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 = {R1, R2 …… Rn} be the pending request for flash

memory and are arranged according to its deadline T1, T2,…Tn. Here, T1 < T2 <…Tn

pseudo code For i=1:n

Schedule task Ri at low voltage Find total time if total time > Ti

adjust first K tasks at high voltage (make sure that k is minimized)

end End

New version of DVA Pseudo code of proposed algorithm

For i=1:n

Schedule task Ri at low voltage Find total time if total time > Ti

adjust shortest K tasks at high voltage (make sure that k is minimized)

endEnd

Simulation Set Up

0.3 S480 mW0.4 S540 mW12 V

0.4 S250 mW0.5 S375 mW5 V

PerformancePower ConsumptionPerformancePower

Consumption

Block EraseBlock WriteVpp

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?????