Hardware Software Co-Design

Fundamental Issues in Hardware Software Co-Design

1. Selecting the model

2. Selecting the architecture

3. Selecting the language

4. Partitioning system requirements into Hardware and Software

1. Selecting the model

Models are used for capturing and describing the system characteristics
A model is a formal system consisting of objects and composition rules
Designers switch between variety of models from the requirements specifications to the implementation aspect of the system design
Specifications stage --> functionality
Implementation stage --> system components, system structure

2. Selecting the architecture

Architecture specifies how a system is going to implement in terms number of and type of different components and their interconnection

Architecture are controller architecture, Datapath architecture, Complex Instruction Set Computing(CISC), Reduced Instruction Set Computing (RISC), Very long Instruction Word (VLIW), Single Instruction Multiple Data (MIMD)

Application specific architecture class -> Controller architecture, etc.
General purpose architecture class -> CISC, RISC, etc.
Parallel processing class -> VLIW, SIMD, MIMD, etc.

a) Controller architecture

Implements the finite state machine model using a state register and two combinational circuits
State register holds the present state, and
Combinational circuits implement the logic for next state and output

b) Datapath architecture

Implements the data flow graph model
The output is generated as a result of a set of predefined computations on the input data
Datapath represents a channel between the input and output
Datapath contain registers, counters, register files, memories and ports, high speed arithmetic units

c) Finite State Machine Datapath (FSMD)

Combines controller architecture with data-path architecture
It implements a controller with data-path
Controller generates the control input
Datapath processes the data
Datapath contains two types of I/O ports

Control port for receiving/ sending the control signals from / to the controller unit
Datapath port interfaces the external world for data input and data output

Datapath is implemented in a chip

d) CISC

Use of a single complex instruction in place of multiple simple instructions reduces the program memory access and program memory size requirement
Datapath for CISC is complex
EX: CJNE instruction for 8051 ISA

e) RISC

Uses Instruction set representing simple operation
Datapath of RISC architecture contains a large register file for string operands and output
RISC supports pipelining

f) VLIW

Implements multiple functional units(ALU'S, multipliers, etc.) in the data-path
VLIW instruction packages one standard instruction for functional unit of data-path

g) Parallel processing architecture

Implements multiple concurrent processing elements (PEs) and each PE associates a data-path containing register and local memory
SMID --> Single instruction is executed in parallel with the help of PEs
Single controller schedules the instruction execution and controls each PE
SMID forms basis of re-configurable processor
MIMD--> PEs execute different instructions at a given point of time
MIMD forms the basis of multiple processor systems
PES communicates through mechanism like shared memory and memory passing

3. Selecting the language

Language should capture the computational model easily and maps it into architecture
Software implementation --> C, C++, C#, Java, etc.
Hardware implementation --> VHDL, System C, Verilog, etc.
A single language can be used for capturing a variety of models
EX: C++ captures an object oriented model

4. Partitioning System Requirements into Hardware and Software

From implementation point of view, it may be possible to implement the system requirements in either hardware or software (firmware)

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