In this paper we introduce a novel error resilient memory architecture potentially applicable to a large range of memory technologies. In contrast with state of the art memory error correction schemes, which rely on (extended Hamming) Error Correcting Codes (ECC), we make use of Low Density Parity Check (LDPC) codes due to their close to the Shannon performance limit error correction capabilities. To allow for a cost-effective implementation we build our approach on top of a 3D memory organization which inherently fast and customizable wide-I/O vertical access allows for a smooth transfer of the required LDPC long code-words to/from an error correction dedicated die. To make the error correction process transparent to the memory users, e.g., processing cores, we propose an online memory scrubbing policy that performs the LDPC-based error detection and correction decoupled from the normal memory operation. For evaluation purposes we consider 3D memories protected by the proposed LDPC mechanism with various data width codes implementations. Simulation results indicate that our proposal clearly outperforms state of the art ECC schemes with fault tolerance improvements by a 4710× factor being obtained when compared to extended Hamming ECC. Furthermore, we evaluate instances of the proposed memory concept equipped with different LDPC codecs implemented on a commercial 40nm low-power CMOS technology and evaluate them on actual memory traces in terms of error correction capability, area, latency, and energy. Our results indicate that the LDPC protected memories offer substantially improved error correction capabilities, when compared to state of the art extended Hamming ECC, being able to assure clean runs for memory error rates α <; 3 × 10-2, which demonstrate that our proposal can potentially successfully protect system on a chip memory systems even in very harsh environmental conditions.@en

In this paper we propose a novel error correction scheme/architecture specially tailored for polyhedral memories which: (i) allows for the formation of long codewords without interfering with the memory architecture/addressing mode/data granularity and (ii) make use of codecs located on a dedicated tier of the 3D memory stack. For a transparent error correction process we propose an online memory scrubbing policy that performs the error detection and correction decoupled from the normal memory operation. To evaluate our proposal we consider as a case study a 4-die 4-MB polyhedral memory and simulate various data width codes implementations. The simulations indicate that our proposal outperforms state of the art single error correction schemes in terms of error correction capability, being able to diminish the Word Error Rates (WER) by many orders of magnitude, e.g., WER from 10^-10 to 10^-21 are achieved for bit error probabilities between 10^-4 and 10^-6, while requiring less redundancy overhead. The scrubbing mechanism hides the codec latency and provides up to 10% and 25% write and read latency reductions, respectively. In addition, by relocating the encoders/decoders from the memory dies to a dedicated one a 13% footprint reduction is obtained and parallel energy effective scrubbing can be enabled, which results in further WER reductions.

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Speed and placement quality are two very important attributes of a good online placement algorithm, because the time taken by the algorithm is considered as an overhead to the application overall execution time. To solve this problem, we propose three techniques: Merging Only if Needed (MON), Partial Merging (PM), and Direct Combine (DC). Our IM (intelligent merging) algorithm uses dynamically these three techniques to exploit their specific advantages. IM outperforms Bazargan's algorithm as it has placement quality within 0.89% but is 1.72 times faster.@en