Creating Configurable Environments with Hierarchical and Global Options (vmm_opts) in VMM

Verification environments need to accommodate changing specifications and at 
the same time cater to the requirements of different clusters and subsystems.
vmm_opts provides the ability to provide a high level of configurability so 
that environments can work for different DUTs. This article shows how to use 
vmm_opts not just to set the switches globally and hierarchically, but also to 
specify the address ranges in scenarios from the test cases and the 
command-line.


First, you need to create a list of controls/switches that should be 
provided as global options (like simulation timeout, scoreboard/coverage enable,
etc.) and then another set of hierarchical options to control instance specific
behavior (like number of transactions to be generated, burst enables, 
transaction speed, address ranges to be generated by a specific instance, etc.)


Global options:
Step 1:
Declare an integer, say simulation_timeout in the environment class or wherever
it is required and use vmm_opts::get_int(..) method as shown below. Specify a 
default value as well just in case, if the variable is not set anywhere.


simulation_timeout = vmm_opts::get_int("TIMEOUT", 10000);


Step 2:
Then either at the test case or at the command-line, this can be overridden
using vmm_opts::set_int or +vmm_opts+ runtime option.


Overridding from the test case:


vmm_opts::set_int("%*:TIMEOUT", 50000); 


In the examples above, "%*" specified any hierarchy and hence this will apply
to all classes wherever there is a TIMEOUT variable.
Overridding from the command-line.


./simv +vmm_opts+TIMEOUT=80000


Options can also be overridden from a command file. Also, options can be a 
string or Boolean variable as well.


Hierarchical options:
In order to use hierarchical options, the parent child hierarchy should be 
established across components while creating the verification environment. This
is possible by passing the parent handle to any component during construction
or through the set_parent_object() method. Since all VMM base classes extend
from vmm_object, all derived classes can thus use this method. This is required
since the hierarchy specified externally (from test case/command line) will be
used to map the hierarchy in the environment. The following steps shows how 
hierarchical options are used.


Step 1:
Declare options, say burst_enable and num_of_trans in a subenv class and use 
vmm_opts::get_object_bit(..) and vmm_opts::get_object_int(..) to retrieve 
appropriate values. This is done by passing the current hierarchy and default 
values as arguments. Also, for setting ranges, declare min_addr and max_addr,
 and use get_object_range().


class master_subenv extends vmm_subenv;
    bit burst_enable;
    int num_of_trans;
    int min_addr;
    int max_addr;
    function void configure();
          bit is_set; //to determine if the default value is overridden
          burst_enable = vmm_opts::get_object_bit(is_set, this, "BURST_ENABLE");
          num_of_trans = vmm_opts::get_object_int(is_set, this, "NUM_TRANS", 100);
          vmm_opts::get_object_range(is_set, this, "ADDR_RANGE", 0, 32'hFFFF_FFFF);
          ....
    endfunction
 endclass


Step 2:
Build the environment with parent/child hierarchy either by passing the parent
handle through the constructor to every child, or using 
vmm_object::set_parent_object() method. This is easy as almost all base classes
 are extended from vmm_object by default.


class  dut_env extends vmm_env;
       virtual function build();
         .....
         mst0 = new("MST0", ....);
         mst0.set_parent_object(this);
         mst1 = new("MST1", ...);
         mst1.set_parent_object(this);
        ....
       endfunction
endclass


Step 3:
From the test case, you can override the default value using vmm_opts::set_bit 
or vmm_opts::set_int(..) specifying the hierarchy. You can also use pattern 
matching as well to avoid specifying the overrides only for specific instances
as in the patterns mentioned.  


vmm_opts::set_int("%*:MST0:NUM_TRANS", 50);
This will only override the NUM_TRANS value in MST0 instance to 50.


vmm_opts::set_int("%*:MST1:NUM_TRANS", 100); 
This will only override the NUM_TRANS value in MST1 instance.


vmm_opts::set_bit("%*:burst_enable);
This will override the burst_enable variable and set it to 1 in all instances.


vmm_opts::set_range("%*:MST1:ADDR_RANGE", 32'h1000_0000, 32'h1000_FFFF);
This will override the ADDR_RANGE in MST1 instance.


The default value can be overriden from the command-line as well.
./simv +vmm_opts+NUM_TRANS=50@%*:MST0+NUM_TRANS=100@%*:MST1+burst_enable@%*


In summary, vmm_opts provides a powerful and user friendly way of configuring 
the environment from the command-line or the test case. 
There is also a possibility to auto-document these options. You can provide the 
explanation of each of the options in the get_object_*() and get_*() methods 
and this will be displayed when vmm_opts::get_help() is called or 
+vmm+help is passed at runtime. The details of the override from different
hierarchies including the line numbers and the file numbers will also be 
displayed. For more details on these classes, please refer to the VMM User Guide.