////////////////////////////////////////////////////////////////////// //// //// //// File name "wbr_fifo_control.v" //// //// //// //// This file is part of the "PCI bridge" project //// //// http://www.opencores.org/cores/pci/ //// //// //// //// Author(s): //// //// - Miha Dolenc (mihad@opencores.org) //// //// //// //// All additional information is avaliable in the README //// //// file. //// //// //// //// //// ////////////////////////////////////////////////////////////////////// //// //// //// Copyright (C) 2001 Miha Dolenc, mihad@opencores.org //// //// //// //// 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 //// //// //// ////////////////////////////////////////////////////////////////////// // // CVS Revision History // // $Log: pci_wbr_fifo_control.v,v $ // Revision 1.1 2007-03-20 17:50:56 sithglan // add shit // // Revision 1.4 2003/08/14 13:06:03 simons // synchronizer_flop replaced with pci_synchronizer_flop, artisan ram instance updated. // // Revision 1.3 2003/07/29 08:20:11 mihad // Found and simulated the problem in the synchronization logic. // Repaired the synchronization logic in the FIFOs. // // Revision 1.2 2003/03/26 13:16:18 mihad // Added the reset value parameter to the synchronizer flop module. // Added resets to all synchronizer flop instances. // Repaired initial sync value in fifos. // // Revision 1.1 2003/01/27 16:49:31 mihad // Changed module and file names. Updated scripts accordingly. FIFO synchronizations changed. // // Revision 1.6 2002/11/27 20:36:12 mihad // Changed the code a bit to make it more readable. // Functionality not changed in any way. // More robust synchronization in fifos is still pending. // // Revision 1.5 2002/09/30 16:03:04 mihad // Added meta flop module for easier meta stable FF identification during synthesis // // Revision 1.4 2002/09/25 15:53:52 mihad // Removed all logic from asynchronous reset network // // Revision 1.3 2002/02/01 15:25:13 mihad // Repaired a few bugs, updated specification, added test bench files and design document // // Revision 1.2 2001/10/05 08:14:30 mihad // Updated all files with inclusion of timescale file for simulation purposes. // // Revision 1.1.1.1 2001/10/02 15:33:47 mihad // New project directory structure // // /* FIFO_CONTROL module provides read/write address and status generation for FIFOs implemented with standard dual port SRAM cells in ASIC or FPGA designs */ `include "pci_constants.v" // synopsys translate_off `include "timescale.v" // synopsys translate_on module pci_wbr_fifo_control ( rclock_in, wclock_in, renable_in, wenable_in, reset_in, flush_in, empty_out, waddr_out, raddr_out, rallow_out, wallow_out ) ; parameter ADDR_LENGTH = 7 ; // independent clock inputs - rclock_in = read clock, wclock_in = write clock input rclock_in, wclock_in; // enable inputs - read address changes on rising edge of rclock_in when reads are allowed // write address changes on rising edge of wclock_in when writes are allowed input renable_in, wenable_in; // reset input input reset_in; // flush input input flush_in ; // empty status output output empty_out; // read and write addresses outputs output [(ADDR_LENGTH - 1):0] waddr_out, raddr_out; // read and write allow outputs output rallow_out, wallow_out ; // read address register reg [(ADDR_LENGTH - 1):0] raddr ; // write address register reg [(ADDR_LENGTH - 1):0] waddr; assign waddr_out = waddr ; // grey code register reg [(ADDR_LENGTH - 1):0] wgrey_addr ; // next write gray address calculation - bitwise xor between address and shifted address wire [(ADDR_LENGTH - 2):0] calc_wgrey_next = waddr[(ADDR_LENGTH - 1):1] ^ waddr[(ADDR_LENGTH - 2):0] ; // grey code register reg [(ADDR_LENGTH - 1):0] rgrey_addr ; // next read gray address calculation - bitwise xor between address and shifted address wire [(ADDR_LENGTH - 2):0] calc_rgrey_next = raddr[(ADDR_LENGTH - 1):1] ^ raddr[(ADDR_LENGTH - 2):0] ; // FF for registered empty flag wire empty ; // write allow wire wire wallow = wenable_in ; // write allow output assignment assign wallow_out = wallow ; // read allow wire wire rallow ; // clear generation for FFs and registers wire clear = reset_in /*|| flush_in*/ ; // flush changed to synchronous operation assign empty_out = empty ; //rallow generation assign rallow = renable_in && !empty ; // reads allowed if read enable is high and FIFO is not empty // rallow output assignment assign rallow_out = renable_in ; // at any clock edge that rallow is high, this register provides next read address, so wait cycles are not necessary // when FIFO is empty, this register provides actual read address, so first location can be read reg [(ADDR_LENGTH - 1):0] raddr_plus_one ; // address output mux - when FIFO is empty, current actual address is driven out, when it is non - empty next address is driven out // done for zero wait state burst assign raddr_out = rallow ? raddr_plus_one : raddr ; always@(posedge rclock_in or posedge clear) begin if (clear) begin raddr_plus_one <= #`FF_DELAY 2 ; raddr <= #`FF_DELAY 1 ; end else if (flush_in) begin raddr_plus_one <= #`FF_DELAY waddr + 1'b1 ; raddr <= #`FF_DELAY waddr ; end else if (rallow) begin raddr_plus_one <= #`FF_DELAY raddr_plus_one + 1'b1 ; raddr <= #`FF_DELAY raddr_plus_one ; end end /*----------------------------------------------------------------------------------------------- Read address control consists of Read address counter and Grey Address register --------------------------------------------------------------------------------------------------*/ // grey coded address always@(posedge rclock_in or posedge clear) begin if (clear) begin rgrey_addr <= #`FF_DELAY 0 ; end else if (flush_in) begin rgrey_addr <= #`FF_DELAY wgrey_addr ; // when flushed, copy value from write side end else if (rallow) begin rgrey_addr <= #`FF_DELAY {raddr[ADDR_LENGTH - 1], calc_rgrey_next} ; end end /*-------------------------------------------------------------------------------------------- Write address control consists of write address counter and Grey Code Register ----------------------------------------------------------------------------------------------*/ // grey coded address for status generation in write clock domain always@(posedge wclock_in or posedge clear) begin if (clear) begin wgrey_addr <= #1 0 ; end else if (wallow) begin wgrey_addr <= #1 {waddr[(ADDR_LENGTH - 1)], calc_wgrey_next} ; end end // write address counter - nothing special except initial value always@(posedge wclock_in or posedge clear) begin if (clear) // initial value is 1 waddr <= #`FF_DELAY 1 ; else if (wallow) waddr <= #`FF_DELAY waddr + 1'b1 ; end /*------------------------------------------------------------------------------------------------------------------------------ Empty control: Gray coded write address pointer is synchronized to read clock domain and compared to Gray coded read address pointer. If they are equal, fifo is empty. --------------------------------------------------------------------------------------------------------------------------------*/ wire [(ADDR_LENGTH - 1):0] rclk_sync_wgrey_addr ; reg [(ADDR_LENGTH - 1):0] rclk_wgrey_addr ; pci_synchronizer_flop #(ADDR_LENGTH, 0) i_synchronizer_reg_wgrey_addr ( .data_in (wgrey_addr), .clk_out (rclock_in), .sync_data_out (rclk_sync_wgrey_addr), .async_reset (clear) ) ; always@(posedge rclock_in or posedge clear) begin if (clear) rclk_wgrey_addr <= #`FF_DELAY 0 ; else rclk_wgrey_addr <= #`FF_DELAY rclk_sync_wgrey_addr ; end assign empty = (rgrey_addr == rclk_wgrey_addr) ; endmodule