Digital embedded design a comparative an

Student, 2,3 Assistant Professor, Arya Institute of Engineering & Technology, Jaipur, INDIA Abstract—the inquisitiveness to present this paper arises after making projects on microcont

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com ( ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 3, March 2013)

161

Digital Embedded Design:A Comparative Analysis on

Methodoligies

Jai Gidwani1, Pranay Lahoty2,Vidhi Vart Chandrodaya3, Gaurav Kumar Sharma4

1,4

B.Tech Student, 2,3 Assistant Professor, Arya Institute of Engineering & Technology, Jaipur, INDIA

Abstract—the inquisitiveness to present this paper arises

after making projects on microcontroller, FPGA and CPLD in

trainings This paper will clear the architectural and

programming differences between them The microcontrollers

are computers in an IC while FPGA comprises logical blocks

only that can be rewired with software tools CPLD has

architectural features of both PAL and FPGA, but it has less

complexity than FPGA The knowledge of hardware circuits is

needed to implement VHDL programs but a algorithm

approach is sufficient to write a code in C

Keywords—ASM, FPGA, HDL, Microcontroller, UCF

I INTRODUCTION

The word „digital‟ is used for the systems operating on

discrete values [1] Converting the real world information

into these discrete values is the main idea used in all digital

systems The entry of microprocessor and embedded system

in the 1970‟s changed the concept of „control‟ Embedded

systems are dedicated to specific tasks (not stand alone like

a personal computer) The number of transistors that can be

designed on silicon wafer are increasing and realizing

complex functions on them is not a daunting task And

hence the cost per unit is decreasing The concept of

programmable logic came by combining gates and

flip-flops Gate array is the basic component used in VLSI It is

the repetition of pattern of gates fabricated in area of silicon

Interconnection between these gate arrays is done according

the requirement This paper will cover the various aspects of

microcontroller, FPGA and CPLD

The first commercial FPGA was launched in 1985 The

computer based tools in mid 1980‟s has transformed

electronic industry worldwide By changing the program in

a programmable device, the same hardware can be used for

many applications After that, commercialization of

development boards started Digital designers are diverting

their attention from microcontroller to FPGA But it is not

appropriate to state that FPGA will rule over

microcontroller due to its complex pin configuration and

synthesis tools used for it The paper is intended to throw

light on their internal architectures and the available tools to

configure them

II MICROCONTROLLER AND FPGA

A microcontroller is a computing system The structure

of microcontroller is compatible to a simple computer placed in a single chip with all necessary components like memory and timing inside It is programmed to do simple task for other hardware It has lots of hierarchical rules and commands over its input and output It has its own processing unit It can perform loops, execute timed instructions, and process calculations like a small PC under program control

FPGA, the first thing which creates problems into mind is related with acronym‟s meaning i.e field programmable gate array or field gate programmable area Hence they are a matrix of logic gates which can be programmed (or better said reprogrammed) in any way to suits the needs of the application With the help of flip-flop and a logic gate any digital circuit can be designed This is how they work They are programmable logic means the hardware configuration may change according to the application

This is the first basic difference that microcontroller cannot be rewired It stuck to the configuration that the supplier provides But the FPGA, on the other hand, do not stick to any hardware configuration [2]

The next difference is in terms of program execution On FPGA code is executed concurrently [in parallel] and on MCU‟s the code written in C is transformed into machine code via a compile-linking process and then executed step

by step by the processor

Parallel calculation and increased execution speed made FPGA quite useless in application where power consumption is critical For example they will never replace ARMs in the Smartphone

FPGA is only an array of gate that can be connected as the user wishes That does not mean the user has to define switch connections individually It is done using software It will translate HDL‟s code and then places and routes the translated design Some circuits are already made in libraries and optimized for speed or area It is not computing system FPGA‟s are used for relatively simpler operations but higher processing speeds in comparison to microcontrollers [3]

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The greatest advantage that FPGA bring into play is that

they can host completely different and independent digital

systems executing, in parallel of course, absolutely non

related tasks But the power consumption and cost of FPGA

dominate its incredible flexibility and above discussed

advantages

In case of MCU‟s the hardware is pre-decided at

fabrication The hardware consists of a CPU, a program

memory and a data memory There is always explicit

separation between data path and program memory All

commands are read from program memory and executed

sequentially Also number of modules, called on-chip

peripherals as timers and communication interfaces are

integrated [4]

