SystemVerilog Unpacked Arrays

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