1.4.4.1. Dual Clock FIFO Example in Verilog HDL

Quartus® Prime Pro Edition User Guide: Design Recommendations

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Date 9/30/2024
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1.4.4.1. Dual Clock FIFO Example in Verilog HDL

// Copyright 2021 Intel Corporation. 
//
// This reference design file is subject licensed to you by the terms and 
// conditions of the applicable License Terms and Conditions for Hardware 
// Reference Designs and/or Design Examples (either as signed by you or 
// found at https://www.altera.com/common/legal/leg-license_agreement.html ).  
//
// As stated in the license, you agree to only use this reference design 
// solely in conjunction with Intel FPGAs or Intel CPLDs.  
//
// THE REFERENCE DESIGN IS PROVIDED "AS IS" WITHOUT ANY EXPRESS OR IMPLIED
// WARRANTY OF ANY KIND INCLUDING WARRANTIES OF MERCHANTABILITY, 
// NONINFRINGEMENT, OR FITNESS FOR A PARTICULAR PURPOSE. Intel does not 
// warrant or assume responsibility for the accuracy or completeness of any
// information, links or other items within the Reference Design and any 
// accompanying materials.
//
// In the event that you do not agree with such terms and conditions, do not
// use the reference design file.
/////////////////////////////////////////////////////////////////////////////

module dcfifo_example
#(
    parameter LOG_DEPTH      = 5,
    parameter WIDTH          = 20,
    parameter ALMOST_FULL_VALUE = 30,
    parameter ALMOST_EMPTY_VALUE = 2,    
    parameter NUM_WORDS = 2**LOG_DEPTH - 1,
    parameter OVERFLOW_CHECKING = 0, // Overflow checking circuitry is \
       using extra area. Use only if you need it
    parameter UNDERFLOW_CHECKING = 0 // Underflow checking circuitry is \
       using extra area. Use only if you need it        
)
(
    input aclr,
    
    input wrclk,
    input wrreq,
    input [WIDTH-1:0] data,
    output reg wrempty,
    output reg wrfull,
    output reg wr_almost_empty,
    output reg wr_almost_full,
    output [LOG_DEPTH-1:0] wrusedw,
    
    input rdclk,
    input rdreq,
    output [WIDTH-1:0] q,
    output reg rdempty,
    output reg rdfull,
    output reg rd_almost_empty,    
    output reg rd_almost_full,    
    output [LOG_DEPTH-1:0] rdusedw
);
       
initial begin
    if ((LOG_DEPTH > 5) || (LOG_DEPTH < 3))
        $error("Invalid parameter value: LOG_DEPTH = %0d; valid range is 2 \
        < LOG_DEPTH < 6", LOG_DEPTH);
        
    if ((ALMOST_FULL_VALUE > 2 ** LOG_DEPTH - 1) || (ALMOST_FULL_VALUE < 1))
        $error("Incorrect parameter value: ALMOST_FULL_VALUE = %0d; valid \
        range is 0 < ALMOST_FULL_VALUE < %0d", 
            ALMOST_FULL_VALUE, 2 ** LOG_DEPTH);     

    if ((ALMOST_EMPTY_VALUE > 2 ** LOG_DEPTH - 1) || (ALMOST_EMPTY_VALUE < 1))
        $error("Incorrect parameter value: ALMOST_EMPTY_VALUE = %0d; valid \
        range is 0 < ALMOST_EMPTY_VALUE < %0d", 
            ALMOST_EMPTY_VALUE, 2 ** LOG_DEPTH);  

    if ((NUM_WORDS > 2 ** LOG_DEPTH - 1) || (NUM_WORDS < 1))
        $error("Incorrect parameter value: NUM_WORDS = %0d; \
        valid range is 0 < NUM_WORDS < %0d", 
            NUM_WORDS, 2 ** LOG_DEPTH);  
end

