the table features like High Speed link, ordered sets, lane initialization, lane adapter state machine, low power, lane bonding, RS-FEC, side band channel, sleep and wake, error checking.

All of these put together give rise to a very large verification space against which a USB4 router design should be verified. If we were to break down this space it can be broadly put in the following major dimensions,

• Protocol Adapter Layer
  • USB3 tunneling
  • DP tunneling
  • PCIe tunneling
• Host Interface Adapter Layer
• Transport Layer
  • Flow control
  • Routing
  • Paths
• Configuration layer and control packet protocol
• Configuration spaces
• Logical Layer

The independent verification of these dimensions is not all that would qualify the design as verified. They have to be verified in various combinations of each other too. Overall, all the parts of a USB4 router system need to be working together coherently.

For example, the following diagram depicts the various layers that a USB4 router may comprise of,

A USB4 router or a domain of routers does not work on its own. There is a Connection Manager per domain, which is a software-based entity managing a domain. A router provides the various capabilities for a Connection Manager to carry out its responsibilities of managing a domain.

It would not be an exaggeration to say that the spectrum of verification of a USB4 router ranges from the very minute details of logical layer to the system-level like multiple dependencies as the whole USB4 system is brought up layer by layer, step-by-step.

Cadence has a mature Verification IP solution that can help in the verification of USB4 designs. Cadence has taken an active part in the working group that defined the USB4 specification and has created a comprehensive Verification IP that is being used by multiple members in the last two years.

If you plan to have a USB4 compatible design, you can reduce the risk of adopting a new technology by using our proven and mature USB4 Verification IP. Please contact your Cadence local account team for more details and to get connected.