3. Context
Society Needs
• Smaller & denser circuits which consume much less power
However
• Current technology (CMOS) reaches its limits
State of the art
• Different architectural propositions based on emergent
technologies
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Nanoscale Architectures
5. What is a Crossbar ?
Crosspoint
Different devices:
• Diode
• FET
• Etc.
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Nanoscale Architectures
6. utilization and performance.
5N I Ah c rs
. ACr ie u
S ct t e
Example: NASIC
Large scale computing systems may be designed using the NASIC fabric and the associated
framework of building blocks, xnwFET based circuits, and logic styles discussed in the
preceding sections. This section discusses two key architectures for the NASIC fabric: the WISP-
0 general purpose processor and a massively parallel architectural framework with
programmable templates for image processing.
5
.1 W te i grc s ( I P
Ie ra nP eoW-)
r S m os r S 0
WISP-0 is a stream processor that implements a 5-stage
microprocessor pipeline architecture including fetch,
decode, register file, execute and write back stages.
WISP-0 consists of five nanotiles: Program Counter (PC),
ROM, Decoder (DEC), Register File (RF) and Arithmetic
Logic Unit (ALU). Figure 17 shows its layout. A nanotile
is shown as a box surrounded by dashed lines in the
figure. In WISP designs, in order to preserve the density
advantages of nanodevices, data is streamed through the
fabric with minimal control/feedback paths. All hazards Figure 17. WISP-0 Processor Floorplan
are exposed to the compiler. It uses dynamic circuits and
pipelining on the wires to eliminate the need for explicit
flip-flops and therefore improve the density considerably.
WISP-0 supports a simple instruction set including nop,
mov, movi, add and multiply functions. It uses a 7-bit
instruction format with 3-bit instruction and 2-bit source
and destination addresses. The WISP-0 is used as a design
prototype for evaluating key metrics such as area and
performance as well as the impact of various fault-
tolerance techniques on chip yield and process variation
mitigation. Additional enhancements to this design are Figure 18. WISP-0 Program Counter
ongoing in the NASIC group.
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5.
. 1 W - Pgm ue
1 I P r r C nr
S0 o a o t Nanoscale Architectures
7. Common Features of Crossbar Fabrics
Nanowire based
Regularity of assembly leads to:
• a crossbar-like structure
• PLA and/or FPGA-like fabric architecture
CMOS superstructure, thus a nano-CMOS interface
Large number of defects
Logic implementation
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Nanoscale Architectures
8. Differences Between Crossbar Fabrics
Architectural differences
• Nano-role, CMOS-role
• Fabrication strategy
Physical parameters used for evaluation
• CMOS/NW pitch / device characteristics
Evaluation strategies
• Yield simulation
• Place & Route on predefined array
Hypotheses during evaluation
• Defect/Faults models
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Nanoscale Architectures
9. Research Questions
How to maximize the reuse of design-tools?
Is it possible to create a generic design toolkit?
How to separate the algorithmic and architectural concerns?
How to add a tools axis to design-space exploration problem?
How to integrate multi-level fault tolerance?
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Nanoscale Architectures
10. Contributions
Model-driven physical- R2D NASIC:
Nanoscale
design @ nanoscale
architecture
template
Max-rate
Common Tools as model Reified design DSE bootstrap
pipeline
vocabulary transformation flow methodology
routing
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Nanoscale Architectures
15. Structural Domain Modeling
Common abstract model
• Hierarchical annotated port graph
• Specialized to model applications and
architectures
• Provides a common vocabulary (Entities and API)
• Enables the creation of generic utilities
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Nanoscale Architectures
20. Tools as Transformations
Decouple the algorithms from the domain models
The tools are implemented as composite model-to-
model transformations
The tools refine the domain models
Integration of external tools and algorithms
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Nanoscale Architectures
22. Architectural Model Application Model Placed App Model
RRGraph Extraction TGraph Extraction Nets Extraction
RRGraph TGraph Nets
add routes update costs add AT add RT
Pathfinder
Routes
Post-routing FPGA Model Refinement
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Nanoscale Architectures
23. Tool-Flow Modeling
Reified tool-flow as a composite transformation
The physical-design tool-flow is a DAG of tools
Capacity to create tool-flow derivations
Enables incremental tool-flow creation
Enables Architecture/Tools exploration
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Nanoscale Architectures
31. R2D NASIC – Main Characteristics
Compatibility with NASIC technology and fabrication
Adaptability to technological and applicative constraints
Compatibility with NASIC fault-tolerance techniques
Custom placement and routing due to structural regularity
Max-rate pipeline designs due to pipelined routing architecture
Simplified delay estimation
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Nanoscale Architectures
44. Conclusions
Generic physical-design toolkit for nanoscale crossbar
fabrics
• Model-driven approach: structure, algorithmics, and flow reified.
• Two main abstraction levels considered
• Quantitative incremental DSE, bootstrapped with standard tools +
new exploration axis
Nanoscale architecture template
• Enables arbitrary routing for NASIC
• Shows the impact of pipelined (dynamic logic) routing
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Nanoscale Architectures
45. Future Research
MoNaDe toolkit
• Formalize the models and the API
• Hardware accelerated physical-design using external transformations
• Create an optimizing tool-flow execution engine
• Open infrastructure for architectural exploration in the context of new technologies
Nanoscale architectures @ techno level
• Fault tolerance for dynamic routing
• Parameter variability impact on multi-tile design
• Clock distribution in highly constrained 2D topologies
Nanoscale architecture @ design level
• Creation and/or improvement of pipeline aware tools (placement, routing, etc)
• Study the extent to which dynamic logic evaluation impacts the physical design for
other architectures besides R2D NASIC
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Nanoscale Architectures
47. Configuration Management
Configuration types:
• Structural
• Fine-grain functional
• Coarse-grain functional
Configuration state-machine reified in the model
Different configuration policies
• One-time configuration
• Reconfiguration
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Nanoscale Architectures
48. Fault-Modeling and Injection
Domain concepts specialized to faulty entities
• FET -> StuckAt0FET and StuckAt1FET
Two ways to inject faults:
• Object swapping: injects faulty devices by replacing
model instances
• Fault-configuration: uses a probabilistic configuration
controller
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Nanoscale Architectures