SV Function Coverage手册笔记

1、covergroup	2、coverpoint	bins
	3、cross coverpoint
	4、options
	5、methods
	6、systemtasks
	7、coverage computation
cover property	8、cover

 

1、covergroup

  我以前的领导告诉我：任何事，要有一种做的方法，还要有一种检查的方法。在验证中，随机是一种高效产生激励以覆盖待测空间的方法，与此同时，我们还需要一种检查待测空间是否真的被覆盖、是否足够覆盖的方法，也就是验证中常说的覆盖率收集。

覆盖率种类	特点	方法步骤
代码覆盖率	与设计无关	仿真工具独立完成
功能覆盖率	与设计相关	1、验证者在验证环境中加入相应语句：    covergroup    cover property 2、仿真工具编译执行上述语句

 

功能覆盖率不一定用coverage or cover property实现，但SV提供的这两种语法，相当于在EDA软件层搭建了一种专门的轮子，可大大减少验证者的coding工作量，且运行效率更高。

 

covergroup可被看成一种SV Built-In Class，因为它的语法结构和用法实在是太像class了。covergroup可以（往往）用在class中，这和“covergroup像class”这一说法并不矛盾，因为这和class可以用在class中是一样的。

 

covergroup		covergroup cg; ... endgroup cg cg_inst = new;   class xyz; bit [3:0] m_x; int m_y; bit m_z; covergroup cov1 @m_z;  // embedded covergroup  coverpoint m_x;  coverpoint m_y; endgroup function new(); cov1 = new; endfunction endclass
coverpoint	object:   variable   expression bins:   state bins   transition bins	c: coverpoint color;
cross coverpoint		Hue: coverpoint pixel_hue; Offset: coverpoint pixel_offset; AxC: cross color, pixel_adr;
formal argument	input ref	covergroup cv (int arg) @(posedge clk); option.at_least = arg; coverpoint x; endgroup
event		clocking_event | with function sample ( [ tf_port_list ] ) | @@( block_event_expression )   block_event_expression ::= block_event_expression or block_event_expression | begin hierarchical_btf_identifier | end hierarchical_btf_identifier
coverage options		option.member_identifier = expression type_option.member_identifier= constant_expression

 

2、coverpoint

coverpoint

coverpoint	coverpoint expression [ iff ( expression ) ] bins_or_empty
	bins_or_empty ::= { {attribute_instance} { bins_or_options ; } } | ;
	[ wildcard ] bins_keyword bins_keyword::= bins | illegal_bins | ignore_bins
	{ covergroup_range_list } [ with ( with_covergroup_expression ) ]
	[ iff ( expression ) ]
	default [ iff ( expression ) ]
	default sequence [ iff ( expression ) ]

 

bins

[] $ default	coverpoint v_a{ bins a = { [0:63],65 }; bins b[] = { [127:150],[148:191] }; bins c[] = { 200,201,202 }; bins d = { [1000:$] }; bins others[] = default;}
with	a: coverpoint x{ bins mod3[] = {[0:255]} with (item % 3 == 0);}
=>	3 => 2 1,5 => 6, 7
[* m:n]	3 [* 5] is equivalent to 3=>3=>3=>3=>3 3 [* 3:5] is equivalent to ( 3=>3=>3 ), ( 3=>3=>3=>3 ), ( 3=>3=>3=>3=>3 )
[-> m:n]	3 [-> 3] is equivalent to ...=>3...=>3...=>3 1 => 3 [ -> 3] => 5 is equivalent to 1...=>3...=>3...=>3 =>5
[= m:n]	1 => 3 [=2] => 6 is equivalent to 1...=>3...=>3...=>6   coverpoint v_a{ bins sa = (4 => 5 => 6), ([7:9],10=>11,12); bins sb[] = (4=> 5 => 6), ([7:9],10=>11,12); bins sc = (12 => 3 [-> 1]); bins allother = default sequence ;}
auto_bin_max	If a coverage point does not define any bins, SystemVerilog automatically creates state bins.
wildcard	wildcard bins g12_15 = { 4'b11?? }; wildcard bins g12_15_array[] = { 4'b11?? }; wildcard bins T0_3 = (2'b0x => 2'b1x); wildcard bins T0_3_array[] = (2'b0x => 2'b1x);
ignore_bins	All values or transitions associated with ignored bins are excluded from coverage. ignore_bins ignore_vals = {7,8}; ignore_bins ignore_trans = (1=>3=>5);
illegal_bins	All values or transitions associated with illegal bins are excluded from coverage. If an illegal value or transition occurs, a runtime error is issued. illegal_bins bad_vals = {1,2,3}; illegal_bins bad_trans = (4=>5=>6);
Value resolution	bit [2:0] p1; // type expresses values in the range 0 to 7 bit signed [2:0] p2; // type expresses values in the range –4 to covergroup g1 @(posedge clk); coverpoint p1 { bins b1 = { 1, [2:5], [6:10] }; bins b2 = { -1, [1:10], 15 }; } coverpoint p2 { bins b3 = {1, [2:5], [6:10] }; bins b4 = { -1, [1:10], 15 }; } endgroup   For b1, a warning is issued for the range [6:10]. b1 is treated as though it had the specification {1, [2:5], [6:7]}. — For b2, a warning is issued for the range [1:10] and for the values –1 and 15. b2 is treated as though it had the specification { [1:7] }. — For b3, a warning is issued for the ranges [2:5] and [6:10]. b3 is treated as though it had the specification { 1, [2:3] }. — For b4, a warning is issued for the range [1:10] and for the value 15. b2 is treated as though it had the specification { -1, [1:3] }.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3、cover_cross

