8/14/2019 Optimization for Embedded System

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Optimization forEmbedded System

Performance I ndices

Peformance

Memory Usage

Power

Layers

Embedded processor architecture

80/20

80% of time is spent in standby mode

20% of time is spent in operating mode

80% of operating time is a subset ofperipherals and functions used

20% of operating time is spent with allfunctions in use

ArchitectureVon Neumann

Harvard

Power

Software Techniques

Saving power at boot timeScaling voltage and frequency

Using sleep modes and idling clock domain

Coordinating sleep and scaling

Chip level

Reduce power supply voltage

Run at low clock frequency

Disable function units with control signals when not in use

Disconnect part from power supply when not in use

Pick Criteria

Optimal performance key algorithm

Low power for key algorithm

Efficient management of memory (cache)

Memory hierarchy

Register

Different levels of cache

Main memory

Disc space

OS layerPower Manager

Loosely coupled to OS kernel

Set of library coutines; execute in client's context

Configurable as necessary

Use platform-specific adaptation library for V/F scaling

Application, drivers, CLK register for notifications

Application trigger actions

Algorithm

Code

Prevent obsessive optimization

Developing eff icient code

Inline functions

Table lookups

Hand coded assembly

Register variables

Polling

Fixed point arithmetic

Decreasing code size

Avoid standard library routine

Native word size

C++

Subtopic

Top 10 SW power optimization

Architecture SW to have natural "idle" points

Use interrupt-driven programming

Code and data placement close toprocessor to minimize off-chip accesses

Smart placement to allow frequencylyaccessed code/data close to CPU

Size optimizations to reduce footprint,memory, and corresponding leakage

Optimize for speed for more CPU idlemode or reduce CPU frequency

Don't over calculate

Use DMA for efficient transfer

Use co-processors to efficientlyhandle/accerlate frequent/specializedprocessing

Use more buffering and batch processingto allow more computation at once andmore time in low power modes

Optimization levels

-o0 (register)

Simplifies control flow

Allocates variables to registersEliminates unused code

Simplifies expressions and statements

Expands calls to inline functions

-o1 (local)

Performs local copy/constant propagation

Removes unused assignments

Eliminates local common expressions

-o2 (global)

Performs local loop o ptimizations

Eliminates global commonsub-expressions

Eliminates global unused assignments

Perform loop unrolling

-o3 (file)

Removes functions that are never called

Simplifies functions with return value that are never used

Reorder functions so that attributes ofcalled function are known when caller isoptimized

Identifies file-level variable characteristics

ptimization for Embedded System.mmap - 2007/8/26 -