Razor 1: Low Power Design using Circuit-Level Timing Speculation

Professors:

• David Blaauw

Students:

• Shidhartha Das
• Sanjay Pant
• Toan Pham
• Rajeev Rao
• Nam Sung Kim

Sponsor

ARM, GSRC, NSF

Primary Contact

Shidhartha Das    [email protected]

With increasing clock frequencies and silicon integration, power aware computing has become a critical concern in the design of embedded processors and systems-on-chip. One of the more effective and widely used methods for power-aware computing is dynamic voltage scaling (DVS). In order to obtain the maximum power savings from DVS, it is essential to scale the supply voltage as low as possible while ensuring correct operation of the processor. The critical voltage is chosen such that under a worst-case scenario of process and environmental variations, the processor always operates correctly. However, this approach leads to a very conservative supply voltage since such a worst-case combination of different variabilities will be very rare. In this work, we propose a new approach to DVS, called Razor, based on dynamic detection and correction of circuit timing errors. The key idea of Razor is to tune the supply voltage by monitoring the error rate during circuit operation, thereby eliminating the need for voltage margins and exploiting the data dependence of circuit delay. A Razor flip-flop is introduced that double-samples pipeline stage values, once with a fast clock and again with a time-borrowing delayed clock. A metastability-tolerant comparator then validates latch values sampled with the fast clock. In the event of a timing error, a modified pipeline mispeculation recovery mechanism restores correct program state. A prototype Razor pipeline was designed in 0.18 µm technology and was analyzed. Razor energy overheads during normal operation are limited to 3.1%. Analyses of a full-custom multiplier and a SPICE-level Kogge-Stone adder model reveal that substantial energy savings are possible for these devices (up to 64.2%) with little impact on performance due to error recovery (less than 3%).

Publications:

Razor: A Low-Power Pipeline Based on Circuit-Level Timing Speculation

Dan Ernst, Nam Sung Kim, Shidhartha Das, Sanjay Pant, Toan Pham, Rajeev Rao, Conrad Ziesler, David Blaauw, Todd Austin, Trevor Mudge, “Razor: A Low-Power Pipeline Based on Circuit-Level Timing Speculation,”ACM/IEEE International Symposium on Microarchitecture (MICRO), December 2003, pg. 7-18.  Best Paper Award ©IEEE