Generic FIFO implemented in verilog.

fifo.v

/**
 * Generic FIFO.
 * Author: Carlos Diaz (2017)
 *
 * DISCLAIMER (2021): This implementation was done when I had a few days of
 * experience using verilog, I was at school and not really sure what
 * I was doing. I choose to make it public in case of me needing it
 * in the future, but that was not the case, it's been a long time
 * since I tried to learn any HDL.
 * 
 * Parameters:
 *  WIDTH: Width of the data on the FIFO, default to 4.
 *  DEPTH: Depth of the FIFO, default to 4.
 * 
 * Input signals:
 *  data_in: Data input, width controlled with WIDTH parameter.
 *  clk: Clock input.
 *  write: Enable writing into the FIFO.
 *  read: Enable reading from the FIFO.
 * 
 * Output signals:
 *  data_out: Data output, witdh controlled with WIDTH parameter.
 *  fifo_full: 1bit signal, indicate when the FIFO is full.
 *  fifo_empty: 1bit signal, indicate when the FIFO is empty.
 *  fifo_not_empty: 1bit signal, indicate when the FIFO is not empty.
 *  fifo_not_full: 1bit signal, indicate when the FIFO is not full.
 *
**/

`timescale 1ns / 1ps
`default_nettype none

module fifo #(
    parameter WIDTH = 4,
    parameter DEPTH = 4
)(
    input [WIDTH-1:0] data_in,
    input wire clk,
    input wire write,
    input wire read,
    output reg [WIDTH-1:0] data_out,
    output wire fifo_full,
    output wire fifo_empty,
    output wire fifo_not_empty,
    output wire fifo_not_full
);

    // memory will contain the FIFO data.
    reg [WIDTH-1:0] memory [0:DEPTH-1];
    // $clog2(DEPTH+1)-2 to count from 0 to DEPTH
    reg [$clog2(DEPTH)-1:0] write_ptr;
    reg [$clog2(DEPTH)-1:0] read_ptr;

    // Initialization
    initial begin
    
        // Init both write_cnt and read_cnt to 0
        write_ptr = 0;
        read_ptr = 0;

        // Display error if WIDTH is 0 or less.
        if ( WIDTH <= 0 ) begin
            $error("%m ** Illegal condition **, you used %d WIDTH", WIDTH);
        end
        // Display error if DEPTH is 0 or less.
        if ( DEPTH <= 0) begin
            $error("%m ** Illegal condition **, you used %d DEPTH", DEPTH);
        end

    end // end initial

    assign fifo_empty   = ( write_ptr == read_ptr ) ? 1'b1 : 1'b0;
    assign fifo_full    = ( write_ptr == (DEPTH-1) ) ? 1'b1 : 1'b0;
    assign fifo_not_empty = ~fifo_empty;
    assign fifo_not_full = ~fifo_full;

    always @ (posedge clk) begin

        if ( write ) begin
            memory[write_ptr] <= data_in;
        end

        if ( read ) begin
            data_out <= memory[read_ptr];
        end

    end

    always @ ( posedge clk ) begin
        if ( write ) begin
            write_ptr <= write_ptr + 1;
        end

        if ( read && fifo_not_empty ) begin
            read_ptr <= read_ptr + 1;
        end
    end

endmodule

I can send you my (modified) code if you would like...

…

-Lennie

On Tue, Sep 28, 2021 at 5:45 PM Carlos Diaz ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ Hi @lennia <https://github.com/lennia> and @futurelink <https://github.com/futurelink>, Thanks for letting me know about this mistakes and improvement opportunities, this chunk of verilog was one of my first attempts, as you already noticed. I will try to fix it, not sure about how to fix the write_ptr and read_ptr and fifo_full tho. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <https://gist.github.com/e299230c65b82a87d7fc83579d78b168#gistcomment-3908504>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAPCMHI2AVZTXWVZKPEO2C3UEJOTBANCNFSM4WLCDXRQ> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

That or posting it here should be good, so everyone can see it.

Here is the file.

…

On Tue, Sep 28, 2021 at 7:56 PM Carlos Diaz ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ That or posting it here should be good, so everyone can see it. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <https://gist.github.com/e299230c65b82a87d7fc83579d78b168#gistcomment-3908802>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAPCMHLO3HZC5L2PVNHPXJTUEJ54JANCNFSM4WLCDXRQ> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

Carlos, apparently this FIFO is the most googlable FIFO on the internet. Thank you for sharing and maintenance! :)

It's nice to know it's been useful for others, but I did it at school when I didn't knew much, so it's been good to receive feedback to improve it.

Since this is one of the top google results for verilog fifo I'll post my hdl.

module RXFIFO #(
  parameter PACKET_WIDTH = 248,
  parameter FIFO_DEPTH   = 256, 
  parameter PTR_MSB      = 8,
  parameter ADDR_MSB     = 7
  )
  (
  input                           zedClk100MHz_i,
  input                           reset_ni,
  input                           read_i,
  input                           write_i,
  input        [PACKET_WIDTH-1:0] packet_i,
  output logic [PACKET_WIDTH-1:0] packet_o,
  output logic                    fifoFull_o,
  output logic                    fifoEmpty_o
  );
  
  logic [PACKET_WIDTH-1:0] memory [0:FIFO_DEPTH-1];
  logic [       PTR_MSB:0] readPtr, writePtr;
  wire  [      ADDR_MSB:0] writeAddr = writePtr[ADDR_MSB:0];
  wire  [      ADDR_MSB:0] readAddr = readPtr[ADDR_MSB:0]; 
  
  always_ff@(posedge zedClk100MHz_i or negedge reset_ni)begin
    if(~reset_ni)begin
      readPtr     <= '0;
      writePtr    <= '0;
    end
    else begin
      if(write_i && ~fifoFull_o)begin
        memory[writeAddr] <= packet_i;
        writePtr         <= writePtr + 1;
      end
      if(read_i && ~fifoEmpty_o)begin
        packet_o <= memory[readAddr];
        readPtr <= readPtr + 1;
      end
    end
  end
  
    assign fifoEmpty_o = (writePtr == readPtr) ? 1'b1: 1'b0;
    assign fifoFull_o  = ((writePtr[ADDR_MSB:0] == readPtr[ADDR_MSB:0])&(writePtr[PTR_MSB] != readPtr[PTR_MSB])) ? 1'b1 : 1'b0;

endmodule