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

////                                                              ////

////  OR1200's Store Buffer                                       ////

////                                                              ////

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

////  http://www.opencores.org/cores/or1k/                        ////

////                                                              ////

////  Description                                                 ////

////  Implements store buffer.                                    ////

////                                                              ////

////  To Do:                                                      ////

////   - byte combining                                           ////

////                                                              ////

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

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

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2002 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                     ////

////                                                              ////

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

//

// CVS Revision History

//

// $Log: or1200_sb.v,v $

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

// Minor update: 

// Bugs fixed. 

//

// Revision 1.2  2002/08/22 02:18:55  lampret

// Store buffer has been tested and it works. BY default it is still disabled until uClinux confirms correct operation on FPGA board.

//

// Revision 1.1  2002/08/18 19:53:08  lampret

// Added store buffer.

//

//

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`include "or1200_defines.v"

module or1200_sb(

        // RISC clock, reset

        clk, rst,

        // Internal RISC bus (SB)

        sb_en,

        // Internal RISC bus (DC<->SB)

        dcsb_dat_i, dcsb_adr_i, dcsb_cyc_i, dcsb_stb_i, dcsb_we_i, dcsb_sel_i, dcsb_cab_i,

        dcsb_dat_o, dcsb_ack_o, dcsb_err_o,

        // BIU bus

        sbbiu_dat_o, sbbiu_adr_o, sbbiu_cyc_o, sbbiu_stb_o, sbbiu_we_o, sbbiu_sel_o, sbbiu_cab_o,

        sbbiu_dat_i, sbbiu_ack_i, sbbiu_err_i

);

parameter dw = `OR1200_OPERAND_WIDTH;

parameter aw = `OR1200_OPERAND_WIDTH;

//

// RISC clock, reset

//

input                   clk;            // RISC clock

input                   rst;            // RISC reset

//

// Internal RISC bus (SB)

//

input                   sb_en;          // SB enable

//

// Internal RISC bus (DC<->SB)

//

input   [dw-1:0] dcsb_dat_i;     // input data bus

input   [aw-1:0] dcsb_adr_i;     // address bus

input                   dcsb_cyc_i;     // WB cycle

input                   dcsb_stb_i;     // WB strobe

input                   dcsb_we_i;      // WB write enable

input                   dcsb_cab_i;     // CAB input

input   [3:0]            dcsb_sel_i;     // byte selects

output  [dw-1:0] dcsb_dat_o;     // output data bus

output                  dcsb_ack_o;     // ack output

output                  dcsb_err_o;     // err output

//

// BIU bus

//

output  [dw-1:0] sbbiu_dat_o;    // output data bus

output  [aw-1:0] sbbiu_adr_o;    // address bus

output                  sbbiu_cyc_o;    // WB cycle

output                  sbbiu_stb_o;    // WB strobe

output                  sbbiu_we_o;     // WB write enable

output                  sbbiu_cab_o;    // CAB input

output  [3:0]            sbbiu_sel_o;    // byte selects

input   [dw-1:0] sbbiu_dat_i;    // input data bus

input                   sbbiu_ack_i;    // ack output

input                   sbbiu_err_i;    // err output

`ifdef OR1200_SB_IMPLEMENTED

//

// Internal wires and regs

//

wire    [4+dw+aw-1:0]    fifo_dat_i;     // FIFO data in

wire    [4+dw+aw-1:0]    fifo_dat_o;     // FIFO data out

wire                    fifo_wr;

wire                    fifo_rd;

wire                    fifo_full;

wire                    fifo_empty;

wire                    sel_sb;

reg                     sb_en_reg;

reg                     outstanding_store;

reg                     fifo_wr_ack;

//

// FIFO data in/out

//

assign fifo_dat_i = {dcsb_sel_i, dcsb_dat_i, dcsb_adr_i};

assign {sbbiu_sel_o, sbbiu_dat_o, sbbiu_adr_o} = sel_sb ? fifo_dat_o : {dcsb_sel_i, dcsb_dat_i, dcsb_adr_i};

//

// Control

//

assign fifo_wr = dcsb_cyc_i & dcsb_stb_i & dcsb_we_i & ~fifo_full & ~fifo_wr_ack;

assign fifo_rd = ~outstanding_store;

assign dcsb_dat_o = sbbiu_dat_i;

assign dcsb_ack_o = sel_sb ? fifo_wr_ack : sbbiu_ack_i;

assign dcsb_err_o = sel_sb ? 1'b0 : sbbiu_err_i;        // SB never returns error

assign sbbiu_cyc_o = sel_sb ? outstanding_store : dcsb_cyc_i;

assign sbbiu_stb_o = sel_sb ? outstanding_store : dcsb_stb_i;

assign sbbiu_we_o = sel_sb ? 1'b1 : dcsb_we_i;

assign sbbiu_cab_o = sel_sb ? 1'b0 : dcsb_cab_i;

assign sel_sb = sb_en_reg & (~fifo_empty | (fifo_empty & outstanding_store));

//

// SB enable

//

always @(posedge clk or posedge rst)

        if (rst)

                sb_en_reg <= 1'b0;

        else if (sb_en & ~dcsb_cyc_i)

                sb_en_reg <= #1 1'b1; // enable SB when there is no dcsb transfer in progress

        else if (~sb_en & (~fifo_empty | (fifo_empty & outstanding_store)))

                sb_en_reg <= #1 1'b0; // disable SB when there is no pending transfers from SB

//

// Store buffer FIFO instantiation

//

or1200_sb_fifo or1200_sb_fifo (

        .clk_i(clk),

        .rst_i(rst),

        .dat_i(fifo_dat_i),

        .wr_i(fifo_wr),

        .rd_i(fifo_rd),

        .dat_o(fifo_dat_o),

        .full_o(fifo_full),

        .empty_o(fifo_empty)

);

//

// fifo_rd

//

always @(posedge clk or posedge rst)

        if (rst)

                outstanding_store <= #1 1'b0;

        else if (sbbiu_ack_i)

                outstanding_store <= #1 1'b0;

        else if (sel_sb | fifo_wr)

                outstanding_store <= #1 1'b1;

//

// fifo_wr_ack

//

always @(posedge clk or posedge rst)

        if (rst)

                fifo_wr_ack <= #1 1'b0;

        else if (fifo_wr)

                fifo_wr_ack <= #1 1'b1;

        else

                fifo_wr_ack <= #1 1'b0;

`else   // !OR1200_SB_IMPLEMENTED

assign sbbiu_dat_o = dcsb_dat_i;

assign sbbiu_adr_o = dcsb_adr_i;

assign sbbiu_cyc_o = dcsb_cyc_i;

assign sbbiu_stb_o = dcsb_stb_i;

assign sbbiu_we_o = dcsb_we_i;

assign sbbiu_cab_o = dcsb_cab_i;

assign sbbiu_sel_o = dcsb_sel_i;

assign dcsb_dat_o = sbbiu_dat_i;

assign dcsb_ack_o = sbbiu_ack_i;

assign dcsb_err_o = sbbiu_err_i;

`endif

endmodule