assignment operator type check failed (expecting datatype compatible with

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problem on clone

By chenyong September 16, 2011 in UVM SystemVerilog Discussions

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I met a problem on clone. In my code for scoreboard, I defined a variable as this:

timer_pkt_item chk_pkt;

the timer_pkt_item is defined as a class in other place. I then register it as:

`uvm_component_utils_begin(timer_scoreboard)

`uvm_field_object(chk_pkt, UVM_DEFAULT)

`uvm_component_utils_end

In my write function for export implementation, I would like to do this:

function void write_pkt(timer_pkt_item rcv_pkt);

chk_pkt = rcv_pkt.clone();

endfunction

My purpose is to save received data of rcv_pkt.

When I start to compile the code, irun reports error as:

assignment operator type check failed (expecting datatype compatible with 'class timer_pkt_item' but found 'class uvm_object' instead). so what is the problem to the code? I think I have defined the variable type as timer_pkt_item, why there is problem? please give me some help. thanks.

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clone() returns a uvm_object, which you need to cast. Your code should be :

$cast ( chk_pkt , rcv_pkt.clone())

• chandan and ljepson74

yes, you are right. thanks.

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SystemVerilog queue initialization using ncverilog +sv?

Steven Wilson

--- news:// freenews.netfront.net/ - complaints: [email protected] ---

Jonathan Bromley

>I have a question for the assembled masses.

>I have a declaration similar to the following: > >integer my_q[$] = {1,2,3,4,5,6}; > >This is accepted by Modelsim using the -sv switch.

>If I compile this with ncverilog +sv I get the following gripes: > >ncvlog: *E,TYCMPAT ( queue.sv ,5|18): assignment operator type check >failed (expecting datatype compatible with 'queue of integer' but >found 'packed array' instead). >integer my_q[$] = {1,2,3,4,5,6}; > | >ncvlog: *E,NONOWD ( queue.sv ,5|19): Illegal use of a constant without >an explicit width specification [4.1.14(IEEE)]. >integer my_q[$] = {1,2,3,4,5,6}; >etc... > >Any suggestions as to what I'm doing wrong here?

I will try to write up an appnote-style description of unpacked array concatenation somewhere, soon; it's a very useful construct, and deserves to be widely known so that people start demanding it from their vendors. -- Jonathan Bromley

SystemVerilog Polymorphism

Polymorphism allows the use of a variable of the base class type to hold subclass objects and to reference the methods of those subclasses directly from the superclass variable. It also allows a child class method to have a different definition than its parent class if the parent class method is virtual in nature.

Parent and Child Assignment

A class handle is just a container to hold either parent or child class objects. It is important to understand how parent class handles holding child objects and vice-versa behave in SystemVerilog.

Assign Child Class to Base Class

Taking the same example from Inheritance , we'll assign a sub/child class instance sc to a base class handle bc .

Even though bc points to the child class instance, when display() function is called from bc it still invoked the display() function within the base class. This is because the function was called based on the type of the handle instead of the type of object the handle is pointing to. Now let's try to reference a subclass member via a base class handle for which you'll get a compilation error.

Assign Base Class to Child Class

It is illegal to directly assign a variable of a superclass type to a variable of one of its subclass types and hence you'll get a compilation error.

However, $cast can be used to assign a superclass handle to a variable of a subclass type provided the superclass handle refers to an object that is assignment compatible with the subclass variable.

Although the code will compile well, it will have a run-time simulation error because of the failure of $cast . This is because bc is not pointing to an object that is compatible with sc .

Let's make bc point to another subclass called sc2 and try the same thing. In this case, bc simply acts like a carrier.

Virtual Methods

A method in the parent class can be declared as virtual which will enable all child classes to override the method with a different definition, but the prototype containing return type and arguments shall remain the same.

Click here to learn more on Virtual Methods

Rules to follow

• Assignment of derived class handle to base class handle is allowed.
• Assignment of base class handle to derived class handle is NOT allowed and results in compilation error.
• $cast returns 0 if the cast failed, so use the return type to throw an error. Use if or assert to ensure that the cast is successful.