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//////////////////////////////////////////////////////////////////////

////                                                              ////

////  File name "pciw_pcir_fifos.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) 2000 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: not supported by cvs2svn $

// Revision 1.10  2002/10/18 03:36:37  tadejm

// Changed wrong signal name scanb_sen into scanb_en.

//

// Revision 1.9  2002/10/17 22:51:08  tadejm

// Changed BIST signals for RAMs.

//

// Revision 1.8  2002/10/11 10:09:01  mihad

// Added additional testcase and changed rst name in BIST to trst

//

// Revision 1.7  2002/10/08 17:17:06  mihad

// Added BIST signals for RAMs.

//

// Revision 1.6  2002/09/30 16:03:04  mihad

// Added meta flop module for easier meta stable FF identification during synthesis

//

// Revision 1.5  2002/09/25 15:53:52  mihad

// Removed all logic from asynchronous reset network

//

// Revision 1.4  2002/03/05 11:53:47  mihad

// Added some testcases, removed un-needed fifo signals

//

// 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

//

//

`include "pci_constants.v"

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

module pci_pciw_pcir_fifos

(

    wb_clock_in,

    pci_clock_in,

    reset_in,

    pciw_wenable_in,

    pciw_addr_data_in,

    pciw_cbe_in,

    pciw_control_in,

    pciw_renable_in,

    pciw_addr_data_out,

    pciw_cbe_out,

    pciw_control_out,

//    pciw_flush_in,    // not used

    pciw_two_left_out,

    pciw_almost_full_out,

    pciw_full_out,

    pciw_almost_empty_out,

    pciw_empty_out,

    pciw_transaction_ready_out,

    pcir_wenable_in,

    pcir_data_in,

    pcir_be_in,

    pcir_control_in,

    pcir_renable_in,

    pcir_data_out,

    pcir_be_out,

    pcir_control_out,

    pcir_flush_in,

    pcir_full_out,

    pcir_almost_empty_out,

    pcir_empty_out,

    pcir_transaction_ready_out

`ifdef PCI_BIST

    ,

    // debug chain signals

    scanb_rst,      // bist scan reset

    scanb_clk,      // bist scan clock

    scanb_si,       // bist scan serial in

    scanb_so,       // bist scan serial out

    scanb_en        // bist scan shift enable

`endif

) ;

/*-----------------------------------------------------------------------------------------------------------

System inputs:

wb_clock_in - WISHBONE bus clock

pci_clock_in - PCI bus clock

reset_in - reset from control logic

-------------------------------------------------------------------------------------------------------------*/

input wb_clock_in, pci_clock_in, reset_in ;

/*-----------------------------------------------------------------------------------------------------------

PCI WRITE FIFO interface signals prefixed with pciw_ - FIFO is used for posted writes initiated by external

PCI master through PCI target interface, traveling through FIFO and are completed on WISHBONE by

WISHBONE master interface

write enable signal:

pciw_wenable_in = write enable input for PCIW_FIFO - driven by PCI TARGET interface

data input signals:

pciw_addr_data_in = data input - data from PCI bus - first entry of transaction is address others are data entries

pciw_cbe_in       = bus command/byte enable(~#BE[3:0]) input - first entry of transaction is bus command, other are byte enables

pciw_control_in   = control input - encoded control bus input

read enable signal:

pciw_renable_in = read enable input driven by WISHBONE master interface

data output signals:

pciw_addr_data_out = data output - data from PCI bus - first entry of transaction is address, others are data entries

pciw_cbe_out      = bus command/byte enable output - first entry of transaction is bus command, others are byte enables

pciw_control_out = control input - encoded control bus input

status signals - monitored by various resources in the core

pciw_flush_in = flush signal input for PCIW_FIFO - when asserted, fifo is flushed(emptied)

pciw_almost_full_out = almost full output from PCIW_FIFO

pciw_full_out = full output from PCIW_FIFO

pciw_almost_empty_out = almost empty output from PCIW_FIFO

pciw_empty_out = empty output from PCIW_FIFO

pciw_transaction_ready_out = output indicating that one complete transaction is waiting in PCIW_FIFO

-----------------------------------------------------------------------------------------------------------*/

// input control and data

input        pciw_wenable_in ;

input [31:0] pciw_addr_data_in ;

input [3:0]  pciw_cbe_in ;

input [3:0]  pciw_control_in ;

