Top 25 System Verilog Interview Questions and Answers 2021


System Verilog Interview Questions and Answers

Out of all the means of landing a job, performing well in an interview is the surest. Employers usually invite potential employees to interviews to gauge their ability and expertise before serving in different positions.

In this article, we take a look at some of the most common questions in system Verilog interviews. System Verilog is a technical term encompassing hardware description and verification language. It is used in the chip industry and calls for experts.

These 25 questions should help you land the system Verilog job of your desire.

1.    Why Are You Interested in This Role?

I have been working in the chip industry for over ten years and have all it takes to succeed in this role. This job’s description further fits my expertise. I have also always wanted to work for your company since my internship days, and therefore, it will be an honor if given a chance to do so.

2.    Mention the Difference Between a Virtual and Pure Virtual Function in System Verilog

A virtual function allows the overriding of implementation of a function in a given derived class. Therefore, the base class doesn’t need to implement the virtual function. 0n the other hand, a pure virtual function only has the declaration and lacks any implementation. Therefore, any derivative class must implement the function.

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3.    What Do You Understand by Semaphores? Do You Know When They Are Used?

A semaphore is used to control access to shared resources. One can view it as a bucket with several keys during its creation. Before any process that uses a semaphore can continue to execute, it must procure a key first from this bucket. Therefore, any process without a key must wait until the ones with procured keys give them back. This mechanism is therefore used for mutual exclusion, primary synchronization, and accessing control to shared resources.

4.    Have You Interacted with Mailboxes? What Are They and Some of Their Uses?

A mailbox allows the exchange of a message between two processes. Usually, data is sent to the mailbox using one process and retrieved by the other. Placing and retrieving a message in a mailbox, therefore,  takes the support of two methods. There are two different types of mailboxes: bounded and unbounded. The unbounded mailbox has no size limit, whereas the bounded mailbox has a limited size limit set during its creation.

5.    What Does a Virtual Interface Mean to You? Where Is It Used?

It is a variable that leads to an actual interface. A virtual interface provides a connection point that allows access to the signals in an interface via the virtual interface pointer.

6.    Explain the Concept of Factory and Factory Pattern

A factory (in object-oriented programming) is a function used to create different objects of a prototype. This happens when the different classes are registered with the factory, enabling the factory method to create objects of any registered class type by calling the corresponding constructor. Objects can also be created instead of calling the constructor method directly in a process known as factory pattern. It engages factory objects and allows for the use of polymorphism for object creation.

7.    What Do You Understand by Callback?

Whenever a function calls another function that takes the first one as an argument, we get a callback. It is usually called when an event happens. It comes in handy in several applications in a verification testbench. Some of these include calling back a function to inject error on transactions sent from the driver, calling a function to drain pending transactions, and calling a coverage sample function in the event of a specific occurrence.



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8.    What Kind of Strategies and Mindset Is Needed for This Role?

Working in the chip industry comes with its fair share of requirements.  Given the sensitivity and technicality involved, I have found out that the best strategy is bringing together different minds when working on a project. Teamwork has constantly helped me in my career. As for the right mindset, one needs to be focused and result-oriented when working on different projects.

9.    What Do You Understand by a DPI Call?

DPI is the short form for Direct Programming Interface, a bridge between SystemVerilog and any foreign programming language such as Python. It enables direct inter-language function calls between the languages on each side of the interface.

Through the DPI layer, both imported and exported functions implemented in the C language can be expelled. DPI, therefore, supports both functions and tasks across the boundary. Only the Verilog data types can cross the boundary between System Verilog and a foreign language both ways.

10. While Still on DPI, Could You Tell Us the Difference Between DPI Import and DPI export

A DPI imported function is implemented in the C language and is usually called in the SystemVerilog code. On the other hand, a DPI exported function is implemented in the SystemVerilog and exported to the C language, from where it is called. Both functions and tasks can be imported and exported.

11. What Do You Understand by System Tasks and Functions? Please Give Us Some Examples of System Tasks and Functions

There are several built-in system tasks and functions for different utilities supported by SystemVerilog language. These are generally called with a given prefix to the task/ function name. This language also allows one to add user-defined system tasks and functions.

There are different examples of system tasks and functions which are grouped based on functionality. These are simulation control tasks, conversion functions, bit vector system functions, severity tasks, assertion control tasks, and sampled value system functions.

12. Could You Please Differentiate Parameter in System Verilog and Typedef?

A parameter in system Verilog is a constant value within the module structure. It can be used to define several attributes for the module and normally characterizes the behavior and the physical representation of the module. The parameter can be overridden at instantiation time.

Parameters have to be overridden in the order in which they were defined if they exist in multiples. However, if the overriding value is not specified, one can use the default parameter declaration values.

