Body Bias Domain Partitioning Size Exploration for a Coarse Grained Reconfigurable Accelerator

Yusuke MATSUSHITA  Hayate OKUHARA  Koichiro MASUYAMA  Yu FUJITA  Ryuta KAWANO  Hideharu AMANO  

Publication
IEICE TRANSACTIONS on Information and Systems   Vol.E100-D   No.12   pp.2828-2836
Publication Date: 2017/12/01
Online ISSN: 1745-1361
Type of Manuscript: Special Section PAPER (Special Section on Parallel and Distributed Computing and Networking)
Category: Architecture
Keyword: 
CGRA,  body bias,  power reduction,  cool mega array,  

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Summary: 
Body biasing can be used to control the leakage power and performance by changing the threshold voltage of transistors after fabrication. Especially, a new process called Silicon-On-Thin Box (SOTB) CMOS can control their balance widely. When it is applied to a Coarse Grained Reconfigurable Array (CGRA), the leakage power can be much reduced by precise bias control with small domain size including a small number of PEs. On the other hand, the area overhead for separating power domain and delivering a lot of wires for body bias voltage supply increases. This paper explores the grain of domain size of an energy efficient CGRA called CMA (Cool Mega Array). By using Genetic Algorithm based body bias assignment method, the leakage reduction of various grain size was evaluated. As a result, a domain with 2x1 PEs achieved about 40% power reduction with a 6% area overhead. It has appeared that a combination of three body bias voltages; zero bias, weak reverse bias and strong reverse bias can achieve the optimal leakage reduction and area overhead balance in most cases.