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//////////////////////////////////////////////////////////////////////
//// ////
//// File name "generic_fifo_ctrl.v" ////
//// ////
//// This file is part of the "10GE MAC" project ////
//// http://www.opencores.org/cores/xge_mac/ ////
//// ////
//// Author(s): ////
//// - A. Tanguay (antanguay@opencores.org) ////
//// ////
//////////////////////////////////////////////////////////////////////
//// ////
//// Copyright (C) 2008 AUTHORS. All rights reserved. ////
//// ////
//// This source file may be used and distributed without ////
//// restriction provided that this copyright statement is not ////
//// removed from the file and that any derivative work contains ////
//// the original copyright notice and the associated disclaimer. ////
//// ////
//// This source file is free software; you can redistribute it ////
//// and/or modify it under the terms of the GNU Lesser General ////
//// Public License as published by the Free Software Foundation; ////
//// either version 2.1 of the License, or (at your option) any ////
//// later version. ////
//// ////
//// This source is distributed in the hope that it will be ////
//// useful, but WITHOUT ANY WARRANTY; without even the implied ////
//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ////
//// PURPOSE. See the GNU Lesser General Public License for more ////
//// details. ////
//// ////
//// You should have received a copy of the GNU Lesser General ////
//// Public License along with this source; if not, download it ////
//// from http://www.opencores.org/lgpl.shtml ////
//// ////
//////////////////////////////////////////////////////////////////////
module generic_fifo_ctrl(
wclk,
wrst_n,
wen,
wfull,
walmost_full,
mem_wen,
mem_waddr,
rclk,
rrst_n,
ren,
rempty,
ralmost_empty,
mem_ren,
mem_raddr
);
//---
// Parameters
parameter AWIDTH = 3;
parameter RAM_DEPTH = (1 << AWIDTH);
parameter EARLY_READ = 0;
parameter CLOCK_CROSSING = 1;
parameter ALMOST_EMPTY_THRESH = 1;
parameter ALMOST_FULL_THRESH = RAM_DEPTH-2;
//---
// Ports
input wclk;
input wrst_n;
input wen;
output wfull;
output walmost_full;
output mem_wen;
output [AWIDTH:0] mem_waddr;
input rclk;
input rrst_n;
input ren;
output rempty;
output ralmost_empty;
output mem_ren;
output [AWIDTH:0] mem_raddr;
//---
// Local declarations
// Registers
reg [AWIDTH:0] wr_ptr;
reg [AWIDTH:0] rd_ptr;
reg [AWIDTH:0] next_rd_ptr;
// Combinatorial
wire [AWIDTH:0] wr_gray;
reg [AWIDTH:0] wr_gray_reg;
reg [AWIDTH:0] wr_gray_meta;
reg [AWIDTH:0] wr_gray_sync;
reg [AWIDTH:0] wck_rd_ptr;
wire [AWIDTH:0] wck_level;
wire [AWIDTH:0] rd_gray;
reg [AWIDTH:0] rd_gray_reg;
reg [AWIDTH:0] rd_gray_meta;
reg [AWIDTH:0] rd_gray_sync;
reg [AWIDTH:0] rck_wr_ptr;
wire [AWIDTH:0] rck_level;
wire [AWIDTH:0] depth;
wire [AWIDTH:0] empty_thresh;
wire [AWIDTH:0] full_thresh;
// Variables
integer i;
//---
// Assignments
assign depth = RAM_DEPTH[AWIDTH:0];
assign empty_thresh = ALMOST_EMPTY_THRESH[AWIDTH:0];
assign full_thresh = ALMOST_FULL_THRESH[AWIDTH:0];
assign wfull = (wck_level == depth);
assign walmost_full = (wck_level >= (depth - full_thresh));
assign rempty = (rck_level == 0);
assign ralmost_empty = (rck_level <= empty_thresh);
//---
// Write Pointer
always @(posedge wclk or negedge wrst_n)
begin
if (!wrst_n) begin
wr_ptr <= {(AWIDTH+1){1'b0}};
end
else if (wen && !wfull) begin
wr_ptr <= wr_ptr + {{(AWIDTH){1'b0}}, 1'b1};
end
end
//---
// Read Pointer
always @(ren, rd_ptr, rck_wr_ptr)
begin
next_rd_ptr = rd_ptr;
if (ren && rd_ptr != rck_wr_ptr) begin
next_rd_ptr = rd_ptr + {{(AWIDTH){1'b0}}, 1'b1};
end
end
always @(posedge rclk or negedge rrst_n)
begin
if (!rrst_n) begin
rd_ptr <= {(AWIDTH+1){1'b0}};
end
else begin
rd_ptr <= next_rd_ptr;
end
end
//---
// Binary to Gray conversion
assign wr_gray = wr_ptr ^ (wr_ptr >> 1);
assign rd_gray = rd_ptr ^ (rd_ptr >> 1);
//---
// Gray to Binary conversion
always @(wr_gray_sync)
begin
rck_wr_ptr[AWIDTH] = wr_gray_sync[AWIDTH];
for (i = 0; i < AWIDTH; i = i + 1) begin
rck_wr_ptr[AWIDTH-i-1] = rck_wr_ptr[AWIDTH-i] ^ wr_gray_sync[AWIDTH-i-1];
end
end
always @(rd_gray_sync)
begin
wck_rd_ptr[AWIDTH] = rd_gray_sync[AWIDTH];
for (i = 0; i < AWIDTH; i = i + 1) begin
wck_rd_ptr[AWIDTH-i-1] = wck_rd_ptr[AWIDTH-i] ^ rd_gray_sync[AWIDTH-i-1];
end
end
//---
// Clock-Domain Crossing
generate
if (CLOCK_CROSSING) begin
// Instantiate metastability flops
always @(posedge rclk or negedge rrst_n)
begin
if (!rrst_n) begin
rd_gray_reg <= {(AWIDTH+1){1'b0}};
wr_gray_meta <= {(AWIDTH+1){1'b0}};
wr_gray_sync <= {(AWIDTH+1){1'b0}};
end
else begin
rd_gray_reg <= rd_gray;
wr_gray_meta <= wr_gray_reg;
wr_gray_sync <= wr_gray_meta;
end
end
always @(posedge wclk or negedge wrst_n)
begin
if (!wrst_n) begin
wr_gray_reg <= {(AWIDTH+1){1'b0}};
rd_gray_meta <= {(AWIDTH+1){1'b0}};
rd_gray_sync <= {(AWIDTH+1){1'b0}};
end
else begin
wr_gray_reg <= wr_gray;
rd_gray_meta <= rd_gray_reg;
rd_gray_sync <= rd_gray_meta;
end
end
end
else begin
// No clock domain crossing
always @(wr_gray or rd_gray)
begin
wr_gray_sync = wr_gray;
rd_gray_sync = rd_gray;
end
end
endgenerate
//---
// FIFO Level
assign wck_level = wr_ptr - wck_rd_ptr;
assign rck_level = rck_wr_ptr - rd_ptr;
//---
// Memory controls
assign mem_waddr = wr_ptr;
assign mem_wen = wen && !wfull;
generate
if (EARLY_READ) begin
// With early read, data will be present at output
// before ren is asserted. Usufull if we want to add
// an output register and not add latency.
assign mem_raddr = next_rd_ptr;
assign mem_ren = 1'b1;
end
else begin
assign mem_raddr = rd_ptr;
assign mem_ren = ren;
end
endgenerate
endmodule
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