Memory modelling and Memory module in Verilog synthesis

Question

I am using a synthesis tool and when I am synthesizing a verilog file

module test();
reg reg1;
reg [1:0] reg2;
reg reg3 [1:0];
reg [1:0] reg4 [0:4];
endmodule

It's giving an error to "use memory module" with the help of a option. So what I need is to make a memory module. I tried to read this link but it didn't help me very much.

How can we create a memory module that can be used with the above test case. I am new to verilog. So can't understand what "Memory.list file" in the link means.

Answer 1

I am not sure why you need a special option, the use of memories are pretty standard for use inside modules. Unless you are trying to imply a special low area/power cell similar to a ram.

For a standard memory it is just the same as having multiple regs. memory does not imply RAM the same way reg does not automatically imply flip-flop.

The 'memory.list' is a plain text file which contains the values which you want to load in to the memory, this is not required if you just wanted to reset the memory and have every element at 0.

memory.list should look like :

//Comments are allowed 
1100_1100   // This is first address i.e 8'h00
1010_1010   // This is second address i.e 8'h01
@ 55        // Jump to new address 8'h55
0101_1010   // This is address 8'h55
0110_1001   // This is address 8'h56

The use of the file would then follow :

module  memory();
  reg [7:0] my_memory [0:255];

  initial begin
    $readmemh("memory.list", my_memory);
  end
endmodule

alternatively :

module  memory();
  reg [7:0] my_memory [0:255];
  integer i;

  initial begin
    for( i=0; i<256; i=i+1) //Can be statically unrolled
      my_memory[i] = 8'h00 ;
  end
endmodule

If using as a bank of flip-flops with async-reset:

module  memory(
  input clk,
  input rst_n,
  input [7:0] addr_wr,
  input [7:0] data_wr
);
  reg [7:0] my_memory [0:255];
  integer i;

  always @(posedge clk or negedge rst_n) begin
    if (~rst_n) begin
      for( i=0; i<256; i=i+1) //Can be statically unrolled
        my_memory[i]  <= 8'h00 ;
    end
    else begin
      my_memory[addr_wr] <= data_wr ;
    end
  end
endmodule