Using of uvm_config_db# in virtual sequence

UVM
,
1

Hello,

This is my example of how I use uvm_config_db# in my virtual sequence.

I have a configuration class like this:

class l2_config extends uvm_object;
int i_rsp_credit = 12;

`uvm_object_utils_begin( l2_config )
    `uvm_field_int      ( i_rsp_credit, UVM_DEFAULT + UVM_DEC )
`uvm_object_utils_end

function new ( string name = "l2_config" );
    super.new( name );
endfunction : new

endclass: l2_config

And I want to change “i_rsp_credit” during my virtual sequence. I’ve made this in virtual sequence, but it didn’t work:
…
virtual task body();
…
uvm_config_db#(int)::set(uvm_root::get(), “*” ,“i_rsp_credit”, 14);

Can anyone explane what is wrong and is it a good practice to change configuration class in sequnces?

2

In reply to Danil:

Hi Danil,
unfortunately I do not see all your code and I do not understand why you want to modify the variable i_rsp_credit in the virtual sequence.
It is good practice to pass variables/paramters through the testbench hierarchy. This allows you to retrieve the actual value of a variable in any component of your testbench. Typically it should be set in a corresponding test.
By the way there is no reason to register a configuration object with the factory. This gives you more freedom to implement the configuration class.
Hope this helps.

3

In reply to chr_sue:

Thank you for reply chr_sue. But if I don’t register a configuration object with the factory I can’t use uvm_config_db#. Am I right?

4

In reply to Danil:

Hi Danil,
the factory and the configuration database are two different mechanisms for customizing UVM testbenches.
The macro `uvm_component_utils registers a UVM component with the factory.
With uvm_config_db you are making an entry in the configuration data base. This is a way to make data available across the whole testbench hierarchy.
The factory allows you to replace components of the same type in a testbench.

5

In reply to chr_sue:

Thanks again chr_sue. Now I clearly understand the difference.

Here is my another example. For instance, I have a configuration object:


class my_config extends uvm_object;
     int a = 0;

    `uvm_object_utils( my_config )

    function new ( string name = "my_config" );
       super.new( name );
    endfunction : new
endclass: my_config

And also I have a driver like this:


class my_driver uvm_driver #(my_item);
    my_config cfg;

    `uvm_component_utils_begin( my_driver )
          `uvm_field_object(  cfg , UVM_DEFAULT )
    `uvm_component_utils_end
    

     function new (string name = "my_driver", uvm_component parent);
        super.new(name, parent);
     endfunction

     function void build_phase( uvm_phase phase );
        super.build_phase( phase );
        if( !uvm_config_db#( my_config )::get( this, "", "cfg", cfg ) )
            `uvm_error( "NOCONFIG", 
                      { "Config not set for...", get_full_name() } )   
     endfunction: build_phase

     ....
endclass: my_driver

And there is a simple test:


class my_test extends uvm_test;
    `uvm_component_utils(my_test)

    my_driver driver;
    my_config cfg;

    virtual function void build_phase( uvm_phase phase );
        super.build_phase(phase);
        driver = my_driver::type_id::create( "driver", this );

        //this slice of code changes "a" value in configuration
        cfg = my_config::type_id::create( "cfg", this );
        cfg.a = 1;
        uvm_config_db#(my_config)::set( uvm_root::get(), "driver*", "cfg" , cfg );
        // but if i want to change "a" value like this, it doesn't work
        uvm_config_db#(int)::set( uvm_root::get(), "driver.cfg", "a" , 1 );
     endfunction
endclass

Could you explain why?

6

In reply to Danil:

Hi Danil,
it might not work because of the hierachy in the uvm_config_db command.
The first argument in uvm_config_db ist the context. Finally this describes the hierarchy.
There are two useful ways to define this:

  1. uvm_config_db#(int)::set( null, ".driver", <string_name>, value);
    ‘null’ as the first argument means you want to use the full hierarchical path
    '    .driver’(second argument) means you are pointing to a component named driver in the hierarchy
    <string_name> is a simple name under which the value is stored in the config database

  2. uvm_config_db#(int)::set( this, “driver”, <string_name>, value);
    ‘this’ as the first argument indicates you are using a hierarchical path
    ‘driver’ means you are pointing to a component named driver and instantiated in test.

Remark to class my_config: there is no need to register this with the factory.
Remark to class my_driver: (1) insert extends between my_driver and uvm_driver
(2) don’t use the field macro for the config.

Hope you get it running.

Christoph

7

In reply to chr_sue:

Thank you chr_sue. I’ll use your advices.