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

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////  adbg_or1k_biu.v                                             ////

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////                                                              ////

////  This file is part of the SoC Advanced Debug Interface.      ////

////                                                              ////

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

////       Nathan Yawn (nathan.yawn@opencores.org)                ////

////                                                              ////

////                                                              ////

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

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//// Copyright (C) 2008        Authors                            ////

////                                                              ////

//// 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: adbg_or1k_biu.v,v $

// Revision 1.2  2009/05/17 20:54:56  Nathan

// Changed email address to opencores.org

//

// Revision 1.1  2008/07/22 20:28:30  Nathan

// Changed names of all files and modules (prefixed an a, for advanced).  Cleanup, indenting.  No functional changes.

//

// Revision 1.5  2008/07/08 19:04:03  Nathan

// Many small changes to eliminate compiler warnings, no functional 

// changes.  System will now pass SRAM and CPU self-tests on Altera 

// FPGA using altera_virtual_jtag TAP.

//

module adbg_or1k_biu

  (

   // Debug interface signals

   tck_i,

   rst_i,

   data_i,

   data_o,

   addr_i,

   strobe_i,

   rd_wrn_i,           // If 0, then write op

   rdy_o,

   // OR1K SPR bus signals

   cpu_clk_i,

   cpu_addr_o,

   cpu_data_i,

   cpu_data_o,

   cpu_stb_o,

   cpu_we_o,

   cpu_ack_i

   );

   // Debug interface signals

   input tck_i;

   input rst_i;

   input [31:0] data_i;  // Assume short words are in UPPER order bits!

   output [31:0] data_o;

   input [31:0]  addr_i;

   input         strobe_i;

   input         rd_wrn_i;

   output        rdy_o;

   // OR1K SPR bus signals

   input         cpu_clk_i;

   output [31:0] cpu_addr_o;

   input [31:0]  cpu_data_i;

   output [31:0] cpu_data_o;

   output        cpu_stb_o;

   output        cpu_we_o;

   input         cpu_ack_i;

   reg           rdy_o;

   reg           cpu_stb_o;

   // Registers

   reg [31:0]     addr_reg;

   reg [31:0]     data_in_reg;  // dbg->WB

   reg [31:0]     data_out_reg;  // WB->dbg

   reg           wr_reg;

   reg           str_sync;  // This is 'active-toggle' rather than -high or -low.

   reg           rdy_sync;  // ditto, active-toggle

   // Sync registers.  TFF indicates TCK domain, WBFF indicates cpu_clk domain

   reg           rdy_sync_tff1;

   reg           rdy_sync_tff2;

   reg           rdy_sync_tff2q;  // used to detect toggles

   reg           str_sync_wbff1;

   reg           str_sync_wbff2;

   reg           str_sync_wbff2q;  // used to detect toggles

   // Control Signals

   reg           data_o_en;    // latch wb_data_i

   reg           rdy_sync_en;  // toggle the rdy_sync signal, indicate ready to TCK domain

   // Internal signals

   wire          start_toggle;  // CPU domain, indicates a toggle on the start strobe

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

   // TCK clock domain

   // There is no FSM here, just signal latching and clock

   // domain synchronization

   // Latch input data on 'start' strobe, if ready.

   always @ (posedge tck_i or posedge rst_i)

     begin

        if(rst_i) begin

           addr_reg <= 32'h0;

           data_in_reg <= 32'h0;

           wr_reg <= 1'b0;

        end

        else

          if(strobe_i && rdy_o) begin

             addr_reg <= addr_i;

             if(!rd_wrn_i) data_in_reg <= data_i;

             wr_reg <= ~rd_wrn_i;

          end

     end

   // Create toggle-active strobe signal for clock sync.  This will start a transaction

   // to the CPU once the toggle propagates to the FSM in the cpu_clk domain.

