US20070283204A1 - Method and system for deterministic bist - Google Patents

Abstract

Methods, systems and articles of manufactures are provided for built-in self-testing of high-performance circuits configured to generate and apply test patterns to a circuit under test (CUT). A logic structure in communication with the CUT and a memory device generates a plurality of test patterns from original test seeds, wherein a response suppression circuit suppresses CUT test responses not generated responsive to a deterministic test pattern of the test pattern plurality prior to compacting a remainder of test pattern responses not suppressed. In one aspect a logic twist counter, a logic shift counter and a logic seed counter are used to generate the test patterns with a seed generation algorithm, determine a subset deterministic test pattern plurality from the original test seeds by looping the original seeds through an input scan register, and suppress responses.

Description

CROSS REFERENCE TO RELATED APPLICATION
• Commonly assigned United States patent application by Shivakumar Swaminathan entitled BUILT-IN SELF-TEST (BIST) FOR HIGH PERFORMANCE CIRCUITS, filed Aug. 11, 2004, Ser. No. 10/915,981, now U.S. Pat. No. 7,228,478 issued Jun. 5, 2007, is hereby incorporated by reference.
FIELD OF THE INVENTION
• The present invention generally relates to integrated circuits and, more particularly, to a method and system for built-in self-test (BIST) architecture for high-performance circuits.
BACKGROUND OF THE INVENTION
• A large number of test patterns must be applied to high-performance circuits in order to detect and diagnose realistic defects. This can be achieved using a test-per-clock built-in self-test (TPC-BIST) 1 architecture illustrated in FIG. 1, in which a test pattern is applied by a test generator circuit (TGC) 2 to the circuit under test (CUT) 4 every clock cycle, and the test response is captured by an appropriate response monitoring circuit 6.
• Alternatively, prior art BIST methods may rely on a test-per-scan architecture 11, wherein a TGC 3 serially loads test patterns into a scan chain register 9 in communication with the CUT 5, with test response output from the scan chain register 9 to the response monitoring circuit 7. In this test-per-scan method, one test pattern is applied to an n-input CUT 5 every n+1 cycles. While test-per-clock BIST architecture 1 methods require less testing time, they introduce mapping logic between input scan register elements in the TGC 2 and the CUT 4. The associated performance degradation makes these methods unsuitable for testing high-performance circuits. For example, in some prior art systems, test-per-clock methods require combinational mapping logic for transforming pseudorandom patterns generated by a linear-feedback shift-register (LFSR) incorporated in the TGC to useful test patterns targeted at hard-to-detect faults.
• “Reseeding” techniques are commonly used to generate test seeds by using a starting test pattern “seed” or starting plurality of seeds in a scan chain and looping the initial test pattern(s) through the scan chain to generate more seeds, wherein seeds are pushed through at every test iteration. It is known to apply test-per-clock BIST architecture by reconfiguring the input scan register into a twisted ring counter (TRC), also known as a Johnson counter. The key idea is to employ “reseeding” to embed an entire pre-computed deterministic test set T_D in a slightly longer test sequence that is applied to the CUT. The TRC-based test pattern generator can be designed by adding a multiplexer and an inverter to the serial input of the scan register feeding the CUT. Since no redesign of the CUT is necessary and no additional logic is added to the critical paths beyond that required for scan, this test architecture is especially suitable for high-performance circuits.
• TRC-based architecture offers a number of advantages. The test control logic is simple and can result in a lower overhead implementation than that required for LFSRs. In addition, the number of seed bits required is in many cases less than for previously published (LFSR-based) reseeding schemes. And TRC configuration is CUT-independent; it can be employed for testing multiple CUTs by simply changing seeds. In fact, this aspect of the TRC-based architecture can be especially appealing for BIST tool vendors who tend to prefer generic BIST circuits that do not have to be tailored to specific CUTs.
