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OVM Methodology

March09

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What is OVM??

Open Verification Methodology is combine effort fromMentor Graphics (AVM) and Cadence (URM).

Uses the best practices of AVM and URM.

Provides the structure and libraries of base class whichuser can use to create modular, reusable verificationenvironment in which component talk through TLM.

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Class Hierarchy in OVM Objects

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OVM Features

Provides reusable components (base class libraries)

Use TLM interface communication between differentcomponents

Data Design : Infrastructure for class property abstracting and

simplifying the user code for setting, getting, and printing (text and gui)property variables

Stimulus Generation: Provide control for random stimulus generation.

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OVM Features

Coverage Driven Verification

Provide base classes for each functional aspect of

verification environment.

Provides inbuilt report properties for unified reporting andmessages.

Implements OOP Factory method.

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OVM Verification Components (OVC)

OVC is encapsulated, ready-to-use, configurableverification environment

Following are the building blocks of OVM: Data Item(ovm_transaction/ovm_sequence_item)

Represents Inputs to DUT.

Can be randomized and constrained.

Ovm_sequence_item inherits from ovm_transaction

Adds a property other than inherited one

Sequencers and Drivers use ovm_sequence_item

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OVM Verification Components (OVC)

Driver (ovm_driver)

Drivers role is to drive the data items to the bus following interface

protocol Gets transactions from sequencer.

Derive pins at the DUT (using interface) and based on thetransaction received.

Sequencer (ovm_sequencer) Advanced stimulus generator, controls the data items that are

provided to driver

By default, is a simple stimulus generator that provide random datatransaction to driver

a sequencer captures important randomization requirements out-of-the-box

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OVM Verification Components (OVC)

Monitor (ovm_monitor)

Is a passive entity that samples the DUT signals.

Can includes coverage information and protocol checkers. Creates a trancation and send it to other components (scoreboard,

coverage collectors etc)

Check status information and events

Agent (ovm_agent) Encapsulate driver, monitor and sequencer.

Has an active mode and passive mode (is_active).

Passive agent only monitors DUT.

Should be configurable so that they can be made active/passive

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OVM Verification Components (OVC)

Environment (ovm_env)

Encapsulates a number of drivers, monitors, agents, scoreboards.

Has properties to customize its components behavior (eg changingan agent from active to passive)

Environments can be hierarchical and contain more env.

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OVM Verification Components (OVC)

Typical Verification Environment using OVC

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TLM

Defines Semantics/Behaviors for communicating transactionbetween components.

Provides Transfer of Transactions thru standard interfaces Ports: Defines the set of Methods (API) to be used for a particular

connection .

Export: Supplies the implementation of those methods.

Imp: Provides implementations of the methods in tlm_if_base to

Ports and exports if they require it.

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TLM

TLM Components

ovm_port_base

ovm_*_export ovm_*_port ovm_*_imp

tlm_fifo tlm_req_resp_channel

tlm_transport_channelanalysis_fifo

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TLM

Uni-directional Interfaces Put, get, peek, get_peek, analysis

Bi-directional Interfaces Master, slave, transport

Channels tlm_fifo, analysis_fifo

tlm_req_resp_channel, tlm_transport_channel

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TLM example

class producer extends ovm_component;

ovm_blocking_put_port #( int ) put_port;

task run();

for( int i = 0; i < 10; i++ )

begin$display("about to put %d",i);

put_port.put( i );

end

endtask;

endclass

class consumer extends ovm_component;

ovm_blocking_get_port#( int ) get_port;task run();

for( int i = 0; i < 10; i++ )begin

$display(Just got %d",i);

get_port.get( i );

end

endtask;endclass

Producer Consumertlm_fifo

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TLM example

class env;

producer p = new;

consumer c = new;tlm_fifo #( int ) f = new;

function void connect;

p.put_port = f.blocking_put_export;

c.get_port = f.blocking_get_export;

endfunction

endclass

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Structure of OVM Test-Bench

ovm_test Individual test-cases inherit from this class.

Each test-case instantiates environments and configures them.

Test-Bench Top level TB instantiates interfaces that connect to DUT.

Instantiate DUT

Call run_test() +OVM_TESTNAME = (select which ovm_test class to instantiate and

run

Run_test() is a method from ovm_root that is automaticallyinstantiated.