How to output a multidimensional array slice

Question

Let's say I have a multidimensional array:

logic [7:0] mda [7:0];

What I'm now trying to do, is assigning mda[7:4] to an output port, i.e. defined as follow:

output [31:0] odata;

Of course, I can do it by using concatenation:

assign odata = {mda[7], mda[6], mda[5], mda[4]};

But there should be (and probably is) an easier way to do this. The first try would be:

assign odata = mda[7:4];

which is wrong, because types (unpacked <-> packed array) don't match. All my tries of casting (e.g. 32'(mda[7:4])) failed. Question is: what is the best way to assign that slice to an output port?

Answer 1

You can use a for loop... Most synthesis tools have no trouble with for loops over constant ranges:

module dut(output [31:0] odata);

  logic [7:0] mda [7:0];  

  reg[31:0] data;
  always @* begin
    data = 0;
    for(int i=7; i >=4; i--) begin
      data <<= 8;
      data |= mda[i];
    end
  end

  assign odata = data;

endmodule

Here's a quick test: http://www.edaplayground.com/x/GfM