Array in SystemVerilog
Table of Contents
Array
An array is a collection of variables, all of the same type, and accessed using the same name plus one or more indices. there are different types of arrays, few array declaration examples are given below.
int array1 [6]; //fixed size single dimension array int array2 [5:0]; //fixed size single dimension array int array3 [3:0][2:0]; //fixed size multi dimension array bit [7:0] array4[2:0]; //unpacked array declaration bit [2:0][7:0] array5; //packed array declaration bit [2:0][7:0] array6 [3]; //mixed packed and unpacked array
In SystemVerilog vector width/dimensions declared before the object name is referred to as packed array and array size/dimensions declared after the object name is referred to as an unpacked array.
A packed array is a mechanism for subdividing a vector into sub-fields which can be conveniently accessed as array elements.
Fixed size array
In fixed size array, array size will be constant throughout the simulation, Once the array is declared no need to create it. By default, the array will be initialized with value ‘0’.
Single dimensional array
int array1 [6]; //Compact declaration int array2 [5:0]; // Verbose declaration
Multidimensional array
Multidimensional arrays are also known as an array of arrays.
Two-dimensional arraY
int arr[2][3];
This array has total 2*3 = 6 elements.
Three-dimensional array
int arr[2][2][2];
This array has total 2*2*2 = 8 elements.
Two-dimensional array declaration
int array3 [2:0][3:0];
The data in a two-dimensional array is stored in a tabular form as shown in the below diagram.
array assignment
array1 = '{0,1,2,3,4,5};
array2 = '{0,1,2,3,4,5};
array3 = '{ '{0,1,2,3},'{4,5,6,7},'{8,9,10,11}};
Fixed Size Array Example
This example shows array declaration and array manipulation using for and foreach loop.
module fixedsize_array;
//declaration of array’s
int array1[6]; //single dimension array
int array2[5:0]; //single dimension array
int array3[2:0][3:0]; //multi dimension array
int array4[4:0];
initial begin
//array initialization
array1 = '{0,1,2,3,4,5};
array2 = '{0,1,2,3,4,5};
array3 = '{'{0,1,2,3},'{4,5,6,7},'{8,9,10,11}};
//displaying array elements
$display("-------displaying array1-------");
foreach(array1[i]) $display("\t array1[%0d] = %0d",i,array1[i]);
$display("-------displaying array2-------");
for(int i=0;i<6;i++) $display("\t array2[%0d] = %0d",i,array2[i]);
$display("-------displaying array3-------");
foreach(array3[i,j]) $display("\t array3[%0d][%0d] = %0d",i,j,array3[i][j]);
$display("-------displaying uninitialized array4-------");
for(int i=0;i<5;i++) $display("\t array4[%0d] = %0d",i,array4[i]);
end
endmodule
Simulator Output:
-------displaying array1-------
array1[0] = 0
array1[1] = 1
array1[2] = 2
array1[3] = 3
array1[4] = 4
array1[5] = 5
-------displaying array2-------
array2[0] = 5
array2[1] = 4
array2[2] = 3
array2[3] = 2
array2[4] = 1
array2[5] = 0
-------displaying array3-------
array3[2][3] = 0
array3[2][2] = 1
array3[2][1] = 2
array3[2][0] = 3
array3[1][3] = 4
array3[1][2] = 5
array3[1][1] = 6
array3[1][0] = 7
array3[0][3] = 8
array3[0][2] = 9
array3[0][1] = 10
array3[0][0] = 11
-------displaying uninitialized array4-------
array4[0] = 0
array4[1] = 0
array4[2] = 0
array4[3] = 0
array4[4] = 0