// output control and data

input         pciw_renable_in ;

output [31:0] pciw_addr_data_out ;

output [3:0]  pciw_cbe_out ;

output [3:0]  pciw_control_out ;

// flush input

//input pciw_flush_in ;     // not used

// status outputs

output pciw_two_left_out ;

output pciw_almost_full_out ;

output pciw_full_out ;

output pciw_almost_empty_out ;

output pciw_empty_out ;

output pciw_transaction_ready_out ;

/*-----------------------------------------------------------------------------------------------------------

PCI READ FIFO interface signals prefixed with pcir_ - FIFO is used for holding delayed read completions

initiated by master on PCI bus and completed on WISHBONE bus,

write enable signal:

pcir_wenable_in = write enable input for PCIR_FIFO - driven by WISHBONE master interface

data input signals:

pcir_data_in      = data input - data from WISHBONE bus - there is no address entry here, since address is stored in separate register

pcir_be_in        = byte enable(~SEL[3:0]) input - byte enables - same through one transaction

pcir_control_in   = control input - encoded control bus input

read enable signal:

pcir_renable_in = read enable input driven by PCI target interface

data output signals:

pcir_data_out = data output - data from WISHBONE bus

pcir_be_out      = byte enable output(~SEL)

pcir_control_out = control output - encoded control bus output

status signals - monitored by various resources in the core

pcir_flush_in = flush signal input for PCIR_FIFO - when asserted, fifo is flushed(emptied)

pcir full_out = full output from PCIR_FIFO

pcir_almost_empty_out = almost empty output from PCIR_FIFO

pcir_empty_out = empty output from PCIR_FIFO

pcir_transaction_ready_out = output indicating that one complete transaction is waiting in PCIR_FIFO

-----------------------------------------------------------------------------------------------------------*/

// input control and data

input        pcir_wenable_in ;

input [31:0] pcir_data_in ;

input [3:0]  pcir_be_in ;

input [3:0]  pcir_control_in ;

// output control and data

input         pcir_renable_in ;

output [31:0] pcir_data_out ;

output [3:0]  pcir_be_out ;

output [3:0]  pcir_control_out ;

// flush input

input pcir_flush_in ;

// status outputs

output pcir_full_out ;

output pcir_almost_empty_out ;

output pcir_empty_out ;

output pcir_transaction_ready_out ;

`ifdef PCI_BIST

/*-----------------------------------------------------

BIST debug chain port signals

-----------------------------------------------------*/

input   scanb_rst;      // bist scan reset

input   scanb_clk;      // bist scan clock

input   scanb_si;       // bist scan serial in

output  scanb_so;       // bist scan serial out

input   scanb_en;       // bist scan shift enable

`endif

/*-----------------------------------------------------------------------------------------------------------

Address length parameters:

PCIW_DEPTH = defines PCIW_FIFO depth

PCIR_DEPTH = defines PCIR_FIFO depth

PCIW_ADDR_LENGTH = defines PCIW_FIFO's location address length - log2(PCIW_DEPTH)

PCIR_ADDR_LENGTH = defines PCIR_FIFO's location address length - log2(PCIR_DEPTH)

-----------------------------------------------------------------------------------------------------------*/

parameter PCIW_DEPTH = `PCIW_DEPTH ;

parameter PCIW_ADDR_LENGTH = `PCIW_ADDR_LENGTH ;

parameter PCIR_DEPTH = `PCIR_DEPTH ;

parameter PCIR_ADDR_LENGTH = `PCIR_ADDR_LENGTH ;

/*-----------------------------------------------------------------------------------------------------------

pciw_wallow = PCIW_FIFO write allow wire - writes to FIFO are allowed when FIFO isn't full and write enable is 1

pciw_rallow = PCIW_FIFO read allow wire - reads from FIFO are allowed when FIFO isn't empty and read enable is 1

-----------------------------------------------------------------------------------------------------------*/

wire pciw_wallow ;

wire pciw_rallow ;

/*-----------------------------------------------------------------------------------------------------------

pcir_wallow = PCIR_FIFO write allow wire - writes to FIFO are allowed when FIFO isn't full and write enable is 1

pcir_rallow = PCIR_FIFO read allow wire - reads from FIFO are allowed when FIFO isn't empty and read enable is 1

