Abstract: Test pattern generation is performed for a sequential circuit by first separating the circuit into overlapping pipelines by controlling corresponding clocks for one or more registers of the circuit so as to break feedback loops of the circuit, and then processing each of the pipelines separately in order to determine if particular target faults are detectable in the pipelines. Independent clocks may be provided for each of a number of registers of the circuit in order to facilitate the breaking of the feedback loops. The processing of the pipelines may include a first processing operation which detects target faults in a single time frame, and a second processing operation which detects target faults in two or more time frames. The first processing operation generates as many combinational test vectors as possible for each of the pipelines, while the second processing operation generates sequences of two or more combinational test vectors for each of the pipelines.

Abstract: A method of testing field programmable gate array (FPGA) resources and identifying faulty FPGA resources during normal on-line operation includes configuring an FPGA into a working area and an initial self-testing area. The working area maintains normal operation of the FPGA throughout testing and identifying of the resources. Within the initial and subsequent self-testing areas, the FPGA resources are initially tested for faults. Upon detection of a fault in the FPGA resources, the initial self-testing area resources are reconfigured or subdivided and further tested in order to identify the faulty resource. Dependent upon the further test results, the FPGA resources may be further subdivided and tested until the faulty resource is identified. Once the faulty resource is identified, the FPGA is reconfigured to replace unusable faulty resources or to avoid faulty modes of operation of partially faulty resources diagnosed during further testing.

Abstract: Techniques for testing a sequential circuit comprising a plurality of flip-flops or other types of registers. The circuit is first configured such that substantially all feedback loops associated with the registers, other than one or more self-loops each associated with a corresponding one of the registers, are broken. Test patterns are then generated for application to the circuit. The test patterns are applied to the circuit in conjunction with partitioned clock signals each of which is associated with a corresponding level of the circuit containing at least one of the self-loops. In an illustrative embodiment, a design for testability (DFT) structure is used to provide partitioning of a master clock into multiple clock signals each associated with a corresponding one of the levels of self-loops, so as to permit breaking of the feedback loops other than the self-loops.

Abstract: A method of self-testing the programmable routing network in a field programmable gate array (FPGA) during normal on-line operation includes configuring the FPGA into an initial self-testing area and a working area. The initial self-testing area is preferably configured to include an horizontal self-testing area primarily for testing horizontal wire segments and a vertical self-testing area primarily for testing vertical wire segments. Programmable logic blocks located within the self-testing areas are configured to function as a test pattern generator and an output response analyzer, and a portion of the programmable routing resources within the self-testing areas is configured as groups of wires under test. An exhaustive set of test patterns generated by the test pattern generator is applied to the groups of wires under test which are repeatedly reconfigured in order to completely test the programmable routing resources within the self-testing areas.

Abstract: A method of self-testing the programmable logic blocks of field programmable gate arrays (FPGAs) during normal on-line operation includes configuring the FPGA into an initial self-testing area and a working area. The self-testing area may be further subdivided into self-testing tiles for concurrent testing if desired. The programmable logic blocks located within the self-testing area or self-testing tiles are established to function as a test pattern generator, an output response analyzer, and equivalently configured programmable logic blocks under test for testing. An exhaustive set of test patterns generated by the test pattern generator are applied to the programmable logic blocks under test which are repeatedly reconfigured in order to completely test the programmable logic blocks in all possible modes of operation.

Abstract: A method of fault tolerant operation of field programmable gate arrays (FPGAs) utilizing incremental reconfiguration during normal on-line operation includes configuring an FPGA into initial self-testing areas and a working area. Within the self-testing areas, programmable logic blocks (PLBs) of the FPGA are tested for faults. Upon the detection of one or more faults within the PLBs, the faulty PLBs are isolated and their modes of operation exhaustively tested. Partially faulty PLBs are allowed to continue operation in a diminished capacity as long as the faulty modes of operation do not prevent the PLBs from performing non-faulty system functions. After testing the programmable logic blocks in the initial self-testing areas, the FPGA is reconfigured such that a portion of the working area becomes a subsequent self-testing area and at least a portion of the initial self-testing area replaces that portion of the working area.

Abstract: A virtual logic system for solving satisfiability problems on reconfigurable hardware, such that the reconfigurable hardware can be used to solve problems much larger than its available capacity. In an illustrative embodiment, a set of reconfigurable hardware including a number of field programmable gate arrays (FPGAs) is configured to solve a satisfiability problem. The satisfiability problem is decomposed into a number of independent and disjoint subproblems, e.g., using a simple decomposition in conjunction with disjoint partitioning, such that each of the subproblems is implementable within a given one of the FPGAs without the need for any inter-FPGA communication. Each FPGA then independently determines a satisfiability indication for one of the subproblems. At least a subset of the FPGAs may each be used to process more than one of the subproblems.

