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/*********************************************************************

  This file is part of the sdram controller project

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

  Description: WISHBONE to SDRAM Controller Bus Transalator

     1. This module translate the WISHBONE protocol to custom sdram controller i/f

     2. Also Handle the clock domain change from Application layer to Sdram layer

  To Do:

    nothing

  Author(s):  Dinesh Annayya, dinesha@opencores.org

  Version  : 0.0 - Initial Release

             0.1 - 2nd Feb 2012

                   Async Fifo towards the application layer is selected

                   with Registered Full Generation

             0.2 - 2nd Feb 2012

                   Pending Read generation bug fix done to handle backto back write

                   followed by read request

 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

*******************************************************************/

module wb2sdrc (

      // WB bus

                    wb_rst_i            ,

                    wb_clk_i            ,

                    wb_stb_i            ,

                    wb_ack_o            ,

                    wb_addr_i           ,

                    wb_we_i             ,

                    wb_dat_i            ,

                    wb_sel_i            ,

                    wb_dat_o            ,

                    wb_cyc_i            ,

                    wb_cti_i            ,

      //SDRAM Controller Hand-Shake Signal 

                    sdram_clk           ,

                    sdram_resetn        ,

                    sdr_req             ,

                    sdr_req_addr        ,

                    sdr_req_len         ,

                    sdr_req_wr_n        ,

                    sdr_req_ack         ,

                    sdr_busy_n          ,

                    sdr_wr_en_n         ,

                    sdr_wr_next         ,

                    sdr_rd_valid        ,

                    sdr_last_rd         ,

                    sdr_wr_data         ,

                    sdr_rd_data

      );

parameter      dw              = 32;  // data width

parameter      tw              = 8;   // tag id width

parameter      bl              = 9;   // burst_lenght_width 

parameter      APP_AW          = 26;  // Application Address Width

//--------------------------------------

// Wish Bone Interface

// -------------------------------------      

input                   wb_rst_i           ;

input                   wb_clk_i           ;

input                   wb_stb_i           ;

output                  wb_ack_o           ;

input [APP_AW-1:0]      wb_addr_i          ;

input                   wb_we_i            ; // 1 - Write , 0 - Read

input [dw-1:0]          wb_dat_i           ;

input [dw/8-1:0]        wb_sel_i           ; // Byte enable

output [dw-1:0]         wb_dat_o           ;

input                   wb_cyc_i           ;

input  [2:0]            wb_cti_i           ;

/***************************************************

The Cycle Type Idenfier [CTI_IO()] Address Tag provides

additional information about the current cycle.

The MASTER sends this information to the SLAVE. The SLAVE can use this

information to prepare the response for the next cycle.

Table 4-2 Cycle Type Identifiers

CTI_O(2:0) Description

‘000’ Classic cycle.

‘001’ Constant address burst cycle

‘010’ Incrementing burst cycle

‘011’ Reserved

‘100’ Reserved

‘101 Reserved

‘110’ Reserved

‘111’ End-of-Burst

****************************************************/

//--------------------------------------------

// SDRAM controller Interface 

//--------------------------------------------

input                   sdram_clk          ; // sdram clock

input                   sdram_resetn       ; // sdram reset

output                  sdr_req            ; // SDRAM request

output [APP_AW-1:0]           sdr_req_addr       ; // SDRAM Request Address

output [bl-1:0]         sdr_req_len        ;

output                  sdr_req_wr_n       ; // 0 - Write, 1 -> Read

input                   sdr_req_ack        ; // SDRAM request Accepted

input                   sdr_busy_n         ; // 0 -> sdr busy

output [dw/8-1:0]       sdr_wr_en_n        ; // Active low sdr byte-wise write data valid

input                   sdr_wr_next        ; // Ready to accept the next write

input                   sdr_rd_valid       ; // sdr read valid

input                   sdr_last_rd        ; // Indicate last Read of Burst Transfer

output [dw-1:0]         sdr_wr_data        ; // sdr write data

input  [dw-1:0]         sdr_rd_data        ; // sdr read data

//----------------------------------------------------

// Wire Decleration

// ---------------------------------------------------

wire                    cmdfifo_full       ;

wire                    cmdfifo_empty      ;

wire                    wrdatafifo_full    ;

wire                    wrdatafifo_empty   ;

wire                    tagfifo_full       ;

wire                    tagfifo_empty      ;

wire                    rddatafifo_empty   ;

wire                    rddatafifo_full    ;

reg                     pending_read       ;

//-----------------------------------------------------------------------------

// Ack Generaltion Logic

//  If Write Request - Acknowledge if the command and write FIFO are not full

//  If Read Request  - Generate the Acknowledgment once read fifo has data

//                     available

//-----------------------------------------------------------------------------

assign wb_ack_o = (wb_stb_i && wb_cyc_i && wb_we_i) ?  // Write Phase

                          ((!cmdfifo_full) && (!wrdatafifo_full)) :

                  (wb_stb_i && wb_cyc_i && !wb_we_i) ? // Read Phase 

                           !rddatafifo_empty : 1'b0;

//---------------------------------------------------------------------------

// Command FIFO Write Generation

//    If Write Request - Generate write, when Write fifo and command fifo is

//                       not full

//    If Read Request - Generate write, when command fifo not full and there

//                      is no pending read request.