(* altera_attribute = "-name AUTO_CLOCK_ENABLE_RECOGNITION OFF" *) reg \
     [LOG_DEPTH-1:0] write_addr = 0;
(* altera_attribute = "-name AUTO_CLOCK_ENABLE_RECOGNITION OFF" *) reg \
     [LOG_DEPTH-1:0] read_addr = 0;
reg [LOG_DEPTH-1:0] wrcapacity = 0;
reg [LOG_DEPTH-1:0] rdcapacity = 0;

wire [LOG_DEPTH-1:0] wrcapacity_w;
wire [LOG_DEPTH-1:0] rdcapacity_w;

wire [LOG_DEPTH-1:0] rd_write_addr;
wire [LOG_DEPTH-1:0] wr_read_addr;

wire wrreq_safe;
wire rdreq_safe;
assign wrreq_safe = OVERFLOW_CHECKING ? wrreq & ~wrfull : wrreq;
assign rdreq_safe = UNDERFLOW_CHECKING ? rdreq & ~rdempty : rdreq;

initial begin 
    write_addr = 0;
    read_addr = 0;
    wrempty = 1;
    wrfull = 0;
    rdempty = 1;
    rdfull = 0;
    wrcapacity = 0;
    rdcapacity = 0;    
    rd_almost_empty = 1;
    rd_almost_full = 0;
    wr_almost_empty = 1;
    wr_almost_full = 0;
end


// ------------------ Write -------------------------

add_a_b_s0_s1 #(LOG_DEPTH) wr_adder(
    .a(write_addr),
    .b(~wr_read_addr),
    .s0(wrreq_safe),
    .s1(1'b1),
    .out(wrcapacity_w)
);

always @(posedge wrclk or posedge aclr) begin

    if (aclr) begin
        write_addr <= 0;
        wrcapacity <= 0;
        wrempty <= 1;
        wrfull <= 0;
        wr_almost_full <= 0;
        wr_almost_empty <= 1;
    end else begin
        write_addr <= write_addr + wrreq_safe;
        wrcapacity <= wrcapacity_w;
        wrempty <= (wrcapacity == 0) && (wrreq == 0);
        wrfull <= (wrcapacity == NUM_WORDS) || (wrcapacity == NUM_WORDS - 1) \
        && (wrreq == 1);
        
        wr_almost_empty <=
            (wrcapacity < (ALMOST_EMPTY_VALUE-1)) || 
            (wrcapacity == (ALMOST_EMPTY_VALUE-1)) && (wrreq == 0);
        
        wr_almost_full <= 
            (wrcapacity >= ALMOST_FULL_VALUE) ||
            (wrcapacity == ALMOST_FULL_VALUE - 1) && (wrreq == 1);    
    end
end

assign wrusedw = wrcapacity;

// ------------------ Read -------------------------

add_a_b_s0_s1 #(LOG_DEPTH) rd_adder(
    .a(rd_write_addr),
    .b(~read_addr),
    .s0(1'b0),
    .s1(~rdreq_safe),
    .out(rdcapacity_w)
);

always @(posedge rdclk or posedge aclr) begin
    if (aclr) begin
        read_addr <= 0;
        rdcapacity <= 0;
        rdempty <= 1;
        rdfull <= 0;    
        rd_almost_empty <= 1;
        rd_almost_full <= 0;
    end else begin
        read_addr <= read_addr + rdreq_safe;
        rdcapacity <= rdcapacity_w;
        rdempty <= (rdcapacity == 0) || (rdcapacity == 1) && (rdreq == 1);
        rdfull <= (rdcapacity == NUM_WORDS) && (rdreq == 0);    
        rd_almost_empty <= 
            (rdcapacity < ALMOST_EMPTY_VALUE) || 
            (rdcapacity == ALMOST_EMPTY_VALUE) && (rdreq == 1);
            
        rd_almost_full <= 
            (rdcapacity > ALMOST_FULL_VALUE) ||
            (rdcapacity == ALMOST_FULL_VALUE) && (rdreq == 0);                
    end
end

assign rdusedw = rdcapacity;

// ---------------- Synchronizers --------------------

wire [LOG_DEPTH-1:0] gray_read_addr;
wire [LOG_DEPTH-1:0] wr_gray_read_addr;
wire [LOG_DEPTH-1:0] gray_write_addr;
wire [LOG_DEPTH-1:0] rd_gray_write_addr;

binary_to_gray #(.WIDTH(LOG_DEPTH)) rd_b2g (.clock(rdclk), .aclr(aclr), \
     .din(read_addr), .dout(gray_read_addr));
synchronizer_ff_r2 #(.WIDTH(LOG_DEPTH)) rd2wr (.din_clk(rdclk), .din(gray_read_addr), \
     .dout_clk(wrclk), .dout(wr_gray_read_addr));
gray_to_binary #(.WIDTH(LOG_DEPTH)) rd_g2b (.clock(wrclk), .aclr(aclr), \
     .din(wr_gray_read_addr), .dout(wr_read_addr));


binary_to_gray #(.WIDTH(LOG_DEPTH)) wr_b2g (.clock(wrclk), .aclr(aclr), .din(write_addr), \
     .dout(gray_write_addr));
synchronizer_ff_r2 #(.WIDTH(LOG_DEPTH)) wr2rd (.din_clk(wrclk), .din(gray_write_addr), \
     .dout_clk(rdclk), .dout(rd_gray_write_addr));
gray_to_binary #(.WIDTH(LOG_DEPTH)) wr_g2b (.clock(rdclk), .aclr(aclr), \
     .din(rd_gray_write_addr), .dout(rd_write_addr));

