UVM- run test() in top block and Macros

I'm reading the following guide: https://colorlesscube.com/uvm-guide-for-beginners/chapter-3-top-block/

In Code 3.2 line 24- run_test(); I realized that it supposed to execute the test, but how it know which test, and how, and why should I write it in the top block.

In Code 4.1 lines 11-14 (https://colorlesscube.com/uvm-guide-for-beginners/chapter-4-transactions-sequences-and-sequencers/):

`uvm_object_utils_begin(simpleadder_transaction)
`uvm_field_int(ina, UVM_ALL_ON)
`uvm_field_int(inb, UVM_ALL_ON)
`uvm_field_int(out, UVM_ALL_ON)
`uvm_object_utils_end

Why should I add the "uvm_field_int" , what would happend if i didn't add them, and what is "UVM_ALL_ON"?

Solution

run_test is a helper global function , it calls the run_test function of the uvm_root class to run the test case. There are two ways by which you can pass the test name to the function.The first is via the function argument and the second is via a command line argument. The command line argument takes precedence over the test name passed via the function argument.

  +UVM_TESTNAME=YOUR_TEST_NAME

  run_test("YOUR_TEST_NAME");

run_test function in the uvm_root uses the factory mechanism to create the appropriate instance of the umm_test class and so the test case must register itself with the factory using the macro `uvm_component_utils for the factory mechanism (create_component_by_name) to function.

class YOUR_TEST_NAME extends umm_test ; 
 // register the class with the factory 
 // so that run_test can find this class when the 
 // string test_name is passed to it.
 `uvm_component_utils(YOUR_TEST_NAME)
.....
endclass

The run_test function then kicks of the uvm_phases (..,build_phase,connect_phase,...) starting the uvm portion of the simulation. There should be no time ticks consumed before the run_phase starts , so it is essential that run_test case is called in the initial block itself. Also we want the uvm and test bench to be ready to drive and receive data as soon as the RTL is ready for which it is essential that we start the run_test at the earliest. Any delay in doing so will generate an error.

`uvm_field_int/uvm_field_object/.. are called field automation macros. They are not mandatory in the class definition and are provided as a helper macros to ease the use of many common/routine functions of the uvm_object. Examples of thse functions in uvm_object are - copy,compare,pack,unpack,print, etc and these macros generate code to automatically use these functions.

If you are not using the uvm_object common functions leaving out these macros from the class definition will not produce any errors. In case you implement you own version of the common operations you can also leave out these macros from the class.

UVM_ALL_ON - enables all functions like compare/copy/... to be implemented for the particular field.

link with examples - http://www.testbench.in/UT_04_UVM_TRANSACTION.html

For example the uvm_object has a compare function which compare two instances of the same class and return true if all the variables in the class are equal.

    virtual function bit do_compare( uvm_object rhs, uvm_comparer comparer );

       .....
      // return 1 if all the variables match
      return ( super.do_compare( rhs, comparer )  &&
               this.var_1    == rhs.var_1           &&
               this.var_2    == rhs.var_2          &&
               ......
               this.var_n      == rhs.var_n );
   endfunction: do_compare




          // use in main code 
           if ( new_class.compare(old_classs) ) 
           ...

           //instead of 
           if ( new_class.var1 == old_class.var1 && new_class.var2 == old_class.var2 && ... new_class.varn == old_class.varn ) 
        ...

The above compare has to be written for each class and updated and maintained for every new variable that is added to the class. This could become error prone as newer variables are added. A similar process has to be followed for all the standard functions uvm_object provides.

The field automation macro generates function to address all these functionality automatically. So doing a do_print for a class with the macros will print out all the fields without explicitly writing any code for it.

// compare/print/.. functions for class simpleadder_transaction are provided by using `uvm_field_int  macro.
`uvm_object_utils_begin(simpleadder_transaction)
`uvm_field_int(ina, UVM_ALL_ON)
`uvm_object_utils_end

BUT a word of caution , the use of these macros are discouraged as they add a significant amount of code into the class.. Most of these functions may not be needed by the class yet they get generated by default.