Wednesday, 29 February 2012

Automatic Coverage Weight Calculator Utility

If you want to get Specman coverage number in linear fashion (i.e. coverage numbers = (total buckets hit) / (total buckets in valid space) ), then you need to set the weight of individual items and coverage groups properly. Updating the code for proper weights to each item and cover group is tedious and error prone task. Maintaining the code is also a problem. What if you can do it automatically by using Coverage API? I hope people, who are looking such kind of solution will benefit from this post.

Specman overall coverage grade is calculated in hierarchical manner by default. It means that coverage is calculated from leaf level to the top level in following manner. I've assumed that weight is not set manually and default weight value 1 is applied here.

1. Individual item grade is calculated by dividing buckets hit by total bucket for that item.
2. Individual cover group grade is calculated by dividing total of all items grade by total number of items
3. Overall coverage grade is calculated by dividing total of all cover groups graade by total number of cover groups

Take a look at the following example code.

<'
extend sys
{
config : config_s;
};
struct config_s
{
a : uint(bits: 3);
b : uint(bits: 3);
c : bool;
event cov1_e;
event cov2_e;
cover cov1_e is
{
item a using ignore = (a in [0, 1, 7, 8]);
item b using ignore = (b in [0, 1, 7, 8]);
cross a, b using
ignore =
(a in  and b in ) or
(a in  and b in  );
};
cover cov2_e is
{
item a using ignore = (a in [0, 1, 7, 8]);
item c using ignore = (c == TRUE);
cross a, c;
};
keep soft a == select
{
40 : 2;
10 : 3;
40 : 4;
10 : 5;
10 : 6;
};
keep soft b == select
{
40 : 2;
10 : 3;
40 : 4;
10 : 5;
10 : 6;
};
keep soft c == TRUE;
run() is also
{
for i from 1 to 10
{
gen a; gen b; gen c;
emit cov1_e;
emit cov2_e;
outf ("a=%d b=%d c=%s\n", a, b, c);
};
};
};
'>

When you run the above code with Intelligen with seed 1, Specman generates following combinations of a, b and c.

a=4 b=4 c=TRUE
a=4 b=4 c=TRUE
a=4 b=3 c=TRUE
a=2 b=2 c=TRUE
a=6 b=2 c=TRUE
a=2 b=4 c=TRUE
a=2 b=2 c=TRUE
a=2 b=4 c=TRUE
a=2 b=2 c=TRUE
a=4 b=6 c=TRUE

Let's analyze the coverage now.

 Item Hit Valid Space Grade a 3 5 60.00% (hit/valid space) b 4 5 80.00% (hit/valid space) cross_a_b 5 23 21.74% (hit/valid space)
So, cov1_e cover group's grade = (grade of item a*weight + grade of item b*weight + grade of item cross_a_b*weight)/3 = 1.6174/3 = 53.91 %

 Item Hit Valid Space Grade a 3 5 60.00% (hit/valid space) c 1 1 100.00% (hit/valid space) cross_a_c 3 5 60.00% (hit/valid space)
So, cov2_e cover group's grade = (grade of item a + grade of item c + grade of item cross_a_c)/3 = 2.20/3 = 73.33 %

But, if you need the linear coverage, it should be
(Total number of hit buckets) / (Total number of buckets in valid space) = ((3+4+5) + (3+1+3))/((5+5+23) + (5+1+5)) = 43.18 %

This can be achieved by adjusting the weitage of individual item and cover group. If you set the weight of each item equal to the total number of valid buckets, linear coverage is achieved. Let's see how it works.

