Low Power Microprocessors Low Power Microprocessors Low Power - PowerPoint PPT Presentation

Advanced Digital IC Design Outline Why is Low-Power Important? Low Power Microprocessors Low Power Microprocessors Low Power Technology Gao Wei & Tian Youge Conclusions References Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Why is Low-Power Important? Background Battery Control, I /O Last longer Last longer Clock More powerful Datapath Thermal Issues Cooling Memory [ 1] Reliability Save Energy—it’s limited after all ! Where should the emphasis on power reduction be? Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 1

Low Power Technology Clock � clock gating Clock Reconfigurable Cache Asynchronous Logic register latch-based clock gating circuit [ 2] Dynamic Voltage Scaling y g g Circuit without clock gating [ 2] g g [ ] EN= 1 Gray Code EN= 0 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Clock � variable frequency clock [ 2] Reconfigurable Cache [ 3] Core Clock Multiplier Processor CPUPLL Frequency 16MHz Multiplier Multiplier 32kHz Soc/Memory Clock SysPLL Multiplier Multiplier Peripheral Clock Peripheral Clock Divider Peripheral Clock Divider Gated clock a special Gated clock a special case of the variable Tw o virtual levels frequency clock. Cache Configuration L1- activated L2- unactivated Dynam ic Selector part part Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 2

Reconfigurable Cache Outline Asynchronous Logic y g Dynamic Voltage Scaling [ 4] Gray Code Reconfigurable cache state transition diagram Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Types of Sequential Circuit Asynchronous Logic Benefits: Synchronous Asynchronous 70% lower power consumption compared to synchronous design. The same clock signal is An asynchronous circuit is applied to each flip-flop. a circuit in which the parts Less stress on the power distribution network. are largely autonomous. Changes in state occur when the clock changes state from the clock changes state from Not governed by a clock Not governed by a clock one level to another. circuit or global clock signal. Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 3

Asynchronous CPU Dynamic Voltage Scaling P = ACV 2 f + tAVI short f + VI leak In 2004, Epson , p Capacitive Power Dissipation Capacitive Power Dissipation – ACV 2 f ACV f manufactured the dynamic – processor activity influences power world's first bendable loss microprocessor called ACT11, an 8-bit C – Output Capacitance asynchronous chip .[ 5] V – Supply Voltage A – Gate Activity f – System Frequency Most dominant term in the power equation Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Dynamic Voltage Scaling Dynamic Voltage Scaling DVS work steps Overvolting: To increase computer performance, or in rare To increase computer performance, or in rare Predict P di t cases, to increase reliability Next period Collect signals Compute the performance system load Transform Compute Undervolting: Voltage Frequency To conserve power, particularly in laptops and other mobile devices, where energy comes other mobile devices where energy comes Need a power management chip from a battery and thus is limited. to adjust the small voltage Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 4

Dynamic Voltage Scaling Binary codes Natural binary codes, these two positions would be right next to each other: … 011 100 ... The problem: it is very unlikely that switches will change states exactly in synchrony. Measured Energy Savings for DVS Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Gray Code Gray Code Dec Gray Binary Advantages: 0 000 000 The gray code solves g y 1 001 001 this problem by Changes by only one bit as it sequences from 2 011 010 changing only one one number to the next. 3 010 011 switch at a time, so there is never any 4 110 100 Reduce the switching activity at the address ambiguity of position. 5 111 101 lines by 30~ 50% compared to using normal 6 101 110 6 101 110 binary code addressing binary code addressing. 7 100 111 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 5

Conclusions References [ 1] D.W. Dobberpuhl et. al, “A 200-MHz 64b Dual Issue The development trends of low power CMOS Microprocessor,” IEEE JSSC”, vol 27, No. 11, Nov microprocessor: microprocessor: 1992, pp 1555 l 566. 1992 pp 1555-l 566 [ 2] J. Schutz, “A 3.3V 0.6um BiCMOS SuperScalar Microprocessor”, ISSCC DigTech. Papers, pp 202-203, Feb On system-level design——Higher level of 1994. abstraction. [ 3] Yang J.Gupta R Energy Efficient Frequent Value Data Cache Design 2002. Co-design of hardware and software. [ 4] Vijaykrishman N.Kandemir M.Irwin M J Energy-driven Integrated Hardware software Optimization Using Integrated Hardware-software Optimization Using More research on asynchronous circuits. Simp; ePower 2000. [ 5] Karaki, A flexible 8b asynchronous microprocessor based on low-temperature poly-silicon TFT technology, 2005. Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 Advanced Digital IC Design Thank you! Thank you! & Questions? Low Power Microprocessors, Gao Wei & Tian Youge, 2012/ 2/ 16 6