Is there specific reason why seq_items are declared inside task body() in sequence?

UVM
1

Is there specific reason why seq_items are declared inside task body()? Can it be declared outside body() or it is just bad practise? All the examples I saw have them declared inside body(), so I was wondering if that is some kind of UVM coding guideline.

class example_seq extends uvm_sequence #(example_seq_item);
 
`uvm_object_utils(example_seq )
 
function new (string name = "example_seq ");
 super.new(name);
endfunction
 
task body;
 example_seq_item item;
 
 item= example_seq_item::type_id::create("item");

...
 
endtask: body
endclass: example_seq
2

There is no need to declare any sequence items in your sequence. The uvm_sequence class already has the variables ‘req’ and ‘rsp’, with the appropriate type based on the sequence parameterization. These variables should be used instead of declaring new variables.

3

Thanks for the answer. What if I want to declare instance of another sequence type? All the examples I saw declares it inside body(). Is there specific reason?

class example_seq extends uvm_sequence;
 
`uvm_object_utils(example_seq )
 
function new (string name = "example_seq ");
 super.new(name);
endfunction
 
task body();
 another_seq  seq;

`uvm_do(seq)

endtask: body
endclass: example_seq
4

It depends. If your sequence will only be dealing with one sequence_item at any one point in time, the using the req variable in the sequence base class is best. Declaring additional sequence_item variables inside a method makes it have an automatic lifetime–that might make it harder for debug tools capture that in waveforms. My suggestion is to declare sequence_item variables as class properties unless they are being used by methods that are reentrant.