Abstract: Test pattern generation is performed for a sequential circuit by first separating the circuit into overlapping pipelines by controlling corresponding clocks for one or more registers of the circuit so as to break feedback loops of the circuit, and then processing each of the pipelines separately in order to determine if particular target faults are detectable in the pipelines. Independent clocks may be provided for each of a number of registers of the circuit in order to facilitate the breaking of the feedback loops. The processing of the pipelines may include a first processing operation which detects target faults in a single time frame, and a second processing operation which detects target faults in two or more time frames. The first processing operation generates as many combinational test vectors as possible for each of the pipelines, while the second processing operation generates sequences of two or more combinational test vectors for each of the pipelines.

Abstract: The invention provides methods and apparatus for implementing a satisfiability algorithm on reconfigurable hardware. An illustrative embodiment is in the form of a parallel-backtrace satisfier which includes clause logic, literal logic and variable logic for implementing logic functions associated with clauses, literals and variables, respectively, of a circuit to be analyzed. The satisfier also includes a controller, e.g., a synchronization unit, for directing the operation of the clause logic, literal logic and variable logic so as to provide parallel backtracing of objectives along a plurality of circuit paths from a primary output of the circuit toward its primary inputs. Enhanced parallelism is implemented in the illustrative embodiment not only by providing the parallel backtracing of the multiple objectives, but also by, e.g., providing concurrent assignments of multiple primary inputs.

Abstract: A method of fault tolerant reconfiguration and operation of a field programmable gate array (FPGA) during normal on-line operation includes selecting a programmable logic block as a programmable logic block under test, testing the programmable logic block under test, and detecting the existence of any faults in the programmable logic block under test. During testing, the programmable logic block under test is repeatedly reconfigured in order to test the programmable logic block completely in all possible modes of operation. Based on the results of the test, a test result indication is sent to a controller in communication with a memory for storing usage and fault status data for each programmable logic block. If a partially faulty test result indication is present, the controller determines an intended mode of operation of the partially faulty programmable logic block under test and reconfigures the logic block for further use, thus allowing a more gradual degradation of the field programmable gate array.

Abstract: A method of built-in self-testing field programmable gate arrays (FPGAs) including the programmable logic blocks, the programmable routing networks and the programmable input/output cells or boundary ports at the device, board or system level includes testing the programmable logic blocks, reconfiguring a first group of he programmable logic blocks to include a test pattern generator and an output response analyzer, and configuring the programmable routing network into groups of wires under test. This step is followed by generating test patterns propagated along the wires under test and comparing the outputs utilizing the output response analyzer. Based on the result of the comparison a pass/fail test result indication is routed to the associated boundary port. The results from a plurality of output response analyzers can be compared utilizing an iterative comparator in order to reduce the number of boundary ports required during testing.

Abstract: A method of testing field programmable gate arrays (FPGAs) includes establishing a first group of programmable logic blocks as test pattern generators or output response analyzers and a second group of programmable logic blocks as blocks under test. This is followed by generating test patterns and comparing outputs of two blocks under test with one output response analyzer. Next is the combining of results of a plurality of output response analyzers utilizing an iterative comparator in order to produce a pass/fail indication. The method also includes the step of reconfiguring each block under test so that each block under test is tested in all possible modes of operation. Further, there follows the step of reversing programming of the groups of programmable logic blocks so that each programmable logic block is configured at least once as a block under test.

Abstract: A set of reconfigurable hardware includes a number of field programmable gate arrays (FPGAs), a controller referred to as a page manager, and a RAM-based local memory. In an illustrative embodiment, each of the FPGAs is suitable for implementing any one of a number of different portions of a logic circuit. A netlist or other descriptive information characterizing the logic circuit is partitioned into a number of pages, each of the pages corresponding to one of the portions of the circuit. The page manager controls the loading and unloading of the pages from the local memory into the FPGAs of the reconfigurable hardware, and controls storage and transfer of inter-page signals. The page manager is configured to detect "page faults" such as, for example, an unloaded page with a full input buffer. The page manager responds to a given page fault by subsequently loading the previously unloaded page into one of the FPGAs.

