Intro to Design for Testability

1. Increasingly complex circuit → more difficult & more expensive testing Testability: a design parameter :the ability to test easily or cost effectively Testability analysis: To measure controllability and observability Controllability: a measure of how easily the internal logic of the circuit can be controlled from its primary inputs. Observability: a measure of how easily the internal logic of the circuit can be observed at its primary outputs. Intro to Design for Testability

2. The testability measure of Stephenson and Grason -To each line s, CY(s) and OY(s) are assigned. 0≤CY(s)≤1, 0≤OY(s)≤1. CY(zj) = CTF x 1/n ∑{n,i=1}CY(xi) CTF: controllability transfer function; the ability to control outputs of circuit by applying input values. : 1/k ∑{k,j=1} (1- abs(Nj(0) – Nj(1))/ 2^n) -Nj(0): # of input values for which output zj has output 0. e.g. (more lines = more observability + more controllability)

3. OY(xi) = OTF x 1/k ∑{k,i=1} OY(zk) OTF: observability transfer function: measure the probability that a fault value at any input of the circuit will propagate to its outputs. : 1/n x ∑{n, i=1} NSi/ 2^n -NSi: # of input values that can sensitize a path from xi to its output of the circuit.