Date post: | 15-Dec-2015 |
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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
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
Mesh Based Architectures
• Arranges PEs in a 2-D array• Encourages nearest neighbor links between
adjacent PEs • Eg. KressArray, Matrix, RAW, CHESS
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
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
EGRA
• Architectural template to enable design space exploration
• Execute expressions as opposed to operations• Supports heterogeneous cells and various
memory interfaces
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
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 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
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