Power Management of Flash Memory for Portable Devices ELG 4135, Fall 2006 Faculty of Engineering, University of Ottawa November 1, 2006 Thayalan Selvam Suganthan Vivekananthan Thushitha Kanagaratnam

Outline Introduction to Flash Memory Why power optimization? Dynamic Voltage Scaling Simulation Conclusion

Flash Memory Non-volatile data storage devices Storage of trapped electrons in cells Cells have different logical functions: NOR or NAND NOR flash memory:- Faster read time longer erase and write times NAND flash memory:- Longer read time Faster erase and write times

Usage of Flash Memory Computer's BIOS chip Digital cameras Mp3 players Memory Stick PCMCIA Type I and Type II memory cards PDA

Advantages of Flash Memory Maintain stored information without power source High storage capacity and compatibility No physical disk to spun as in hard disks High processing speed:- Virtually the speed is same as light’s speed. Limiting factor is USB 2.0 Compact size:- 2mm to 3mm in width

Why Power Optimization ? Demand for portable electronics devices have increased Power consumption is major obstacle in any mobile portable devices. Main task to maintain low power consumption Low power increases the performance and makes the devices durable

Limitations on Power Optimization Low power consumption Supply voltage Clock frequency Performance time Circuit delay Low cost

System Block Diagram of a Portable Device (mp3 player)

Power Optimization Algorithms Dynamic Voltage Scaling Static Voltage Scaling Voltage Clock Scaling

Dynamic Voltage Scaling Algorithm Allows devices to change voltage and speed Uses different voltage level for program, write and erase Uses high voltage when the work load is high Uses low voltage when the work load is low

Advantages of Dynamic Voltage Scaling Algorithm Advanced electronic chips allows to have different voltage levels in devices Intelligence power management allows to lengthen the operational time by operating the devices at low power level, whenever possible Save the battery power

Our Contributions Literature search on various power management algorithms Selected one Dynamic Voltage Scaling algorithm: Dynamic Voltage Adjustment algorithm We proposed a new version of existing dynamic voltage adjustment algorithm The performance of the new algorithm is compared with the existing algorithm

Dynamic Voltage Adjustment (DVA) Algorithm NOR Flash Memory: Block read uses constant voltage level. Power management is required only for write and erase operations Each tasks have deadline time This algorithm based on Earliest Deadline First (EDF) algorithm. That is earliest deadline tasks are scheduled very first First K tasks are operated at high voltage level and rest of the tasks are at low voltage level This algorithm make sure that K is minimized

DVA (Cont’d.) Let S = {R 1, R 2 …… R n } be the pending request for flash memory and are arranged according to its deadline T 1, T 2,…T n. Here, T 1 < T 2 <…T n pseudo code For i=1:n Schedule task R i at low voltage Find total time if total time > T i adjust first K tasks at high voltage (make sure that k is minimized) end End

New version of DVA Pseudo code of proposed algorithm Pseudo code For i=1:n Schedule task R i at low voltage Find total time if total time > T i adjust shortest K tasks at high voltage (make sure that k is minimized) end End

Simulation Set Up V pp Block WriteBlock Erase Power Consumption Performance Power Consumption Performance 5 V375 mW0.5 S250 mW0.4 S 12 V540 mW0.4 S480 mW0.3 S  Considered NOR Flash memory: - Read time is constant. Write and Erase are considered  Block Size: 64 kb  Two levels of operating voltages: 5V and 12V

Simulation Results (Voltage Level)  First 5 tasks are operated at high voltage  Rest of the tasks are operated at low voltage  This algorithms make sure that the number of high voltage tasks are minimized  Proposed algorithm set shortest k tasks at high voltage

Simulation Results (Power Consumption) This graph compares the power consumption of the algorithms Graph clearly indicates the performance of the DVA (Dynamic Voltage Adjustment) algorithm and the proposed algorithm However, proposed algorithm have 6.475% improvement compare to existing DVA algorithm

Conclusion Dynamic Voltage Adjustment algorithm is considered The simulation results shows efficiency of the power management algorithm Dynamic Voltage Adjustment algorithm is useful in the implementation of portable devices which saves battery power We gained a good knowledge in various power management algorithms.

Future work! In this context, we considered heuristic approaches for power management and therefore the solution is near optimum Explore efficient optimization tools to find exact optimal solution Online arrival of tasks can be incorporated Consider multi voltage levels. (This project we have considered two voltage levels). However, voltage levels cannot be increased as many since the electronic circuit’s limitations

References [1] Tanzawa T, Takano Y, Taura T, Atsumi S. “A Novel Bit-Line Direct- Sense Circuit that uses a feedback system for High-Speed Flash Memory.” Research Institute of Electrical Communication, Tohoku University, Japan. January 2006 [2] Li-Pin Chang, Tei Wei Kuo, Shi-Wu Lo. “ A Dynamic- Voltage- Adjustment in reducing the power consumption of flash memory for portable devices.” Taipei,Taiwan. [3] Yehua Du, Ming Cai, Jinxiang Dong. “Dynamic Voltage Scaling of Flash Memory Storage Systems for Low-Power Real-Time Embedded Systems.” Zhejiang University, Hangzhou, China

Thank You Special Thanks to Dr. Habash and TA’s for help and supports. Questions?????