S. Prashanth, Verification & Design Engineer, LSI Logic
To accommodate changing specifications and to support different clusters/subsystems which would have multiple processors/memory connected through a bridge), I am building a reusable environment which can support any number of masters and slaves of any standard bus protocols. The environment requires high level of configurability since it should work for different DUTs. So, I decided to use vmm_opts not just to set the switches globally/hierarchically, but also to specify the ranges (like setting address ranges in scenarios) from the test cases/command line.
I created a list of controls/switches that need to be provided as global options (like simulation timeout, scoreboard/coverage enable, etc) and hierarchical options to control instance specific behaviors (like number of transactions to be generated , burst enables, transaction speed, address ranges to be generated by a specific instance, set of instances, etc). Let’s see how these options can be used and what all things are required for it through examples.
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/and at the command line, I can override the default value using vmm_opts::set_int or +vmm_opts+ runtime option.
Override from the test case.
vmm_opts::set_int(“%*:TIMEOUT”, 50000);
Override from the command line.
./simv +vmm_opts+TIMEOUT=80000
Options can also be overridden from a command file, if it is difficult to specify all options in the command line. Also, options can be a string or Boolean as well.
Hierarchical Options
In order to use hierarchical options, I am building the environment with parent/child hierarchy which is a very useful feature of vmm_object. This is required since the hierarchy specified externally (from test case/command line) will be used to map the hierarchy in the environment.
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 passing 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, I can override the default value using vmm_opts::set_bit or vmm_opts::set_int(..) specifying the hierarchy. I can use pattern matching as well to avoid specifying to every instance
vmm_opts::set_int(“%*:MST0:NUM_TRANS”, 50);
vmm_opts::set_int(“%*:MST1:NUM_TRANS”, 100);
vmm_opts::set_bit(“%*:burst_enable);
vmm_opts::set_range(“%*:MST1:ADDR_RANGE”, 32’h1000_0000, 32’h1000_FFFF);
I can also override the default value 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. User can provide explanation of each of the options while calling get_object_*() and get_*() methods which will be displayed when vmm_opts::get_help() is called.
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