In the early days of digital design, we were concerned with the logical correctness of circuits. We knew that if we slowed down the clock signal sufficiently, the circuit would function correctly. With improvements in the semiconductor process technology, our expectations on speed have soared. A frequently asked question in the last decade has been how fast can the clock run.
Too much backtracking undoing a previous decision and making a different choice in some circuits. All possible choices may have to be tried in the worst case. Propagates D after initial objective is reached. New Concepts used:. Immediate assignment of uniquely-determined signals.
Unique sensitization. Stop Back trace at head lines. Multiple Back trace. The generation of tests is usually much more difficult for sequential circuits than for combinational ones. This is due mainly to the poor controllability and observability of sequential logic. This is clearly not a viable solution for test generation.
Consider extending the D-algorithm for the case of sequential circuits. Here the storage circuits are transformed into combinational logic circuits valid at one clock cycle. However, the controllability and observability of sequential circuits i. Those techniques allow tests for sequential circuits to be reduced to test of the same sort that are used for combinational circuits. Time-frame expansion : convert time domain into space domain and use combinational ATPG. Simulation-based approach : search for test vectors guided by cost functions and simulations. Checking experiment : formal approach to derive test sequence for FSM.
System-on-Chip Test Architectures
Scan : modify the circuit to facilitate combinational ATPG. Functional test : testing that a part of a system operates correctly in a functional sense. To determine a test sequence the following assumptions are to be followed.
Homing Sequence:. Distinguishing Sequence. Synchronizing Sequence. A Synchronizing Sequence for an FSM is an input sequence which takes the machine to a specified final state regardless of the output sequence or the initial state. The tool is able to generate the test vectors for all the faults in the circuit. A fault set is formulated considering both stuck at 0 fault and stuck at 1 fault for all the points where fault occurs.
The tool generates a test vector if at all it exists. The tool also has an intelligence to avoid unnecessary back traces and thus enable it to generate a test vector as soon as possible. The tool generates test vectors for Combinational circuits, Sequential circuits, State Machines. A fault is picked up from the fault set and the test vector to detect the test by first considering the fault as stuck at 0, and then considering the fault as stuck at 1.acechunbo.tk
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For a combinational circuit the set of test vectors are presented. Thus it implies that by giving this test vector as input one can detect whether a circuit is a faulty one or not. A test sequence is generated for the sequential circuit which is a combination of input and output sequence. By applying the input test sequence if the circuit generates corresponding output sequence the circuit could be identified as non-faulty circuit. The case is similar for the state machine too. It has been observed that the sequence generated by the equivalent sequential circuit from the state machine and the sequence generated by the state machine is not so related to each other.
The input to the tool is a Verilog net list, which is generated by any standard tool, or a net list written by a user. The syntax to be followed is similar to that of Verilog. The instantiation of gates are not forced to write in an order.
The gates in inner level can be declared before the declaration of outer gates and vice versa. The order of arguments in declaration of gate can also be varied. The circuit to be tested is read by the tool through Verilog net list format. This is done by parsing the given net list and is read to entities gate and port correspondingly. These are represented as structures for which the memory is allocated dynamically whenever required. The tool also gets the fault set after parsing the input net list file. Fault set contains faults, for which test vector at each stuck at fault is to be calculated.
Library for the tool:.
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- Generation of high quality non-robust tests for path delay faults.
- Sleeping Dogs.
The tool uses a standard library formulated. The syntax for input library is as follows. Truth table to be followed. The propagation D cubes are calculated only for the gates that are considered by the library. The newly constructed propagation D cube is appended to the primitive D cube for reference to generate test vector using any algorithm. The basic algorithm that is implemented is D-Algorithm. The test vector is first initialized before starting of the algorithm and the various steps in flowchart are followed to generate the test vector for the fault and marking the fault in fault set as generated.
Implications are done after each step of algorithm to accelerate the generation of test vector. Line justification is also done verify that the circuit is justified or not.
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If all the trails has been finished and test vector cannot be generated. It generates an empty test vector. Test File 1. Output from the tool for the above circuit. Test file 2. Output for test 2 from the tool. VCC ix Y nx ;. GND ix Y GND ;. AN3 ix Z zout ,. A nx ,.
B nx ,. C nx ;.
NR4 ix Z nx ,. A y ,. B y ,. C y ,. D y ;. ND4 ix Z y ,. C nx ,. D nx ;. AO2 ix A a ,. C nx42 ,. D nx90 ;. NR4P ix IVP ix EO ix Z nx42 ,. A a ,.
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B b ;. ND2 ix A nx14 ,. B nx86 ;. NR3P ix Z nx14 ,.