Multiple-seed TPG structures

Linear feedback shift registers (LFSRs) are popular mechanisms for built-in test pattern generation (TPG). They are normally used with a primitive characteristic polynomial because, in that case, only one initialization state (seed) is required. We show that if the characteristic polynomial is nonprimitive irreducible, the required seeds can still be efficiently generated. We establish a formula that shows how the seeds of any nonprimitive irreducible polynomial relate to each other. This leads to an efficient hardware implementation with small hardware overhead, irrespective of the number of seeds, and enhances the choices available for the design of appropriate TPG structures in the case of pseudoexhaustive TPG that were previously limited to primitive characteristic polynomials only.