   always @ (posedge tck_i or posedge rst_i)

     begin

        if(rst_i) str_sync <= 1'b0;

        else if(strobe_i && rdy_o) str_sync <= ~str_sync;

     end

   // Create rdy_o output.  Set on reset, clear on strobe (if set), set on input toggle

   always @ (posedge tck_i or posedge rst_i)

     begin

        if(rst_i) begin

           rdy_sync_tff1 <= 1'b0;

           rdy_sync_tff2 <= 1'b0;

           rdy_sync_tff2q <= 1'b0;

           rdy_o <= 1'b1;

        end

        else begin

           rdy_sync_tff1 <= rdy_sync;       // Synchronize the ready signal across clock domains

           rdy_sync_tff2 <= rdy_sync_tff1;

           rdy_sync_tff2q <= rdy_sync_tff2;  // used to detect toggles

           if(strobe_i && rdy_o) rdy_o <= 1'b0;

           else if(rdy_sync_tff2 != rdy_sync_tff2q) rdy_o <= 1'b1;

        end

     end

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

   // Direct assignments, unsynchronized

   assign cpu_data_o = data_in_reg;

   assign cpu_we_o = wr_reg;

   assign cpu_addr_o = addr_reg;

   assign data_o = data_out_reg;

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

   // Wishbone clock domain

  // synchronize the start strobe

  always @ (posedge cpu_clk_i or posedge rst_i)

          begin

             if(rst_i) begin

                str_sync_wbff1 <= 1'b0;

                str_sync_wbff2 <= 1'b0;

                str_sync_wbff2q <= 1'b0;

             end

             else begin

                str_sync_wbff1 <= str_sync;

                str_sync_wbff2 <= str_sync_wbff1;

                str_sync_wbff2q <= str_sync_wbff2;  // used to detect toggles

             end

          end

   assign start_toggle = (str_sync_wbff2 != str_sync_wbff2q);

   // CPU->dbg data register

   always @ (posedge cpu_clk_i or posedge rst_i)

     begin

        if(rst_i) data_out_reg <= 32'h0;

        else if(data_o_en) data_out_reg <= cpu_data_i;

     end

   // Create a toggle-active ready signal to send to the TCK domain

   always @ (posedge cpu_clk_i or posedge rst_i)

     begin

        if(rst_i) rdy_sync <= 1'b0;

        else if(rdy_sync_en) rdy_sync <= ~rdy_sync;

     end

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

   // Small state machine to create OR1K SPR bus accesses

   // Not much more that an 'in_progress' bit, but easier

   // to read.  Deals with single-cycle and multi-cycle

   // accesses.

   reg cpu_fsm_state;

   reg next_fsm_state;

`define STATE_IDLE     1'h0

`define STATE_TRANSFER 1'h1

   // Sequential bit

   always @ (posedge cpu_clk_i or posedge rst_i)

     begin

        if(rst_i) cpu_fsm_state <= `STATE_IDLE;

        else cpu_fsm_state <= next_fsm_state;

     end

   // Determination of next state (combinatorial)

   always @ (cpu_fsm_state or start_toggle or cpu_ack_i)

     begin

        case (cpu_fsm_state)

          `STATE_IDLE:

            begin

               if(start_toggle && !cpu_ack_i) next_fsm_state <= `STATE_TRANSFER;  // Don't go to next state for 1-cycle transfer

               else next_fsm_state <= `STATE_IDLE;

            end

          `STATE_TRANSFER:

            begin

               if(cpu_ack_i) next_fsm_state <= `STATE_IDLE;

               else next_fsm_state <= `STATE_TRANSFER;

            end

        endcase

     end

   // Outputs of state machine (combinatorial)

   always @ (cpu_fsm_state or start_toggle or cpu_ack_i or wr_reg)

     begin

        rdy_sync_en <= 1'b0;

        data_o_en <= 1'b0;

        cpu_stb_o <= 1'b0;

        case (cpu_fsm_state)

          `STATE_IDLE:

            begin

               if(start_toggle) begin

                  cpu_stb_o <= 1'b1;

                  if(cpu_ack_i) begin

                     rdy_sync_en <= 1'b1;

                  end

                  if (cpu_ack_i && !wr_reg) begin  // latch read data

                     data_o_en <= 1'b1;

                  end

               end

            end

          `STATE_TRANSFER:

            begin

               cpu_stb_o <= 1'b1;  // OR1K behavioral model needs this.  OR1200 should be indifferent.

               if(cpu_ack_i) begin

                  data_o_en <= 1'b1;

                  rdy_sync_en <= 1'b1;

               end

            end

        endcase

     end

endmodule