Partial scan design of register-transfer level circuits

Register-transfer level designs that are derived from high-level synthesis systems generally consist of functional blocks and registers that are interconnected by multiplexers and buses to maximize resource sharing These multiplexer and bus structures have the unique ability to behave asswitches, i.e., to logically partition the circuit when their control inputs are manipulated in different ways. The presence of switches, the selection of scan registers can be influenced. This leads to an efficient partial scan methodology presented in this paper. Second, switches help set up data transfer paths calledI-paths. By employingI-paths to transport test data, the functional logic in the circuit can be separated from the switching logic for the purpose of test generation. This can lead to a reduction in test generation costs for a partial scan design. Thus the techniques presented in this paper help to minimize both testability overhead and test generation cost in bus-based circuits. This methodology is implemented in the SIESTA system for serial scan design.     

Partial Scan Testing on the Register-Transfer Level

This paper presents a methodology to insert scan paths in a design that is specified on the Register Transfer Level (RT-Level). The results indicate that selecting registers on this level guarantees a reduction in DFT design time and improvement of fault coverage, without incurring high hardware overhead.     

全扫描设计中多扫描链的构造

本文在交迭测试体系 的基础上提出了一种多扫描链的区间构造法,对于确定的测试向量集能够显著地减少测试应用时间.该构造方法根据规定的扫描链数,通过求解线性规划问题的方法确定扫描寄存器在扫描链上的优化的分布区间,从而构造多扫描链,最后根据对多扫描链进行连线复杂度的定性分析,求得连线复杂度最低的多扫描链的最优构造.     

Reducing Average and Peak Test Power Through Scan Chain Modification

Parallel test application helps reduce the otherwise considerable test times in SOCs; yet its applicability is limited by average and peak power considerations. The typical test vector loading techniques result in frequent transitions in the scan chain, which in turn reflect into significant levels of circuit switching unnecessarily. Judicious utilization of logic in the scan chain can help reduce transitions while loading the test vector needed. The transitions embedded in both test stimuli and the responses are handled through scan chain modifications consisting of logic gate insertion between scan cells as well as inversion of capture paths. No performance degradation ensues as these modifications have no impact on functional execution. To reduce average and peak power, we herein propose computationally efficient schemes that identify the location and the type of logic to be inserted. The experimental results confirm the significant reductions in test power possible under the proposed scheme.     

基于Multi-Capture结构的扫描链优化算法

提出了一种基于多扫描链Multi-capture结构的扫描链优化算法,通过构造具有最小相关度的多扫描链结构,并利用Multi-capture内部响应复用为激励以侦测故障的原理,达到极大压缩测试向量长度的目的。实验结果表明,该优化算法平均优化率可以达到30％左右。     

A test methodology for finite state machines using partial scan design

This paper presents an efficient automatic test pattern generation technique for loop-free circuits. A partial scan technique is used to convert a sequential circuit (finite state machine) with arbitrary feedback paths into a pipelined circuit for testing. Test generation for these modified circuits can be performed with a modified combinational automatic test pattern generator (ATPG), which is much faster than a sequential ATPG. A combinational model is obtained by replacing all flipflops by buffers. It is shown that a test vector for a fault in this model obtained by a combinational test generator can be expanded into a sequence of identical vectors to detect the same fault in the original sequential circuit. This technique may abort a few faults which can then be resolved with a sequential ATPG. Experiments on the ISCAS89 circuits show that only 30% to 70% of flipflops require scanning in larger circuits and 96% to 100% fault coverage for almost all the circuits without resorting to a sequential ATPG.This research was sponsored by the Semiconductor Research Corporation, Contract 90-DP-142.     

Partial scan design and test sequence generation based on reduced scan shift method

This paper presents a partial scan algorithm, calledPARES (PartialscanAlgorithm based onREduced Scan shift), for designing partial scan circuits. PARES is based on the reduced scan shift that has been previously proposed for generating short test sequences for full scan circuits. In the reduced scan shift method, one determines proch FFs must be controlled and observed for each test vector. According to the results of similar analysis, PARES selects these FFs that must be controlled or observed for a large number of test vectors, as scanned FFs. Short test sequences are generated by reducing scan shift operations using a static test compaction method. To minimize the loss of fault coverage, the order of test vectors is so determined that the unscanned FFs are in the state required by the next test vector. If there are any faults undetected yet by a test sequence derived from the test vectors, then PARES uses a sequential circuit test generator to detect the faults. Experimental results for ISCAS'89 benchmark circuits are given to demonstrate the effectiveness of PARES.     

动态向量调整的多扫描链测试数据压缩

 由于多扫描链测试方案能够提高测试进度,更适合大规模集成电路的测试,因此提出了一种应用于多扫描链的测试数据压缩方案.该方案引入循环移位处理模式,动态调整向量,能够保留向量中无关位,增加向量的外延,从而提高向量间的相容性和反向相容性;同时,该方案还能够采用一种有效的参考向量更替技术,进一步提高向量间的相关性,减少编码位数.另外,该方案能够利用已有的移位寄存器,减少不必要的硬件开销.实验结果表明所提方案在保持多扫描链测试优势的前提下能够进一步提高测试数据压缩率,满足确定性测试和混合内建自测试.     

