An unpacked array is used to refer to dimensions declared after the variable name.
Unpacked arrays may be fixed-size arrays, dynamic arrays, associative arrays or queues.
Single Dimensional Unpacked Array
module tb;
byte stack [8]; // depth = 8, 1 byte wide variable
initial begin
// Assign random values to each slot of the stack
foreach (stack[i]) begin
stack[i] = $random;
$display ("Assign 0x%0h to index %0d", stack[i], i);
end
// Print contents of the stack
$display ("stack = %p", stack);
end
endmodule
Simulation Log
Assign 0x24 to index 0
Assign 0x81 to index 1
Assign 0x9 to index 2
Assign 0x63 to index 3
Assign 0xd to index 4
Assign 0x8d to index 5
Assign 0x65 to index 6
Assign 0x12 to index 7
stack = '{'h24, 'h81, 'h9, 'h63, 'hd, 'h8d, 'h65, 'h12}
Multidimensional Unpacked Array
module tb;
byte stack [2][4]; // 2 rows, 4 cols
initial begin
// Assign random values to each slot of the stack
foreach (stack[i])
foreach (stack[i][j]) begin
stack[i][j] = $random;
$display ("stack[%0d][%0d] = 0x%0h", i, j, stack[i][j]);
end
// Print contents of the stack
$display ("stack = %p", stack);
end
endmodule
Simulation Log
ncsim> run
stack[0][0] = 0x24
stack[0][1] = 0x81
stack[0][2] = 0x9
stack[0][3] = 0x63
stack[1][0] = 0xd
stack[1][1] = 0x8d
stack[1][2] = 0x65
stack[1][3] = 0x12
stack = '{'{'h24, 'h81, 'h9, 'h63}, '{'hd, 'h8d, 'h65, 'h12}}
ncsim: *W,RNQUIE: Simulation is complete.
Packed + Unpacked Array
The example shown below illustrates a multidimensional packed + unpacked array.
module tb;
bit [3:0][7:0] stack [2][4]; // 2 rows, 4 cols
initial begin
// Assign random values to each slot of the stack
foreach (stack[i])
foreach (stack[i][j]) begin
stack[i][j] = $random;
$display ("stack[%0d][%0d] = 0x%0h", i, j, stack[i][j]);
end
// Print contents of the stack
$display ("stack = %p", stack);
// Print content of a given index
$display("stack[0][0][2] = 0x%0h", stack[0][0][2]);
end
endmodule
Simulation Log
ncsim> run
stack[0][0] = 0x12153524
stack[0][1] = 0xc0895e81
stack[0][2] = 0x8484d609
stack[0][3] = 0xb1f05663
stack[1][0] = 0x6b97b0d
stack[1][1] = 0x46df998d
stack[1][2] = 0xb2c28465
stack[1][3] = 0x89375212
stack = '{'{'h12153524, 'hc0895e81, 'h8484d609, 'hb1f05663}, '{'h6b97b0d, 'h46df998d, 'hb2c28465, 'h89375212}}
stack[0][0][2] = 0x15
ncsim: *W,RNQUIE: Simulation is complete.
In a multidimensional declaration, the dimensions declared before the name vary more faster than the dimensions following the name.
bit [1:4] m_var [1:5] // 1:4 varies faster than 1:5
bit m_var2 [1:5] [1:3] // 1:3 varies faster than 1:5
bit [1:3] [1:7] m_var3; // 1:7 varies faster than 1:3
bit [1:3] [1:2] m_var4 [1:7] [0:2] // 1:2 varies most rapidly, followed by 1:3, then 0:2 and then 1:7