• However, there are some disadvantages to TRC-based test architecture. Since the seeds are stored on-chip, it is essential that a very small number of seeds must be sufficient for embedding T_D. Unfortunately, the number of seeds required for the test architecture is sometimes too high. And, in particular, the problem of compacting a large number of distinct test responses during deterministic BIST reseeding must be addressed. Deterministic BIST reseeding solutions are gaining importance because they require a small number of seeds to be stored to embed a complete automatic test pattern generation (ATPG) program test set T_D providing complete fault coverage for all detectable stuck at faults. However, a large number of distinct responses in such reseeding approaches result in a large number of outputs for space compaction of these responses.
• What is needed is a method to compact only those responses corresponding to patterns which are part of the original test set T_D. No existing solutions are available in the prior art which selectively compact responses in deterministic BIST approaches. Selective response compaction in LFSR based reseeding approaches are tougher to implement because the location of deterministic patterns in a pseudorandom sequence cannot be determined in a precise way.
SUMMARY OF THE INVENTION
• Methods, systems and articles of manufactures are provided for built-in self-testing of high-performance circuits configured to generate and apply test patterns to a circuit under test (CUT). A logic structure in communication with the CUT and a memory device generates a plurality of test patterns from original test seeds, wherein a response suppression circuit suppresses CUT test responses not generated responsive to a deterministic test pattern of the test pattern plurality prior to compacting a remainder of test pattern responses not suppressed. In one aspect a logic twist counter, a logic shift counter and a logic seed counter are used to generate the test patterns with a seed generation algorithm, determine a subset deterministic test pattern plurality from the original test seeds by looping the original seeds through an input scan register, and suppress responses.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a block diagram of a prior art test-per-clock built-in self-test (TPC-BIST) system.
• FIG. 2 is a block diagram of a prior art enhanced TRC-BIST pattern generator.
• FIG. 3 is a state diagram of a prior art twisted ring counter seed pattern.
• FIG. 4 is a state diagram of a prior art twisted ring counter finite-state machine seed pattern.
• FIG. 5 is a block diagram of a prior art TRC-BIST pattern generator response compaction method.
• FIG. 6 is a block diagram of a response suppression circuit according to the present invention.
• FIG. 7 is a detail view diagram of the response suppression circuit of FIG. 6.
• FIG. 8 is an article of manufacture comprising a computer usable medium having a computer readable program according to the present invention embodied in said medium.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
• While test set embedding helps to reduce test data volume, it also impacts the size of the space compactor since the space compactor now has to deal with a larger number of distinct fault free responses. What is new in the present invention is a system and method that effectively suppresses extra CUT responses to patterns in reseeding-based pattern applications. Suppressing superfluous responses helps to reduce the number of outputs of a space compactor and thereby reduces test bandwidth and tester cost. In one aspect of the present invention, test-set embedding is used for storing a small number of seeds and compressing only responses of ATPG patterns embedded in a deterministic sequence obtained from those seeds. The present invention uses the test set embedding scheme described in an enhanced TRC-BIST architecture for pattern application.
• An enhanced TRC-BIST pattern generator architecture 20 appropriate for use with the present invention is illustrated in FIG. 2 and taught in “On Using Twisted-Ring Counters for Test Set Embedding in BIST” by S. Swaminathan and by K. Chakrabarty, Journal of Electronic Testing: Theory and Application, 2001, which is hereby incorporated by reference, wherein high-performance circuits are tested by test patterns generated by reseeding in the TRC input scan register 32. A commonly assigned United States patent application by Shivakumar Swaminathan entitled BUILT-IN SELF-TEST (BIST) FOR HIGH PERFORMANCE CIRCUITS, filed Aug. 11, 2004, Ser. No. 10/915,981 (“Swaminathan”), also provides a TRC-BIST pattern generator architecture relevant to the present invention, the disclosure of which is hereby incorporated by reference.
• The above-incorporated references teach that a small number of seeds are adequate for generating test sequences that embed complete test sets for ISCAS benchmark circuits, and can either be stored on-chip, for example in a random access memory (ROM) module 24, or scanned in through a “scan in” input 26 using a low-cost, slower tester; each input option is connected to the input scan register 32 through a MUX 30, which also provides BIST control logic 28 input responsive to ROM counter 22 enablement. The seeds can thus be viewed as an encoded version of the test set: during testing, the patterns derived from the seeds are applied test-per-clock to the circuit under test 34. This enables the effective combination of high-quality BIST with external testing using slower testers. CUT 34 responses are outputted to a response monitor 36 through a response monitor input bus 35.
