Register transfer level VHDL models without clocks

Several hardware compilers on the market convert from so-called RT level VHDL subsets to logic level descriptions. Such models still need clock signals and the notion of physical time in order to be executable. In a stage of a top-down design starting from the algorithmic level, register transfers are considered where the timing is not controlled by clock signals and where physical time is not yet relevant. We propose an executable VHDL subset for such register transfer models.