Monsoon: an explicit token-store architecture

Dataflow architectures tolerate long unpredictable communication delays and support generation and coordination of parallel activities directly in hardware, rather than assuming that program mapping will cause these issues to disappear. However, the proposed mechanisms are complex and introduce new mapping complications. This paper presents a greatly simplified approach to dataflow execution, called the explicit token store (ETS) architecture, and its current realization in Monsoon. The essence of dynamic dataflow execution is captured by a simple transition on state bits associated with storage local to a processor. Low-level storage management is performed by the compiler in assigning nodes to slots in an activation frame, rather than dynamically in hardware. The processor is simple, highly pipelined, and quite general. It may be viewed as a generalization of a fairly primitive von Neumann architecture. Although the addressing capability is restrictive, there is exactly one instruction executed for each action on the dataflow graph. Thus, the machine oriented ETS model provides new understanding of the merits and the real cost of direct execution of dataflow graphs.