SystemVerilog Interview Set 1

How will you test the functionality of interrupts using functional coverage?

Testing the functionality of interrupts using functional coverage involves the following steps:

1. Define functional coverage goals: First, you need to define your functional coverage goals. These goals should be specific to the interrupts you want to test. For example, you might define goals for interrupt latency, interrupt frequency, or interrupt priority handling.
2. Create a testbench for interrupts: Next, you need to create a testbench that generates interrupts with different characteristics. This testbench should also monitor the behavior of the design under test (DUT) in response to the interrupts.
3. Implement functional coverage: You can then implement functional coverage in your testbench to track how often each of the defined functional goals is achieved. You can use standard SystemVerilog constructs like covergroups, coverpoints, and bins to define and track the functional coverage.
4. Analyze the functional coverage results: Finally, you can analyze the functional coverage results to determine how well your testbench tests the desired interrupt functionality. Based on the results, you can make adjustments to your testbench to improve the tests.

What is the use of scope resolution operator?

The scope resolution operator in SystemVerilog is denoted by the double colon '::' symbol. The basic purpose of this operator is to specify the scope in which an identifier is defined or should be searched for.

Here are some common uses of the scope resolution operator:

1. Accessing variables or modules within a hierarchy: When a design has a hierarchy of modules or sub-modules, the scope resolution operator can be used to access variables or modules that are defined in different scopes. For example, if a variable 'clk' is defined in a top-level module and is used in a lower-level module, then we use the scope resolution operator to specify the scope of 'clk'.
2. Resolving naming conflicts: When a design has two or more variables or modules with the same name, the scope resolution operator can be used to differentiate the variables or modules by specifying their scope.

  	package ahb_pkg;
  		typedef enum {READ, WRITE} e_access;
  	endpackage
  
  	package wishbone_pkg;
  		typedef enum {WRITE, READ} e_access;
  	endpackage
  
  	ahb_pkg::e_access 	m_access; 		// m_access = 1 indicates WRITE
  

3. Accessing static variables and functions: The scope resolution operator is also used to access static properties and methods in a class.
4. Accessing items in package: Elements in a package can be imported using import with scope resolution operator.

	import ahb_pkg::*; 	 		// Imports everything in the package called "ahb_pkg"
	import enum_pkg::global; 	// Imports everything under "global" from enum_pkg

Read more on SystemVerilog Scope Resolution Operator.

How do you implement randc in SystemVerilog?

The randc keyword in SystemVerilog will first exhaust all combinations possible before repeating a value. This is different from rand keyword where the same value may repeat even before all combinations are exercised.

Here's an example :

class ABC;
	rand 	bit [1:0] 	x; 		// randomization can give x = 3, 1, 1, 0, 3, 0, 2, 2
	randc 	bit [1:0] 	y; 		// randomization can give y = 1, 3, 0, 2, 3, 1, 2, 0 
endclass

Read more on SystemVerilog rand Variables.

What is inheritance?

Inheritance is a concept in object-oriented programming that allows creating a new class by inheriting or extending the properties and behavior of an existing class. The existing class is called the parent or base class, and the new class is called the child or derived class. The child class inherits all the members of the parent class, such as variables, methods, and constructors, and can also add new members or override the inherited members.

Read more on SystemVerilog Inheritance.

What is DPI? Explain DPI export and import.

DPI stands for Direct Programming Interface, which is a mechanism in SystemVerilog for integrating SystemVerilog design and verification code with external C/C++ code. It enables interoperability between SystemVerilog and other high-level programming languages, which is not possible with traditional Verilog.

DPI export is used to export C/C++ functions to SystemVerilog. This means that a C/C++ function can be used as a task or function in SystemVerilog by creating an import task or import function.

extern "C" void my_function(int arg1, int arg2) {
	// Do something here
}

And here's an example of how to import this function in SystemVerilog using DPI import:

import "DPI-C" context function void my_function(int arg1, int arg2);

Read more on SystemVerilog DPI.

What is semaphore and in what scenario is it used?

Semaphore is a synchronization mechanism used to control access to shared resources. It is a variable or an abstract data type that is used to indicate the status of a shared resource, whether it is free, in use, or unavailable.

In a multi-tasking or multi-threaded environment where multiple processes or threads access shared resources concurrently, semaphores can ensure that only one process or thread can access the shared resource at a time. This helps to avoid conflicts and data inconsistency caused by simultaneous access, which could result in unexpected behavior.

Read more on SystemVerilog Semaphore.

Difference between fork-join, fork-join_any, and fork-join_none

They are all used to spawn processes in parallel.

• fork-join will exit only after all child processes finish.
• fork-join_any will exit after any of the child processes finish.
• fork-join_none will exit immediately without waiting for any child process to finish.

See examples of fork join, fork join_any and fork join_none.

Difference between static and automatic variables

The main difference is that a static variable gets initialized once before time 0 at some memory location and future accesses to this variable from different threads or processes access the same memory location. However, an automatic variable gets initialized every time the scope where it is declared gets executed and stored in a different location every time.

Read more on SystemVerilog Static Variables & Functions.

Difference between module and program block?

A module is the primary container for all RTL design code and allows hierarchical structuring of design intent. A program block on the other hand is a verification container introduced in SystemVerilog to avoid race conditions in the testbench by executing its contents at the end of the time step.

Read more on Verilog module and SystemVerilog Program Blocks.

Difference between dynamic and associative arrays

A dynamic array is an array whose size can be changed during runtime. Elements of the array are stored in a contiguous block of memory, and the size is determined when the array is created. An associative array, on the other hand, is also known as a dictionary or a map. It is a collection of key-value pairs where each key has a corresponding value.

In a dynamic array, the elements are accessed using an index, which refers to the position of the element in the array. In an associative array, elements are accessed using the key.

Read more on SystemVerilog Dynamic Array and Associative Array.