Functional units with conditional input/output behavior in VLIW processors

Summary form only given. In this paper we extend the method to deal with coarse-grain operations in static scheduled VLIW processors as is introduced by Busa (2000). We allow functional units with a controller that does not traverse its states in a predefined way. This makes it possible to execute a function that contains a conditional construct like an if-statement as a single operation on a functional unit. In this way the performance penalty otherwise caused by branch instructions is reduced. By adding valid input and output signals, the problem is circumvented that during compilation it is, for this type of functional unit, not known when and how many samples will be consumed or produced. We refer to these units as Conditional Input/output Units (CIUs). The operations that are executed on CIUs are called Conditional Input/output Operations (CIOs). The difference with guarded operations is that the production of a result of a CIO depends on the state of the CIU.