class Transaction;
rand bit read_write;
constraint c1 { read_write dist {0:= 25, 1:= 25}; }
function void pre_randomize();
$display("Entering randomization \n");
endfunction
function void post_randomize();
$display("Done with randomization \n");
endfunction
endclass
module top;
Transaction tr;
int write_cnt, read_cnt;
int constraint_status=0;
initial begin
tr = new;
write_cnt = 0;
read_cnt = 0;
repeat(100) begin
assert(tr.randomize());
constraint_status = tr.c1.constraint_mode();
if(tr.read_write == 1) write_cnt++;
else read_cnt++;
end
$display("Writes are %d, reads are %d, status is %d \n", write_cnt, read_cnt, constraint_status);
end
endmoduleIn the above code, I expect
Writes are 50, reads are 50, status is 1 .
But I get
Writes are 52, reads are 48, status is 1
Why isn't the constraint solver giving me accurate solution? When I reduce my run count to say small number like 6, I even get strange results
Writes are 2, reads are 4, status is 1