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

////                                                              ////

////  OR1200's WISHBONE BIU                                       ////

////                                                              ////

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

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

////                                                              ////

////  Description                                                 ////

////  Implements WISHBONE interface                               ////

////                                                              ////

////  To Do:                                                      ////

////   - if biu_cyc/stb are deasserted and wb_ack_i is asserted   ////

////   and this happens even before aborted_r is asssrted,        ////

////   wb_ack_i will be delivered even though transfer is         ////

////   internally considered already aborted. However most        ////

////   wb_ack_i are externally registered and delayed. Normally   ////

////   this shouldn't cause any problems.                         ////

////                                                              ////

////  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                     ////

////                                                              ////

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

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

// Revision 1.3  2002/08/12 05:31:37  lampret

// Added optional retry counter for wb_rty_i. Added graceful termination for aborted transfers.

//

// Revision 1.2  2002/07/14 22:17:17  lampret

// Added simple trace buffer [only for Xilinx Virtex target]. Fixed instruction fetch abort when new exception is recognized.

//

// Revision 1.1  2002/01/03 08:16:15  lampret

// New prefixes for RTL files, prefixed module names. Updated cache controllers and MMUs.

//

// Revision 1.12  2001/11/22 13:42:51  lampret

// Added wb_cyc_o assignment after it was removed by accident.

//

// Revision 1.11  2001/11/20 21:28:10  lampret

// Added optional sampling of inputs.

//

// Revision 1.10  2001/11/18 11:32:00  lampret

// OR1200_REGISTERED_OUTPUTS can now be enabled.

//

// Revision 1.9  2001/10/21 17:57:16  lampret

// Removed params from generic_XX.v. Added translate_off/on in sprs.v and id.v. Removed spr_addr from dc.v and ic.v. Fixed CR+LF.

//

// Revision 1.8  2001/10/14 13:12:10  lampret

// MP3 version.

//

// Revision 1.1.1.1  2001/10/06 10:18:35  igorm

// no message

//

// Revision 1.3  2001/08/09 13:39:33  lampret

// Major clean-up.

//

// Revision 1.2  2001/07/22 03:31:54  lampret

// Fixed RAM's oen bug. Cache bypass under development.

//

// Revision 1.1  2001/07/20 00:46:23  lampret

// Development version of RTL. Libraries are missing.

//

//

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`include "or1200_defines.v"

module or1200_wb_biu(

        // RISC clock, reset and clock control

        clk, rst, clmode,

        // WISHBONE interface

        wb_clk_i, wb_rst_i, wb_ack_i, wb_err_i, wb_rty_i, wb_dat_i,

        wb_cyc_o, wb_adr_o, wb_stb_o, wb_we_o, wb_sel_o, wb_cab_o, wb_dat_o,

        // Internal RISC bus

        biu_dat_i, biu_adr_i, biu_cyc_i, biu_stb_i, biu_we_i, biu_sel_i, biu_cab_i,

        biu_dat_o, biu_ack_o, biu_err_o

);

parameter dw = `OR1200_OPERAND_WIDTH;

parameter aw = `OR1200_OPERAND_WIDTH;

//

// RISC clock, reset and clock control

//

input                   clk;            // RISC clock

input                   rst;            // RISC reset

input   [1:0]            clmode;         // 00 WB=RISC, 01 WB=RISC/2, 10 N/A, 11 WB=RISC/4

