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

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////  File name: pci_target32_clk_en.v                            ////

////                                                              ////

////  This file is part of the "PCI bridge" project               ////

////  http://www.opencores.org/cores/pci/                         ////

////                                                              ////

////  Author(s):                                                  ////

////      - Tadej Markovic, tadej@opencores.org                   ////

////                                                              ////

////  All additional information is avaliable in the README.txt   ////

////  file.                                                       ////

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//// Copyright (C) 2000 Tadej Markovic, tadej@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                     ////

////                                                              ////

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//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

//

// module is used to separate logic which uses criticaly constrained inputs from slower logic.

// It is used to synthesize critical timing logic separately with faster cells or without optimization

`include "constants.v"

module PCI_TARGET32_CLK_EN

(

    addr_phase,

    config_access,

    addr_claim_in,

    disconect_wo_data_in,

    pcir_fifo_data_err_in,

    rw_cbe0,

    pci_frame_in,

    pci_irdy_in,

    state_wait,

    state_transfere,

    state_backoff,

    state_default,

    clk_enable

);

input           addr_phase ;                    // indicates registered address phase on PCI bus

input           config_access ;                 // indicates configuration access

input           addr_claim_in ;                 // indicates claimed input PCI address

input           disconect_wo_data_in ;  // indicates disconnect without data termination from backend

input           pcir_fifo_data_err_in ; // indicates FIFO data error termination from backend

input           rw_cbe0 ;                               // registered (through all cycle) RW (CBE[0]) input signal from PCI bus

input           pci_frame_in ;                  // critical constrained input signal

input                   pci_irdy_in ;                   // critical constrained input signal

input                   state_wait ;                    // indicates WAIT state of FSM

input                   state_transfere ;               // indicates TRANSFERE state of FSM

input                   state_backoff ;                 // indicates BACKOFF state of FSM

input                   state_default ;                 // indicates DEFAULT state of FSM

output                  clk_enable ;                    // FSM clock enable output

// clock enable signal when FSM is in IDLE state

wire s_idle_clk_en      =       ((addr_phase && config_access) ||

                                                (addr_phase && ~config_access && addr_claim_in)) ;

// clock enable signal when FSM is in WAIT state or in DEFAULT state    

wire s_wait_clk_en      =       (state_wait || state_default) ;

// clock enable signal when FSM is in TRANSFERE state

wire s_tran_clk_en      =       state_transfere &&

                                                ((disconect_wo_data_in && ~pci_irdy_in && ~pci_frame_in) || (pci_frame_in) ||

                                                (~rw_cbe0 && pcir_fifo_data_err_in && ~pci_irdy_in && ~pci_frame_in)) ;

// clock enable signal when FSM is in BACKOFF state     

wire s_bcko_clk_en      =       (state_backoff && pci_frame_in) ;

// Clock enable signal for FSM with preserved hierarchy for minimum delay!

assign clk_enable       =       (s_idle_clk_en || s_wait_clk_en || s_tran_clk_en || s_bcko_clk_en) ;

endmodule