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PARTIAL RECONFIGURATION USING FPGAs:

ARCHITECTURE

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Agenda• Introduction• Partial Reconfiguration Basics• Design Considerations• Advantages of Partial Reconfiguration• Challenges of Partial Reconfiguration• Application Examples• Case Study

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Introduction• Basic Premise : Hardware reconfiguration is allowed

during execution of an application.

FPGA Chip

Design A

Design B

Design C

Some Interesting Applications • Dynamic Instruction Set

Architecture• Software Defined Radio• Video encoding techniques• Cryptography• Networking protocols

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Introduction• Classification of FPGA with respect to configuration capabilities

• Dynamic Partial Reconfiguration : Reconfiguring only a part of the device at run time while the rest of the device executes.

• Useful for systems which can time share the FPGA resources.

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Introduction

• Area reduction• Power reduction• Hardware Reuse• Flexibility• Performance Improvement

• Higher Level of Parallelism• Time sliced resource sharing

• Fast system start• Load a basic module to enable a fast system boot up• Load peripheral modules later.• Smaller bitstreams sizes

• Application Portability • Encapsulation of reconfigurable system into a portable application.

Benefits

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Partial Reconfiguration Basics• Each vendor’s products can have different characteristics

and utilities• Some common terminology are as below.TERMINOLOGY• Reconfigurable Partition(RP)• Dynamic Partial Reconfiguration (DPR)• Reconfigurable Module (PRM)• Configuration Memory (CM)• Frames• Partial Bitstream• Merged Bitstream• Static Logic (Base Region)• Bus Macro

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Partial Reconfiguration Basics

• Overall Structure• CLBs – Configurable logic blocks• IOBs – Input-output buffers• DSP48s – Xilinx’s digital signal

processing units• BRAMs – Block Random Access

Memories• FIFOs – First-in First-out buffers• DCMs – Digital Clock Managers

Structure Overview CLBs

IOBs

DCMs and Clock Dist.

DSP48s

BRAMS and FIFOs

Figure 1. Virtex-4 LX15 FPGA layout

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Partial Reconfiguration BasicsStructure Overview

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Partial Reconfiguration BasicsBit Stream and Frames

• FPGAs are reprogrammed by writing bits into CM

• Organized in small blocks called ‘Frames’

• Multiple frames required to program a column of tiles(After Virtex II )

• Contains both routing and logic tile configuration.

• Virtex-6 Frame size: 81 x 32 bits (81 words)• Typical Bit streams for Virtex-6

are in the range of 43Mb to 190 Mb

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Partial Reconfiguration Basics

• Different columns of FPGA fabric can have different bit streams

• PR overhead for full flexibility

• Possible to reduce Bit stream Size : - Compression Techniques - Partial Reconfiguration

Bit Stream

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Partial Reconfiguration Basics

• Row address – 0 to 9 • Top/Bottom row – with respect to HCLK

• Together with row address can locate the tile • Major Address : Columns 0 onwards• Minor Address : No. of frames in tile • Block type : Logic Blocks, BRAMs, Routing Blocks.

Frames

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Partial Reconfiguration Basics

• Bus Macros: Means of communication between PRMs and static design

• All connections between PRMs and static design must pass through a bus macro with the exception of a clock signal

• Type of Bus Macros Tri-state buffer (TBUF) based bus macros Slice-based (or LUT-based) bus macros

Bus Macros

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Partial Reconfiguration Basics

• Used for connecting points to link Static and reconfigurable part• Introduced in 2002• Fixed positions on the FPGA fabric • Present along a thin vertical slice • Extra hardware required. No longer supported in modern FPGAs.

Xilinx Bus Macros (Tri state Buffer Based)

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Partial Reconfiguration Basics

• LUTs and Switch matrix acts as the connection points (2004)• Passes the boundary of static and reconfigurable regions in a

predefined manner.• Uses 2 LUTs per wire• Increased latency and area• Not used any more.• Partition Pins replace Bus Macros

Xilinx Bus Macros (LUT Based)

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Partial Reconfiguration Basics

• Partition Pins are the logical and physical connection between static logic and reconfigurable logic.• Automatically created for all RP ports.• Also referred to as Proxy LUTs.• It is single LUT1 • No special instantiations required• Not Bidirectional

Partition Pins

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• Externally • Serial configuration port• JTAG (Boundary Scan) port• Select Map port

• Internally• Though the Internal configuration access port (ICAP) using

an embedded microcontroller or state machine

Partial Reconfiguration BasicsMethods of Reconfiguration

Summary of Configuration Options

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Partial Reconfiguration Basics

Reconfiguration via a processor

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Partial Reconfiguration Basics

• Port to read and write the FPGA configuration at run time

• Enables a user to write software programs for an embedded processor that modifies the circuit structure and functionality during the circuit’s operation.

