Design of reconfigurable access wrappers for embedded core based SoC test

Testing of embedded core based system-on-chip (SoC) ICs is a well known problem, and the upcoming IEEE P1500 Standard on Embedded Core Test (SECT) standard proposes DFT solutions to alleviate it. One of the proposals is to provide every core in the SoC with test access wrappers. Previous approaches to the problem of wrapper design have proposed static core wrappers, which are designed for a fixed test access mechanism (TAM) width. We present the first report of a design of reconfigurable core wrappers which allow for a dynamic change in the width of the TAM executing the core test. Analysis of the corresponding scheduling problem indicates that good approximate schedules can be achieved without significant computational effort. Specifically, we derive a O(N/sub C//sup 2/B) time algorithm which can compute near optimal SoC test schedules, where N/sub C/ is the number of cores and B is the number of top level TAMs. Experimental results on benchmark SoCs are presented which improve upon integer programming based methods, not only in the quality of the schedule, but also significantly reduce the computation time.     

A Novel Reconfigurable Wrapper for Testing of Embedded Core-Based SOCs and its Associated Scheduling Algorithm

In this paper a mathematical formulation and an efficient solution, of the embedded core-based system-on-chip (SOC) test scheduling problem (ECTSP) is presented. The ECTSP can be stated as follows; given a chip with N _C cores each having a test T _i; where T _i takes time to execute on a test access mechanism (TAM) of width w _j, and a constraint W on the number of top-level test pins; calculate the TAM assignment vector and the schedule for each test T _i, such that the completion time of the full chip test is minimized. All existing approaches have solved the ECTSP by solving the TAM partition and scheduling problem sequentially. In this paper we present an unified approach to solve the ECTSP. We present the first report of a design of reconfigurable core wrapper which allows for a dynamic change in the width of the test access mechanism (TAM) executing a core test. An automatic procedure for the creation of DfT hardware required for reconfiguration using a graph theoretic representation of core wrappers is also presented. For the case of reconfigurable wrappers, efficient algorithms to compute the schedule are presented based upon some recent results in the field of malleable task scheduling. Cases in which the degree of reconfigurability are constrained are considered; the case when only a single core can have reconfigurable wrapper, a schedule with zero TAM idle time can be found in time O(N _C(N _C + W)lgW), and the case when only 2 different wrapper configurations are allowed can be solved in time O(N _C ³). Comparison with existing results on benchmark SOCs show that our algorithms outperform state-of-art ILP formulations not only in schedule makespan, but also significantly reduce computation time.     

A Reconfigurable Power Conscious Core Wrapper and its Application to System-on-Chip Test Scheduling

The increasing test application times required for testing system-on-chips (SOCs) is a problem that leads to higher costs. For modular core based SOCs it is possibly to employ a concurrent test scheme in order to lower the test application times. To allow each core to be tested as a separate unit, a wrapper is inserted for each core, the scan chains at each core are configured into a fixed number of wrapper chains, and the wrapper chains are connected to the test access mechanism. A problem with concurrent testing is that it leads to higher power consumption as several cores are active at a time. Power consumption above the specified limit of a core or above the limit of the system will cause damage and must be avoided. The power consumption must be controlled both at core level as well as on system level. In this paper, we propose a reconfigurable power conscious core wrapper that we include in a preemptive power constrained test scheduling algorithm. The advantages with the wrapper are that the number of wrapper chains at each core can dynamically be changed during test application and the possibility, through clock gating, to select the appropriate test power consumption for each core. The scheduling technique produces optimal solutions in respect to test time and selects wrapper configurations in a systematic manner while ensuring the power limits at core level and system level are not violated. The wrapper configurations are selected such that the number of wrapper configurations as well as the number of wrapper chains at each wrapper are minimized, which minimizes the wrapper logic as well as the total TAM routing. We have implemented the technique and the experimental results show the efficiency of our approach. The research is supported by the Swedish Foundation on Strategic Research (SFS) under the Strategic Integrated Electronic Systems Research (STRINGENT) program.     

