A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications T.K. Tan, A. Raghunathan, N.K. Jha, Dept. of Electr. Eng., Princeton Univ., NJ, USA. Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions, Sept. 2003, pp Presenter: Ching-Chi Hu

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 2/ /6/26 Abstract  Energy consumption has become a major focus in the design of embedded systems (e.g., mobile computing and wireless communication devices). In particular, a shift of emphasis from hardware-oriented low-energy design techniques to energy-efficient embedded software design has occurred progressively in the past few years. To that end, various techniques have been developed for the design of energy-efficient embedded software. In operating system (OS)-driven embedded systems, the OS has a significant impact on the system's energy consumption directly (energy consumption associated with the execution of the OS functions and services), as well as indirectly (interaction of the OS with the application software).

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 3/ /6/26 Abstract(Cont.)  As a first step toward designing energy-efficient OS- based embedded systems, it is important to analyze the energy consumption of embedded software by taking the OS energy characteristics into account. To facilitate such studies, we present, in this work, an energy simulation framework that can be used to analyze the energy consumption characteristics of an embedded system featuring the embedded Linux OS running on the StrongARM processor. The framework allows software designers to study the energy consumption of the system software in relation to the application software, identify the energy hot spots, and perform design changes based on the knowledge of the OS energy consumption characteristics as well as application-OS interactions.

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 4/ /6/26 Outline  Related Work  What’s the problem  Simulation framework  Energy accounting  Simulator validation  Limitations  Conclusion

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 5/ /6/26 Related Work  Instruction-level power model  Mehta et al: evaluate compiler optimization techniques for low-power software  Li et al: a framework based on Fujitsu’s SPARClite processor  Simunic et al: cycle accurate model based on StrongARM SA-1100 to estimate energy consumption and battery life  JouleTrack: a web-based energy simulation tools separate into frequency and voltage, and instruction statistics  Structure-based power model

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 6/ /6/26 Related Work (cont.)  Embedded OS simulator  Rosenblum et al: SimOS, a machine simulator that simulates the hardware of MIPS-based multiprocessor  Dick et al: a framework for real-time OS  Cignetti et al: based on discrete device states for PalmOS family  Flinn et al: PowerScope, a hardware instrumentation tool to map energy consumption to program structures  Acquaviva et al: a hardware instrumentation method to perform energy characterization related to the OS

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 7/ /6/26 What’s the problem?  Most of energy-simulation tools are only targeted at providing feedback from the hardware architecture standpoint  A few have been adapted to evaluate the software energy consumption  Even fewer evaluate of embedded systems considering the effects of an embedded OS

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 8/ /6/26 Simulation framework  StrongARM SA-1100 core  Consisting of an ISS,D-cache,I-cache,MMU  Simulation model  32MB system memory  interrupt controller  two timers  two UARTs  Linux OS  arm-linux ver 2.2.2,configure for the EBSA-110 platform  mount an initial RAM disk

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 9/ /6/26 Simulation framework (cont.) Energy analysis framework

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 10/ /6/26 Simulation framework (cont.)  Energy modeling  E t_sys =E t_proc +E t_idle +E t_mem +E t_uart +E t_peri E t_proc =ΣE proc [instr_type(i)]*N cyc (i)  Σ from i=1 to total number of instructions executed E t_idle =P idle *T cyc *N idle_cyc  P idle =65mW E t_mem =E mem *N mem_cyc  E mem =4.70nJ E t_uart =E uart *N uart_cyc  E uart =0.21nJ E t_peri =E peri *N peri_cyc

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 11/ /6/26 Energy accounting  The process executed is task by task  illustrated that sequence of event during Linux OS initialization  Idle task :hardware initialization  Init task :software initialization,mount root file

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 12/ /6/26 Energy accounting (cont.)  application in the task-based simulator  A separate TEBS for each task running  TEBS :task energy balance sheet  A function energy stack (FES) for each task  an FES mirrors the function call stack for the corresponding task  The information stored in FES is the energy value of the task at the time of entry into a function

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 13/ /6/26 Energy accounting (cont.) The example of two tasks and it’s function

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 14/ /6/26 Energy accounting (cont.)

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 15/ /6/26 Energy Accounting (cont.)  each task running has a separate TEBS  Similarly,the simulator maintain a FES for each task

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 16/ /6/26 Simulator validation  Functional Validation  Dining philosopher  Priority inversion  Time-of-flight  Two robots  Energy modeling accuracy  Both in the simulator and on an Itsy evaluation board

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 17/ /6/26 Limitations  Context switch detection  special function in is not always fit for other OS  Asynchronous operation  The simulator is task-and-function based  It can’t recognize that the actual work done should be attributed to the task requesting it  Energy estimation error  Cycle-counts based on the time information provided in the manual

A Simulation Framework for Energy-Consumption Analysis of OS-Driven Embedded Applications 18/ /6/26 Conclusion  Conclusion  presented an energy simulation framework for an embedded system run the Linux OS starting from initialization to the spawning of multiple application tasks validated for both its functionality and its modeling accuracy  Future work  improved in software architectural exploration for low energy consumption