248VLSI Test Principles and Architectures4.11.5Designing a High-Level ATPGBecause of the exponentially complex nature of ATPG, its performance can beseverely limited to the size of the circuit. As a result, conventional gate-level ATPGmay produce unsatisfactory results for large circuit sizes. On the other hand, higherlevel ATPGs have the advantages of fewer circuit primitives and easier access tocircuit functional information that may enhance the ATPG effort.The circuit is first given in a high-level description such as VHDL, Verilog, orSystemC. Then, the design is read in and an intermediate representation is con-structed. Similar to gate-level ATPGs, the representation allows the high-level ATPGto traverse through the circuit and make decisions on the search. However, becausethe signals may not be Boolean, value justification and fault-effect propagationmust work on the integer level. Backtracking mechanisms also have to be modified.
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The Circuit, FSM description, high-level atpg