-----------------------------------------------------------------------------------------------------------*/

wire pcir_wallow ;

wire pcir_rallow ;

/*-----------------------------------------------------------------------------------------------------------

wires for address port conections from PCIW_FIFO control logic to RAM blocks used for PCIW_FIFO

-----------------------------------------------------------------------------------------------------------*/

wire [(PCIW_ADDR_LENGTH - 1):0] pciw_raddr ;

wire [(PCIW_ADDR_LENGTH - 1):0] pciw_waddr ;

/*-----------------------------------------------------------------------------------------------------------

wires for address port conections from PCIR_FIFO control logic to RAM blocks used for PCIR_FIFO

-----------------------------------------------------------------------------------------------------------*/

wire [(PCIR_ADDR_LENGTH - 1):0] pcir_raddr ;

wire [(PCIR_ADDR_LENGTH - 1):0] pcir_waddr ;

/*-----------------------------------------------------------------------------------------------------------

PCIW_FIFO transaction counters: used to count incoming transactions and outgoing transactions. When number of

input transactions is equal to number of output transactions, it means that there isn't any complete transaction

currently present in the FIFO.

-----------------------------------------------------------------------------------------------------------*/

reg [(PCIW_ADDR_LENGTH - 1):0] pciw_inTransactionCount ;

reg [(PCIW_ADDR_LENGTH - 1):0] pciw_outTransactionCount ;

/*-----------------------------------------------------------------------------------------------------------

FlipFlops for indicating if complete delayed read completion is present in the FIFO

-----------------------------------------------------------------------------------------------------------*/

/*reg pcir_inTransactionCount ;

reg pcir_outTransactionCount ;*/

/*-----------------------------------------------------------------------------------------------------------

wires monitoring control bus. When control bus on a write transaction has a value of `LAST, it means that

complete transaction is in the FIFO. When control bus on a read transaction has a value of `LAST,

it means that there was one complete transaction taken out of FIFO.

-----------------------------------------------------------------------------------------------------------*/

wire pciw_last_in  = pciw_control_in[`LAST_CTRL_BIT] ;

wire pciw_last_out = pciw_control_out[`LAST_CTRL_BIT] ;

/*wire pcir_last_in  = pcir_wallow && (pcir_control_in == `LAST) ;

wire pcir_last_out = pcir_rallow && (pcir_control_out == `LAST) ;*/

wire pciw_empty ;

wire pcir_empty ;

assign pciw_empty_out = pciw_empty ;

assign pcir_empty_out = pcir_empty ;

// clear wires for clearing FFs and registers

wire pciw_clear = reset_in /*|| pciw_flush_in*/ ; // PCIW_FIFO's clear signal - flush not used

wire pcir_clear = reset_in /*|| pcir_flush_in*/ ; // PCIR_FIFO's clear signal - flush changed to synchronous op.

/*-----------------------------------------------------------------------------------------------------------

Definitions of wires for connecting RAM instances

-----------------------------------------------------------------------------------------------------------*/

wire [39:0] dpram_portA_output ;

wire [39:0] dpram_portB_output ;

wire [39:0] dpram_portA_input = {pciw_control_in, pciw_cbe_in, pciw_addr_data_in} ;

wire [39:0] dpram_portB_input = {pcir_control_in, pcir_be_in, pcir_data_in} ;

/*-----------------------------------------------------------------------------------------------------------

Fifo output assignments - each ram port provides data for different fifo

-----------------------------------------------------------------------------------------------------------*/

assign pciw_control_out = dpram_portB_output[39:36] ;

assign pcir_control_out = dpram_portA_output[39:36] ;

assign pciw_cbe_out     = dpram_portB_output[35:32] ;

assign pcir_be_out      = dpram_portA_output[35:32] ;

assign pciw_addr_data_out = dpram_portB_output[31:0] ;

assign pcir_data_out      = dpram_portA_output[31:0] ;

`ifdef PCI_RAM_DONT_SHARE

    /*-----------------------------------------------------------------------------------------------------------

    Piece of code in this ifdef section is used in applications which can provide enough RAM instances to

    accomodate four fifos - each occupying its own instance of ram. Ports are connected in such a way,

    that instances of RAMs can be changed from two port to dual port ( async read/write port ). In that case,

    write port is always port a and read port is port b.