• In a TRC, an n-bit ring counter is a group of n flip-flops F1, F2, . . . , Fn connected as a shift register, with the output of Fn fed back to the input of F1. It behaves as a counter with up to n distinct states, depending on the initial value (seed). The TRC is a ring counter with an inverter added between the output of Fn and the input of F1. Depending on the seed, an n-bit TRC behaves as a counter with up to 2n distinct states.
• The ROM 24 for storing seeds can be eliminated if an external tester 25 is used to scan in the seed patterns through the “scan in” input 26. The TRC n-bit input register 32 is configured into a length n during testing. The TRC-BIST pattern generator 20 operates in two modes, namely the “shift” and “twist” modes, which correspond to an n-bit ring counter and TRC, respectively.
• A much larger number of patterns can be generated within the input scan register 32 from a given seed by clocking the TRC for 2n²+n cycles. This is shown in FIG. 3 where a total of s seeds 37 are used for test application. The twisted ring counter 39 test control circuit 38 is derived from a simple finite-state machine (FSM) defined within the input scan register 32 with three states—Load, Twist and Shift.
• The state diagram for a Moore-type FSM 40 is shown in FIG. 4. (The Twist state is depicted in the state diagram as two substates—Twist1 42 and Twist2 44.) Two k-bit counters 41, k=[log₂n], with enable inputs are required to generate the signals “Twist Enable” (TE) and “Shift Enable” (SE) that feed the test control logic. One of these counters is required in any autonomous scan-based BIST scheme. The control circuit generates a “Shift-Counter Enable” (SCE) signal which enables the shift counter.
• The finite-state machine FSM 40 operation is described as follows:
• 1. The FSM 40 is initially in the Load state (encoded as the 00 binary pattern). The seed pattern is serially loaded into the n-bit input scan register 32 in n clock cycles.
• 2. At the end of the Load operation, TE goes high and the FSM 40 goes into the Twist state (encoded as two substates corresponding to the binary patterns 01 and 10, respectively). The content of the input scan register 32 undergoes 2n twists in 2n clock cycles. After 2n cycles, the input scan register 32 contains the seed pattern.
• 3. After 2n twists are completed, SCE goes high, and the FSM 40 goes into the Shift state (encoded as the 11 binary pattern). It remains in this state for only one clock cycle. A 1-bit shift is performed on the content of the input register.
• 4. The FSM 40 now re-enters the Twist state, and remains in this state for 2n cycles. This process repeats until n shift operations are completed, at which point SE goes high and a new seed is loaded into the input register.
• The TRC-BIST 20 uses an Algorithm A for selecting a small set of seeds that generates all the test patterns in T_D: “If a pattern t_k lies either on the shift cycle or on the twist cycle of another pattern t_j, then |TC(t_j)−TC(t_k)≦1”; wherein the transition count of a fully-specified pattern t_j is the sum of the number of 1-to-0 and 0-to-1 transitions in t _j. If t_j is defined as the vector b₁b₂. . . b_n then the transition count is defined as: $\mathrm{TC}\left(t_j\right)=\sum _{i=1}^{n-1}{b}_i\oplus b_{i+1}.$
• A pattern t_j is compatible with pattern t_k if there is no bit position in t_j and t_k that are specified and different. For example, 1011X is compatible with X01X0 but is not compatible with 11X1X because of the conflict in the second bit position. Finally, a pattern t_k lies on the shift cycle of pattern t_j if it can be obtained from t_j by performing at most n consecutive shift operations. Similarly, t_k lies on the twist cycle of t_j if it can be obtained from t_j by performing at most 2n consecutive twist operations.
• 2n shift operations are performed on each of n patterns that are obtained by carrying out shift operations on a seed, as illustrated in FIG. 3. The following Algorithm B, which is based on Algorithm A, provides a necessary condition for two patterns to be derived from the same seed during 2n²+n clock cycles: “If patterns t_j and t_k are derived from a common seed s during the 2n²+n cycles in which s is used for pattern generation, then:
  |TC(t_j)−TC(t_k)|≦3.
• In order to select the seeds to be used for generating test patterns using a TRC, a heuristic algorithm may determine the seeds in reasonable time. The seed selection procedure is described in pseudocode form in Table 1.

