Functions and tasks allow for code reusability in Verilog. Functions are used for combinational logic, execute immediately without delays, and return a single value. Tasks can contain delays and timing controls, are used for both combinational and sequential logic, and can pass multiple values through input/output arguments but do not return a value. The key differences are that functions cannot enable other tasks or contain delays while tasks can enable other tasks and functions and can contain delays.

1. Functions & Tasks
ANINDRA

2. Functions
Tasks
Function vs Tasks

3. Functions:-
This is used for reusability of code.
Decreases the size of the program(where the same statements are used for many times).
This functions are used for combinational circuits only.
In this functions no delay is used.
There is no nonblocking assignments.

4. Functions (cont’d..)
a function can enable another function but not another task.
Function executes always at 0 simulation time.
In functions not only delay and also there is no event or timing control statements.
Function must have at least one input argument. They can have more than input.
Function always return a single value.

5. Funtions (cont’d….)
They cannot have output or inout arguments.
This contains only behavioral statements only.
This not contain always and initial but are called from always blocks , initial block.
In this no wires are used.
Functions have local variables , registers , time variables , integers , real , or events.

6. Functions(cont’d…)
The keywords are function and endfunction.
The function is declared as follows :
<function>
function <range_or_type>? <name_of_function> ;
<tf_declaration>+
<statement_or_null>
endfunction

7. Function(cont’d…)
 <range_or_type>
<range>
||= integer
||= real
<name_of_function>
<IDENTIFIER>
<task and function_declaration>
||= <parameter_declaration>
||= <input_declaration>
||= <reg_declaration>
||= <time_declaration>
||= <integer_declaration>
||= <real_declaration>
||= <event_declaration>

8. Functions (cont’d…)
The calling of function is as follows:-
<function_call>
<name_of_function> ( <expression> <,<expression>>* )
<name_of_function>
<identifier>

9. Tasks :-
A task can be enable other task and functions.
Tasks may executes in non-zero simulation time.
Task may contain delay , event , or timing control statements.
Tasks may have zero or more arguments.
In this input , output , inout are used.
Tasks do not return with a value , but can pass multiple values through output and inout arguments.

10. Tasks (cont’d…)
In this both comb and seq circuit are designed.
This also contains only behavioral statements.
No always and initial but called from always block , initial blocks ,other tasks and function.
Keywords are task and endtask are used.

11. Tasks (cont’d....)
Task syntax is declared as follows:
<task>
task <name_of_task> ;
<tf_declaration>
<statement_or_null>
endtask

12. Tasks (cont’d…)
<name_of_task>
<IDENTIFIER>
<tf_declaration>
||= <parameter_declaration>
||= <input_declaration>
||= <output_declaration>
||= <inout_declaration>
||= <reg_declaration>
||= <time_declaration>
||= <integer_declaration>
||= <real_declaration>
||= <event_declaration>

13. Tasks (cont’d…)
Task will be called as follows:
<task_enable>
<name_of_task> ;
<name_of_task> ( <expression> <,<expression>> ) ;

14. Functions vs Tasks:-

15. Thank you