FPGAField Programmable Gate Array

With an overview of different Reconfigurable Technologies

Presented by:Ramtin Raji Kermani(http://www.cse.shirazu.ac.ir/~ramtinraji)Senior student of Computer EngineeringShiraz University

Spring 2006

Covered subjectsCovered subjects

• What is Reconfigurable Computing?

• Application Specific Integrated Circuits (ASICs)

• Programmable Logic Devices (PLDs)

• Programmable Logic Arrays (PLAs)

• Field Programmable Gate Array : FPGA

• Why FPGA?

• FPGA Architecture

• FPGA Implmentation

• FPGA design Process

• Hardware Description Languages : HDLs

What is Reconfigurable Computing?

• Concept from 1960’s, But still a new field of research.

• The ability to change the Processing unit at Run-Time.

• Computer processing with highly flexible computing fabrics.

• The ability to changes the data path, in addition to the control flow.

• Run-Time and On-board reconfiguration

A Computer consisting:• A Standard processor• An array of reconfigurable hardware

Initial Ideas …

• Software Flexibility

• Hardware Speed

Reconfigurable Logic Characteristics:

1. Granularity: size of the smallest functional unit (CLB) Low granularity (Fine-Grained) : like FPGAs

Greater Flexibility

Increased power, delay, area due to greated Qtty. of routing

Bit level manipulation

High granularity (Coarse-grained) : like rDPAs

Consists of big elements

Optimized for standard data path applications

Drawback: loosing some of its utilisation for smaller computations

Word-with data paths

A larger block instead of smaller connected units

What is Reconfigurable Computing?

Reconfigurable Logic Characteristics:

2. Rate of Configuration:

• Reconfiguration can happen at deployment time

• Between execution or During execution (at Run-Time)

• Bit streams is used t reprogram the device at Deployment time

• Fine grained systems require more config. Time

• Partial Reconfiguration: A part is being reconfgured while the other is

performing

What is Reconfigurable Computing?

3. Routing / Interconnects:• Flwxibility of a Reconfigurable Device come from its routing interconnects

Island Style Layout: Blocks in Vertical and Horizental routing (in FPGAs)

What is Reconfigurable Computing?

Island Style layout

Application Specific Integrated Circuits : ASICsApplication Specific Integrated Circuits : ASICs

• Used to design a system on a chip• To do a VERY specific job, no reconfiguration• Interconnect of standard cells• Highly automated design flow• ASICs design flow:

1. RTL description

2. Functional simulation

3. Synthesis

4. Design verification

5. Layout

Processors Vs. ASICsProcessors Vs. ASICs

Processors:• Take longer to compute

•Slow• Flexible• Need instructions to determine what to do on each cycle

ASICS:• Take shorter time to compute

•Fast• Not Flexible• No instruction• Same calculation every cycle

Processors Vs. ASICsProcessors Vs. ASICs

Actual computation

Processor ASIC

Processors Vs. ASICsProcessors Vs. ASICs

Temporal Spatial

SingleProcessor

ASIC

• Slow• Flexible

• Fast• Inflexible

ReconfigurableComputing

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Programmable array logic: PAL

• A programmable Logic Device• Used to implement combinational logic circuits • First introduced by Monolithic Memories Inc. (MMI) in 1978• Priviously FPLA by Signetics (1975)

Field programmable Gate Arrays

• dimensional array of logic blocks and flip-flops

• with a electrically programmable interconnections

FPGA provides its user a way to configure:

• The intersection between the logic blocks

• The function of each logic block.

FPGA Logic Blocks can be configured to offer functions:

• As simple as a transistor

• As Complex as a CPU

Simplified FPGA Architecture

Block Interconnections (Switch Box)

FPGA Logic Blocks

FPGAs has four different logic block structures:

1. Crosspoint FPGA

2. Plessey FPGA

3. Actel Logic Block

4. Xilinx Logic block

Crosspoint FPGA

Crosspoint FPGA: consist of two types of logic blocks. One is transistor pair tiles in which transistor pairs run in parallel lines as shown in figure below:

Plessey FPGA

Plessey FPGA: basic building block here is 2-input NAND gate which is connected to each other to implement desired function.

Actel Logic Block

Actel Logic Block: If inputs of a multiplexer are connected to a constant or to a signal, it can be used to implement different logic functions.

Xilinx Logic block:

Xilinx Logic block: Look up table is used to implement any number of different functionality.

SRAM programming technology

Static RAM cells are used to control pass gates or multiplexers

Floating Gate Programming

The programmable switch is a transistor that permanently be disabled

FPGA Design Flow

The FPGA design process of xillinx products are as follows:(the other products have similar process)

For more info : http://toolbox.xilinx.com/docsan/xilinx7/help/iseguide/html/ise_fpga_design_flow_overview.htm

Hardware Description Languages: HDLs

For programming FPGAs, we need a special kind of programming

language to describe hardware functions.

Three Major HDLs:

1. VHDL (VHSIC Hardware Description Language)

2. VeriLog

3. JHDL (Java implementation as HDL)

References

• As Always: My dear GoOgLe : www.google.com !!!

• www.Wikipedia.com

• www.tutorial-reports.com/computer-science/fpga

• www.netrino.com/Articles/RCPrimer/

• Introduction to Reconfigurable Computing, Hayden So

• Digital Logic Circuit Analysis & Design, V.Nelson

• XILINX documentations

• ACTEL documentation

• www.tutorial-reports.com

The End …

Questions ? Comments ?