  TABLE 1
  Procedure SelectSeed( )

  /* select & set of seeds to generate test patterns in TD */

  begin

  	k := l; /*seed index */
  	shift_count := 0;
  	S := φ; /Initialize seed set */
  	sk := t1; /* first test pattern chosen as first seed */

  while(all_test_patterns_not_marked)

  while(shift_count ≠ n)

  for(number_of_twists = 1 to 2n)

  begin

  	twist(sk);
  	for(j := 1 to m)

  if compatible(sk, tj) and mark(tj) = 0

  	/* Check whether sk and tj are
  	compatible and tj not yet covered */
  	break;

  	end for;
  	sk := assign(tj);

  mark(tj) := l;

  	/* assign dont cares in sk appropriately
  	and mark tj as covered */

  	end for;
  	one_bit_shift(sk); Increment shift_count;
  	/* Carry out a 1-bit shift on sk */
  	for(j := 1 to m)

  if compatible(sk, tj) and mark(tj) = 0

  break;

  	end for;
  	sk := assign(tj);

  mark(tj) := l;

  	end while;
  	S := S U sk;

  Increment k;

  /* add sk to seed set */

  for(j := 1 to m)

  if (mark(tj = 0))

  sk := tj;

  break;

  /* pick next, seed sk */

  end if;

  end for;

  	end while;
  	return(S);

  end Procedure;

