Open Core Protocol (OCP) Clock Domain Crossing Interfaces

The open core protocol (OCP) is an openly licensed configurable and scalable interface protocol for on-chip subsystem communications. The protocol defines read and write transactions from a master towards a slave across a point-to-point connection and the protocol assumes a single common clock. This paper presents the design of two OCP clock domain crossing interface modules that can be used to construct systems with multiple clock domains.

An OCP interface typically has control signals related to both the master issuing a read or write request and the slave producing a response. If all these control signals are passed across the clock-domain boundary and synchronized it may add significant latency to the duration of a transaction. Our interface designs avoid this and synchronize only a single signal transition in each direction during a read or a write transaction.

While the problem of synchronizing a simple streaming interface is well described in the literature and often solved using bi-synchronous FIFOs we found surprisingly little published material addressing synchronization of bus-style read-write transaction interfaces.