Test Wrapper and Test Access Mechanism Co-Optimization for System-on-Chip

Test access mechanisms (TAMs) and test wrappers are integral parts of a system-on-chip (SOC) test architecture. Prior research has concentrated on only one aspect of the TAM/wrapper design problem at a time, i.e., either optimizing the TAMs for a set of pre-designed wrappers, or optimizing the wrapper for a given TAM width. In this paper, we address a more general problem, that of carrying out TAM design and wrapper optimization in conjunction. We present an efficient algorithm to construct wrappers that reduce the testing time for cores. Our wrapper design algorithm improves on earlier approaches by also reducing the TAM width required to achieve these lower testing times. We present new mathematical models for TAM optimization that use the core testing time values calculated by our wrapper design algorithm. We further present a new enumerative method for TAM optimization that reduces execution time significantly when the number of TAMs being designed is small. Experimental results are presented for an academic SOC as well as an industrial SOC.     

A Graph-Based Approach to Power-Constrained SOC Test Scheduling

The test scheduling problem is one of the major issues in the test integration of system-on-chip (SOC), and a test schedule is usually influenced by the test access mechanism (TAM). In this paper we propose a graph-based approach to power-constrained test scheduling, with TAM assignment and test conflicts also considered. By mapping a test schedule to a subgraph of the test compatibility graph, an interval graph recognition method can be used to determine the order of the core tests. We then present a heuristic algorithm that can effectively assign TAM wires to the cores, given the test order. With the help of the tabu search method and the test compatibility graph, the proposed algorithm allows rapid exploration of the solution space. Experimental results for the ITC02 benchmarks show that short test length is achieved within reasonable computation time.     

Test infrastructure design for mixed-signal SOCs with wrapped analog cores

Many system-on-chips (SOCs) today contain both digital- and analog-embedded cores. Even though the test cost for such mixed-signal SOCs is significantly higher than that for digital SOCs, most prior research in this area has focused exclusively on digital cores. We propose a low-cost test development methodology for mixed-signal SOCs that allows the analog and digital cores to be tested in a unified manner, thereby minimizing the overall test cost. The analog cores in the SOC are wrapped such that they can be accessed using a digital test access mechanism (TAM). We evaluate the impact of the use of analog test wrappers on area overhead and test time. To reduce area overhead, we present an analog test wrapper optimization technique, which is then combined with TAM optimization in a cost-oriented heuristic approach for test scheduling. We also demonstrate the feasibility of using analog wrappers by presenting transistor-level simulations for an analog wrapper and a representative core. We present experimental results for three SOCs from the ITC '02 test benchmarks that have been augmented with three analog cores: an I-Q transmit path pair and an audio CODEC path used in cellular phone applications.     

IPRM: IP core resource multiplexing of core wrapper design for reducing test application time in DVFS-based multicore SoCs

A modify wrapper/test access mechanism(TAM) structure is described to explore the maximal potential capacity of TAM, named “IP cores resource multiplexing(IPRM)”, reducing test application time for DVFS-based multicore System-on-Chips(MSoCs). The IPRM core wrappers, different from standard wrappers, enable to isolated core wrapper resource again to store test data for embedded cores under test. An integer linear programming (ILP) formulation with IPRM wrapper is proposed to improve multi-site test. Experimental results of the ITC’02 SoC Benchmark show that IPRM core wrapper reduces the burdens on ATE effectively, and can reduce the test application time by 10–50%.     

MTNet: Design of a Wireless Test Framework for Heterogeneous Nanometer Systems-on-Chip

The rapid migration to nanometer design processes has brought an unprecedented level of integration by allowing system designers to pack a wide variety of functionalities on-chip, namely, systems-on-a-chip (SoCs). In the meantime, electronic testing becomes an enabling technology for this SoC paradigm, since the integration of various core tests is a big challenge, and has revealed a widening gap between design and manufacturing. In particular, the increasing complexity and density of nanometer SoCs have led to the problem of visibility and accessibility in testing. In this paper, we propose an integrated wireless test framework to resolve the acerbated core accessibility problem and to eliminate the incompatibility between the existing SoC test strategies and the next generation billion-transistor SoC specification. Under such a test strategy, the intra-chip wireless links form the wireless test access mechanism (TAM) to transport test data chip-wide. We present a self-configurable multi-hop wireless test micronetwork, dubbed MTNet, with simple and efficient data transmission protocols, and develop a system level design-for-testability structure. Consequently, we propose a geographic routing algorithm to find the test access paths for the deeply embedded cores and a path driven test scheduling algorithm to design and integrate the MTNet-based SoC test access architecture. Extensive simulation study show the feasibility and applicability of MTNet.     