• The heuristic according to the present invention procedure works as follows. An arbitrary ordering is first imposed on the test patterns in T_D. The first (partially-specified) test pattern in the test set T_D is then chosen as the starting seed s. This seed undergoes 2n twists. If a pattern on the twist cycle is compatible with a test pattern in T_D, the don't-care bits in the generated pattern (and, therefore, the don't-care bits in s) are appropriately assigned binary values and the corresponding test pattern is marked as “covered.” (The objective is to keep as many don't-care bits unassigned as possible since more don't-cares increase the likelihood of covering patterns from T_D.) This is followed by a 1-bit shift operation on s, and the process is repeated until all n shift operations are carried out. At the end of n shift operations (complete shift cycle of s), if there are test patterns that are not yet covered, the first “unmarked” (partially-specified) test pattern is chosen as the next seed. The procedure terminates when all patterns in the test set are covered. The worst-case complexity of this procedure is O(m²n²).
• What is new in the present invention is a synthesis-based approach to selectively suppress test responses. This does not change the number of outputs needed for zero aliasing space compactors. Among the advantages provided by the present invention:
• • (1) The present invention enables very small hardware overhead for zero aliasing space compactors due to almost same size fault free response set compared to methods which do not use response suppression. The space compactors need at the most one additional output for error propagation.
  • (2) No CUT modifications are required.
  • (3) Reduced Tester pin requirements (at most one extra pin) result in reduced test costs and increased efficiencies.
  • (4) Logic may be shared for test generation and response compaction.
  • (5) Small overhead for the response suppression logic.
  • (6) Counter states are used as inputs for RSL design which is easily scalable.
• FIG. 5 shows the general block diagram of a typical prior art response compaction method 100. A space compactor 112 and a time compactor 116 are located in series between the CUT and a response monitor input bus 120. Test patterns 102 are applied to the inputs 104 of the CUT 106, and output responses 108 are then input through k pin connections 110 to the space compactor 112. Compacted responses are then input through z pins 114 to the time compactor 116, which outputs time compacted response to the response monitor input bus 120.
• While test set embedding helps to reduce test data volume, it also impacts the size of the space compactor since the space compactor now has to deal with a larger number of distinct fault free responses. According to the present invention, the minimum number of outputs of a zero aliasing space compactor may be determined by the following:
• • Algorithm 1: Let p be the number of distinct fault free responses to a circuit under the application of the ATPG test set T_D. The minimum number of outputs q of a zero aliasing space compactor designed just using the response vectors is given by q>=log(p+1).
• It follows from Algorithm 1 that if the number of distinct fault free responses increases (very likely due to the long test embedding sequence in BIST reseeding) to a value d, d>p, a larger number of space compactor outputs (=log(d+1)) will have to be monitored. The present invention describes a response suppression method and system which will result in at most one extra space compactor output pin than what is required when only vectors in T_D are applied. Specifically, a second algorithm may be described as follows:
• • Algorithm 2: Let p be the number of distinct fault free responses to a circuit under the application of TD. The minimum number of outputs (q) of a zero aliasing space compactor designed just using response vectors for an enhanced TRC-BIST architecture twist ring based pattern application scheme is given by:
    log(P+1)<=q<=log(P+2).
• What is novel in the present invention is the design of a response suppression circuit which disables the compaction of test responses to test patterns in a twist ring sequence which is not part of the original ATPG generated test set T_D. FIG. 6 is a block diagram of such a novel circuit 200 appropriate for use with a TRC-BIST system 20 of FIG. 2; accordingly, the elements depicted herein as shown may be incorporated between a CUT 234 and a response monitor input bus 235. (Although the present embodiment of the invention will be described with respect to the prior art TRC-BIST system 20 of FIG. 2, it is to understood that the present invention may be incorporated with other deterministic test-set embedding-based BIST systems, and is not restricted to the specific examples and prior art applications provided herein.)
• Test responses are correlated with individual deterministic seeds for identification and suppression purposes according to the present invention. Where seeds are generated using a seed selection algorithm, such as, for example, the seed selection algorithm taught by the related patent application to Swaminathan (incorporated above), the location of deterministic patterns which are of interest (i.e. part of T_D) from the ATPG test set T_D can be determined by working backwards. Thus, for a two-bit test pattern structure, if T={00, 10, 11} and seed set={00}, then, using the Swaminathan twisted ring method, the deterministic patterns of interest can be determined as illustrated in Table 2 below.

  TABLE 2
  SDC	SHC	TWC	RSL output	(Comments)
  0	00	00	1
  0	01	10	1
  0	10	11	1
  0	11	01	0 ----------->	not part of T
  1	XX	XX		0 ----------->	all tests already covered
  1	XX	XX		0 ----------->	only 1 seed,
  				so output = 0 for SDC = 1

• According to the present invention, let s be the number of deterministic seeds required to embed T_D. Let n be the length of an input scan register 232. The states of a log s seed counter (SDC) 202, log n shift counter (SHC) 204 and a log 2n twist counter (TWC) 206 and a test mode bit (TM) 208 are the inputs to the response suppression circuit 210 containing the response suppression logic (RSL) 211, which generates a single output 212. Note that SHC 204 and TWC 206 are shared for pattern application as well. The RSL output 212 is input to a series of AND gates 216 along with the CUT 234 response inputs 214, the RSC output 212 thereby controlling the application of the CUT responses 214 to the inputs 218 of the space compactor 220, and thereby the compacted inputs 222 to the time compactor 224.
• In another aspect of the present invention, the counters 41 logic illustrated in FIG. 4 may be shared for test generation and response compaction. Accordingly, the test control logic structure 207 for test generation provided to control testing of the CUT 234 comprises the shift counter 204, seed counter 202 and twist counter 206 structures, thereby enabling sharing of the twist counters and associated logic structures. What is new is that the seed counter 202 and twist counter 206 structures are used for both applying test patterns and for test response compaction. Thus, the present invention provides economies in reducing hardware overhead through the sharing of the logic resources.
• Synthesis of RSL: In order to synthesize the RSL 211, we need to determine the exact location of the deterministic patterns of T_D in the twist ring embedding sequence. This can be expressed as a function of the states of SDC 202, SHC 204 and TWC 206 because that is the way the seeds are pre-determined in software.
• The information about the precise location of the deterministic patterns for a four-bit test pattern structure can be formulated in Table 3, a state table shown below.

