The Microprocessor is no more General Purpose

Design Gap

Problems with Fine Grained Approach FPGAs

• Area in-efficient– Percentage of chip area for wiring far too high

• Too slow– Unavoidable critical paths too long

• Routing and Placement is very complex

Problems with Fine Grained FPGAs

Coarse Grained Reconfigurable computing

• Uses reconfigurable arrays with path-widths greater than 1 bit

• More area-efficient• Massive reduction in configuration memory

and configuration time• Drastic reduction in complexity of Placement

& Routing

Coarse Grained ArchitecturesClassification

• Mesh-based• Linear Arrays based• Cross-bar based

Mesh Based Architectures

• Arranges PEs in a 2-D array• Encourages nearest neighbor links between

adjacent PEs • Eg. KressArray, Matrix, RAW, CHESS

Matrix – Mesh based Architecture

Matrix – Mesh Based Architecture

Architectures based on Linear Arrays

• Aimed at mapping pipelines on linear arrays• If pipeline has forks longer lines spanning

whole or part of the array are used• Eg. RaPiD, PipeRench

PipeRench – Linear Array based architecture

PipeRench – Linear Array Based Architecture

Cross-bar based Architectures

• Communication Network is easy to route• Uses restricted cross-bars with hierarchical

interconnect to save area• Eg. PADDI-1, PADDI-2, Pleiades

PADDI-2 – Cross-bar based architecture

PADDI-2 Cross-bar based Architecture

Coarse Grained Architectures

EGRA

• Architectural template to enable design space exploration

• Execute expressions as opposed to operations• Supports heterogeneous cells and various

memory interfaces

EGRA

Evolution of fine grained and coarse grained architectures

EGRA – at Cell Level

Architectural Exploration

Architectural exploration

EGRA vs CGRA vs FPGA

EGRA – at array level

• Organized as a mesh of cells of three types– RACs– Memories– Multipliers

• Cells are connected using both nearest neighbor and horizontal-vertical buses

• Each cell has a I/O interface, context memory and core

Control Unit

EGRA Operation

• DMA mode– Used to transfer data in bursts to EGRA– To program cells and to read/write from

scratchpad memories• Execution mode– Control unit orchestrates data flow between cells

EGRA – at array level

Experimental Results

Experimental Results

Experimental Results

EGRA Memory Interface

• Data register at the output of computational cells

• Memory cells can be scattered around in the array

• A scratchpad memory outside reconfigurable mesh

Architectural exploration - Area

Architectural exploration - Delay

MORA

The reconfigurable Cell

Operating modes of RC

Interconnection Topology

• Hierarchical– Level 1 used within 4x4 quadrant to provide

nearest neighbor connectivity– Interleaved Horizontal and Vertical connectivity of

length two– Each RC can receive data from at most two other

RCs and send data to at-most four other RCs– Data and control across quadrants is guaranteed

over Level 2 interconnection

Interconnection Topology

Computational Strategies

•Temporal computational load balancing•Spatial computational load balancing