Goossens defined a structural operational semantics for a subset of VHDL-87 and proved that the parallelism present in VHDL is benign. We extend this work to include VHDL-93 features such as shared variables and postponed processes that change the underlying semantic model. In the presence of shared variables, nondeterministic execution of VHDL-93 processes destroys the unique meaning property. We identify and characterize a class of portable VHDL-93 descriptions for which unique meaning property can be salvaged. Our specification can serve as a correctness criteria for a VHDL-93 simulator.
& Ewing, R.
(1997). Characterizing a Portable Subset of Behavioral VHDL-93. Hardware Description Languages and Their Applications, 3, 97-113.