  	TABLE 3
  	SDC	SHC	TWC	RSL output
  	0000	0000	0000	1
  			0001	0
  			0010	0
  			0011	1
  			0100	1
  			0101	0
  			0110	1
  			0111	0
  			1XXX	X
  	0000	0001	0000	1
  			1XXX	X
  	0000	1XXX	XXXX	X
  	1XXX	XXXX	XXXX	X

• A “1” value in the RSL Output column of Table 3 corresponds to the response of the CUT to a deterministic pattern belonging to the test set T_D. A “0” value in the RSL Output column corresponds to the response of the CUT to a pattern NOT belonging to T_D. An “X” value in the RSL Output column implies that we will never reach the corresponding states of SDC 202, SHC 204 and TWC 206.
• What is important in the present invention is that even where a large number of test cells are utilized, in the scale of thousands, due to the logarithmic characteristics of the component structures according to the present invention, only a small number of test inputs and outputs are required. The Table 3 state table can be synthesized using logic synthesis tools to generate a circuit from the invention embodiment component structure (log s SDC 202, log n SHC 204 and log 2n TWC 206 and TM 208), thus log s+log n+log 2n inputs+one output.
• FIG. 7 provides a detail view of the response suppression circuit 210. The RSL 211 output 213 is input to an OR gate 215. The test mode bit 208 enters an inverter 217, and the inverted output 219 is combined with the RSL 211 output 213 at the OR gate 215, which generates the response suppression circuit 210 output 212. As is readily apparent, the inverter 217/OR gate 215 structure functions to enable the RSL 211 only when test mode is indicated by a test mode 208 bit value of 1. If instead the circuit is in a functional mode, the test mode 208 bit value is 0 and RSL 211 response suppression is disabled.
• Scan chains found in common benchmark test architecture include those 61 or 100 cells in length, wherein multiples of chains are typically run: for example, 32 chains at 61 cells each results in a number n of test inputs of 1,952. For single chain test, 2000 cells may be provided, or n=2000. Where n=2000, using the enhanced TRC-BIST architecture method described above to determine the requisite number of seeds required, s results in s=10. And, therefore, according to the present invention, a number of test mode inputs for the RSL 211 is=log s+log 2n+log n+1=log 10+log 4000+log 2000+1=4+12+11+1=28. Thus, the resultant RSL 211 is basically a combinational circuit with 28 inputs and 1 output.
• In one embodiment of the present invention, a superset (order n²) of T_D is applied to the CUT 207 using s seeds. For example, in order to embed T_D=10,000 patterns, 2*(1464)*(1464)+1464 vectors are applied, where n=1464 is the length of a scan chain in the benchmark (s)38584 using s=22 seeds. Hence, there are a large number of responses to vectors not part of T_D. Suppressing these responses helps to reduce the number of outputs of the space compactor and thereby reduces test bandwidth and tester cost.
• The inventions described above may be tangibly embodied in a computer program residing on a computer-readable medium or carrier 800. The medium 800 may comprise one or more of a fixed and/or removable data storage device, such as a floppy disk or a CD-ROM, or it may consist of some other type of data storage or data communications device. The computer program may be loaded into a memory device in communication with a network processor for execution. The computer program comprises instructions which, when read and executed by the processor, causes the processor to perform the steps necessary to execute the steps or elements of the present invention.
• While embodiments of the invention have been described herein, variations in the design may be made, and such variations may be apparent to those skilled in the art of computer architecture, systems and methods, as well as to those skilled in other arts. The present invention is by no means limited to the specific programming language and exemplary programming commands illustrated above, and other software and hardware implementations will be readily apparent to one skilled in the art. The scope of the invention, therefore, is only to be limited by the following claims.

