The UVM Factory is a software design pattern employed in UVM. It operates as a singleton, meaning it maintains a single class instance. This pattern enables the overriding of objects and UVM components. In essence, it allows the creation and replacement of these elements without requiring modifications to the testbench.
Consider an example involving a testbench with an Ethernet agent. The test environment might be structured as follows:
Each component would be defined as shown in the following figures:
If an update to the Ethernet protocol requires a modification to the sequence item, such as changing it to "eth_v2_pkt," it would demand altering all files that utilize that sequence item. However, the UVM Factory allows for overriding all sequence items with a single statement, as illustrated below:
This override can be applied selectively to each test case, enabling specific tests to utilize different sequence items. In other words, UVM override allows it to maintain tests for both Ethernet versions by adding or removing the UVM Factory override statement.
UVM Factory requirements
Three requirements must be achieved to leverage the UVM Factory features:
- Polymorphic compatibility
In the aforementioned example, the newer sequence item must extend from the older version.
- UVM FACTORY registration
Within the class definition, the corresponding statement must be added to register objects or components to the UVM factory.
- UVM FACTORY creation
The components and objects must be created using the UVM factory methods instead of the `new()` method.
Override options
While Figure 8 demonstrates overriding by type, it is also possible to override by name, or even override instances by type or name. The following templates illustrate these four cases:
This function examines the entire UVM environment and performs the corresponding override actions.
The UVM Factory provides a print method that displays all registered types within the factory, along with the methods being overridden. This print method should be called from the Test's `build_phase` only once (as it is a singleton).
The transcript will display the test configuration and overrides.
Conclusion
UVM factory can save us headaches and countless editing hours when there are changes in UVM objects that are involved in several files through verification codebases. This method, if the code is written smartly, can change an entire environment with just one line of code.
Bibliography
- https://verificationacademy.com/cookbook/uvm-universal-verification-methodology/
- Salemi, Ray, The UVM Primer: An Introduction to the Universal Verification Methodology, Boston Light Press, (2013)
- https://www.chipverify.com/uvm/uvm-factory-override
Written by Roberto Millon Tello, Patricio Gallo & Marcelo Pouso
Edited by Adrian Evaraldo
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