The bins construct allows the creation of a separate bin for each value in the given range of possible values of a coverage point variable.
Usage
coverpoint mode {
// Manually create a separate bin for each value
bins zero = {0};
bins one = {1};
// Allow SystemVerilog to automatically create separate bins for each value
// Values from 0 to maximum possible value is split into separate bins
bins range[] = {[0:$]};
// Create automatic bins for both the given ranges
bins c[] = { [2:3], [5:7]};
// Use fixed number of automatic bins. Entire range is broken up into 4 bins
bins range[4] = {[0:$]};
// If the number of bins cannot be equally divided for the given range, then
// the last bin will include remaining items; Here there are 13 values to be
// distributed into 4 bins which yields:
// [1,2,3] [4,5,6] [7,8,9] [10, 1, 3, 6]
bins range[4] = {[1:10], 1, 3, 6};
// A single bin to store all other values that don't belong to any other bin
bins others = default;
}
Examples
module tb;
bit [2:0] mode;
// This covergroup does not get sample automatically because
// the sample event is missing in declaration
covergroup cg;
coverpoint mode {
bins one = {1};
bins five = {5};
}
endgroup
// Stimulus : Simply randomize mode to have different values and
// manually sample each time
initial begin
cg cg_inst = new();
for (int i = 0; i < 5; i++) begin
#10 mode = $random;
$display ("[%0t] mode = 0x%0h", $time, mode);
cg_inst.sample();
end
$display ("Coverage = %0.2f %%", cg_inst.get_inst_coverage());
end
endmodule
Simulation Log
ncsim> run [10] mode = 0x4 [20] mode = 0x1 [30] mode = 0x1 [40] mode = 0x3 [50] mode = 0x5 Coverage = 100.00 % ncsim: *W,RNQUIE: Simulation is complete.
Automatic Bins
covergroup cg;
coverpoint mode {
// Declares a separate bin for each values -> Here there will 8 bins
bins range[] = {[0:$]};
}
endgroup
4 out of the total possible 8 values have been sampled and hence coverage is 50%.
Simulation Log
ncsim> run
[10] mode = 0x4
[20] mode = 0x1
[30] mode = 0x1
[40] mode = 0x3
[50] mode = 0x5
Coverage = 50.00 %
ncsim: *W,RNQUIE: Simulation is complete.
Fixed Number of automatic bins
covergroup cg;
coverpoint mode {
// Declares 4 bins for the total range of 8 values
// So bin0->[0:1] bin1->[2:3] bin2->[4:5] bin3->[6:7]
bins range[4] = {[0:$]};
}
endgroup
mode never got a value of 6 or 7 and hence bin3 does not get hit. But all the other bins are hit and hence coverage is 75%.
Simulation Log
ncsim> run [10] mode = 0x4 [20] mode = 0x1 [30] mode = 0x1 [40] mode = 0x3 [50] mode = 0x5 Coverage = 75.00 % ncsim: *W,RNQUIE: Simulation is complete.
Split fixed number of bins between a given range
covergroup cg;
coverpoint mode {
// Defines 3 bins
// Two bins for values from 1:4, and one bin for value 7
// bin1->[1,2] bin2->[3,4], bin3->7
bins range[3] = {[1:4], 7};
}
endgroup
Only 2/3 of the bins were hit and hence coverage is at 66.67%. To be specific, bin1 and bin2 were hit because mode was sampled to have 1 and [3,4] respectively.
Simulation Log
ncsim> run [10] mode = 0x4 [20] mode = 0x1 [30] mode = 0x1 [40] mode = 0x3 [50] mode = 0x5 Coverage = 66.67 % ncsim: *W,RNQUIE: Simulation is complete.
