Parallel and distributed VHDL simulation

This paper presents a methodology for parallel and distributed simulation of VHDL using the PDES (parallel discrete-event simulation) paradigm. To achieve better features and performance, some PDES protocols assume that simultaneous events may be processed in arbitrary order. We describe a solution of how to apply these algorithms to have a correct simulation of the distributed VHDL cycle, including the delta cycle. The solution is based on tie-breaking the simultaneous events using Lamport's logical clocks to causally order them according to the VHDL simulation cycle, and defining the VHDL virtual time as a pair of simulation physical time and cycle/phase logical time. The paper also shows how to use this method with a PDES protocol that relaxes the simulation of simultaneous events to arbitrary order; allowing the LPs to self-adapt to optimistic or conservative mode, without the lookahead requirement. The lookahead is application-dependent and for some systems may be zero or unknown. The parallel simulation of VHDL designs ranging from 5531 to 14704 LPs using these methods obtained a promising, almost linear speedup.