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| − | Глава 1.4 из книги glasser_m__open_verification_methodology_cookbook__2009.pdf
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| − | == Layered Organization of Testbenches ==
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| − | Just as a design is a network of design components, a testbench is a network
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| − | of verification components. The OVM defines verification components, their
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| − | structure, and interfaces. This section describes the essential OVM
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| − | components.
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| − | OVM testbenches are organized in layers. The bottommost layer is the DUT,
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| − | an RTL device with pin-level interfaces. Above that is a layer of transactors,
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| − | devices that convert between the transaction-level and pin-level worlds. The
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| − | components in the layers above the transactor layer are all transaction-level
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| − | components. The diagram below illustrates the layered testbench
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| − | organization. The box on the left identifies the name of the layer. The box on
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| − | the right lists the type of components in that layer. The vertical arrows show
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| − | which layers communicate directly. For example, the control layer
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| − | communicates with the analysis, operational, and transactor layers, but not
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| − | directly with the DUT.
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| − | <center>'''Figure 1-7 OVM Testbench Architecture Layers'''</center>
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| − | You can also view a testbench as a concentric organization of components.
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| − | The innermost ring maps to the bottom layer, and the outermost ring maps to
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| − | the top layer. Some find it easier to understand the relationships between the
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| − | layers using a netlist style diagram.
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| − | Figure 1-8 Concentric Testbench Organization
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| − | === Transactors ===
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| − | The role of a transactor in a testbench is to convert a stream of transactions to
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| − | pin-level activity or vice versa. Transactors are characterized by having at
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| − | least one pin-level interface and at least one transaction-level interface.
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| − | Transactors come in a wide variety of shapes, colors, and styles. We’ll focus
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| − | on monitors, drivers, and responders.
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| − | Monitor. A monitor, as the name implies, monitors a bus. It watches the pins
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| − | and converts their wiggles to a stream of transactions. Monitors are passive,
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| − | meaning they do not affect the operation of the DUT in any way.
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| − | Driver. A driver converts a stream of transactions (or sequence items) into
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| − | pin-level activity.
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| − | Responder. A responder is much like a driver, but it responds to activity on
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| − | pins rather than initiating activity.
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| − |
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| − | === Operational Components===
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| − | The operational components are the set of components that provide all the
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| − | things the DUT needs to operate. The operational components are responsible
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| − | for generating traffic for the DUT. They are all transaction-level components
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| − | and have only transaction-level interfaces. The ways to generate stimulus are
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| − | as varied as the kinds of devices there are to verify. We’ll look at three general
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| − | kinds of operational components: stimulus generators, masters, and slaves.
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| − | Stimulus Generator. Stimulus generators create a stream of transactions for
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| − | exercising the DUT. Stimulus generators can be random, directed, or directed
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| − | random; they can be free running or have controls; and they can be
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| − | independent or synchronized. The simplest stimulus generator randomizes
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| − | the contents of a request object and sends that object to a driver. OVM also
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| − | provides a modular, dynamic facility for building complex stimulus called
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| − | sequences. These are discussed in detail in Chapter 8.
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| − | Master. A master is a bidirectional component that sends requests and
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| − | receives responses. Masters initiate activity. Like stimulus generators, they
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| − | can send individual randomized transactions or sequences of directed or
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| − | directed-random transactions. Masters may use the responses to determine
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| − | their next course of action. Masters can also be implemented in terms of
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| − | sequences.
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| − | Slave. Slaves, like masters, are bidirectional components. They respond to
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| − | requests and return responses (in contrast to masters, which send requests
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| − | and receive responses).
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