Claims (17)

1. A method for testing circuits, comprising:

providing a plurality of original test seeds;

generating a plurality of test patterns from the plurality of original test seeds, the generated test pattern plurality comprising a subset deterministic test pattern plurality;

loading the generated test pattern plurality into a circuit-under-test;

the circuit-under-test producing a plurality of test pattern responses from the generated test pattern plurality, one test pattern response for each of the generated test pattern plurality;

suppressing each of the plurality of test pattern responses not correlated with at least one of the deterministic test pattern plurality subset;

compacting a remainder of the plurality of test pattern responses not suppressed; and

outputting the compacted remainder of test pattern responses to a response monitor.

2. The method of claim 1, further comprising:

generating the plurality of test patterns from the plurality of original test seeds through a seed generation algorithm; and

using the seed generation algorithm to identify each of the subset deterministic test pattern plurality.

3. The method of claim 2, further comprising:

providing an input scan register configured to load the generated test pattern plurality into the circuit-under-test and a logic structure in communication with the circuit-under-test, the logic structure comprising a twist counter, a shift counter and a seed counter, the seed counter, the shift counter and the twist counter using the seed generation algorithm to generate the plurality of test patterns;

the twist counter and shift counter generating the subset deterministic test pattern plurality from the original test seeds by looping the original seeds through the input scan register.

4. The method of claim 3, wherein the plurality of original test seeds has a quantity value s, the input scan register has a length n, the seed counter is a log₂ s bit seed counter, the shift counter is a log₂ n bit shift counter, and the twist counter is a log₂ 2n bit twist counter, further comprising:

providing a response suppression logic component for suppressing the plurality of test pattern responses not correlated, the response suppression circuit having a number of inputs x; and

defining the number of inputs x by the formula x=log s+log 2n+log n+1.

5. The method of claim 3, wherein using the seed generation algorithm to generate the plurality of test patterns and identify each of the subset deterministic test pattern plurality comprises:

imposing an arbitrary ordering on the deterministic test pattern subset;

choosing a first starting seed for the deterministic test pattern subset;

performing 2n twists on the first starting seed;

if an original test seed on a logic twist cycle is compatible with a deterministic test pattern subset seed, marking a responsively generated test response as covered;

performing a 1-bit shift operation on the original test seeds;

repeating the last five steps of imposing, choosing, performing 2n twists, marking and performing the 1-bit shift operation until n shift operations are carried out;

if there are original test seeds not marked covered, choosing a first unmarked original test seed as a second starting seed and repeating the last six steps of imposing, choosing, performing 2n twists, marking, performing the 1-bit shift operation and repeating with the second starting seed; and

terminating the algorithm when all test seeds are marked covered.

6. A testing apparatus, comprising:

a memory comprising a plurality of original test seeds;

a logic structure in communication with a circuit-under-test and the memory device, the logic structure comprising a seed counter, a twist counter and a shift counter configured to use a seed generation algorithm to produce a plurality of test patterns from the original test seeds;

an input scan register in communication with the logic structure and configured to load the plurality of test patterns into the circuit-under-test; and

a response suppression circuit in communication with the circuit-under-test and the logic structure, the response suppression circuit configured to use the twist counter and the shift counter to:

generate a deterministic test pattern subset of the plurality of test patterns by looping the original test seeds through the input scan register, and

suppress each of a plurality of test pattern responses generated by the circuit-under-test in response to the generated test pattern plurality not correlated with at least one of the deterministic test pattern plurality subset; and

output a remainder of the plurality of test pattern responses not suppressed;

a compacter in communication with the response suppression circuit output configured to compress the response suppression circuit output; and

a response monitor configured to receive the compressed response suppression circuit output.

7. The apparatus of claim 6, wherein the logic structure is configured to use a seed generation algorithm to generate the plurality of test patterns from the plurality of original test seeds and identify each of the subset deterministic test pattern plurality.