In case of FPGA the hardware is programmable A high

number of programmable logic blocks is available which

can be individually connected by programmable

interconnect matrices Execution is of parallel nature, but

sequential behavior can be realized through the use of state

matrices, control/enable signals and pipelining

The processor could also be integrated into FPGA‟s so

called soft processors [5]

The microcontroller as stated is a sequential logic

machine that requires a program counter to execute a next

instruction (indeterminate timing), the FPGA has no

program counter and instructions processed simultaneously

(determinate timing) The fact that there is no sequential

program counter make FPGA less vulnerable to missed

instruction more commonly associated with

microcontroller

III FPGAAND CPLD

An FPGA is an IC designed to configured after

manufacturing, hence it is called field programmable

FPGA‟s contain programmable logic components termed as

“logic blocks” and hierarchy of reconfigurable interconnects

that allows the blocks to be wired together [6]

The primary difference between CPLD and FPGA are

architectural A CPLD has restrictive structure which results

in less flexibility The FPGA architecture is dominated by

interconnects which makes them not only far more flexible

but also far more complex to design The one more major

difference between architecture of CPLD and FPGA device

is that FPGA‟s are internally based on look up

tables(LUT‟s) and CPLD„s form the logic functions with

sea of gates K input LUT can implement any K input 1

output logic functions [7, 8]

Figure1 FPGA Architecture [9]

CPLD has architectural feature of both PAL and FPGA but less complex than FPGA Macro cell is the building block of CPLD A macro cell on most modern CPLD‟s contains a SOP combinational logic function and an optional flip-flop

Figure 2.CPLD Architecture [9]

Configurable Logic Blocks (CLB‟s) is the logical unit of FPGA FPGA have latches available in their CLB‟s to store the input data FPGA‟s are “fine grained” devices that mean they contain a lot (up to 100000) of tiny blocks of logic with flip- flops CPLD‟s are coarse-grained devices- they contain relatively few (a few 100‟s) large blocks of logic with flip-flops

We can build large digital designs on FPGA while CPLD can contain small designs only

FPGA‟s lose their functionality when the power goes away (like RAM in the computer that loses its content) [9] CPLD is typically a device that retains its configuration once programmed

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IV IMPLEMENTATION [10-15]

We have implemented some projects on both FPGA and

microcontroller as well Here is a description of blinking of

LED‟s A variety of available tools are available to

accomplish the design entry step for FPGA Some

designers prefer to use their favorite schematic entry

package while others prefer to specify their design using a

hardware description language such as Verilog, VHDL, or

ABEL For programming FPGA‟s we have learnt VHDL

(Very High Speed Integrated Circuit Hardware Description

Language) This language has the biggest advantage that it

allows the modeling of the digitals system (description) and

verification before translating it to real hardware The pre

testing of IC is done using VHDL The language supports

9-valued logic(U,X,0,1,Z,W,H,L,-), while in case of

assembly or C, the designer is only capable of sending or

receiving „1‟ or „0‟ to the pins of microcontroller The

VHDL code for blinking of LED‟s with time interval of

one second look like-

Process (clk1, cnt)

Begin

If (clk1'event and clk1='1') then

cnt <= cnt + 1;

If ( cnt = 5000000 ) then 1Hz from 10 MHz

clk_tmp <= not clk_tmp;

cnt <= 0;

End if;

End process;

clk2 <= clk_tmp ;

Process (clk2)

Variable m: integer: =0;

Begin

If (rising_edge(clk2))then

m:=m+1;

If (m=1) then

Led (0) <='1';

Led (1) <='1';

End if;

If (m=2) then

Led (0) <='0';

Led (1) <='0';

End if;

If (m>=2) then

m:=0;

End if;

End Process;

