Verification of the Lane Adapter FSM of a USB4 Router Design Is Not Simple

By _Cadence - Cadence IP Blog

February 10, 2020

Verifying lane adapter state machine in a router design is quite an involved task and needs verification from several aspects including that for its link training functionality.

The diagram below shows two lane adapters connected to each other and each going through the link training process. Each training sub-state transition is contingent on conditions for both transmission and reception of relevant ordered sets needed for a transition. Until conditions for both are satisfied an adapter cannot transition to the next training sub-state.

As deduced from the lane adapter state machine section of USB4 specification, the reception condition for the next training sub-state transition is less strict than that of the transmission condition. For ex., for LOCK1 to LOCK2 transition, the reception condition requires only two SLOS symbols in a row being detected, while the transmission condition requires at least four complete SLOS1 ordered sets to be sent.

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