功能覆盖率的类型
在验证计划中编写test case时，需要编写功能覆盖率计划。一般而言，在验证环境中有4个地方可以编写coverage points.
F1 : Functional coverage points are very near the randomization
F2 : Functional coverage points are sampled at input interface of DUT
F3 : Functional coverage points which sample internal DUT states
F4 : Functional coverage points which sample output interface of DUT
功能覆盖率的简单例子：
1 //+++++++++++++++++++++++++++++++++++++++++++++++++ 2 // DUT With Coverage 3 //+++++++++++++++++++++++++++++++++++++++++++++++++ 4 module simple_coverage(); 5 6 logic [7:0] addr; 7 logic [7:0] data; 8 logic par; 9 logic rw; 10 logic en; 11 //================================================= 12 // Coverage Group 13 //================================================= 14 covergroup memory @ (posedge en); 15 address : coverpoint addr { 16 bins low = {0,50}; 17 bins med = {51,150}; 18 bins high = {151,255}; 19 } 20 parity : coverpoint par { 21 bins even = {0}; 22 bins odd = {1}; 23 } 24 read_write : coverpoint rw { 25 bins read = {0}; 26 bins write = {1}; 27 } 28 endgroup 29 //================================================= 30 // Instance of covergroup memory 31 //================================================= 32 memory mem = new(); 33 //================================================= 34 // Task to drive values 35 //================================================= 36 task drive (input [7:0] a, input [7:0] d, input r); 37 #5 en <= 1; 38 addr <= a; 39 rw <= r; 40 data <= d; 41 par <= ^d; 42 $display ("@%2tns Address :%d data %x, rw %x, parity %x", 43 $time,a,d,r, ^d); 44 #5 en <= 0; 45 rw <= 0; 46 data <= 0; 47 par <= 0; 48 addr <= 0; 49 rw <= 0; 50 endtask 51 //================================================= 52 // Testvector generation 53 //================================================= 54 initial begin 55 en = 0; 56 repeat (10) begin 57 drive ($random,$random,$random); 58 end 59 #10 $finish; 60 end 61 62 endmodule