 Item Hit Valid Space Weight Grade a 3 5 5 60.00 % (hit/valid space) b 4 5 5 80.00 % (hit/valid space) cross_a_b 5 23 23 21.74 % (hit/valid space)

So, cov1_e cover group's grade = (grade of item a*weight + grade of item b*weight + grade of item cross_a_b*weight)/(weight of a + weight of b + weight of cross_a_b) = (3 + 4 + 5) / (5 + 5 + 23) = 36.36 %

 Item Hit Valid Space Weight Grade a 3 5 5 60.00 % (hit/valid space) c 1 1 1 80.00 % (hit/valid space) cross_a_c 3 5 5 21.74 % (hit/valid space)

So, cov2_e cover group's grade = (grade of item a*weight + grade of item c*weight + grade of item cross_a_c*weight)/(weight of a + weight of c + weight of cross_a_c) = (3 + 1 + 3) / (5 + 1 + 5) = 63.64 %

So, overall grade = (cov1_e grade*weight + cov2_grade*weight)/(weight of cov1_e + weight of cov2_e) = (12+7)/(33+11) = 43.18%

This number looks linear as we can see we've calculated the coverage based on the number of buckets hit divided by total number of bucket for whole of the coverage space. So, setting the weight of the items based its number of buckets, it gives us the correct result.

Setting the weight manually is tedious process as you need to check the exact number of valid buckets of each item and coverage groups by keeping ignores and ranges into the mind. And even you do that, if you want to change the coverage model again, you might need to calculate the valid space again which is tedious and error prone. So, why not automate it using Coverage API calls?

You can use this small utility which uses coveage API to change the weight of all the items and cover group. It gives you the linear overall grade which is total number of buckets hit in valid coverage space divided by total number of buckets in valid coverage space. This utility can also be used in the post processing of coverage database. This utility uses coverage API to recursively parse the whole coverage space of a given unit which can be sys. It counts the total number of buckets of each item and coverage group and uses covers.set_weight() to set the weight of items and cover groups recursively.

You can use it after loading the linear_coverage.e. It defines a specman command using "define as" macro. Example is given below

Specman>adjust weight sys (for whole coverage space)
Specman>adjust weight config_s (for coverage space defined in config_s struct)

-------------------------------------------
liner_coverage.e
-------------------------------------------
<'
define "adjust weight " as {
};

struct cover_info
{
item_name : string;
num_of_buckets: uint;
weight : uint;
};

struct bucket_cover_struct like user_cover_struct
{
collect: bool; // flag to skip specific item
cover_info : list (key: item_name) of cover_info;

main(items: string) is
{
if scan_cover(items) == 0 {
error("Adjust Weight Error: no cover items matching ", items," exist");
};
};

scan_bucket() is
{
if ((collect) and (cross_level == sub_items.size()-1)) then
{
var full_item_name := appendf ("%s.%s.%s", struct_name, group_name, item_name);
if (status in [hole, normal])
{
if cover_info.key_exists(full_item_name)
{
cover_info.first(.item_name == full_item_name).num_of_buckets = cover_info.first(.item_name == full_item_name).num_of_buckets + 1;
}
else
{
var temp_cov_info : cover_info = new;
temp_cov_info.item_name = full_item_name;
temp_cov_info.num_of_buckets = 1;
};
};
};
};

// Output a line of text for item:
end_item() is
{
if collect then
{
var full_item_name := appendf ("%s.%s.%s", struct_name, group_name, item_name);
var num_of_buckets := cover_info.first(.item_name == full_item_name).num_of_buckets;
outf ("%s - %d (weight=%d)\n", full_item_name, num_of_buckets, item_weight);
covers.set_weight(full_item_name, num_of_buckets, FALSE);
};
};

start_group() is
{
collect = (struct_name != "session");//skip session struct
if collect then
{
outf ("\n------------------------------------\n");
};
};

end_group() is
{
if collect then
{
var group_total : uint;
for each (cov_info) in (cover_info)
{
group_total = group_total + cov_info.num_of_buckets;
};
outf ("------------------------------------\n");
outf ("Group and Total Buckets ---> %s - %d (weight=%d)\n", group_name, group_total, group_weight);
covers.set_weight(appendf("%s.%s", struct_name, group_name), group_total, FALSE);
outf ("------------------------------------\n");
cover_info.clear();
};
};
};

// Define an instance of bucket_cover_struct:
extend sys
{ 