//

// WISHBONE interface

//

input                   wb_clk_i;       // clock input

input                   wb_rst_i;       // reset input

input                   wb_ack_i;       // normal termination

input                   wb_err_i;       // termination w/ error

input                   wb_rty_i;       // termination w/ retry

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

output                  wb_cyc_o;       // cycle valid output

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

output                  wb_stb_o;       // strobe output

output                  wb_we_o;        // indicates write transfer

output  [3:0]            wb_sel_o;       // byte select outputs

output                  wb_cab_o;       // consecutive address burst

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

//

// Internal RISC interface

//

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

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

input                   biu_cyc_i;      // WB cycle

input                   biu_stb_i;      // WB strobe

input                   biu_we_i;       // WB write enable

input                   biu_cab_i;      // CAB input

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

output  [31:0]           biu_dat_o;      // output data bus

output                  biu_ack_o;      // ack output

output                  biu_err_o;      // err output

//

// Registers

//

reg     [1:0]            valid_div;      // Used for synchronization

`ifdef OR1200_REGISTERED_OUTPUTS

reg     [aw-1:0] wb_adr_o;       // address bus outputs

reg                     wb_cyc_o;       // cycle output

reg                     wb_stb_o;       // strobe output

reg                     wb_we_o;        // indicates write transfer

reg     [3:0]            wb_sel_o;       // byte select outputs

reg                     wb_cab_o;       // CAB output

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

`endif

`ifdef OR1200_REGISTERED_INPUTS

reg                     long_ack_o;     // normal termination

reg                     long_err_o;     // error termination

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

`else

wire                    long_ack_o;     // normal termination

wire                    long_err_o;     // error termination

`endif

wire                    aborted;        // Graceful abort

reg                     aborted_r;      // Graceful abort

wire                    retry;          // Retry

`ifdef OR1200_WB_RETRY

reg     [`OR1200_WB_RETRY-1:0] retry_cntr;       // Retry counter

`endif

//

// WISHBONE I/F <-> Internal RISC I/F conversion

//

//

// Address bus

//

`ifdef OR1200_REGISTERED_OUTPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                wb_adr_o <= #1 {aw{1'b0}};

        else if ((biu_cyc_i & biu_stb_i) & ~wb_ack_i & ~aborted & ~(wb_stb_o & ~wb_ack_i))

                wb_adr_o <= #1 biu_adr_i;

`else

assign wb_adr_o = biu_adr_i;

`endif

//

// Input data bus

//

`ifdef OR1200_REGISTERED_INPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                biu_dat_o <= #1 32'h0000_0000;

        else if (wb_ack_i)

                biu_dat_o <= #1 wb_dat_i;

`else

assign biu_dat_o = wb_dat_i;

`endif

//

// Output data bus

//

`ifdef OR1200_REGISTERED_OUTPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                wb_dat_o <= #1 {dw{1'b0}};

        else if ((biu_cyc_i & biu_stb_i) & ~wb_ack_i & ~aborted)

                wb_dat_o <= #1 biu_dat_i;

`else

assign wb_dat_o = biu_dat_i;

`endif

//

// Valid_div counts RISC clock cycles by modulo 4

// and is used to synchronize external WB i/f to

// RISC clock

//

always @(posedge clk or posedge rst)

        if (rst)

                valid_div <= #1 2'b0;

        else

                valid_div <= #1 valid_div + 'd1;

//

// biu_ack_o is one RISC clock cycle long long_ack_o.

// long_ack_o is one, two or four RISC clock cycles long because

// WISHBONE can work at 1, 1/2 or 1/4 RISC clock.

//

assign biu_ack_o = long_ack_o

`ifdef OR1200_CLKDIV_4_SUPPORTED

                & (valid_div[1] | ~clmode[1])

`ifdef OR1200_CLKDIV_2_SUPPORTED

                & (valid_div[0] | ~clmode[0])

`endif

`endif

                ;

//

// Acknowledgment of the data to the RISC

//

// long_ack_o

//

`ifdef OR1200_REGISTERED_INPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                long_ack_o <= #1 1'b0;

        else

                long_ack_o <= #1 wb_ack_i & ~aborted;

`else

assign long_ack_o = wb_ack_i & ~aborted_r;

`endif

//

// biu_err_o is one RISC clock cycle long long_err_o.

// long_err_o is one, two or four RISC clock cycles long because

// WISHBONE can work at 1, 1/2 or 1/4 RISC clock.

