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# A METHOD FOR THE DETECTION OF INITIALIZATION PROBLEMS IN 2-STATE SIMULATION

IP.com Disclosure Number: IPCOM000008348D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2002-Jun-07
Document File: 1 page(s) / 80K

Motorola

## Abstract

In a multi-state simulator, signals and registers are pre-initialized to "unknown" logic values (e.g. "X"). A multi-state simulator will propagate these unknowns through logic according to rules in the simulator. The advantage in doing this is that the appearance of these unknowns later in simulation often indicates a problem in a model's reset logic. By definition, a Z-state simulator can only represent signal or register values of "0" and "I", and thus problems in a model's reset logic are more difficult to detect.

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MO-AA Technical Developments

A METHOD FOR THE DETECTION OF INITIALIZATION PROBLEMS IN 2-STATE SIMULATION

by Mike Braddock, Richard Duerden, and Jeff Freeman

INTRODUCTION

In a multi-state simulator, signals and registers are pre-initialized to "unknown" logic values (e.g. "X"). A multi-state simulator will propagate these unknowns through logic according to rules in the simulator. The advantage in doing this is that the appearance of these unknowns later in simulation often indicates a problem in a model's reset logic. By definition, a Z-state simulator can only represent signal or register values of "0" and "I", and thus problems in a model's reset logic are more difficult to detect.

Another way to detect reset logic errors with a 2-state simulator is to perform a check during simulation for the condition where a state value is used before it is ever written or updated. This can be referred to as a "read-before-write check." However, since 2-state simulation is used to get maximum simulation rates (as in cycle-based simu- lation), such an approach is undesirable because it introduces a performance penalty in the execution time of the simulator.

Described here is a 2-state method for detecting problems in a model's reset logic, with a minimal performance penalty.

DESCRlPTlON

Based on the assumption that proper initializa- tion (by a model's reset logic) is necessary for a model's correct operation, the 2-state simulator optionally pre-initializes signals and registers with arbitrary patterns of "0" and "I". If the model's reset logic does not correctly overwrite these

arbitrary values, they can propagate and eventually cause an observable malfunction in the model,

These arbitrary values may be specified at the

time the 2-state sim...