// ------------------ MLAB ---------------------------

generic_mlab_dc #(.WIDTH(WIDTH), .ADDR_WIDTH(LOG_DEPTH)) mlab_inst (
    .rclk(rdclk),
    .wclk(wrclk),
    .din(data),
    .waddr(write_addr),
    .we(1'b1),
    .re(1'b1),
    .raddr(read_addr),
    .dout(q)
);

endmodule

module add_a_b_s0_s1 #(
    parameter SIZE = 5
)(
    input [SIZE-1:0] a,
    input [SIZE-1:0] b,
    input s0,
    input s1,
    output [SIZE-1:0] out
);
    wire [SIZE:0] left;
    wire [SIZE:0] right;
    wire temp;
    
    assign left = {a ^ b, s0};
    assign right = {a[SIZE-2:0] & b[SIZE-2:0], s1, s0};
    assign {out, temp} = left + right;
    
endmodule

module binary_to_gray #(
    parameter WIDTH = 5
) (
    input clock,
    input aclr,
    input [WIDTH-1:0] din,
    output reg [WIDTH-1:0] dout
);

	always @(posedge clock or posedge aclr) begin
		 if (aclr)
			  dout <= 0;
		 else
			  dout <= din ^ (din >> 1);
	end

endmodule

module gray_to_binary #(
    parameter WIDTH = 5
) (
    input clock,
    input aclr,
    input [WIDTH-1:0] din,
    output reg [WIDTH-1:0] dout
);

	wire [WIDTH-1:0] dout_w;

	genvar i;
	generate
		 for (i = 0; i < WIDTH; i=i+1) begin : loop
			  assign dout_w[i] = ^(din[WIDTH-1:i]);
		 end
	endgenerate

	always @(posedge clock or posedge aclr) begin
		 if (aclr)
			  dout <= 0;
		 else
			  dout <= dout_w;
	end

endmodule

(* altera_attribute = "-name SYNCHRONIZER_IDENTIFICATION OFF" *)
module generic_mlab_dc #(
    parameter WIDTH = 8,
    parameter ADDR_WIDTH = 5
)(
    input rclk,
    input wclk,
    input [WIDTH-1:0] din,
    input [ADDR_WIDTH-1:0] waddr,
    input we,
    input re,
    input [ADDR_WIDTH-1:0] raddr,
    output [WIDTH-1:0] dout
);

	localparam DEPTH = 1 << ADDR_WIDTH;
	(* ramstyle = "mlab" *) reg [WIDTH-1:0] mem[0:DEPTH-1];

	reg [WIDTH-1:0] dout_r;
	always @(posedge wclk) begin
		 if (we)
			  mem[waddr] <= din;
	end
	always @(posedge rclk) begin
		 if (re)
			  dout_r <= mem[raddr];
	end
	assign dout = dout_r;

endmodule


module synchronizer_ff_r2 #(
    parameter WIDTH = 8
)(
    input din_clk,
    input [WIDTH-1:0] din,
    input dout_clk,
    output [WIDTH-1:0] dout
);

	reg [WIDTH-1:0] ff_launch = {WIDTH {1'b0}} 
    /* synthesis preserve dont_replicate */;
	always @(posedge din_clk) begin
		 ff_launch <= din;
	end

	reg [WIDTH-1:0] ff_meta = {WIDTH {1'b0}} 
    /* synthesis preserve dont_replicate */;
	always @(posedge dout_clk) begin
		 ff_meta <= ff_launch;
	end

	reg [WIDTH-1:0] ff_sync = {WIDTH {1'b0}} 
   /* synthesis preserve dont_replicate */;
	always @(posedge dout_clk) begin
		 ff_sync <= ff_meta;
	end

	assign dout = ff_sync;
endmodule
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Quartus® Prime Pro Edition User Guide: Design Recommendations

1.4.4.1. Dual Clock FIFO Example in Verilog HDL
