Donald Chai

1
Interface-based Design

• Donald Chai
• EE249

2
Outline

• Orthogonalization of concerns
• Formalisms
• Interface-based Design Example
• Cheetah Simulator
• Future Inroads

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Orthogonalization of Concerns

• Behavior
• (or computation, coordination)
• Communication
• (or interfaces)
• These two are (or should be) independent

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Interface-based Design

• Done all the time
• OSI stack
• Memory mapped I/O
• Virtual memory

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Required Tools

• A good formalism with which to perform
• Abstraction (and hierarchy)
• Decomposition (and composition)
• These concepts exist for both computation and
  communication

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Formalism Models of Computation

• All models of computation specify a set of actors
  and a communication mechanism
• FSMs synchronous composition
• CFSMs event broadcast
• Dataflow/KPN lossless queues
• CSP rendezvous
• Some models conflate communication and computation

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Refinement (Abstraction-1)

• Simple channel through which tokens are passed
• REQ/ACK protocol
• Master requests, slave acknowledges
• Repartition

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(De)composition

• Largely ignored in this paper
• Consider at least three communicating processes

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Design Example

• What
• Software thread sending packets through a
  hardware transmitter
• Asynchronous Transfer Mode (ATM)
• How
• Communication through bus (PCI, EISA, or PI)
• Single byte transmission or burst mode?

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Cheetah Simulator

• Event driven
• Built with communication platforms

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Cheetah Simulator (II)

• At most abstract level, channel has a simple
  delay
• With more detail, expands in both space and time
• Simulation speed varies from 7x to 175x RTL

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Future Inroads

• Better modeling and design exploration
• Can mix and match communication and behaviors
• Better synthesis
• Allows design reuse
• Improves dont care extraction
• Composeability

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Future Inroads (II)

• Verification
• Abstraction and Decomposition are necessary
• Can be used between steps in communication
  platform
• Formal specification allows test generation