cover_cross	[ cross_identifier : ] cross list_of_cross_items [ iff ( expression ) ] cross_body   list_of_cross_items ::= cross_item , cross_item { , cross_item } cross_item ::= cover_point_identifier | variable_identifier   cross_body_item ::= function_declaraton | bins_selection_or_option ; bins_selection_or_option ::= { attribute_instance } coverage_option | { attribute_instance } bins_selection
	! select_condition
	select_expression && select_expression
	select_expression || select_expression
	select_expression with ( with_covergroup_expression ) [ matches integer_covergroup_expression ]
	cross_set_expression [ matches integer_covergroup_expression ]
	select_condition ::= binsof ( bins_expression ) [ intersect { covergroup_range_list } ]
auto-cross expression	covergroup cov2 @(posedge clk); BC: coverpoint b+c; aXb : cross a, BC; endgroup
auto-cross variable	bit [3:0] a, b; covergroup cov @(posedge clk); aXb : cross a, b; endgroup   covergroup cov3 @(posedge clk); A: coverpoint a_var { bins yy[] = { [0:9] }; } CC: cross b_var, A; endgroup   Variable b_var automatically creates 16 bins (auto[0]...auto[15])   No cross coverage bins shall be created for coverpoint bins that are specified as default, ignored, or illegal bins.
User-defined cross bins	User-defined cross bins and automatically generated bins can coexist in the same cross. Automatically generated bins are retained for those cross products that do not intersect cross products specified by any user-defined cross bin.   int i,j; covergroup ct; coverpoint i { bins i[] = { [0:1] }; } coverpoint j { bins j[] = { [0:1] }; } x1: cross i,j; x2: cross i,j { bins i_zero = binsof(i) intersect { 0 }; } endgroup   Cross x1 has the following bins:   Cross x2 has the following bins: i_zero    // user-specified bin for and // an automatically generated bin that is retained // an automatically generated bin that is retained
! && ||	c : cross a, b { bins c1 = ! binsof(a) intersect {[100:200]};// 4 cross products bins c2 = binsof(a.a2) || binsof(b.b2);// 7 cross products bins c3 = binsof(a.a1) && binsof(b.b4);// 1 cross product }
with match	bins apple = X with (a+b < 257) matches 127; bins cherry = (binsof(b) intersect {[0:50]}             && binsof(a.low) intersect {[0:50]}) with (a==b) );  bins plum = binsof(b.two) with (b > 12)           || binsof(a.low) with (a & b & mask);
cross set '{m,n}	coverpoint a { bins x[] = {[0:10]}; } coverpoint b { bins y[] = {[0:20]}; } aXb : cross a, b { bins one = '{ '{1,2}, '{3,4}, '{5,6} }; }
ignore_bins	covergroup yy; cross a, b { ignore_bins ignore = binsof(a) intersect { 5, [1:3] }; } endgroup
illegal_bins	covergroup zz(int bad); cross x, y { illegal_bins illegal = binsof(y) intersect {bad}; } endgroup

 

4、options

 

 

struct // covergroup option declaration { string name ; int weight ; int goal ; string comment ; int at_least ; int auto_bin_max ; int cross_num_print_missing ; bit detect_overlap ; bit per_instance ; bit get_inst_coverage ; } option;   struct // coverpoint option declaration { int weight ; int goal ; string comment ; int at_least ; int auto_bin_max ; bit detect_overlap ; } option;   struct // cross option declaration { int weight ; int goal ; string comment ; int at_least ; int cross_num_print_missing ; } option;   struct // covergroup type_option declaration { int weight ; int goal ; string comment ; bit strobe ; bit merge_instances ; } type_option;   struct // coverpoint and cross type_option declaration { int weight ; int goal ; string comment ; } type_option;

 

5、methods

6、systemtasks

$set_coverage_db_name( filename )	sets the file name of the coverage database into which coverage information is saved at the end of a simulation run.
$load_coverage_db( filename )	loads from the given file name the cumulative coverage information for all coverage group types.
$get_coverage ( )	returns as a real number in the range of 0 to 100 the overall coverage of all coverage group types. This number is computed as previously described.

 

7、coverage computation

略

 

8、cover property

以下内容来自：http://testbench.in/CO_17_COVER_PROPERTY.html

Comparison Of Cover Property And Cover Group. Cover groups can reference data sets where as cover property references a temporal expression. Cover group can be triggered using .sample method () Cover property dont have this option. Cover group has multiple bins options. Cover property has only one bin. Cover group cannot handle complex temporal relationships. Cover properties can cover complex temporal expressions. Cover group automatically handles the crosses. Cover properties cannot do crosses. Cover group has lot of filtering options. Cover property has no specific filtering constructs but it can be filtered. Cover properties cannot be used in classes. Cover groups can be used in classes. So, cover groups can reference the variables in class. Cover groups are most useful at a higher level of abstractions where as cover property makes sense to use when we want to work at low level signals. We can mix cover group and cover property to gain the OO and temporal advantages. Using properties for temporal expressions and trigger the cover group.