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Software Thread Integration Software Thread Integration for Concurrency and ILP infor Concurrency and ILP in

Embedded SystemsEmbedded Systems

Alex Dean alex_dean@ncsu.edu

Center for Embedded Systems ResearchDepartment of Electrical and Computer Engineering

North Carolina State Universitywww.cesr.ncsu.edu/agdean

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STI and ASTI Eliminate Context Switches and STI and ASTI Eliminate Context Switches and Interrupts Where They Limit PerformanceInterrupts Where They Limit Performance

• Problem: Embeddedsystems are inherently multithreaded, but most processors are single-threaded

• Solution: Create efficient implicitly multithreaded (integrated) functions

• Use a compiler at design time to create the functions (compile for low-cost concurrency)

• Build the task/function scheduling decisions into scheduler or ISRsBreak down the barrier between task scheduling (scheduler and dispatcher) and instruction scheduling (compiler)

• Two efficiencies improved– Integrated threads more efficient– Integration process automated

• Simplifies hardware to software migration

Primary (real-time)

Thread

Secondary Thread

Idle Time

Integrated ThreadGuest

Schedule (Execution

Time Reqts.)

Idle Time Reclaimed

(Asynchronous) Software Thread

IntegrationHardwareFunction

Integration

foo.s

foo.int.sfoo.id

Data-flow Analysis

Control-flow Analysis

Static Timing Analysis

Integration Analysis

GProf

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Demo Systems: NTSC Generator & Hot Soft Demo Systems: NTSC Generator & Hot Soft CANCAN

Byte ClockDivider

Pixel Clock Divider

4-bit Shift Register

4-bit Shift Register

64 kByteSRAM

Latch

Shi

ft

Load

MCU Clock

Sync

Clear

ATmega128MCU

NTSC Video Out

115 kbps serial port

H-LineV-Line D-Line

X-Major-Line

11.8

13.5

12.0

4.0

0

5

10

15

Nor

mal

ized

Per

form

ance

(1/

time)

Discrete

Integrated

Swatch Test.MPG

HoneywellHT83C51

Microcontroller

Serial Data Link to

Controller

CAN Bus

HoneywellHT6256

32K x 8 SRAM

Software CAN

Hardware CAN

HoneywellHT83C51

Microcontroller

Serial Data Link to

Controller

CAN Bus

HoneywellHT6256

32K x 8 SRAM

CANController

Additional4 kBytesof code

STIGlitz: Sync. Threads w/STISTIGlitz: Sync. Threads w/STI HSCAN: Async. Threads w/ASTIHSCAN: Async. Threads w/ASTI

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Other ActivitiesOther Activities• STI for streaming programs on VLIW processors

– Problem: VLIW processors often have many unused issue slots

– Software pipelining doesn’t always work (resource bound < recurrence bound, control flow, calls, register pressure)

– STI can help in many cases– Target System: StreamIt + TI C6x DSP– StreamIt implicitly guarantees data

independence, simplifying analysis– Developing methods to analyze and transform

StreamIt program graph to improve performance

• Energy Efficiency for Low-End Embedded Systems

• Portable Benchmarking for Embedded Systems

Speedup by STI

0

1

2

3

4

5

6

7

8

38 10 61 58 12 62 64 59 60 63 27

Loop ID

Sp

eed

up

nosti/noswp(baseline)sti2/noswpnosti/swpsti2/swp

IPC before and after SWP

0123456789

4 38 13 17 61 56 82 59 3 18 34 49 52 68 31 77 45 7 69 48 39

Loop ID

IPC

noswpswp