• Allows for automated runtime reconfiguration

ICAP Interface

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Partial Reconfiguration Basics

• Storage Device • Bus System• DMA to Storage Device• Read back Support• Configuration manager

ICAP Interface

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Design Considerations

• Partitioning style could be island style• Slot Based• Grid Based

Partitioning Style

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Design Considerations

• Partitioning style affects placement and flexibility• A partition defines the smallest atomic area a module can be assigned• Island style – suffers from fragmentation • Slot style - also suffers from fragmentation but to a lesser extent. Offered

by the current vendors Xilinx and Altera.• Grid Style – Reduced fragmentation. Difficult to support.• To enhance flexibility, the PR module must be placed and routed in every

region it needs to be configured.• Additional stress on Bit stream size.

Placement Flexibility

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Design Considerations

• Column wise layout of different logic primitives• Must be considered when placing• Depending on the type of logic primitives used by the

module(SLICEX, SLICEM, etc), relocation may or may not be possible.

Resource

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Design Considerations

• One of the potential advantages of PR – Power reduction• But PR itself requires power.• Power during PR is spent in: 1. Configuration Data Access – - Spent on the configuration controller - Off/On chip Memory access - Programming interface(ICAP, SelectMAP,etc) 2. Actual configuration of FPGA Resources

Power

Bonamy, R., et al. "Power Consumption Models for the Use of Dynamic and Partial Reconfiguration." Microprocessors and Microsystems (2014).

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Design Considerations

• Tasks switching power graph T1 T2 and T2T1

Power

Bonamy, R., et al. "Power Consumption Models for the Use of Dynamic and Partial Reconfiguration." Microprocessors and Microsystems (2014).

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1. Module-based PR:• Implement any single component separately.• Constrain components to be placed at a given location.• Complete bitstream is finally built as the sum of all partial bit

streams.

2. Difference-based PR:• Implement the complete bitstreams separately.• Implement fix parts + reconfigurable parts with components

constrained at the same location in all the bitstreams.• Compute the difference of two bitstreams to obtain the partial

bitstream needed to move from one configuration to the next one.

Design ConsiderationsDesign Flows

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Design ConsiderationsModule Based P-R

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Design Considerations

• Useful for making small on-the-fly changes to design parameters such as logic equations, Filter Parameters.

• Procedure:1. Designer makes small logic changes using FPGA_Editor:

• changing I/Os, • block RAM contents• LUT programming• muxs• flip-flop initialization and reset values• pull-ups or pull-downs on external pins• block RAM write modes

• Changing any property or value that would impact routing is not recommended due to the risk of internal contention

2. Uses BitGen to generate a bitstream that programs only the difference between the two versions. • Very quick switching

Difference Based P-R

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Design ConsiderationsDifference Based P-R• LUT equations change

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• Changing BRAM contents

Design ConsiderationsDifference Based P-R

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Challenges of Partial Reconfiguration

• Complicated design flow

• Manual assistance for reconfiguring different target devices.

• Security issues

• Decrease performance as compared to full configuration.• Xilinx reports 10% degradation in clock

frequency when using PR.

Xilinx PR Implementation Flow

HDL Design Description

HDL Synthesis

Set Design Constraints

Placement Analysis

Implement Static Design and PR Modules

Merge

Final Bitsreams

Manual steps

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Complete Architecture Overview

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Application examples of Partial Reconfiguration

• Evolution Architectures• Artifical Neural Networks• Evolvable Hardware Platforms• Fuzzy systems• Modular Robotics

• Speed Up• Crypto (Asym)

• Area Saving• Networking (exchange packet filters according to traffic)• Modulation/frequency/encryption hopping in military radios

• Digital Signal Processing• JPEG Encoder/Decoder systems• Edge detection applications

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Case Study

• Fault tolerant Processor• IF ,MAC and ALU are the PRMs• Different configurations available for each module.• Focus on the self healing feature more than the performance itself.

Fault Tolerance – Self Healing Architecture

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Case StudyReconfigurable Crypto processor

• Processor can choose from Different crypto algorithms• Major Area savings • Some Power Savings too.

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Case Study

• Fast Start up is a 2 step configuration• Useful in time critical systems to initiate a swift system start up.• Example : Automotive safety

Fast Start Up

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Thank you

Questions ?