Hardware-Software Co-Design

Cosynthesis and Partitioning

EE8205: Embedded Computer Systems
http://www.ee.ryerson.ca/~courses/ee8205/
Dr. Gul N. Khan
http://www.ee.ryerson.ca/~gnkhan
Electrical and Computer Engineering
Ryerson University______________
Overview
 Traditional Embedded System Design
 Hardware-Software (HW/SW) Co-design
 Co-specification and Cosynthesis
 HW/SW Partitioning
Introductory Articles on Hardware-Software Codesign available at the course webpage, Part of
Chapter 7 of the Text by Wolf
©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 1
 Introduction
Embedded computers are the processing devices.
 Home appliances and entertainment units
 Transportation including automobiles
 Medical instrumentation
 Wireless communication devices,
 Jet engines and other aerospace/space application
 Industrial control, nuclear systems and many more

By many estimates embedded computers make up 99% of

worldwide computers
Embedded Computer Systems are the ideal candidate
for hardware-software codesign.
©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 2
 Embedded System Design

• Separate HW and SW design has been explored

and examined very thoroughly
• Joint design remains an area of rapidly growing
study
• Old embedded devices always built from scratch
– within reasonable amount of time
• Components - smaller and faster - IP cores
• Tools required for the product engineer.

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 3

 Embedded System Architecture Design
• Real-time System Design
 Performance analysis
 Scheduling and allocation
• Accelerated systems
• Use additional computational unit dedicated to some
functions?
 Hardwired Logic e.g. FPGA
 Multiple processing elements (PEs) or an extra CPU
• Hardware/software co-design: a joint design of
hardware and software architectures of
Embedded System.
©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 4
 Traditional Design Practices
• Performance Requirements make it
impossible to execute entire application in
software
• Intensive portions are extracted and
realized as custom hardware
• Early Design Cycle Partitioning
 Design Space is not fully Explored
 High Cost Design
 Inefficient

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 5

 Traditional Embedded System Design

• HW/SW Partitioning
performed at an early
stage.
• Design mistakes have
huge negative effect
• Inability to correct
mistakes performed at
the partitioning phase

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 6

 Traditional Design Practice
Requirements Definition

6-12 Months

Architecture Definition

Hardware Design Software Design

Interface
Design
25-49 Months

Hardware
Software Code and
Manufacture and
Test
Test

Hardware Software
Implementation and Test

Deliverables

Documentation
6-12 Months
Deployment Field Test

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 7

 Advancements
• VLSI Technology
 Smaller, Faster IP Cores
 Reconfigurable Logic
• Matured Hardware Design Methodology
• Matured Software Design Methodology
• Joint design – Still in Infancy but popular!

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 8

 Hardware-Software Co-design

• An approach utilizing the maximum efficiency

of Hardware and Software is needed
• Recent developments in CAD Tools
• Result -- Hardware Software Codesign
 A unified approach
 Large Design Space Exploration
 Improved Time to Market

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 9

 Codesign Methodology

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 10

 Hardware-Software Codesign
• Functional exploration: Define a
System (Embedded)
desired product's requirements and
Functional Exploration produce a specification of the
system behavior.
Architectural Mapping • Map this specification onto various
hardware and software
Hardware-Software architectures.
Partitioning
• Partition the functions between
Hardware
Implementation
Software
Implementation
silicon and code; and map them
directly to hardware or software
System Integration components.
• Integrate system for prototype test.
©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 11
 HW/SW-Codesign
Co-design of (embedded) computer systems
encompassing the following parts:

• Co-Specification: Describe system functionality

at the abstract level
System description is converted into a task
graph representation
• HW-SW Partitioning: Take the task graph and
decide which components are implemented
where/how ?
i.e. Dedicated hardware,
Software -- one CPU or multiple CPUs
©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 12
 HW/SW-Codesign
• HW-SW Co-Synthesis: Analyze the task graph
and decide on the system architecture.
(incorporates HW/SW partitioning as heart of co-
synthesis process)

• HW-SW Co-Simulation: Simulate embedded

device’s functionality before prototype
construction. Simultaneous simulation of hardware
and software.
• Co-Verification: Mathematical or simulation
based verification that device meets requirements.

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 13

 HW/SW Co-Specification
• Model the (embedded) system functionality from an
abstract level.
• Developing system specification that describes
hardware, software modules and relationship
(interface) between the hardware and software.
• No concept of hardware or software yet.
• Common environment
SystemC: based on C++.
• Specification is analyzed to generate a task graph
representation of the system functionality.

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 14

 Hardware-Software Co-Synthesis
Four Principle Phases of Co-synthesis:
 Partitioning
Dividing the functionality of an embedded system into units
of computation.
 Scheduling
Choosing time at which various computation units will
occur.
 Allocation
Determining the processing elements (PEs) on which
computations will occur.
 Mapping
Choosing particular component types for the allocated units
(of computations).
©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 15
 HW/SW Co-Synthesis
Automatic and semi-automatic design of hardware
and software modules to meet the specification.
Automatically derive the system architecture. Tightly
coupled with HW/SW Partitioning along with:
• Allocation: select the number and type of
communication links and processing elements for the
target system.
• Assignment (Mapping): Mapping tasks to processing
elements.
• Scheduling: Timing of task execution and
communications.

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 16

 Common Co-Synthesis Structure

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 17

 System Partitioning
Introduces a design methodology that uses several
techniques:
 Partition the system specification into processes/tasks
The best way to partition a specification depends on the
characteristics of the underlying hardware platform

 Determine the performance of the function when

executed on the hardware platform
We usually rely on approximating

 Allocate processes onto various processing elements

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 18

 HW/SW Partitioning
• An area of significant research

• Analyzes task graph to determine each

task’s placement (HW or SW)

• Many algorithms have been developed.

• Major problem involves the computation

time of partitioning algorithm

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 19

 Hardware-Software Partitioning
Hardware/Software System Design involve:
Modeling, Validation and Implementation
 System implementation involves:
Hardware-Software Partitioning

Finding those parts of the model best implemented

in hardware & those best implemented in software.
 Such partitions can be decided by the designer
with successive refinements
or determined by the CAD tools

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 20

 Hardware-Software Partitioning
For embedded systems, such partitioning represents a
physical partition of the system functionality into:
 Hardware
 Software executing on one or more CPUs
Various formation of the Partitioning Problem that
are based on:
 Architectural Assumptions
 Partitioning Goals
 Solution Strategies
COWARE: A design environment for application specific
architectures targets telecom applications
©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 21
 Partitioning Techniques
Hardware-Software Homogeneous System Model =>
Task Graph
For each node of the task graph, determine implementation
choices (HW or SW):
 Keep the scheduling of nodes at the same time
 Meet real-time constraints
• There is intimate relationship between partitioning and
scheduling.
• Wide variation in timing properties of the hardware and
software implementation of a task.
That effects the overall latency significantly

©G. Khan EE8205: Embedded Computer Systems: Hardware-Software Co-design Page: 22