On the other hand, Typedef lets users craft unique names for type definitions to be frequently used in their codes. They come in handy when building technical array definitions.

13. Could You Explain the Difference Between These Different Data Types: Logic, Reg, and Wire?

Wire data is used in continuous assignments or ports list and is thus treated as a wire. It cannot hold any value but can be driven and read. It is used to connect different modules. Reg is a data storage element in the Verilog system. Even though it is not actual hardware, it can still store values. Logic is an additional datatype in system Verilog that extends the rand. It can be easily driven by a single driver, such as a module.

14. Mention the Need of Clocking Blocks

A clocking block has several users, which system Verilog officers appreciate. It is used to specify synchronization characteristics of a design and helps in testbench driving the signals at the right time. The clocking block also offers a clean way to drive and sample designs and race-free operation in specific applications.

15. What Is the Use of Packages in System Verilog?

The data, task, or function within a module are only specific to the module in Verilog declaration. These cannot be shared between two modules and can only be achieved via cross-module referencing or including the files. However, these are not proper solutions.

Packages, therefore, come in to solve this issue. It allows global data, task, or function declaration to be used across different modules. The package also contains content that can be accessed using scope regulation operator or import. They, therefore, play an essential role in system Verilog.

16. Detail the Difference Between Rand and Randc

Rand is a random variable whose same value may be arrived at before returning all the possible values. It can be compared to throwing dice. Randc, on the other hand, refers to a random cyclic variable whose same value cannot be returned unless all the possible values have been returned. It can be compared to picking a card from a group of cards without making any replacements.

17. Could You Please Explain Pass by Ref and Pass by Value?

Pass by value is the default method by which arguments are relayed into functions and tasks. Each subroutine usually stays with a copy of the argument. This plays one significant role. If the arguments are ever changed within the subroutine declaration, the changes do not at any point affect the caller.

On the other hand, functions and tasks directly access the set out variables passed as arguments in the pass by reference. It can be accurately termed as the passing pointer of the variable.

18. What Do You Understand by Program Block and Module? What are The Differences, If Any?

A program block is a new addition to system Verilog, which has its purposes. It separates the testbench from DUT, ensures that the testbench does not have any race condition with DUT, offers an entry point for testbench execution, and offers syntactic context for scheduling in the reactive regions.

There are several differences between the module and program blocks. Modules can always have blocks inside them, which is not possible for modules. Modules can also have UDP, which program blocks do not have.

Their execution regions also differ. Whereas program blocks are executed in the reactive region of the scheduling queue, module blocks are executed in the active region. Lastly, a program can call a task in modules, which a module cannot do.

19. Why Do You Need an Alias in System Verilog?

A system Verilog has an alias statement that offers bidirectional and short circuit connection. Generally, the Verilog has only a one-way assign statement, which may also have delay and strength change for unidirectional assignment. 

20. Could You Please Tell Us the Difference Between Initial and Final Blocks?

The primary difference between these two types of blocks is that the first one is executed at the beginning of the simulation, whereas the final block at the end. The final block must also be executed promptly, whereas initial blocks have no execution restriction. They can delay and wait.

The final blocks can also be used to display statistical information on the status of the execution.

21. How Do You Check Whether a Handle is Holding Objects or Not?

Checking whether a handle is holding objects or not ascertains whether the object t is initialized. All the uninitialized object handles in SystemVerilog have a null value and can be checked by comparing the object handle to null.

22. What Do You Understand by Bi-Directional Constraints?

Constraints are by default bi-directional. The constraint solver does not, therefore, follow the specified sequence of constraints. All the variables are therefore looked at simultaneously. This also applies to procedural-looking constraints such as if else and -> constraints.

23. Do You Know The Difference Between Always_comb and [email protected](*)?

The first one (mention it in your speech) is executed once at a time, whereas the second one delays until a change occur on a signal. The statement in the always_comb cannot have any blocking timing, fork-join statement, or event control, whereas the latter does not have any of that restriction.

The former is change-sensitive, especially within a function, whereas the latter is only sensitive to changes to the function arguments.

24. Please Tell Us What a Queue Is

A queue is a variable-size and ordered collection of uniform elements. It can be compared to a dimensional unpacked array which automatically grows and reduces in size. Queues are generally used to model a last-in, first-out buffer, and a last-in.

25. Mention Some of The Ways of Avoiding Race Conditioning Between Testbench and RTL

Avoiding race conditioning between testbench and RTL suing system Verilog can be done through program block, clocking block, and use of non-block assignments.

Conclusion

We have exhausted some of the most common system Verilog interview questions and answers. These should help you land your desired system Verilog role.

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