Patent ID: 6059451
Filing Date: 2000-05-09
Classification: G01R

Abstract:
A computer implemented method for selecting test points to increase overall fault coverage of an electrical circuit, the computer including a memory and a display, comprising the steps of:a) providing a netlist describing the electrical circuit in the memory of the computer, the netlist including a plurality of nodes and a plurality of connections between the plurality of nodes;b) determining a signal probability and a transfer probability associated with the nodes in the netlist;c) selecting a set of controllability pseudo-testpoint nodes by iterating through the nodes in the netlist to select a current low controllability node, the current low controllability node having a signal probability outside a first preset range, and performing steps c1 through c3 upon the current low controllability node;c1) determining which nodes are in the fanin cone of the current low controllability node selected in step c, thereby selecting a current set of fanin nodes,c2) selecting a new pseudo-testpoint node from the current set of fanin nodes, and inserting the new pseudo-testpoint node into the netlist, wherein the inserting comprisesadding the new pseudo-testpoint node to the set of controllability pseudo-testpoint nodes,temporarily setting the signal probability of the new pseudo-testpoint node to 1/2,temporarily setting the transfer probability of the new pseudo-testpoint node to 1, thereby affecting the signal probabilities and transfer probabilities of at least the current low controllability node; andtemporarily updating the signal probability and transfer probability of the nodes in the netlist;c3) repeating steps c2 through c3, unless the current low controllability node's updated signal probability is within the first preset range;d) continuing the iteration of step c until all low controllability nodes have been selected;e) upon completion of the step c iteration, using steps f through i to select a set of observability pseudo-testpoint nodes;f) determining a set of potential faults for the netlist, the set of potential faults including a plurality of faults;g) selecting a set of potential observability pseudo-testpoint nodes by iterating through the faults in the set of potential faults to select a current resistant fault, the current resistant fault having a fault coverage probability below a preset confidence level, and performing steps g1 through g2 upon the current low observability node;g1) determining which nodes are downstream from the current resistant fault selected in step g, thereby selecting a current set of downstream nodes;g2) selecting a current potential observability pseudo-testpoint node from the current set of downstream nodes,incrementing an effectiveness measure for the current potential observability pseudo-testpoint node, andadding the current potential observability pseudo-testpoint node to a set of potential observability pseudo-testpoint nodes;h) continuing the iteration of step g until all resistant faults have been selected;i) upon completion of the step g iteration, repeatedly selecting a new pseudo-testpoint node from the set of potential observability pseudo-testpoint nodes and inserting the new pseudo-testpoint node into the netlist,wherein the selection order is based on the effectiveness measures of step g2, andinserting the new pseudo-testpoint node into the netlist comprisesadding the new pseudo-testpoint node to the set of observability pseudo-testpoint nodes,temporarily setting the signal probability of the new pseudo-testpoint node to 1/2,temporarily setting the transfer probability of the new pseudo-testpoint node to 1, andtemporarily updating the signal probability and transfer probability of the nodes in the netlist;j) ranking the set of controllability pseudo-testpoint nodes and observability pseudo-testpoint nodes in accordance with a potential effectiveness thereby generating a combined set of pseudo-testpoints, each of the pseudo-testpoints in the combined set having an associated rank;k) resetting all the temporary signal probabilities and temporary transfer probabilities to the probabilities determined in step b; andl) repeatedly inserting one of the testpoints from the combined set of pseudo-testpoints into the netlist in accordance with the associated rank until a minimum required fault coverage for the electrical circuit described in the netlist is obtained.