4/20/2006 ELEC7250 Project: Grimes 1 Logic Simulator for Hierarchical Bench Hillary Grimes III – Term Project ELEC 7250 – Spring 2006

4/20/2006 2ELEC7250 Project: Grimes Problem Statement Develop a Logic Simulator for Zero-Delay Boolean gates to perform circuit verification. Develop a Logic Simulator for Zero-Delay Boolean gates to perform circuit verification. Inputs: --Hierarchical Bench Circuit Description --Input Vectors and Expected Outputs Inputs: --Hierarchical Bench Circuit Description --Input Vectors and Expected Outputs Outputs when Simulation Fails: --Inputs and Outputs with failed responses --Diagnosis Information Outputs when Simulation Fails: --Inputs and Outputs with failed responses --Diagnosis Information

4/20/2006 3ELEC7250 Project: Grimes Circuit Representation in C Signals Contain: --signal name --level --value Signals Contain: --signal name --level --value Gates Contain: --gate name --gate type --level --input signal list --output signal list --fan in array Each hierarchical block is stored as an element in a block array containing: --block name--input signal list --array of gates--output signal list Each hierarchical block is stored as an element in a block array containing: --block name--input signal list --array of gates--output signal list

4/20/2006 4ELEC7250 Project: Grimes Building the Block Array Each block is flattened as it is read in Each block is flattened as it is read in After POs and PIs are assigned, the gate array is built. Each line from the netlist is either a boolean gate, or a previously defined block. -If boolean gate – add to gate array --gate name: “g0, g1, g2, etc” --assign input and output signals -If not boolean – insert block from previous elements in block array After POs and PIs are assigned, the gate array is built. Each line from the netlist is either a boolean gate, or a previously defined block. -If boolean gate – add to gate array --gate name: “g0, g1, g2, etc” --assign input and output signals -If not boolean – insert block from previous elements in block array

4/20/2006 5ELEC7250 Project: Grimes Insert Gates for an XOR Block XOR Description: Inputs: A, B Output: Y X1=NAND(A,B) X2=NAND(X1,A) X3=NAND(X1,B) Y=NAND(X2,X3) XOR Block’s gate array contains: g0: NAND g1: NAND Inputs: A, B Inputs: X1, A Output: X1 Output: X2 g2: NAND g3: NAND Inputs: X1, B Inputs: X2, X3 Output: X3 Output: Y XOR0.g0: NAND XOR0.g1: NAND Inputs: IN_1, IN_2 Inputs: XOR0.X1, IN_1 Output: XOR0.X1 Output: XOR0.X2 XOR0.g2: NAND XOR0.g3: NAND Inputs: XOR0.X1, IN_2 Inputs: XOR0.X2, XOR0.X3 Output: XOR0.X3 Output: OUT OUT = XOR ( IN_1, IN_2) Inserts Gates:

4/20/2006 6ELEC7250 Project: Grimes Level Block Gates are inserted into gate array such that each gate’s inputs are either PIs, or an output of a previous gate. Gates are inserted into gate array such that each gate’s inputs are either PIs, or an output of a previous gate. To levelize a block, we visit each gate in increasing order: --level of gate = max level of input signals --level of gate’s output = 1+gate level To levelize a block, we visit each gate in increasing order: --level of gate = max level of input signals --level of gate’s output = 1+gate level --increasing order ensures that each input has an assigned level

4/20/2006 7ELEC7250 Project: Grimes Simulation To simulate a block given an input vector: --assign signal values to primary inputs --visit each gate in gate array (increasing order): -evaluate and assign gate’s output signal To simulate a block given an input vector: --assign signal values to primary inputs --visit each gate in gate array (increasing order): -evaluate and assign gate’s output signal Diagnose if output differs from the expected response --diagnoses starts at each failing PO and back tracks through the circuit --information (including signal values) for each gate along a path to the failing PO is printed Diagnose if output differs from the expected response --diagnoses starts at each failing PO and back tracks through the circuit --information (including signal values) for each gate along a path to the failing PO is printed

4/20/2006 8ELEC7250 Project: Grimes Results Circuit Number of Gates Number of Inputs Number of Outputs Execution Time (msec) c c c c c c c c c c c

4/20/2006 9ELEC7250 Project: Grimes Results

4/20/ ELEC7250 Project: Grimes Conclusion Execution times seem to grow with both the number of gates, and the number of inputs/outputs Execution times seem to grow with both the number of gates, and the number of inputs/outputs Diagnosis still needs work --if multiple paths to the failing PO include the same gate, that gate’s information is printed multiple times. --diagnostic resolution could be much better with a better algorithm Diagnosis still needs work --if multiple paths to the failing PO include the same gate, that gate’s information is printed multiple times. --diagnostic resolution could be much better with a better algorithm