Executing Hard Real-Time Programs on NAND Flash Memory Considering Read Disturb Errors

학위논문 (석사)-- 서울대학교 대학원 공과대학 컴퓨터공학부, 2017. 8. 이창건.죄근 IoT 와 임베디드 시스템에 대한 관심이 급증하면서 NAND 플래쉬 메모리를 사용하는 장치들 또한 증가하고 있다. 이러한 장치들은 NAND 플래시 메모리를 사용함으로써 큰 이득을 얻을 수 있지만 여전히 신뢰성 측면에서는 해결되지 않은 이슈들이 있다. 본 논문에서는 이러한 신뢰성 문제를 극복할 수 있는 방안에 대해 논의한다. NAND 플래쉬 메모리는 각 페이지에 대해 읽기 명령을 반복적으로 수행 할 있는 물리적 회수가 한정되어 있기 때문에 읽기 횟수가 한계치에 도달하기 전에 재할당을 해주어야 하는 문제가 있다. 본 논문에서는 프로그램 코드가 저장되어 있는 read-only 페이지를 읽어 코드를 수행하는 실시간 임베디드 시스템에서 실시간 제약 조건을 만족하면서 재할당을 하여 READ DISTURB ERROR 를 줄이는 기법에 대해 제안한다. 본 논문에서 제안하는 기법을 구현하고 실험함으로써, NAND 플래쉬 메모리의 읽기 한계치에 도달하기 전에 재할당이 보장됨을 보인다. 또한 제안하는 기법을 사용 할 경우 요구되는 RAM 크기가 최대 48% 감소함을 확인한다1 Introduction 1 2 Related works 6 3 Background and problem description 10 3.1 NAND flash memory 10 3.2 HRT-PLRU 13 3.3 Reliability issues of the NAND flash memory 18 3.4 Problem description 28 3.5 System notation 30 4 Approach 31 4.1 Per-task analysis 31 4.2 Convex optimization 37 5 Evaluation 41 6 Future works 46 7 Conclusion 47 Summary (Korean) 48 References 49Maste

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