Nested associative arrays OR associative arrays of dynamic arrays

SystemVerilog
1

Hi Folks,

I would like to create an associative array where a string key points to another associative array or to a reference of one.

Similarly I would like to create an associative array where a string key points to a dynamic string array.

Does the language allow the above data types?

-ravi

2

*In reply to ravi.ck.kumar:*Yes. SystemVerilog supports arrays whose elements can be of any type. When dealing with dynamically sized array, you can think of it as arrays of arrays instead of multi-dimensional arrays. because an array element in each dimension can have a different number of elements.
You can declare arrays of arrays by using an intermediate typedef (preferred)

typedef int int_index_by_str_t[string];
int_index_by_str_t lookup[];
or
int lookup[][string];
3

In reply to dave_59:

Hi David,
Thanks for the pointers. Based on that I created a quick example…

module mytest();

typedef string AADD[*]; // create a hash type
AADD arrayOfAAs; // create an array of hashes
arrayOfAAs AAWC2[string]; // create a hash of ‘array-of-hashes’ <<— This Doesn’t.
AADD AAWC3[string]; // create a hash of hash. <<---- This Works!!

…

I get the following error. I would like to have a string to reference an array of hashes OR even
Error-[SE] Syntax error
Following verilog source has syntax error :
memory of unknown type
“a.sv”, 6: token is ‘;’
arrayOfAAs AAWC2[string]; // create a hash of ‘array-of-hashes’

4

*In reply to ravi.ck.kumar:*You need to use a type when declaring a variable.

typedef AADD arrayOfAAs[]; // create type of an array of hashes
arrayOfAAs AAWC2[string]; // create a hash of 'array-of-hashes'

or

AADD arrayOfAAs[]; // create an array of hashes
var type(arrayOfAAs) AAWC2[string]; // create a hash of 'array-of-hashes'

Also, I do not recommend ever using a wildcard associative array index type. Use an actual type. The wildcard index type is antiquated and cannot be used with a number of other systemverilog features.

5

In reply to dave_59:

The second typedef did the trick! Thanks much. Also true about using wildcards. Very little utility in the first place IMHO.

6

In reply to dave_59:

*In reply to ravi.ck.kumar:*You need to use a type when declaring a variable.

typedef AADD arrayOfAAs[]; // create type of an array of hashes
arrayOfAAs AAWC2[string]; // create a hash of 'array-of-hashes'

or

AADD arrayOfAAs[]; // create an array of hashes
var type(arrayOfAAs) AAWC2[string]; // create a hash of 'array-of-hashes'

Also, I do not recommend ever using a wildcard associative array index type. Use an actual type. The wildcard index type is antiquated and cannot be used with a number of other systemverilog features.

AADD arrayOfAAs[]; // create an array of hashes
type(arrayOfAAs) AAWC2[string]; // create a hash of 'array-of-hashes' 

Is this mode of type declaration supported in system-verilog?
7

In reply to yourcheers:
Yes. See 6.23 Type operator of the 1800-2012 LRM. I forgot to add the var keyword in front of the type. I corrected my example.

8

In reply to dave_59:

hi Dave , can we create a typedef using some previous typedef like :
typedef enum bit [1:0] {OKAY, ERROR, RETRY, SPLIT} response
so i want to create an associative array using response as input and logic [31:0] as key
typedef resp_t address_driver_resp [logic [31:0]] ; // will this work ?

if yes , how do we register it in our transaction_item ?

9

In reply to DV@Engineer :
An associative array can have any element type, and any index type as long as equality is defined for the index type.

What do you mean by “register it”?

10

I am unclear by what you mean an array of hashes. Is this the same thing as using a key into an array of arrays?

11

People use many different terms for what SystemVerilog calls an associative array: map, dictionary, symbol table, or hash. However a hash usually refers to the lookup mechanism used to access an element, not necessarily an array. I tend to avoid it, but was just repeating terminology the previous post used.

12

Looks so counter intuitive.

int lookup[][string]

feels more like an associative array of dynamic arrays.

But it is the other way round.

Why is this done?

13

When declaring the 2-dimensional fixed sized array int A[10][20], 10 ius the first dimension and 20 is the second dimension. Selecting A[0] gives you a 1-dimensional array of 20 elements.

Similarly selecting lookup[0] should give you an associative array.