[Emulate] Interface and Channel Design

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Interface and Channel Design1

Interface and Channel

  • Interfaces and channels provide a flexibly way to model communication and system synchronization
    • Interface classes declare the access methods
    • Channels implement the access methods declared within interfaces
  • Interfaces separate the communication from the computation
    • Communication refinement is achieved by allowing one channel to easily be swapped with another

Interface and Channel

Interface Design

  • Good interface design shall reduce the modeling effort, make design refinement easier, and increase design reuse
  • Guidelines for designing interface classes
    • Minimize the number of distinctive interfaces
      • Allow the channel implementation be easily swapped
      • Leave the port instances untouched during the replacement of channels
    • Layer specialized interfaces on more general interfaces
      • Specialized interfaces inherit from generalized interfaces
    • Use class inheritance to group common interface
      • Create a common base class for different interface classes
    • Use multiple inheritance to create a unified interface class
      • Define the unified interface to inherit from separate interfaces without adding any new members

Layered Interface Classes

Allow channel implement interfaces of different specialization.

Channel Reuse

Channel Reuse

Modules use the least specialized interface, but channels that implement more-specialized interfaces can still be attached.

Channel Reuse

Channel Design

  • Primitive channels
    • Derived from sc_prim_channel
    • Contain no hierarchy and processes
    • May implement the request-update mechanism
    • Faster simulation speed
  • Hierarchical channels
    • Derived from sc_channel
    • May contain hierarchy and processes
    • Slower simulation speed due to more processes and context switches
  • What if your channel needs request-update mechanism and contains processes, ports, and modules?
    • Split the channel into a primitive channel and a hierarchical channel
    • Instance the primitive channel in the hierarchical one

Primitive Channels

Primitive Channels with Request-Update

  • Key ideas of request-update
    • Gather state change requests during the evaluation phase
    • Determine the next state of the channel during the update phase
    • Propagate the new channel state during the next delta-cycle
  • Main uses
    • Delta-cycle delay communication for hardware simulation
      • A new value assigned to a channel does not take effect immediately
      • There is always a delta-cycle delay before the new value takes effect
    • Arbitration and resolution of simultaneous actions
      • Simultaneous actions occur within the same simulation phase
      • Either is free to execute before the other
      • Example: multiple processes drive the same channel
  • Primitive channels with request-update in SystemC
    • sc_fifo, sc_signal, sc_buffer, sc_signal_resolved, sc_signal_rv

Primitive Channels without Request-Update

sc_mutex

  • sc_mutex (mutual exclusion object)
    • Allow multiple processes share a common resource
  • Usage
    • The process using the resource locks the mutex and unlocks it afterwards when the resource is no longer needed
    • Other processes must wait for the resource to be freed
    • The process executing first after the unlock will succeed in locking the mutex
    • There is no guarantee about which process will succeed
  • Member functions
    • lock()
      • Lock the mutex (wait until unlocked if in use)
    • trylock()
      • Non-blocking, return true if success, else false
    • unlock()
      • Free previously locked mutex

sc_samphore

  • sc_samphore
    • Allow multiple processes share a set of common resources
    • A generalized version of sc_mutex
  • Member functions
    • wait()
      • If available, occupy one semaphore
      • Otherwise, suspend until there is an available resource
    • trywait()
      • If available, occupy one semaphore
      • Otherwise, return -1
    • get_value()
      • Return number of available semaphore
    • post()
      • Free the previous occupied semaphore

Hierarchical Channels

  • User defined channel
  • May have embedded modules, channels, and processes
  • Provide implementations for one or more interfaces
    • A hierarchical channel is distinguished from a general module by the fact that it implements interfaces
  • Used to encapsulate both the structural elements of a design and the communication protocol or methods

Channel Refinement

Channel Refinement

Communication via sc_fifo

Communication via SC_FIFO

RTL Implementation of FIFO

Definition of input/output.

RTL Implementation of FIFO

Implementation of Wrapper

Implementation of Wrapper

Top Module with Hierarchical Channels

  1. IOC5080(5940) System Model Design and Verification, Department of Computer Science, National Chiao-Tung University ↩