8. The apparatus of claim 7, wherein the plurality of original test seeds has a quantity value s;

the input scan register has a length n;

the seed counter is a log₂ s bit seed counter;

the shift counter is a log₂ n bit shift counter;

the twist counter is a log₂ 2n bit twist counter; and

the response suppression circuit further comprises a test mode bit input and a logic component having a number of inputs x defined by the formula x=log s+log 2n+log n+1.

9. The apparatus of claim 8, wherein the response suppression circuit, the space compactor, the circuit-under-test and the logic structure are in circuit communication through a bus structure configured to arbitrate and thereby pass each of the remainder output to the space compactor responsive to response suppression circuit test suppression data.

10. The apparatus of claim 9, wherein the bus structure comprises a plurality of gates and the space compactor is connected to an output of each of the plurality of gates.

11. The apparatus of claim 10 wherein the memory is a buffer structure within a scan register or an external ROM.

12. The apparatus of claim 11 wherein the response suppression circuit is configured to use the twist counter and the shift counter to generate the deterministic test pattern subset of the plurality of test patterns by looping the original test seeds through the input scan register, and to suppress each of the plurality of test pattern responses not correlated with at least one of the deterministic test pattern plurality subset.

13. An article of manufacture comprising a computer readable medium having a computer readable program embodied in said medium, wherein the computer readable program, when executed on a computer, causes the computer to generate and apply a test pattern to a circuit-under-test by:

generating a plurality of test patterns from a plurality of original test seeds, the generated test pattern plurality comprising a subset deterministic test pattern plurality;

loading the generated test pattern plurality into the circuit-under-test;

suppressing each of a plurality of circuit-under-test test pattern responses not correlated with at least one of the deterministic test pattern plurality subset, the plurality of test pattern responses generated by the circuit-under-test from the generated test pattern plurality;

compacting a remainder of the plurality of test pattern responses not suppressed; and

outputting the compacted remainder of test pattern responses to a response monitor.

14. The article of manufacture of claim 13, wherein the computer readable program, when executed on a computer, further causes the computer to:

generate the plurality of test patterns from the plurality of original test seeds through a seed generation algorithm; and

use the seed generation algorithm to identify each of the subset deterministic test pattern plurality.

15. The article of manufacture of claim 14, wherein the computer readable program, when executed on a computer, further causes the computer to:

use a logic twist counter, a logic shift counter and a logic seed counter to generate the plurality of test patterns with a seed generation algorithm; and

use the twist counter and shift counter to generate the subset deterministic test pattern plurality from the original test seeds by looping the original seeds through an input scan register.

16. The article of manufacture of claim 15 wherein the computer readable program, when executed on a computer, further causes the computer to:

execute response suppression logic in suppressing the plurality of test pattern responses not correlated, the response suppression logic having a number of inputs x; and

define the number of inputs x by the formula x=log s+log 2n+log n+1, wherein the plurality of original test seeds has a quantity value s, the input scan register has a length n, the seed counter is a log₂ s bit seed counter, the shift counter is a log₂ n bit shift counter, and the twist counter is a log₂ 2n bit twist counter.

17. The article of manufacture of claim 16, wherein the computer readable program, when executed on a computer, further causes the computer to apply the seed generation algorithm to generate the plurality of test patterns and identify each of the subset deterministic test pattern plurality by:

imposing an arbitrary ordering on the deterministic test pattern subset;

choosing a first starting seed for the deterministic test pattern subset;

performing 2n twists on the first starting seed;

if an original test seed on a logic twist cycle is compatible with a deterministic test pattern subset seed, marking a responsively generated test response as covered;

performing a 1-bit shift operation on the original test seeds;

repeating the last five steps of imposing, choosing, performing 2n twists, marking and performing the 1-bit shift operation until n shift operations are carried out;

if there are original test seeds not marked covered, choosing a first unmarked original test seed as a second starting seed and repeating the last six steps of imposing, choosing, performing 2n twists, marking, performing the 1-bit shift operation and repeating with the second starting seed; and

terminating the algorithm when all test seeds are marked covered.

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