    -----------------------------------------------------------------------------------------------------------*/

    /*-----------------------------------------------------------------------------------------------------------

    Pad redundant address lines with zeros. This may seem stupid, but it comes in perfect for FPGA impl.

    -----------------------------------------------------------------------------------------------------------*/

    /*

    wire [(`PCIW_FIFO_RAM_ADDR_LENGTH - PCIW_ADDR_LENGTH - 1):0] pciw_addr_prefix = {( `PCIW_FIFO_RAM_ADDR_LENGTH - PCIW_ADDR_LENGTH){1'b0}} ;

    wire [(`PCIR_FIFO_RAM_ADDR_LENGTH - PCIR_ADDR_LENGTH - 1):0] pcir_addr_prefix = {( `PCIR_FIFO_RAM_ADDR_LENGTH - PCIR_ADDR_LENGTH){1'b0}} ;

    */

    // compose complete port addresses

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH-1):0] pciw_whole_waddr = pciw_waddr ;

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH-1):0] pciw_whole_raddr = pciw_raddr ;

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH-1):0] pcir_whole_waddr = pcir_waddr ;

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH-1):0] pcir_whole_raddr = pcir_raddr ;

    wire pciw_read_enable = 1'b1 ;

    wire pcir_read_enable = 1'b1 ;

    `ifdef PCI_BIST

    wire scanb_so_internal ; // wires for connection of debug ports on two rams

    wire scanb_si_internal = scanb_so_internal ;

    `endif

    // instantiate and connect two generic rams - one for pci write fifo and one for pci read fifo

    pci_pci_tpram #(`PCI_FIFO_RAM_ADDR_LENGTH, 40) pciw_fifo_storage

    (

        // Generic synchronous two-port RAM interface

        .clk_a(pci_clock_in),

        .rst_a(reset_in),

        .ce_a(1'b1),

        .we_a(pciw_wallow),

        .oe_a(1'b1),

        .addr_a(pciw_whole_waddr),

        .di_a(dpram_portA_input),

        .do_a(),

        .clk_b(wb_clock_in),

        .rst_b(reset_in),

        .ce_b(pciw_read_enable),

        .we_b(1'b0),

        .oe_b(1'b1),

        .addr_b(pciw_whole_raddr),

        .di_b(40'h00_0000_0000),

        .do_b(dpram_portB_output)

    `ifdef PCI_BIST

        ,

        .scanb_rst      (scanb_rst),

        .scanb_clk      (scanb_clk),

        .scanb_si       (scanb_si),

        .scanb_so       (scanb_so_internal),

        .scanb_en       (scanb_en)

    `endif

    );

    pci_pci_tpram #(`PCI_FIFO_RAM_ADDR_LENGTH, 40) pcir_fifo_storage

    (

        // Generic synchronous two-port RAM interface

        .clk_a(wb_clock_in),

        .rst_a(reset_in),

        .ce_a(1'b1),

        .we_a(pcir_wallow),

        .oe_a(1'b1),

        .addr_a(pcir_whole_waddr),

        .di_a(dpram_portB_input),

        .do_a(),

        .clk_b(pci_clock_in),

        .rst_b(reset_in),

        .ce_b(pcir_read_enable),

        .we_b(1'b0),

        .oe_b(1'b1),

        .addr_b(pcir_whole_raddr),

        .di_b(40'h00_0000_0000),

        .do_b(dpram_portA_output)

    `ifdef PCI_BIST

        ,

        .scanb_rst      (scanb_rst),

        .scanb_clk      (scanb_clk),

        .scanb_si       (scanb_si_internal),

        .scanb_so       (scanb_so),

        .scanb_en       (scanb_en)

    `endif

    );

`else // RAM blocks sharing between two fifos

    /*-----------------------------------------------------------------------------------------------------------

    Code section under this ifdef is used for implementation where RAM instances are too expensive. In this

    case one RAM instance is used for both - pci read and pci write fifo.

    -----------------------------------------------------------------------------------------------------------*/

    /*-----------------------------------------------------------------------------------------------------------

    Address prefix definition - since both FIFOs reside in same RAM instance, storage is separated by MSB

    addresses. pci write fifo addresses are padded with zeros on the MSB side ( at least one address line

    must be used for this ), pci read fifo addresses are padded with ones on the right ( at least one ).

