Soft-Error-Tolerant Dual-Modular-Redundancy Architecture with Repair and Retry Scheme for Memory-Control Circuit on FPGA

Makoto SAEN  Tadanobu TOBA  Yusuke KANNO  

IEICE TRANSACTIONS on Electronics   Vol.E100-C   No.4   pp.382-390
Publication Date: 2017/04/01
Online ISSN: 1745-1353
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design — Architecture, Circuit, Device and Design Methodology)
FPGA,  soft-error tolerance,  memory controller,  configuration RAM,  

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This paper presents a soft-error-tolerant memory-control circuit for SRAM-based field programmable gate arrays (FPGAs). A potential obstacle to applying such FPGAs to safety-critical industrial control systems is their low tolerance. The main reason is that soft errors damage circuit-configuration data stored in SRAM-based configuration memory. To overcome this obstacle, the soft-error tolerance must thus be improved while suppressing the circuit area overhead, and data stored in external memory must be protected when a fault occurs on the FPGA. Therefore, a memory-control circuit was developed on the basis of a dual-modular-redundancy (DMR) architecture. This memory controller has a repair and retry scheme that repairs damaged circuit-configuration data and re-executes unfinished accesses after the repair. The developed architecture reduces circuit redundancy below that of a commonly used triple-modular-redundancy (TMR) architecture. Moreover, a write-invalidation circuit was developed to protect data in external memory, and an external-memory-state recovery circuit was developed to enable resumption of memory access after fault repair. The developed memory controller was implemented in a prototype circuit on an FPGA and evaluated using the prototype. The evaluation results demonstrated that the developed memory controller can operate successfully for 1.03×109 hours (at sea level). In addition, its circuit area overhead was found to be sufficiently smaller than that of the TMR architecture.