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

////                                                              ////

////  OR1200's Freeze logic                                       ////

////                                                              ////

////  This file is part of the OpenRISC 1200 project              ////

////  http://www.opencores.org/project,or1k                       ////

////                                                              ////

////  Description                                                 ////

////  Generates all freezes and stalls inside RISC                ////

////                                                              ////

////  To Do:                                                      ////

////   - make it smaller and faster                               ////

////                                                              ////

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

////      - Damjan Lampret, lampret@opencores.org                 ////

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2000 Authors and 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                     ////

////                                                              ////

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

//

// $Log: or1200_freeze.v,v $

// Revision 2.0  2010/06/30 11:00:00  ORSoC

// Minor update: 

// Bugs fixed. 

//

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`include "or1200_defines.v"

`define OR1200_NO_FREEZE        3'd0

`define OR1200_FREEZE_BYDC      3'd1

`define OR1200_FREEZE_BYMULTICYCLE      3'd2

`define OR1200_WAIT_LSU_TO_FINISH       3'd3

`define OR1200_WAIT_IC                  3'd4

//

// Freeze logic (stalls CPU pipeline, ifetcher etc.)

//

module or1200_freeze

  (

   // Clock and reset

   clk, rst,

   // Internal i/f

   multicycle, wait_on, flushpipe, extend_flush, lsu_stall, if_stall,

   lsu_unstall, du_stall, mac_stall,

   force_dslot_fetch, abort_ex,

   genpc_freeze, if_freeze, id_freeze, ex_freeze, wb_freeze, saving_if_insn,

   fpu_done, mtspr_done,

   icpu_ack_i, icpu_err_i

   );

//

// I/O

//

input                           clk;

input                           rst;

input   [`OR1200_MULTICYCLE_WIDTH-1:0]   multicycle;

input   [`OR1200_WAIT_ON_WIDTH-1:0]      wait_on;

input                           flushpipe;

input                           extend_flush;

input                           lsu_stall;

input                           if_stall;

input                           lsu_unstall;

input                           force_dslot_fetch;

input                           abort_ex;

input                           du_stall;

input                           mac_stall;

output                          genpc_freeze;

output                          if_freeze;

output                          id_freeze;

output                          ex_freeze;

output                          wb_freeze;

input                           saving_if_insn;

input                           fpu_done;

input                           mtspr_done;

input                           icpu_ack_i;

input                           icpu_err_i;

//

// Internal wires and regs

//

wire                            multicycle_freeze;

reg     [`OR1200_MULTICYCLE_WIDTH-1:0]   multicycle_cnt;

reg                             flushpipe_r;

reg [`OR1200_WAIT_ON_WIDTH-1:0]  waiting_on;

//

// Pipeline freeze

//

// Rules how to create freeze signals:

// 1. Not overwriting pipeline stages:

// Freeze signals at the beginning of pipeline (such as if_freeze) can be 

// asserted more often than freeze signals at the of pipeline (such as 

// wb_freeze). In other words, wb_freeze must never be asserted when ex_freeze 

// is not. ex_freeze must never be asserted when id_freeze is not etc.

//

// 2. Inserting NOPs in the middle of pipeline only if supported:

// At this time, only ex_freeze (and wb_freeze) can be deassrted when id_freeze

// (and if_freeze) are asserted.

// This way NOP is asserted from stage ID into EX stage.

//

assign genpc_freeze = (du_stall & !saving_if_insn) | flushpipe_r;

assign if_freeze = id_freeze | extend_flush;

assign id_freeze = (lsu_stall | (~lsu_unstall & if_stall) | multicycle_freeze

                    | (|waiting_on) | force_dslot_fetch) | du_stall | mac_stall;

assign ex_freeze = wb_freeze;

assign wb_freeze = (lsu_stall | (~lsu_unstall & if_stall) | multicycle_freeze

                    | (|waiting_on)) | du_stall | mac_stall | abort_ex;

//

// registered flushpipe

//

always @(posedge clk or `OR1200_RST_EVENT rst)

        if (rst == `OR1200_RST_VALUE)

                flushpipe_r <=  1'b0;

        else if (icpu_ack_i | icpu_err_i)

//      else if (!if_stall)

                flushpipe_r <=  flushpipe;

        else if (!flushpipe)

                flushpipe_r <=  1'b0;

//

// Multicycle freeze

//

assign multicycle_freeze = |multicycle_cnt;

//

// Multicycle counter

//

always @(posedge clk or `OR1200_RST_EVENT rst)

        if (rst == `OR1200_RST_VALUE)

                multicycle_cnt <=  2'b00;

        else if (|multicycle_cnt)

                multicycle_cnt <=  multicycle_cnt - 2'd1;

        else if (|multicycle & !ex_freeze)

                multicycle_cnt <=  multicycle;

//

// Waiting on generation

//

always @(posedge clk or `OR1200_RST_EVENT rst)

  if (rst == `OR1200_RST_VALUE)

    waiting_on <= 0;

  else if ((waiting_on == `OR1200_WAIT_ON_FPU) & fpu_done)

    waiting_on <= 0;

  else if ((waiting_on == `OR1200_WAIT_ON_MTSPR) & mtspr_done)

    waiting_on <= 0;

  else if (!ex_freeze)

    waiting_on <= wait_on;

endmodule