System Verilog Constraints And Interview Questions
If the user wants to ensure that the function doesn’t change the ref argument, they should use the const keyword. To ensure that the original packet contents are not unintentionally changed by the CRC function, for instance, the argument can be declared as a ” const ref ” argument as shown below in the same CRC function.
the port names and connections. An interface supports defining functions that can be called by instantiating design for communication, so in addition to connectivity, functionality can also be abstracted. Additionally, interfaces support procedural (always/initial blocks) and continuous assignments, which are helpful for verification by enabling the addition of assertions and protocol checks.
An interface construct called modport (short for module port) allows you to group signals and specify directions. The example that follows shows how a modport can be used to further group an interface for connecting to various components
Individual members of the instruction_s struct can be accessed or referenced collectively. The total amount of memory allotted would equal the sum of all the data types’ memory requirements. The currect_instruction struct would therefore require a total amount of memory in the example above.
The function new() is the class constructor function in SystemVerilog. It is specified in a class to initialize the class’s data members.
Interviewers frequently ask candidates to create transactions, class objects, or sequence items (they go by many different names) that adhere to predetermined specifications and constraints. Candidates are frequently required to write the class’s code as well as the test-bench code to produce a few objects. Here is an illustration of a straightforward Packet class, whose payload is an array of bytes (8-bits). The other fields are DA (destination address), SA (source address), and LEN (length), in addition to the payload. One byte of the payload contains the FCS (frame check sequence) field, which is an XOR of all the data bytes to prevent data corruption. Let us look at the solution.
Solution: Given is the code for Packet class (Packet. sv) and a testbench code (tb_top. sv). Writing the class’s properties (data members) is simple; however, writing constraints can be challenging, especially for the LEN field, which has a maximum value of 8’hff (255 decimal). Here is the answer and the outcome of the simulation using the Synopsys VCS simulator.
Please let us know if you know of a resource where we can practice constraints randomization problems. YoE: 8 TC:185 Edit: Refreshing the thread and inviting the DV community to submit compelling constraints questions #DV.
FAQ
What are constraints in SystemVerilog?
Users of SystemVerilog can compactly and declaratively specify constraints that are then processed by an internal solver to produce random values that satisfy all requirements. Constraints essentially serve as a means of defining the legal values that should be assigned to the random variables.
Is all constraints are bidirectional in SV?
Due to the bidirectional nature of SystemVerilog constraints, all random variable constraints will be resolved in parallel.
What is hard constraint in SV?
Because the solver must always satisfy the normal constraints, they are referred to as hard constraints. If the solver is unable to produce a solution, the randomization will be unsuccessful.
What is the difference between bit 7 0 and byte in SV?
The distinction between byte and bit [7:0] is that the former is signed and the latter is unsigned.