Multiple-Constraint Driven System-on-Chip Test Time Optimization

The cost of testing SOCs (systems-on-chip) is highly related to the test application time. The problem is that the test application time increases as the technology makes it possible to design highly complex chips. These complex chips include a high number of fault sites, which need a high test data volume for testing, and the high test data volume leads to long test application times. For modular core-based SOCs where each module has its distinct tests, concurrent application of the tests can reduce the test application time dramatically, as compared to sequential application. However, when concurrent testing is used, resource conflicts and constraints must be considered. In this paper, we propose a test scheduling technique with the objective to minimize the test application time while considering multiple conflicts. The conflicts we are considering are due to cross-core testing (testing of interconnections between cores), module testing with multiple test sets, hierarchical conflicts in SOCs where cores are embedded in cores, the sharing of the TAM (test access mechanism), test power limitations, and precedence conflicts where the order in which tests are applied is important. These conflicts must be considered in order to design a test schedule that can be used in practice. In particular, the limitation on the test power consumption is important to consider since exceeding the system's power limit might damage the system. We have implemented a technique to integrate the wrapper design algorithm with the test scheduling algorithm, while taking into account all the above constraints. Extensive experiments on the ITC'02 benchmarks show that even though we consider a high number of constraints, our technique produces results that are in the range of results produced be techniques where the constraints are not taken into account.     

Reusing existing resources for testing a multi-processor system-on-chip

In this article, we propose a test strategy for a multi-processor system-on-chip and model the test time for distributed Intellectual Property (IP) cores. The proposed test methodology uses the existing on-chip resources, IP cores and network elements in network-on-chip. The use of embedded IP cores as a built- in self-test (BIST) module completes the test much faster than an external test and provides flexibility in the test program. Moreover, the reuse of the existing network resources as a test media eliminates additional test access mechanism (TAM) wires in the design and increases test parallelism, reducing the area and test time. Based on the proposed test methodology, we evaluate the test time for distributed IP cores. First, we define the model for a distributed IP core with four parameters in the context of test purposes. Next, the required test time is driven. Finally, we show the characteristics of IP cores for a parallel testing that provides useful information for the test scheduling.     

一种峰值功耗约束下的SoC蚁群测试调度算法

基于扫描链技术的SoC芯片测试可产生比正常使用模式下更大的功耗,这将会对器件可靠性产生不利影响,故在测试时需要将芯片测试功耗控制在允许峰值功耗之下.文中采用蚁群优化思路设计SoC测试调度算法,用于在峰值功耗和TAM总线最大宽度约束下降低SoC测试时间.实验结果表明,本方法优于先前已发表的相关方法.     

A framework for reconfigurable computing: task scheduling andcontext management

Dynamically reconfigurable architectures are emerging as a viable design alternative to implement a wide range of computationally intensive applications. At the same time, an urgent necessity has arisen for support tool development to automate the design process and achieve optimal exploitation of the architectural features of the system. Task scheduling and context (configuration) management become very critical issues in achieving the high performance that digital signal processing (DSP) and multimedia applications demand. This article proposes a strategy to automate the design process which considers all possible optimizations that can be carried out at compilation time, regarding context and data transfers. This strategy is general in nature and could be applied to different reconfigurable systems. We also discuss the key aspects of the scheduling problem in a reconfigurable architecture such as MorphoSys. In particular, we focus on a task scheduling methodology for DSP and multimedia applications, as well as the context management and scheduling optimizations     

Test Scheduling for Network-on-Chip Using XY-Direction Connected Subgraph Partition and Multiple Test Clocks