    -----------------------------------------------------------------------------------------------------------*/

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH - PCIW_ADDR_LENGTH - 1):0] pciw_addr_prefix = {( `PCI_FIFO_RAM_ADDR_LENGTH - PCIW_ADDR_LENGTH){1'b0}} ;

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH - PCIR_ADDR_LENGTH - 1):0] pcir_addr_prefix = {( `PCI_FIFO_RAM_ADDR_LENGTH - PCIR_ADDR_LENGTH){1'b1}} ;

    /*-----------------------------------------------------------------------------------------------------------

    Port A address generation for RAM instance. RAM instance must be full two port RAM - read and write capability

    on both sides.

    Port A is clocked by PCI clock, DIA is input for pciw_fifo, DOA is output for pcir_fifo.

    Address is multiplexed so operation can be switched between fifos. Default is a read on port.

    -----------------------------------------------------------------------------------------------------------*/

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH-1):0] portA_addr = pciw_wallow ? {pciw_addr_prefix, pciw_waddr} : {pcir_addr_prefix, pcir_raddr} ;

    /*-----------------------------------------------------------------------------------------------------------

    Port B is clocked by WISHBONE clock, DIB is input for pcir_fifo, DOB is output for pciw_fifo.

    Address is multiplexed so operation can be switched between fifos. Default is a read on port.

    -----------------------------------------------------------------------------------------------------------*/

    wire [(`PCI_FIFO_RAM_ADDR_LENGTH-1):0] portB_addr  = pcir_wallow ? {pcir_addr_prefix, pcir_waddr} : {pciw_addr_prefix, pciw_raddr} ;

    wire portA_enable      = 1'b1 ;

    wire portB_enable      = 1'b1 ;

    // instantiate RAM for these two fifos

    pci_pci_tpram #(`PCI_FIFO_RAM_ADDR_LENGTH, 40) pciu_fifo_storage

    (

        // Generic synchronous two-port RAM interface

        .clk_a(pci_clock_in),

        .rst_a(reset_in),

        .ce_a(portA_enable),

        .we_a(pciw_wallow),

        .oe_a(1'b1),

        .addr_a(portA_addr),

        .di_a(dpram_portA_input),

        .do_a(dpram_portA_output),

        .clk_b(wb_clock_in),

        .rst_b(reset_in),

        .ce_b(portB_enable),

        .we_b(pcir_wallow),

        .oe_b(1'b1),

        .addr_b(portB_addr),

        .di_b(dpram_portB_input),

        .do_b(dpram_portB_output)

    `ifdef PCI_BIST

        ,

        .scanb_rst      (scanb_rst),

        .scanb_clk      (scanb_clk),

        .scanb_si       (scanb_si),

        .scanb_so       (scanb_so),

        .scanb_en       (scanb_en)

    `endif

    );

`endif

/*-----------------------------------------------------------------------------------------------------------

Instantiation of two control logic modules - one for PCIW_FIFO and one for PCIR_FIFO

-----------------------------------------------------------------------------------------------------------*/

pci_pciw_fifo_control #(PCIW_ADDR_LENGTH) pciw_fifo_ctrl

(

    .rclock_in(wb_clock_in),

    .wclock_in(pci_clock_in),

    .renable_in(pciw_renable_in),

    .wenable_in(pciw_wenable_in),

    .reset_in(reset_in),

//    .flush_in(pciw_flush_in),                     // flush not used

    .two_left_out(pciw_two_left_out),

    .almost_full_out(pciw_almost_full_out),

    .full_out(pciw_full_out),

    .almost_empty_out(pciw_almost_empty_out),

    .empty_out(pciw_empty),

    .waddr_out(pciw_waddr),

    .raddr_out(pciw_raddr),

    .rallow_out(pciw_rallow),

    .wallow_out(pciw_wallow)

