Reconfiguring Cache Associativity: Adaptive Cache Design for Wide-Range Reliable Low-Voltage Operation Using 7T/14T SRAM

Jinwook JUNG  Yohei NAKATA  Shunsuke OKUMURA  Hiroshi KAWAGUCHI  Masahiko YOSHIMOTO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E96-C   No.4   pp.528-537
Publication Date: 2013/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E96.C.528
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design—Architecture, Circuit, Device and Design Methodology)
Category: 
Keyword: 
low-voltage adaptive cache design,  reconfiguring associativity,  dynamic voltage frequency scaling,  7T/14T SRAM,  

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Summary: 
This paper presents an adaptive cache architecture for wide-range reliable low-voltage operations. The proposed associativity-reconfigurable cache consists of pairs of cache ways so that it can exploit the recovery feature of the novel 7T/14T SRAM cell. Each pair has two operating modes that can be selected based upon the required voltage level of current operating conditions: normal mode for high performance and dependable mode for reliable low-voltage operations. We can obtain reliable low-voltage operations by application of the dependable mode to weaker pairs that cannot operate reliably at low voltages. Meanwhile leaving stronger pairs in the normal mode, we can minimize performance losses. Our chip measurement results show that the proposed cache can trade off its associativity with the minimum operating voltage. Moreover, it can decrease the minimum operating voltage by 140 mV achieving 67.48% and 26.70% reduction of the power dissipation and energy per instruction. Processor simulation results show that designing the on-chip caches using the proposed scheme results in 2.95% maximum IPC losses, but it can be chosen various performance levels. Area estimation results show that the proposed cache adds area overhead of 1.61% and 5.49% in 32-KB and 256-KB caches, respectively.