Abstract: A method of testing field programmable gate arrays (FPGAs) includes the step of configuring programmable logic blocks of the FPGAs for completing a built-in self-test. This is followed by the steps of initiating the built-in self-test, generating test patterns with the programmable logic blocks and analyzing a resulting response to produce a pass/fail indication with the programmable logic blocks. More specifically, the configuring step includes establishing a first group of programmable logic blocks as test pattern generators and output response analyzers and a second group of programmable logic blocks as blocks under test. The blocks under test are then repeatedly recongifured in order to completely test each block under test in all possible modes of operation. The programming of the first and second groups of programmable logic blocks is then reversed and the testing of each new block under test is then completed.

Abstract: A method of testing field programmable gate arrays (FPGAs) includes the step of configuring programmable logic blocks of the FPGAs for completing a built-in self-test. Specifically, the FPGA under test may be configured to act as an iterative logic array wherein a first group of programmable logic blocks are configured as test pattern generators, output response analyzers and helper cells, and a second group of programmable logic blocks are configured as blocks under test. The blocks under test are then repeatedly reconfigured in order to completely test each block under test in all possible modes of operation. The first and second groups of programmable logic blocks are then repeatedly rearranged so that all the programmable logic blocks are established as blocks under test at least once. Following the rearrangement, the repeated reconfiguration of the blocks under test is performed once again.

Abstract: A fault simulator for a digital combinational circuit implements a critical path tracing algorithm in reconfigurable hardware and comprises: a forward network capable of emulating the digital combinational circuit and having primary outputs; a second forward network capable of emulating the digital combinational circuit in the presence of a stem fault and having corresponding primary outputs, the first and second forward network receiving identical input test signals at primary inputs thereof; a backward network having one primary input for every primary output of said combinational circuit and one primary output for every primary input of the combinational circuit, the backward network receiving signal values propagated to primary outputs in the first forward network in response to the input test signals; and, circuitry provided in the backward network responsive to signal values propagated in the first forward network for computing criticality of paths, the computed critical paths indicating faults in the c

Abstract: Automatic test pattern generator for generating test patterns that are capable of detecting faults in a digital combinational circuit comprises a first forward network capable of emulating the digital combinational circuit; a second forward network capable of emulating the digital combinational circuit in the presence of any one target fault from a specified set of faults, and receiving a set of control signals for selecting the target fault; a first backward network having one primary input for every primary output of the digital combinational circuit and one primary output for every primary input of the digital combinational circuit, the first backward network generating one fault activation objective corresponding to the selected target fault, and receiving first signal values computed in the first forward network for propagating the fault activation objective towards a primary output; a second backward network having one primary input for every primary output of the digital combinational circuit and one p

Abstract: A method of increasing the testability of sequential circuit designs with use of a clock transformation technique. Circuit states which are difficult to reach, but are nonetheless required to detect at least one fault of the circuit, are automatically identified. In accordance with one illustrative embodiment, estimations of joint line probabilities are compared with a preselected threshold value to identify hard-to-reach states. Then, commonly clocked flip-flops which must be simultaneously assigned values in order to reach the identified states are partitioned into independently clocked groups of flip-flops. In this manner, hard-to-reach circuit states are transformed into easy-to-reach states, which, in turn, results in transforming difficult-to-detect faults into easy-to-detect faults.

Abstract: A method for testing a sequential circuit by applying a number of test vectors to the primary inputs of the sequential circuit between each application of a clock circuit. Once the sequential circuit enters a state and that state is a necessary condition for detecting various faults, test vectors are applied to the primary inputs of the sequential circuit, which vectors are designed to propagate all fault effects that can be propagated at that state of the circuit. Once those vectors have been applied, a state-advancing vector is applied immediately before the application of the clock. The state-advancing vector is designed to condition the circuit to allow more fault effects to be propagated to the primary outputs, and to propagate fault effects into the storage elements of the circuit.

Abstract: A method of identifying untestable faults in a logic circuit. A lead in the circuit is selected and the circuit is analyzed to determine which faults would be untestable if the selected circuit lead were unable to assume a logic 0 and which faults would be untestable if the selected circuit lead were unable to assume a logic 1. Faults that would be untestable in both (hypothetical) cases are identified as untestable faults. Faults which would be untestable if the selected lead were unable to assume a given value may be determined based on an implication procedure. The implication procedure comprises the forward propagation of uncontrollability indicators and the backward propagation of unobservability indicators. An uncontrollability indicator for the given value is assigned to the selected circuit lead and propagated forward through the circuit according to a set of well-defined propagation rules.