The above program uses clock division and then blinks

two LED‟s together

After writing code for it, the next step is to write a UCF (User Constraints File) in which the pin details of various inputs and outputs is mentioned The choices are more here compared to microcontroller And then generate a programming file Finally a bit or XSVF (Xilinx serial Vector Format) file is transformed to a target device Next let‟s consider the same case with microcontroller programming in assembly language In this case generating

a „hex‟ file from „asm‟ file is a bit easier than generating a

„bit‟ or XSVF file The subroutine is designed to give a delay of a second and written at the end of the program The subroutine is doing nothing but eating machine cycles

to generate a delay in microcontroller It is designed for the oscillator‟s frequency 11.0592 MHz

$mod52 Org 0000h main:clr p1.0 clr p1.1 acall delay sjmp main delay:mov r0,#07h main1:mov r1,#0ffh main2:mov r2,#0ffh main3:djnz r2,main3

djnz r1,main2;

djnz r0,main1;

ret end

V RESULT

The output of both the programs is same But that does not imply that one can replace other In fact apart from their set of languages their set of applications are also different due to the differences mentioned above For example logic functions namely AND gate can be implemented by a single statement in VHDL as:

c<=a and b;

But in case of assembly or C used for microcontroller we have to create a logic that „c‟ gets the value 1 when both „a‟ and „b‟ are 1 A pure logical or algorithm thinking is required to write a program in C But a successful VHDL programmer requires the knowledge of hardware circuits and should be able to predict how a given code will be implemented in hardware If synthesis tools of FPGA will

be improved, then FPGA can replace microcontroller For this task, the change of FPGA architecture is needed because they are flexible but very difficult to configure

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VI CONCLUSIONS

Microcontrollers are custom built mini computers in an

IC while FPGA‟s are composed of logical blocks that can

be rewired electrically Microcontroller consumes less

power than FPGA FPGA take considerably longer time to

set up while there are ready built microcontrollers being

sold for specific uses Building devices with FPGA are

more costly than microcontroller There is no need to stick

with one technology In most cases, the choice depends on

a complex combination of factors and no single technology

is perfect Different technology mixes according to the

requirement of digital design are most appropriate at

different stages of lifecycle The part played by FPGA in

context of embedded system is expanding day by day It is

due to the reason that capability of FPGA is on the rise and

now powerful FPGA design software are also available In

current years FPGA is finding its applications for fast

signal processing also

Acknowledgement

We want to deliver our sincere thanks to management of

Arya Institute of Engineering and Technology for

supporting and providing the facilities to carry out project

work in embedded systems, robotics and VHDL which is

presented in the form of this paper

REFERENCES

[1] M Morris Mano,” Digital Design(4 th edition)”, Prentice Hall [2] E.A Bazzerra and M.P Gough A Guide to Migrating From Microprocessor to FPGA coping with support tool limitations.2007 [3] Z Salcic, PROTOS microprocessor/FPGA-based prototyping system for embedded applications, Microprocessor and Microsystems, 21,

1997

[4] pressexposure.com/FPGA_vs_CPLD_vs_Microcontroller-142920.html

[5] Falk Salewski and Adam Taylor Fault Handling in FPGA and Microcontroller in Safety-Critical Embedded Applications: A Comparative Study June 1999

[6] J O Hamblen, Rapid prototyping using field programmable logic devices, IEEE Micro, 20(3), 2000

[7] Philip A, Simpson, “FPGA Design”, Springer

[8] Ian Kuon, Russel Tessier,Jonathan Rose, ”FPGA Architecture: Survey and Challenges”, Now Publishers Inc

[9] www.fpga-site.com/faq.html

[10] Jayaram Bhasker, ”A VHDL Primer”, Prentice Hall

[11] Douglas Perry,” VHDL: Programming By Example”, Mcgraw-Hill Education

[12] Muhammad Ali Mazidi, Janice Gillispe Mazidi,”The 8051 Microcontroller and Embedded Systems”, Prentice Hall

[13] B Martin-Del-Brio and C Bernal-Ruiz, A software tool for teaching microcontroller system principles, Int J Electrical Eng Educ., 36(4), 1999

[14] J W Valvano, Embedded Microcomputer Systems Real Time Interfacing, Brooks/Cole Thomson Learning (2000)

[15] Xilinx, Synthesis and Simulation Design Guide, Xilinx,

1998

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