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

////                                                              ////

////  OR1200's instruction fetch                                  ////

////                                                              ////

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

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

////                                                              ////

////  Description                                                 ////

////  PC, instruction fetch, interface to IC.                     ////

////                                                              ////

////  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_if.v,v $

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

// Major update: 

// Structure reordered and bugs fixed. 

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`include "or1200_defines.v"

module or1200_if(

        // Clock and reset

        clk, rst,

        // External i/f to IC

        icpu_dat_i, icpu_ack_i, icpu_err_i, icpu_adr_i, icpu_tag_i,

        // Internal i/f

        if_freeze, if_insn, if_pc, if_flushpipe, saving_if_insn,

        if_stall, no_more_dslot, genpc_refetch, rfe,

        except_itlbmiss, except_immufault, except_ibuserr

);

//

// I/O

//

//

// Clock and reset

//

input                           clk;

input                           rst;

//

// External i/f to IC

//

input   [31:0]                   icpu_dat_i;

input                           icpu_ack_i;

input                           icpu_err_i;

input   [31:0]                   icpu_adr_i;

input   [3:0]                    icpu_tag_i;

//

// Internal i/f

//

input                           if_freeze;

output  [31:0]                   if_insn;

output  [31:0]                   if_pc;

input                           if_flushpipe;

output                          saving_if_insn;

output                          if_stall;

input                           no_more_dslot;

output                          genpc_refetch;

input                           rfe;

output                          except_itlbmiss;

output                          except_immufault;

output                          except_ibuserr;

//

// Internal wires and regs

//

wire                    save_insn;

wire                    if_bypass;

reg                     if_bypass_reg;

reg     [31:0]           insn_saved;

reg     [31:0]           addr_saved;

reg     [2:0]            err_saved;

reg                     saved;

assign save_insn = (icpu_ack_i | icpu_err_i) & if_freeze & !saved;

assign saving_if_insn = !if_flushpipe & save_insn;

//

// IF bypass 

//

assign if_bypass = icpu_adr_i[0] ? 1'b0 : if_bypass_reg | if_flushpipe;

always @(posedge clk or `OR1200_RST_EVENT rst)

        if (rst == `OR1200_RST_VALUE)

                if_bypass_reg <=  1'b0;

        else

                if_bypass_reg <=  if_bypass;

//

// IF stage insn

//

assign if_insn = no_more_dslot | rfe | if_bypass ? {`OR1200_OR32_NOP, 26'h041_0000} : saved ? insn_saved : icpu_ack_i ? icpu_dat_i : {`OR1200_OR32_NOP, 26'h061_0000};

assign if_pc = saved ? addr_saved : {icpu_adr_i[31:2], 2'h0};

assign if_stall = !icpu_err_i & !icpu_ack_i & !saved;

assign genpc_refetch = saved & icpu_ack_i;

assign except_itlbmiss = no_more_dslot ? 1'b0 : saved ? err_saved[0] : icpu_err_i & (icpu_tag_i == `OR1200_ITAG_TE);

assign except_immufault = no_more_dslot ? 1'b0 : saved ? err_saved[1] : icpu_err_i & (icpu_tag_i == `OR1200_ITAG_PE);

assign except_ibuserr = no_more_dslot ? 1'b0 : saved ? err_saved[2] : icpu_err_i & (icpu_tag_i == `OR1200_ITAG_BE);

//

// Flag for saved insn/address

//

always @(posedge clk or `OR1200_RST_EVENT rst)

        if (rst == `OR1200_RST_VALUE)

                saved <=  1'b0;

        else if (if_flushpipe)

                saved <=  1'b0;

        else if (save_insn)

                saved <=  1'b1;

        else if (!if_freeze)

                saved <=  1'b0;

//

// Store fetched instruction

//

always @(posedge clk or `OR1200_RST_EVENT rst)

        if (rst == `OR1200_RST_VALUE)

                insn_saved <=  {`OR1200_OR32_NOP, 26'h041_0000};

        else if (if_flushpipe)

                insn_saved <=  {`OR1200_OR32_NOP, 26'h041_0000};

        else if (save_insn)

                insn_saved <=  icpu_err_i ? {`OR1200_OR32_NOP, 26'h041_0000} : icpu_dat_i;

        else if (!if_freeze)

                insn_saved <=  {`OR1200_OR32_NOP, 26'h041_0000};

//

// Store fetched instruction's address

//

always @(posedge clk or `OR1200_RST_EVENT rst)

        if (rst == `OR1200_RST_VALUE)

                addr_saved <=  32'h00000000;

        else if (if_flushpipe)

                addr_saved <=  32'h00000000;

        else if (save_insn)

                addr_saved <=  {icpu_adr_i[31:2], 2'b00};

        else if (!if_freeze)

                addr_saved <=  {icpu_adr_i[31:2], 2'b00};

//

// Store fetched instruction's error tags 

//

always @(posedge clk or `OR1200_RST_EVENT rst)

        if (rst == `OR1200_RST_VALUE)

                err_saved <=  3'b000;

        else if (if_flushpipe)

                err_saved <=  3'b000;

        else if (save_insn) begin

                err_saved[0] <=  icpu_err_i & (icpu_tag_i == `OR1200_ITAG_TE);

                err_saved[1] <=  icpu_err_i & (icpu_tag_i == `OR1200_ITAG_PE);

                err_saved[2] <=  icpu_err_i & (icpu_tag_i == `OR1200_ITAG_BE);

        end

        else if (!if_freeze)

                err_saved <=  3'b000;

endmodule