engine for this stepper
externally specified clocks and their properties
handle to top level wall time
This function is (and should only) be used by the VcdReplayTester
This function is (and should only) be used by the VcdReplayTester
clock to bump
new clock value should be zero or one, all non-zero values are treated as one
One step is defined here as the running until the next up clock transition
One step is defined here as the running until the next up clock transition
the number of up clocks to find and execute
Manage multiple top-level clocks step is interpreted here to mean advance to the next clock cycle considering all the clocks multiple clocks may fire at that time