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Base class override in UVM testbench

UVM 5686
Base test 1 class override 3 Factory Overrides 5 Inheritance 2 #systemverilog 78
sv_uvm_49
sv_uvm_49
Forum Access
4 posts
December 11, 2020 at 6:31 pm

Hi all,

I have a testbench with the following testcase heirarchy:
--------------------------------------------------------------------------
class base_test extends uvm_test;
....
endclass

class test_A extends base_test;
.....
endclass

class test_1 extends test_A; .... endclass
class test_2 extends test_A; .... endclass
class test_3 extends test_A; .... endclass

New testcase:
class test_B extends base_test'
....
endclass
---------------------------------------------------------------------------

I want to override the middle base test class(test_A) with another testcase(test_B).
I don't want to change the child classes as they're having some constraints and could be re-used for my new base testcase(test_B).

What is the recommended way to do this?

Appreciate everyone's help.

Thanks

Replies

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tez
tez
Forum Access
7 posts
December 13, 2020 at 9:22 am

In reply to sv_uvm_49:
I think as long as you maintain the integrity (i.e, methods or properties which you are accessing in child class of test_A are also available in test_B) then you can use override macros of uvm.

sv_uvm_49
sv_uvm_49
Forum Access
4 posts
December 13, 2020 at 7:35 pm

Hi tez,
Thanks for your reply.

Could you be a little more specific on where should I do the factory override?

avpchandra
avpchandra
Full Access
33 posts
December 13, 2020 at 8:41 pm

In reply to sv_uvm_49:

Quote:
Hi tez,
Thanks for your reply.

Could you be a little more specific on where should I do the factory override?

Hi,
I think we need use the factory override inside the base_test build_phase() such that test_A is replaced by test_B (you need to have the same methods with its arguments of test_A)

Regards,
A V Pradeep Chandra,
Senior DV Engineer,
Synapse design - Bangalore.
https://www.linkedin.com/in/v-pradeep-chandra-akkinapalli-b030176a/

dave_59
dave_59
Forum Moderator
8757 posts
December 13, 2020 at 9:23 pm

In reply to avpchandra:

You cannot override a class in the middle chain of inheritance.

One option is to rename test_A to test_A_base, then insert a new class into the chain called test_A that is extended from test_A_base.

If that doesn't work for you, you'll have to explain more about what you're trying to accomplish. There might be other ways of organizing your classes. For example, see the links on this post.

— Dave Rich, Verification Architect, Siemens EDA

tez
tez
Forum Access
7 posts
December 13, 2020 at 10:40 pm

In reply to dave_59:
Agreed dave_59. sv_uvm_49, if you aren't having the handle/instance of base_obj in TB then overriding won't help straight away. As dave_59 suggested, we can make a in-between class or other ways available in the link provided by dave_59.

sv_uvm_49
sv_uvm_49
Forum Access
4 posts
December 13, 2020 at 11:10 pm

In reply to dave_59:

Hi Dave,

Thanks for your reply. This is what exactly I need:
I have the following testbench hierarchy:
Your text to link here...
[Capture.png](https://postimg.cc/CZN3JFL9)
https://i.postimg.cc/vBFGYTR8/Capture.png

I want to replace "Middle_base_test 1" with a "NEW middle_base_test 1" as the behaviour/flow of the testcase needs to be changed for verifying a new feature in RTL.
By the above requirement, I dont want to touch the child classes as whatever constraints are implemented in those classes could be re-used for the new feature.

So child testcases will extend from "Middle_base_test 1" always, but when I'm working with the new feature, they type of "Middle_base_test 1" should be overriden by "NEW middle_base_test 1".

I can do the following in my current TB:
1. Go to each and every child class and change the parent class by using an ifdef MACRO (But not an easy task if we have a lot of child testcases)
2. In the "Middle_base_test 1" file, keep two sets of ""Middle_base_test 1"" based ifdef MACRO.

But I would like to know if there are any other recommended ways to do this.

Hope you understood my requirement.
Thanks

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