An Efficient Deterministic Test Pattern Generator for Scan-Based BIST Environment

To obtain satisfactory fault coverage for testing a logic circuit, linear feedback shift registers (LFSRs) have been used to generate not only the pseudorandom, but also the deterministic patterns in the scan-based built-in self-test environment. However, like other scan-based methods, the LFSR based pattern generation schemes take a long test application time to feed deterministic patterns from the LFSR into a scan chain. In this paper we derive a general relationship between the bits in the scan chain and the states of the LFSR and show that any bit to be generated by an LFSR in any future clock cycle can be pre-generated by a linear function of the current LFSR state. With this relationship, we can divide a scan chain into multiple sub-chains and use one LFSR-based multiple sequence generator to simultaneously generate all the subsequences required by the sub-chains, hence can greatly reduce the test application time for deterministic patterns. Moreover, due to the scan time reduction, test power wasted during the scan operation can also be significantly reduced.     

On minimizing aliasing in scan-based compaction

In this article we address the problem of compacting test response data captured in scan paths. We consider linear compactors, e.g., multiple-input signature registers, and the effect of their characteristic polynomials on the number of aliased faults. The novelty of our analysis lies in that it is based on a realistic error model which takes into account the time correlation among the errors in the test response data fed to the compactor. Such a correlation does exist in scan-based compaction, but has not been considered previously. Based on our analysis, we derive three conditions that should be satisfied to minimize aliasing. They impose little restriction on circuit design.This work was supported in part by grants from the Natural Sciences and Engineering Research Council of Canada and in part by the British Columbia Advanced Systems Institute.     

Integration of partial scan and built-in self-test

Partial-Scan based Built-In Self-Test (PSBIST) is a versatile Design for Testability (DFT) scheme, which employs pseudo-random BIST at all levels of test to achieve fault coverages greater than 98% on average, and supports deterministic partial scan at the IC level to achieve nearly 100% fault coverage. PSBIST builds its BIST capability on top a partial scan structure by adding a test pattern generator, an output data compactor, and a PSBIST controller in a way similar to that of deriving a full scan BIST from a full scan structure. However, to make the scheme effective, there is a minimum requirement regarding which flip-flops in the circuit should be replaced by scan flip-flops and/or initialization flip-flops. In addition, test arents are usually added to boost the fault coverage to the range of 95 to 100 percent. These test points are selected based on a novel probabilistic testability measure, which can be computed extremely fast for a special class of circuits. This ciass of circuits is precisely the type of circuits that we obtain after replacing some of the flip-flops.withscan and/or initilization flip-flops. The testability measure is also used for a very useful quick estimation of the fault coverage right after the selection of sean flip-flops, even before the circuit is modified to incorporate PSBIST capability. While PSBIST provides all the benefits of BIST, it incurs lower area overhead and performance degradation than full scan. The area overhead is further reduced when the boundary scan cells are reconfigured for BIST usage.     

Efficient Test Data Compression and Low Power Scan Testing in SoCs

Testing time and power consumption during the testing of SoCs are becoming increasingly important with an increasing volume of test data in intellectual property cores in SoCs. This paper presents a new algorithm to reduce the scan‐in power and test data volume using a modified scan latch reordering algorithm. We apply a scan latch reordering technique to minimize the column hamming distance in scan vectors. During scan latch reordering, the don't‐care inputs in the scan vectors are assigned for low power and high compression. Experimental results for ISCAS 89 benchmark circuits show that reduced test data and low power scan testing can be achieved in all cases.     

基于部分扫描的低功耗内建自测试

在分析全扫描内建自测试 (BIST)过高测试功耗原因的基础上 ,提出了一种选择部分寄存器成为扫描单元的部分扫描算法来实现低功耗 BIST。实验表明 ,提出的方法在保证测试覆盖率的条件下能同时降低 BIST的峰值功耗和平均功耗 ,降幅分别高达 46%和 69%。     

An optimal scheduling algorithm for testing interconnect using boundary scan

Systems will soon be built with ICs that conform with the IEEE 1149.1 boundary scan architecture. Due to the hierarchical nature of such systems, they may contain many boundary scan chains. These chains can be used to test the system, subsystem, and board interconnect. To reduce test time, the application of test vectors to these scan chains must be carefully scheduled. This article deals with problems related to finding an optimal schedule for testing interconnect. This problem is modeled using a directed graph. The following results are obtained: (1) upper and lower bounds on interconnect test time; (2) necessary and sufficient conditions for obtaining an optimal schedule when the graph is acyclic; (3) sufficient condition for obtaining an optimal schedule when the graph is cyclic; and (4) an algorithm for constructing an optimal schedule for any graph.This work was supported by Defense Advanced Research Projects Agency and monitored by the Office of Naval Research under contract No. N00014-87-K-0861. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the Defense Advanced Research Projects Agency or the U.S. Government.     

