Verilog Interview Questions Part #1

1) How re blocking and non-blocking statements executed?

Answer:
In the blocking statement, the RHS will be evaluated and the LHS will be then updated without any interruptions.

In the non-blocking statement, RHS will be evaluated at the beginning of the time step. Then the LHS will be updated at the end of the time step. Within the whole period, the other process can run in parallel.

2) How do you model a synchronous and asynchronous reset in Verilog?

Answer:
Synchronous reset:

always @(posedge clk)
begin
----
if (reset)
begin
-----
end
end

Asynchronous reset:

always @(posedge clk or negedge reset)
begin
-----
if (!reset)
begin
-----
end
end

In asynchronous reset, the always block will invoked at the negative edge of the reset signal, irrespective of clock's value.


3) What happens if there is connecting wires width mismatch?

Answer:

For examples:
RHS[7:0] = LHS[15:0]

The end result is LHS[7:0] = RHS[7:0];
The assignments starts from LSBs of the signals, and ends at the MSB of smaller width signal.


4) What are different options that can be used with $display statement in Verilog?

%b - binary
%c - ASCII character
%d - Decimal
%h - Hexadecimal
%m - Hierarchical name
%o - Octal
%s - Steing
%t - Time
%v - Net signal strength

5) Give the precedence order of the operators in Verilog.

Answer:

Precedence rules for operators

+ - ! ~ (unary)	highest precedence
* / %
+ - (binary)
<< >>
< <= > >=
== != === !==
& ~&
^ ^~
| ~|
&&
||
?: (conditional operator)	lowest precedence

6) Should we include all the inputs of a combinational circuit in the sensitivity lists? Give reason.

Answer:

Yes, in combinational circuit all inputs should be included in the sensitivity lists, otherwise, it will result in a synthesis error.


7) What is the difference between a task and a function in verilog?

Answer:

	Function	Task
Time-Control statements	No, shall execute in one simulation time unit	Yes
Call function or tasks	Cannot call tasks	Can call both tasks and functions
input type argument	at least 1 input type argument and shall not have an output or inout type argument	can have 0 or more arguments of any type
return value	return a single value	shall not return a value