It is attractive to reuse the on-chip functional interconnects as test access mechanism (TAM) in network-on-chip (NoC) system testing. However, in the methodology of NoC-reuse as TAM, the influence factors in NoC testing significantly increased. To further reduce test time and show significant gains over other work, we propose XY-direction connected subgraph partition (XYCSP) approach to eliminate the path conflicts before testing, and concurrently determine the position of test access points. We then present a multiple test clock strategy to bridge the gap between the NoC channel bandwidth and the core test wrapper bandwidth. With the help of adaptive probability gate quantum-inspired evolutionary algorithm (APGQEA) strategy, which blends adaptive strategy and multi-nary oriented techniques, the proposed NoC test scheduling algorithm permits quick exploration and exploitation of the solution space. Moreover, power constraints are also taken into account. Experimental results for the ITC’02 benchmarks show that the proposed scheme can achieve shorter test time compared to prior works.     

Optimal scheduling of coordinated multipoint transmissions in cellular networks

In this paper, we study the optimal scheduling problem in coordinated multipoint (CoMP) transmission–based cellular networks. We consider joint transmission and coordinated scheduling together in CoMP transmission–based cellular networks and develop an optimization framework to compute the optimal max‐min throughput and the optimal scheduling of the transmissions to the users. The optimization problem is found to be a complex linear program with number of variables in for a cellular network of N users and K cells. We solve the optimization problem for several network instances using an optimization tool. The numerical results show that the optimal CoMP transmission provides a significant throughput gain over a traditional transmission. We find that in optimal scheduling the fraction time of coordinated scheduling is higher than that of joint transmission. To solve the optimization problem without any optimization tool, we propose a heuristic algorithm. The performance of the heuristic algorithm is evaluated and found to be provided throughput around 97% of the optimal throughput. Further, we extend the optimization framework to study joint scheduling and power allocation (JSPA) problem in CoMP transmission–based cellular networks. We numerically solve the JSPA problem for the network instances and demonstrate that the optimal power allocation at the base stations is not binary for a significant fraction of time of scheduling. However, the gain in max‐min throughput by the optimal JSPA technique over the optimal scheduling technique is not significant.     

Minimizing Internal Speedup for Performance Guaranteed Switches With Optical Fabrics

We consider traffic scheduling in an N times N packet switch with an optical switch fabric, where the fabric requires a reconfiguration overhead to change its switch configurations. To provide 100% throughput with bounded packet delay, a speedup in the switch fabric is necessary to compensate for both the reconfiguration overhead and the inefficiency of the scheduling algorithm. In order to reduce the implementation cost of the switch, we aim at minimizing the required speedup for a given packet delay bound. Conventional Birkhoff-von Neumann traffic matrix decomposition requires N2 - 2N + 2 configurations in the schedule, which lead to a very large packet delay bound. The existing DOUBLE algorithm requires a fixed number of only 2N configurations, but it cannot adjust its schedule according to different switch parameters. In this paper, we first design a generic approach to decompose a traffic matrix into an arbitrary number of Ns (N² - 2N + 2 > N_S > N) configurations. Then, by taking the reconfiguration overhead into account, we formulate a speedup function. Minimizing the speedup function results in an efficient scheduling algorithm ADAPT. We further observe that the algorithmic efficiency of ADAPT can be improved by better utilizing the switch bandwidth. This leads to a more efficient algorithm SRF (scheduling residue first). ADAPT and SRF can automatically adjust the number of configurations in a schedule according to different switch parameters. We show that both algorithms outperform the existing DOUBLE algorithm.     

Meta‐heuristic algorithms for channel scheduling problem in wireless sensor networks

The channel scheduling problem is to decide how to commit channels for transmitting data between nodes in wireless networks. This problem is one of the most important problems in wireless sensor networks. In this problem, we aim to obtain a near‐optimal solution with the minimal energy consumption within a reasonable time. As the number of nodes increases in the network, however, the amount of calculation for finding the solution would be too high. It can be difficult to obtain an optimal solution in a reasonable execution time because this problem is NP‐hard. Therefore, most of the recent studies for such problems seem to focus on heuristic algorithms. In this paper, we propose efficient channel scheduling algorithms to obtain a near‐optimal solution on the basis of three meta‐heuristic algorithms; the genetic algorithm, the Tabu search, and the simulated annealing. In order to make a search more efficient, we propose some neighborhood generating methods for the proposed algorithms. We evaluate the performance of the proposed algorithms through some experiments in terms of energy consumption and algorithm execution time. The experimental results show that the proposed algorithms are efficient for solving the channel scheduling problem in wireless sensor networks. Copyright © 2011 John Wiley & Sons, Ltd.     