//

assign biu_err_o = long_err_o

`ifdef OR1200_CLKDIV_4_SUPPORTED

                & (valid_div[1] | ~clmode[1])

`ifdef OR1200_CLKDIV_2_SUPPORTED

                & (valid_div[0] | ~clmode[0])

`endif

`endif

                ;

//

// Error termination

//

// long_err_o

//

`ifdef OR1200_REGISTERED_INPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                long_err_o <= #1 1'b0;

        else

                long_err_o <= #1 wb_err_i & ~aborted;

`else

assign long_err_o = wb_err_i & ~aborted_r;

`endif

//

// Retry counter

//

// Assert 'retry' when 'wb_rty_i' is sampled high and keep it high

// until retry counter doesn't expire

// 

`ifdef OR1200_WB_RETRY

assign retry = wb_rty_i | (|retry_cntr);

`else

assign retry = 1'b0;

`endif

`ifdef OR1200_WB_RETRY

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                retry_cntr <= #1 1'b0;

        else if (wb_rty_i)

                retry_cntr <= #1 {`OR1200_WB_RETRY{1'b1}};

        else if (retry_cntr)

                retry_cntr <= #1 retry_cntr - 7'd1;

`endif

//

// Graceful completion of aborted transfers

//

// Assert 'aborted' when 1) current transfer is in progress (wb_stb_o; which

// we know is only asserted together with wb_cyc_o) 2) and in next WB clock cycle

// wb_stb_o would be deasserted (biu_cyc_i and biu_stb_i are low) 3) and

// there is no termination of current transfer in this WB clock cycle (wb_ack_i

// and wb_err_i are low).

// 'aborted_r' is registered 'aborted' and extended until this "aborted" transfer

// is properly terminated with wb_ack_i/wb_err_i.

// 

assign aborted = wb_stb_o & ~(biu_cyc_i & biu_stb_i) & ~(wb_ack_i | wb_err_i);

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                aborted_r <= #1 1'b0;

        else if (wb_ack_i | wb_err_i)

                aborted_r <= #1 1'b0;

        else if (aborted)

                aborted_r <= #1 1'b1;

//

// WB cyc_o

//

// Either 1) normal transfer initiated by biu_cyc_i (and biu_cab_i if

// bursts are enabled) and possibly suspended by 'retry'

// or 2) extended "aborted" transfer

//

`ifdef OR1200_REGISTERED_OUTPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                wb_cyc_o <= #1 1'b0;

        else

`ifdef OR1200_NO_BURSTS

                wb_cyc_o <= #1 biu_cyc_i & ~wb_ack_i & ~retry | aborted & ~wb_ack_i;

`else

                wb_cyc_o <= #1 biu_cyc_i & ~wb_ack_i & ~retry | biu_cab_i | aborted & ~wb_ack_i;

`endif

`else

`ifdef OR1200_NO_BURSTS

assign wb_cyc_o = biu_cyc_i & ~retry;

`else

assign wb_cyc_o = biu_cyc_i | biu_cab_i & ~retry;

`endif

`endif

//

// WB stb_o

//

`ifdef OR1200_REGISTERED_OUTPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                wb_stb_o <= #1 1'b0;

        else

                wb_stb_o <= #1 (biu_cyc_i & biu_stb_i) & ~wb_ack_i & ~retry | aborted & ~wb_ack_i;

`else

assign wb_stb_o = biu_cyc_i & biu_stb_i;

`endif

//

// WB we_o

//

`ifdef OR1200_REGISTERED_OUTPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                wb_we_o <= #1 1'b0;

        else

                wb_we_o <= #1 biu_cyc_i & biu_stb_i & biu_we_i | aborted & wb_we_o;

`else

assign wb_we_o = biu_cyc_i & biu_stb_i & biu_we_i;

`endif

//

// WB sel_o

//

`ifdef OR1200_REGISTERED_OUTPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                wb_sel_o <= #1 4'b0000;

        else

                wb_sel_o <= #1 biu_sel_i;

`else

assign wb_sel_o = biu_sel_i;

`endif

//

// WB cab_o

//

`ifdef OR1200_REGISTERED_OUTPUTS

always @(posedge wb_clk_i or posedge wb_rst_i)

        if (wb_rst_i)

                wb_cab_o <= #1 1'b0;

        else

                wb_cab_o <= #1 biu_cab_i;

`else

assign wb_cab_o = biu_cab_i;

`endif

endmodule