VMM scenario generators and dependent scenarios

Avinash Agrawal, Corporate Applications, Synopsys

Often folks wonder if it possible to have a VMM scenario generator, where one scenario is dependent on another scenario.

The answer is “Yes.”

Consider the testcase below. You can define two scenarios, scn_a and scn_b, both of which have their own set of constraints. The variables generated in scn_b are a multiple of the values that were set when scn_a was generated previously, in this case by variable “ratio”. For more details on how VMM scenario generators work, refer to the VMM user guide.

Systemverilog testcase:

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class packet extends vmm_data;

rand int sa;

rand int da;

`vmm_data_member_begin(packet)

`vmm_data_member_scalar(sa, DO_ALL)

`vmm_data_member_scalar(da, DO_ALL)

`vmm_data_member_end(packet)

endclass

`vmm_channel(packet)

`vmm_scenario_gen(packet, “packet”)

class a_scenario extends packet_scenario;

int unsigned scn_a;

rand int ratio;

function new();

scn_a = define_scenario(“scn_a”, 5);

endfunction

constraint cst_a {

$void(scenario_kind) == scn_a ->  {

foreach(items[i]) {

this.items[i].sa inside {[0:100]};

this.items[i].da inside {[0:100]};

}

ratio inside {[1:5]};

}

}

endclass

class b_scenario extends packet_scenario;

int unsigned scn_b;

function new();

scn_b = define_scenario(“scn_b”, 10);

endfunction

constraint cst_b {

$void(scenario_kind) == scn_b -> {

foreach(items[i]) {

this.items[i].sa inside {[100:300]};

this.items[i].da inside {[100:300]};

}

}

}

endclass

class hier_scenario extends packet_scenario;

rand a_scenario scn_a;

rand b_scenario scn_b;

function new();

this.scn_a = new();

this.scn_b = new();

this.scn_a.set_parent_scenario(this);

this.scn_b.set_parent_scenario(this);

endfunction

virtual task apply(packet_channel channel, ref int unsigned n_insts);

this.scn_a.apply(channel, n_insts);

this.scn_b.apply(channel, n_insts);

endtask

constraint cst_hier {

foreach(scn_b.items[i]) {

// Create a scenario ‘scn_b’ depending upon ‘scn_a’

scn_b.items[i].sa inside {[scn_a.ratio*100:scn_a.ratio*800]};

scn_b.items[i].da inside {[scn_a.ratio*100:scn_a.ratio*800]};

}

}

endclass

program automatic test;

packet_scenario_gen scn_gen;

packet_channel      pkt_chan;

packet pkt;

hier_scenario scn_hier;

initial begin

scn_hier = new();

scn_gen = new(“scn_gen”, -1, pkt_chan);

scn_gen.register_scenario(“scn_hier”, scn_hier);

scn_gen.unregister_scenario_by_name(“Atomic”);

$display(“Size of the scn is %0d”, scn_gen.scenario_set.size());

scn_gen.stop_after_n_insts = 15;

scn_gen.start_xactor();

while(1) begin

#10 scn_gen.out_chan.get(pkt);

$display(“id is %0d , %0d %0d”, pkt.data_id, pkt.sa, pkt.da);

end

end

endprogram

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