Test-access mechanism optimization for core-based three-dimensional SOCs

Embedded cores in a core-based system-on-chip (SOC) are not easily accessible via chip I/O pins. Test-access mechanisms (TAMs) and test wrappers (e.g., the IEEE Standard 1500 wrapper) have been proposed for the testing of embedded cores in a core-based SOC in a modular fashion. We show that such a modular testing approach can also be used for emerging three-dimensional integrated circuits based on through-silicon vias (TSVs). Core-based SOCs based on 3D IC technology are being advocated as a means to continue technology scaling and overcome interconnect-related bottlenecks. We present an optimization technique for minimizing the post-bond test time for 3D core-based SOCs under constraints on the number of TSVs, the TAM bitwidth, and thermal limits. The proposed optimization method is based on a combination of integer linear programming, LP-relaxation, and randomized rounding. It considers the Test Bus and TestRail architectures, and incorporates wire-length constraints in test-access optimization. Simulation results are presented for the ITC 02 SOC Test Benchmarks and the test times are compared to that obtained when methods developed earlier for two-dimensional ICs are applied to 3D ICs. The test time dependence on various 3D parameters (e.g. 3D placement, the number of layers, thermal constraints, and the number of TSVs) is also studied.     

Abort-on-Fail Based Test Scheduling

The long and increasing test application time for modular core-based system-on-chips is a major problem, and many approaches have been developed to deal with the problem. Different from previous approaches, where it is assumed that all tests will be performed until completion, we consider the cases where the test process is terminated as soon as a defect is detected. Such abort-on-fail testing is common practice in production test of chips. We define a model to compute the expected test time for a given test schedule in an abort-on-fail environment. We have implemented three scheduling techniques and the experimental results show a significant test time reduction (up to 90%) when making use of an efficient test scheduling technique that takes defect probabilities into account. The research is partially supported by the Swedish National Program STRINGENT.     

Test Scheduling of NoC‐Based SoCs Using Multiple Test Clocks

Network‐on‐chip (NoC) is an emerging design paradigm intended to cope with future systems‐on‐chips (SoCs) containing numerous built‐in cores. Since NoCs have some outstanding features regarding design complexity, timing, scalability, power dissipation and so on, widespread interest in this novel paradigm is likely to grow. The test strategy is a significant factor in the practicality and feasibility of NoC‐based SoCs. Among the existing test issues for NoC‐based SoCs, test access mechanism architecture and test scheduling particularly dominate the overall test performance. In this paper, we propose an efficient NoC‐based SoC test scheduling algorithm based on a rectangle packing approach used for current SoC tests. In order to adopt the rectangle packing solution, we designed specific methods and configurations for testing NoC‐based SoCs, such as test packet routing, test pattern generation, and absorption. Furthermore, we extended and improved the proposed algorithm using multiple test clocks. Experimental results using some ITC’02 benchmark circuits show that the proposed algorithm can reduce the overall test time by up to 55%, and 20% on average compared with previous works. In addition, the computation time of the algorithm is less than one second in most cases. Consequently, we expect the proposed scheduling algorithm to be a promising and competitive method for testing NoC‐based SoCs.     

On Concurrent Test of Core-Based SOC Design

In this paper, a method to solve the resource allocation and test scheduling problems together in order to achieve concurrent test for core-based System-On-Chip (SOC) designs is presented. The primary objective for concurrent SOC test is to reduce test application time under the constraints of SOC pins and peak power consumption. The methodology used in this paper is not limited to any specific Test Access Mechanism (TAM). Additionally, it can also be applied to SOC budgeting at design phase to predict a tradeoff between test application time and SOC pins needed. The contribution of this paper is the formulation of the problem as a well-known 2-dimensional bin-packing problem. A best-fit heuristic algorithm is adopted to achieve optimal solution.