[sv-ac] Re: Request: example of use of covergroup in combination with cover statements?

Hi Erik,


The first example in my 2088 proposal shows a covergroup which is 
triggered by an (@*posedge* clk) event.  If the checker containing this 
covergroup were placed in a precedural loop, it would be executed only 
once per clock tick, while all the other assertions will be executed 
once for every pass of the enclosing loop.  This will be a little 
non-intuitive for new users, so it probably should be explained in the text.

The second example in the 2088 proposal shows a covergroup which is 
triggered by a call to the default *sample()* method.

The third example might be the most useful.  This shows a covergroup 
triggered by a custom *sample()* method. It should be easy to modify 
this example so it could be placed in a loop.

*checker* op_test (*logic* clk, vld_1, vld_2, *logic* [3:0] opcode)

*    checkvar* *bit* [3:0] opcode_d1;


*    always_check* @(*posedge* clk) opcode_d1 <= opcode;


*    covergroup* cg_op *with* *function* sample(*bit* [3:0] opcode_d1);

        cp_op : *   coverpoint* opcode_d1;

*    endgroup*:cg_op

    cg_op cg_op_1 = *new*();

*    sequence* op_accept;

        @(*posedge* clk) vld_1 ##1 (vld2, cg_op_1.sample(opcode_d1));

*    endsequence*

*endchecker*


Suppose the above checker is placed in a loop where vld1 and vld2 are 
bits of arrays, and opcode is a slice of a two-dimensional array.  The 
checker portion could be written like this (I'll take out vld2 to avoid 
the procedural code in the checker).

*checker* op_test (*logic* clk, vld_1, *logic* [3:0] opcode)

*    checkvar* *bit* [3:0] opcode_d1;

*    covergroup* cg_op *with* *function* sample(*bit* [3:0] opcode_d1);

        cp_op : *   coverpoint* opcode_d1;

*    endgroup*:cg_op

    cg_op cg_op_1 = *new*();

*    sequence* op_accept;

        @(*posedge* clk) (vld1, cg_op_1.sample(opcode));

*    endsequence*

*endchecker
*

*...
logic [3:0] valid;
logic [3:0] opcodes [0:3];
*

*for (i=0; i<=3; i++) begin
    op_test my_op_test (.clk(clk), .vld1(valid[i]), .opcode(opcodes[i]));
end
*


Does this help?

Tom

 
Seligman, Erik wrote:
> Tom-- can you send me a short fragment giving an example of what you 
> were alluding to in the meeting?
> I couldn't find something like this in 2088, or in the current LRM.
>  
> Thanks!
>  
>  
>
> *Erik Seligman*
>
> ***Formal Verification Architect*
>
> *Corporate Design Solutions*
> *Design Technology and Solutions*
>
> *Intel Corporation*
>
> M.S. JF4-402                  
> 2111 NE 25^th Ave
> Hillsboro, OR 97124
>
> Phone:   (503) 712-3134
>
>  

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