In this paper we present a novel integrated approach to on-line FPGA testing, diagnosis, and fault-tolerance, to be used in high-reliability and high-availability hardware. The test process takes place in self-testing areas (STARs) of the FPGA, without disturbing the normal system operation. The entire chip is eventually tested by having (STARs) gradually rove across the FPGA. Our approach guarantees complete testing of programmable logic blocks and interconnect, and provides maximum diagnostic resolution. A new fault-tolerant (FT) technique allows using partially defective FPGA resources for normal operation, providing longer mission life-span in the presence of faults. We also introduce the basic concepts of a new dynamic FT method, spare resources needed to bypass a fault are always in the neighborhood of the located fault, thus simplifying fault-bypassing.

Using roving STARs for on-line testing and diagnosis of FPGAs in fault-tolerant applications

In this paper we present an on-line, multi-level fault tolerant (FT) technique for system functions and applications mapped to partially and dynamically reconfigurable FPGAs. Our method is based on the roving self testing areas (STARs) fault detection/location strategy presented in Abramovici et al. (1999). In STARs, the area under test uses partial reconfiguration properties to modify the configuration of the area under test without affecting the configuration of the system function and dynamic reconfiguration properties to allow uninterrupted execution of the system function while reconfiguration takes place. In this paper we take this one step further. Once a fault (or multiple faults) is detected we dynamically reconfigure the working area application around the fault with no additional system function interruption (other than the interruption when a STAR moves to a new location). We also apply the concept of partially usable blocks to increase fault tolerance. Our method has been successfully implemented and demonstrated on the ORCA 2CA series FPGAs from Lucent Technologies.

Dynamic fault tolerance in FPGAs via partial reconfiguration

We present a built-in self-test (BIST) approach able to detect and accurately diagnose all single and practically all multiple faulty programmable logic blocks (PLBs) in field programmable gate arrays (FPGAs) with maximum diagnostic resolution. Unlike conventional BIST, FPGA BIST does not involve any area overhead or performance degradation. We also identify and solve the problem of testing configuration multiplexers that was either ignored or incorrectly solved in most previous work. We introduce the first diagnosis method for multiple faulty PLBs; for any faulty PLB, we also identify its internal faulty modules or modes of operation. Our accurate diagnosis provides the basis for both failure analysis used for yield improvement and for any repair strategy used for fault-tolerance in reconfigurable systems. We present experimental results showing detection and identification of faulty PLBs in actual defective FPGAs. Our BIST architecture is easily scalable.

BIST-based test and diagnosis of FPGA logic blocks : Reconfigurable and Adaptive VLSI Systems

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BIST-based test and diagnosis of FPGA logic blocks

The very high levels of integration and submicron device sizes used in current and emerging VLSI technologies for FPGAs lead to higher occurrences of defects and operational faults. Thus, there is a critical need for fault tolerance and reconfiguration techniques for FPGAs to increase chip yields (with factory reconfiguration) and/or system reliability (with field reconfiguration). We first propose techniques utilizing the principle of node-covering to tolerate logic or cell faults in SRAM-based FPGAs. A routing discipline is developed that allows each cell to cover-to be able to replace-its neighbor in a row. Techniques are also proposed for tolerating wiring faults by means of replacement with spare portions. The replaceable portions can be individual segments, or else sets of segments, called "grids". Fault detection in the FPGAs is accomplished by separate testing, either at the factory or by the user. If reconfiguration around faulty cells and wiring is performed at the factory (with laser-burned fuses, for example), it is completely transparent to the user. In other words, user configuration data loaded into the SRAM remains the same, independent of whether the chip is detect-free or whether it has been reconfigured around defective cells or wiring-a major advantage for hardware vendors who design and sell FPGA-based logic (e.g., glue logic in microcontrollers, video cards, DSP cards) in production-scale quantities. Compared to other techniques for fault tolerance in FPGAs, our methods are shown to provide significantly greater yield improvement, and a 35 percent non-FT chip yield for a 16/spl times/16 FPGA is more than doubled.

Methodologies for tolerating cell and interconnect faults in FPGAs

Significant increases in chip yield can result if faulty logic cells and wiring in field programmable gate arrays (FPGAs) can be isolated from the remainder of the circuitry to retain a completely usable chip. Utilizing the principle of node-covering, a routing discipline has been developed that allows each logic cell in an FPGA to cover-to be able to replace-its neighbor in a row. An FPGA is factory-reconfigured such that a faulty cell is replaced by its cover, which in turn is replaced by its own cover, and so on until a spare cell in the row is reached. Since wiring channel area is a major portion of chip area in an FPGA, new techniques are also proposed for tolerating wiring faults. As with faulty logic cells, faulty wiring portions are replaced by adjacent ones, until eventually a spare wiring portion is reached. Compared to other techniques for fault tolerance in FPGAs, these methods are shown to provide significantly greater yield improvement.

F. Hanchek

Papers

Methodologies for tolerating cell and interconnect faults in FPGAs

Design methodologies for tolerating cell and interconnect faults in FPGAs