1. A method of processing a dataflow description of a digital processing system implemented using an integrated circuit (IC), comprising: simulating, by a simulator executed on a computer, a model of the digital processing system as specified by the dataflow description given a set of inputs; identifying computational steps performed during the simulation; and generating causation trace data based on the computational steps, the causation trace data including at least one causation trace each of which is a record of dependencies among the computational steps for the set of inputs; wherein the dataflow description includes a network of actors, wherein at least one of the actors includes an interface having one or more ports, at least one of the actors includes state variables, at least one of the actors includes a state machine, and at least one of the actors includes one or more actions, each of the one or more actions configured to be fired to perform a function; wherein each port is an input port or an output port, and for communication from a first actor to a second actor in the network, the first actor outputs a token on an output port of the first actor and the second actor inputs the token on an input port of the second actor; wherein each of the computational steps comprises a firing of an action in the dataflow description; wherein at least one of the dependencies includes a dependency between a pair of actions in an actor of the network accessing a common state variable, at least one of the dependencies includes a dependency between a pair of actions in an actor of the network related by a state machine in the actor, at least one of the dependencies includes a dependency between a pair of actions in an actor of the network accessing a common port of the actor, and at least one of the dependencies includes a dependency between a pair of actions in the dataflow description related by a common token.