parameter与localparam的使用

:parameter可用作在顶层模块中例化底层模块时传递参数的接口，localparam的作用域仅仅限于当前module，不能作为参数传递的接口。

`timescale 1ns/100ps

module mem (

  clka,
  wea,
  addra,
  dina,

  clkb,
  addrb,
  doutb);

  parameter       DATA_WIDTH = 16;
  parameter       ADDR_WIDTH =  5;
  localparam      DW = DATA_WIDTH - 1;
  localparam      AW = ADDR_WIDTH - 1;

  input           clka;
  input           wea;
  input   [AW:0]  addra;
  input   [DW:0]  dina;

  input           clkb;
  input   [AW:0]  addrb;
  output  [DW:0]  doutb;

  reg     [DW:0]  m_ram[0:((2**ADDR_WIDTH)-1)];
  reg     [DW:0]  doutb;

  always @(posedge clka) begin
    if (wea == 1'b1) begin
      m_ram[addra] <= dina;
    end
  end

  always @(posedge clkb) begin
    doutb <= m_ram[addrb];
  end

endmodule

在顶层文件中例化mem module时可以这样做:

mem #(.DATA_WIDTH(DATA_WIDTH), .ADDR_WIDTH(6))
 i_mem (
  .clka (adc_clk),
  .wea (adc_wr),
  .addra (adc_waddr),
  .dina (adc_wdata),
  .clkb (dma_clk),
  .addrb (dma_raddr),
  .doutb (dma_rdata_s));

也可以将底层模块的parameter参数置于module端口声明之前，例如:

`timescale 1ns/100ps
module mem
          #(parameter DATA_WIDTH = 16
            parameter ADDR_WIDTH =  5)
           (
            input    clka,
            input    wea,
            input   [AW:0]  addra,
            input   [DW:0]  dina,
            input           clkb,
            input   [AW:0]  addrb,
            output  [DW:0]  doutb
           );

  localparam      DW = DATA_WIDTH - 1;
  localparam      AW = ADDR_WIDTH - 1;

  reg     [DW:0]  m_ram[0:((2**ADDR_WIDTH)-1)];
  reg     [DW:0]  doutb;

  always @(posedge clka) begin
    if (wea == 1'b1) begin
      m_ram[addra] <= dina;
    end
  end

  always @(posedge clkb) begin
    doutb <= m_ram[addrb];
  end

endmodule