Abstract: Described is a circuit modifier, network, and method for use with an event-driven digital logic simulator for enforcing consistent evaluation of input pin changes at state elements. The invention automatically interposes a fictitious 0-delay defer agent or processor, at the input pin to state elements such as D Flip-Flops. The interposition of the defer agent is handled by the simulator as follows. Defer agents schedule events related to input state changes on a special time or task queue which is not processed until after all other events have been executed for the current time, including any extra iterations caused by 0-delay scheduling activity. Defer agents or processors are placed in a simulation network just prior to one or more of the input pins of state elements, the effect of which is to delay events that normally would propagate to the input pin of a state element until all other normal simulation events are processed.

Abstract: Described is an invention that provides an efficient selection of timing statements for a logic cell in response to cell pin activity when such cell is implemented as one or more instances of simulator primitives. It does so by defining a first storage structure coupled with a logic processor coupled, in turn to a second storage structure. First storage structure defines plural bitfield arrays corresponding with a cell pin and a possible logic level or state, each bitfield array having an entry for an old or a former state of the pin, a next or new state of that pin and a stable state of that pin and each bitfield array defining an index to one or more memory-based look-up tables defining the number of a timing and/or constraint parameter for the given pin of the logic cell. Such timing parameters describe a delay between two pins of the cell, while such constraint parameters describe timing constraints for the logic cell such as setup times, hold times and minimum pulse width times.

Abstract: Method and apparatus for more efficiently using the undefined logic state and mixed multiple state abstractions is described. The method involves dividing gates into two groups: those that require an 8-state table (either because their inputs are sensitive to 8-state values or their output produces an 8-state value), and those that require only 4-state values (their inputs are insensitive to 8-state values and the output produces only 4-state values). The key to obtaining the advantages of the invention is the choice of the 4-state values. Previously, the 4-state values have been 0, 1, X, and Z. By the invented method and apparatus, the 4-state values are defined instead to be 0S, 1S, XS, and U. In the Multi-value Logic 9-state model (MVL-9), U is defined to be the uninitialized state, and thus it is a state that all instances need to process on their inputs and to produce as an output.