);

pci_pcir_fifo_control #(PCIR_ADDR_LENGTH) pcir_fifo_ctrl

(

    .rclock_in(pci_clock_in),

    .wclock_in(wb_clock_in),

    .renable_in(pcir_renable_in),

    .wenable_in(pcir_wenable_in),

    .reset_in(reset_in),

    .flush_in(pcir_flush_in),

    .full_out(pcir_full_out),

    .almost_empty_out(pcir_almost_empty_out),

    .empty_out(pcir_empty),

    .waddr_out(pcir_waddr),

    .raddr_out(pcir_raddr),

    .rallow_out(pcir_rallow),

    .wallow_out(pcir_wallow)

);

// in and out transaction counters and grey codes

reg  [(PCIW_ADDR_LENGTH-2):0] inGreyCount ;

reg  [(PCIW_ADDR_LENGTH-2):0] outGreyCount ;

wire [(PCIW_ADDR_LENGTH-2):0] inNextGreyCount  = {pciw_inTransactionCount[(PCIW_ADDR_LENGTH-2)], pciw_inTransactionCount[(PCIW_ADDR_LENGTH-2):1] ^ pciw_inTransactionCount[(PCIW_ADDR_LENGTH-3):0]} ;

wire [(PCIW_ADDR_LENGTH-2):0] outNextGreyCount = {pciw_outTransactionCount[(PCIW_ADDR_LENGTH-2)], pciw_outTransactionCount[(PCIW_ADDR_LENGTH-2):1] ^ pciw_outTransactionCount[(PCIW_ADDR_LENGTH-3):0]} ;

// input transaction counter is incremented when whole transaction is written to fifo. This is indicated by last control bit written to last transaction location

wire in_count_en  = pciw_wallow     && pciw_last_in ;

// output transaction counter is incremented when whole transaction is pulled out of fifo. This is indicated when location with last control bit set is read

wire out_count_en = pciw_rallow && pciw_last_out ;

always@(posedge pci_clock_in or posedge pciw_clear)

begin

    if (pciw_clear)

    begin

        inGreyCount[(PCIW_ADDR_LENGTH-2)] <= #`FF_DELAY 1'b1 ;

        inGreyCount[(PCIW_ADDR_LENGTH-3):0] <= #`FF_DELAY {(PCIW_ADDR_LENGTH-2),1'b0} ;

    end

    else

    if (in_count_en)

        inGreyCount <= #`FF_DELAY inNextGreyCount ;

end

always@(posedge wb_clock_in or posedge pciw_clear)

begin

    if (pciw_clear)

    begin

        outGreyCount[(PCIW_ADDR_LENGTH-2)]   <= #`FF_DELAY 1'b1 ;

        outGreyCount[(PCIW_ADDR_LENGTH-3):0] <= #`FF_DELAY {(PCIW_ADDR_LENGTH-2),1'b0} ;

    end

    else

    if (out_count_en)

        outGreyCount <= #`FF_DELAY outNextGreyCount ;

end

always@(posedge pci_clock_in or posedge pciw_clear)

begin

    if (pciw_clear)

        pciw_inTransactionCount <= #`FF_DELAY {(PCIW_ADDR_LENGTH-1){1'b0}} ;

    else

    if (in_count_en)

        pciw_inTransactionCount <= #`FF_DELAY pciw_inTransactionCount + 1'b1 ;

end

always@(posedge wb_clock_in or posedge pciw_clear)

begin

    if (pciw_clear)

        pciw_outTransactionCount <= #`FF_DELAY {(PCIW_ADDR_LENGTH-1){1'b0}} ;

    else

    if (out_count_en)

        pciw_outTransactionCount <= #`FF_DELAY pciw_outTransactionCount + 1'b1 ;

end

// transaction is ready when incoming transaction count is not equal to outgoing transaction count ( what comes in must come out )

// anytime last entry of transaction is pulled out of fifo, transaction ready flag is cleared for at least one clock to prevent wrong operation

// ( otherwise transaction ready would stay set for one additional clock even though next transaction was not ready )

wire pciw_transaction_ready_flop_i = inGreyCount != outGreyCount ;

meta_flop #(0) i_meta_flop_transaction_ready

(

    .rst_i      (pciw_clear),

    .clk_i      (wb_clock_in),

    .ld_i       (out_count_en),

    .ld_val_i   (1'b0),

    .en_i       (1'b1),

    .d_i        (pciw_transaction_ready_flop_i),

    .meta_q_o   (pciw_transaction_ready_out)

) ;

assign pcir_transaction_ready_out  = 1'b0 ;

endmodule