Problem with casting a VIF container object obtained from the config db.

[itsmyturn]

My code for the driver's connect phase is shown below. I'm creating a simple VIF container object and setting it as a DB object. When I try to retrive it from the driver, I do get the object, but it seems to be of a different type, and my simulation fails at the casting step in the driver. Can someone help me with this. This is my first attempt with UVM. So, it might be a very simple mistake. Any help in this regard is appreciated.

I have an initial block in my TB that does something like

initial begin

typedef myvif_container #(virtual myInterface) myvif_container_t;

myvif_container_t myvif_container_h;

myvif_container_h = myvif_container_t::type_id::create("myvif_container_h");

set_config_object("*.*driver", "myvif_container", myvif_container_h);

....

end

function void connect();

uvm_object tmp;

typedef myvif_container #(virtual myInterface) myvif_container_t;

myvif_container_t myvif_container_h;

if (!(get_config_object("myvif_container", tmp))) begin

`uvm_fatal(get_type_name(), "VIF container not found")

end

if (tmp == null) begin

`uvm_fatal(get_type_name(), "VIF container is null");

end

if (!($cast(myvif_container_h, tmp))) begin

`uvm_info(get_type_name(), $psprintf ("container type is %s", tmp.get_type_name()), UVM_NONE);

`uvm_fatal(get_type_name(), "Interface container different type")

end

endfunction : connect

class myvif_container #(type VIF=int) extends uvm_object;

`uvm_object_param_utils (myvif_container #(VIF))

VIF m_vif_h;

function new (string name="vif_container");

super.new(name);

endfunction : new

endclass : myvif_container

[dave_59]

There is no need for a vif container in UVM. You can use the uvm_config_db directly.

uvm_config_db #(virtual myinterface)::set(null, "uvm_test_top", "my_vif", myifinstance);

See http://verificationacademy.com/uvm-ovm/Config/VirtInterfaceConfigDb more complete examples.

[itsmyturn]

Dave, thank you so much for the prompt reply. It did the trick. I hate to say that I spent a couple of hours fighting with that casting issue. I still don't understand why that didn't work. Can you think of a reason why that casting didn't work?

Thanks

[amitrana]

HI ,

Casting can be done from a child to parent class.

Forexample,

class A;

endclass

class B extends A;

endclass

module top;

A a;

B b;

initial

begin

b=new();

void'($cast(a,);

endmodule

But in your case you are doing reverse from parent to child ,that's an error.

end

[pjigar]

To further safeguard you with typos in the get(), you can also create a typedef for uvm_config_db parametrized with a specific interface type.

e.g.

In uvm_pkg:

typedef uvm_config_db #(virtual myinterface) myinterface_config_db;

In module testbench:

myinterface_config_db::set(null, "*.tb.uvc.agent.*", "vif", my_if_inst);

And in the driver:

myinterface_config_db::get(this, "", "vif", myifinstance);

-Jigar

[itsmyturn]

Looks like I landed in the right place. Thank you all for the replies. They're quite helpful.

[uwes]

HI ,

Casting can be done from a child to parent class.

hi,

you dont need to cast from child to parent at all since a derived is always a base. you can directly assign a derived class handle to a base class handle. the reverse is not always true therefore you need to check at runtime.

HI ,

But in your case you are doing reverse from parent to child ,that's an error.

not necessarily, have a look at the attached code

module test193;
virtual class car;
endclass
class mercedes extends car;
endclass
class renault extends car;
endclass

car c;
mercedes m;
renault r;

initial
begin
m=new();

// this is not needed since a "mercedes" is always a "car"
void'($cast(c,m));

// do the previous the simple way
c=m;

// the reverse needs a cast since a "car" is not necessarily a "mercedes"
r = new();
c=r;
assert($cast(m,c)); //this should fail
c=m;
assert($cast(m,c)); // this should pass
end
endmodule

[itsmyturn]

hi,

you dont need to cast from child to parent at all since a derived is always a base. you can directly assign a derived class handle to a base class handle. the reverse is not always true therefore you need to check at runtime.

not necessarily, have a look at the attached code

module test193;
virtual class car;
endclass
class mercedes extends car;
endclass
class renault extends car;
endclass

car c;
mercedes m;
renault r;

initial
begin
m=new();

// this is not needed since a "mercedes" is always a "car"
void'($cast(c,m));

// do the previous the simple way
c=m;

// the reverse needs a cast since a "car" is not necessarily a "mercedes"
r = new();
c=r;
assert($cast(m,c)); //this should fail
c=m;
assert($cast(m,c)); // this should pass
end
endmodule

Even I doubted whether amitrana's comments were correct, as I saw uvm_object type objects being casted to VIF container objects everywhere in the UVM manuals/books. But, I wasn't quite sure if I was in a place to comment. Anyway, thanks for the detailed explanation. I didn't know that a derived guy can be assigned to base class handle directly. Thanks again.