An analytical approach to the partial scan problem

The scan design is the most widely used technique used to ensure the testability of sequential circuits. In this article it is shown that testability is still guaranteed, even if only a small part of the flipflops is integrated into a scan path. An algorithm is presented for selecting a minimal number of flipflops, which must be directly accessible. The direct accessibility ensures that, for each fault, the necessary test sequence is bounded linearly in the circuit size. Since the underlying problem is NP-complete, efficient heuristics are implemented to compute suboptimal solutions. Moreover, a new algorithm is presented to map a sequential circuit into a minimal combinational one, such that test pattern generation for both circuit representations is equivalent and the fast combinational ATPG methods can be applied. For all benchmark circuits investigated, this approach results in a significant reduction of the hardware overhead, and additionally a complete fault coverage is still obtained. Amazingly the overall test application time decreases in comparison with a complete scan path, since the width of the shifted patterns is shorter, and the number of patterns increase only to a small extent.     

An Interleaving Technique for Reducing Peak Power in Multiple-Chain Scan Circuits During Test Application

This paper proposes a novel method to reduce the peak power of multiple scan chain based circuits during testing. The peak periodicity and the peak width of the power waveforms for scan-based circuits are analyzed. An interleaving scan architecture based on adding delay buffers among the scan chains is developed which can significantly reduce the peak power. This method can be efficiently integrated with a recently proposed broadcast multiple scan architecture due to the sharing of scan patterns. The effects of the interleaving scan technique applied to the conventional multiple scan and the broadcast multiple scan with 10 scan chains are investigated. Up to 51% peak power reduction can be achieved when the data output of a scan cell is affected by the scan path during scan. When the data output is disabled during scan, up to 76% of peak-power reduction is observed.     

Boundary scan based interconnect testing design for silicon interposer in 2.5D ICs

Interposer-based 2.5-dimensional integrated circuit (2.5D IC) is considered as a promising solution to problems like wire delay and power consumption faced by the semiconductor industry today. Since the interconnect wires in the silicon interposer may be defective during fabrication and assembly, they must be adequately tested to ensure product qualification. This paper presents an efficient interconnect test architecture to detect open, short and delay faults, which is compatible with the IEEE 1149.1 standard. It provides a new boundary scan structure with low test power consumption. To reduce the overall test cost, a data-package based test structure is proposed to match the test data transfer volume between TSVs and scan chains. Interconnects of multiple dies can be tested simultaneously under constrains of test power with minimum external test pins. The simulation results validate the effectiveness of the proposed test method. We also present synthesis results to evaluate the area overhead.     

"龙腾"S2微处理器测试结构设计

介绍了"龙腾"52微处理器测试结构设计方法,详细讨论了采用全扫描测试、内建自测试(BIST)等可测性设计(DFT)技术.该处理器与PC104全兼容,设计中的所有寄存器采用全扫描结构,设计中的存储器采用内建自测试,整个设计使用JTAG作为测试接口.通过这些可测性设计,使芯片的故障覆盖率达到了100%,能够满足流片后测试需求.     

Physical‐Aware Approaches for Speeding Up Scan Shift Operations in SoCs

System‐on‐chip (SoC) designs have a number of flip‐flops; the more flip‐flops an SoC has, the longer the associated scan test application time will be. A scan shift operation accounts for a significant portion of a scan test application time. This paper presents physical‐aware approaches for speeding up scan shift operations in SoCs. To improve the speed of a scan shift operation, we propose a layout‐aware flip‐flop insertion and scan shift operation–aware physical implementation procedure. The proposed combined method of insertion and procedure effectively improves the speed of a scan shift operation. Static timing analyses of state‐of‐the‐art SoC designs show that the proposed approaches help increase the speeds of scan shift operations by up to 4.1 times that reached under a conventional method. The faster scan shift operation speeds help to shorten scan test application times, thus reducing test costs.     

Partial scan flip-flop selection by use of empirical testability

Partial serial scan as a design for testability technique permits automatic generation of high fault coverage tests for sequential circuits with less hardware overhead and less performance degradation than full serial scan. The objective of the partial scan flip-flop selection method proposed here is to obtain maximum fault coverage for the number of scan flip-flops selected. Empirical Testability Difference (ETD), a measure of potential improvement in the testability of the circuit, is used to successively select one or more flip-flops for addition or deletion of scan logic. ETD is calculated by using testability measures based on empirical evaluation of the circuit with the acutal automatic test pattern generation (ATPG) system. In addition, once such faults are known, ETD focuses on the hard-to-detect faults rather than all faults and uses heuristics to permit effective selection of multiple flip-flops without global optimization. Two ETD algorithms have been extensively tested by using FASTEST ATPG [1, 2] on fourteen of the ISCAS89 [3] sequential circuits. The results of these tests indicate that ETD yields, on average, 35% fewer uncovered detectable faults for the same number of scanned flip-flops or 27% fewer scanned flip-flops for comparable fault coverage relative to cycle-breaking methods.This work was performed while the author was with the University of Wisconsin-Madison.