//---------------------------------------------------------------------------

wire           cmdfifo_wr   = (wb_stb_i && wb_cyc_i && wb_we_i && (!cmdfifo_full) ) ? wb_ack_o :

                              (wb_stb_i && wb_cyc_i && !wb_we_i && (!cmdfifo_full)) ? !pending_read: 1'b0 ;

//---------------------------------------------------------------------------

// command fifo read generation

//    Command FIFo read will be generated, whenever SDRAM Controller

//    Acknowldge the Request

//----------------------------------------------------------------------------

wire           cmdfifo_rd   = sdr_req_ack;

//---------------------------------------------------------------------------

// Application layer request is generated towards the controller, whenever

// Command FIFO is not full

// --------------------------------------------------------------------------

assign         sdr_req      = !cmdfifo_empty;

//----------------------------------------------------------------------------

// Since Burst length is not known at the start of the Burst, It's assumed as

// Single Cycle Burst. We need to improvise this ...

// --------------------------------------------------------------------------

wire [bl-1:0]  burst_length  = 1;  // 0 Mean 1 Transfer

//-----------------------------------------------------------------------------

// In Wish Bone Spec, For Read Request has to be acked along with data.

// We need to identify the pending read request.

// Once we accept the read request, we should not accept one more read

// request, untill we have transmitted the read data.

//  Pending Read will 

//     set - with Read Request 

//     reset - with Read Request + Ack

// ----------------------------------------------------------------------------

always @(posedge wb_rst_i or posedge wb_clk_i) begin

   if(wb_rst_i) begin

       pending_read <= 1'b0;

   end else begin

      //pending_read <=  wb_stb_i & wb_cyc_i & !wb_we_i & !wb_ack_o;

      pending_read <=   (cmdfifo_wr && !wb_we_i) ? 1'b1:

                        (wb_stb_i & wb_cyc_i & !wb_we_i & wb_ack_o) ? 1'b0: pending_read;

   end

end

//---------------------------------------------------------------------

// Async Command FIFO. This block handle the clock domain change from

// Application layer to SDRAM Controller

// ------------------------------------------------------------------

   // Address + Burst Length + W/R Request 

    async_fifo #(.W(APP_AW+bl+1),.DP(4),.WR_FAST(1'b0), .RD_FAST(1'b0)) u_cmdfifo (

     // Write Path Sys CLock Domain

          .wr_clk             (wb_clk_i           ),

          .wr_reset_n         (!wb_rst_i          ),

          .wr_en              (cmdfifo_wr         ),

          .wr_data            ({burst_length,

                                !wb_we_i,

                                wb_addr_i}        ),

          .afull              (                   ),

          .full               (cmdfifo_full       ),

     // Read Path, SDRAM clock domain

          .rd_clk             (sdram_clk          ),

          .rd_reset_n         (sdram_resetn       ),

          .aempty             (                   ),

          .empty              (cmdfifo_empty      ),

          .rd_en              (cmdfifo_rd         ),

          .rd_data            ({sdr_req_len,

                                sdr_req_wr_n,

                                sdr_req_addr}     )

     );

// synopsys translate_off

always @(posedge wb_clk_i) begin

  if (cmdfifo_full == 1'b1 && cmdfifo_wr == 1'b1)  begin

     $display("ERROR:%m COMMAND FIFO WRITE OVERFLOW");

  end

end

// synopsys translate_on

// synopsys translate_off

always @(posedge sdram_clk) begin

   if (cmdfifo_empty == 1'b1 && cmdfifo_rd == 1'b1) begin

      $display("ERROR:%m COMMAND FIFO READ OVERFLOW");

   end

end

// synopsys translate_on

//---------------------------------------------------------------------

// Write Data FIFO Write Generation, when ever Acked + Write Request

//   Note: Ack signal generation already taking account of FIFO full condition

// ---------------------------------------------------------------------

wire  wrdatafifo_wr  = wb_ack_o & wb_we_i ;

//------------------------------------------------------------------------

// Write Data FIFO Read Generation, When ever Next Write request generated

// from SDRAM Controller

// ------------------------------------------------------------------------

wire  wrdatafifo_rd  = sdr_wr_next;

//------------------------------------------------------------------------

// Async Write Data FIFO

//    This block handle the clock domain change over + Write Data + Byte mask 

//    From Application layer to SDRAM controller layer

//------------------------------------------------------------------------

   // Write DATA + Data Mask FIFO

    async_fifo #(.W(dw+(dw/8)), .DP(8), .WR_FAST(1'b0), .RD_FAST(1'b1)) u_wrdatafifo (

       // Write Path , System clock domain

          .wr_clk             (wb_clk_i           ),

          .wr_reset_n         (!wb_rst_i          ),

          .wr_en              (wrdatafifo_wr      ),

          .wr_data            ({~wb_sel_i,

                                 wb_dat_i}        ),

          .afull              (                   ),

          .full               (wrdatafifo_full    ),

       // Read Path , SDRAM clock domain

          .rd_clk             (sdram_clk          ),

          .rd_reset_n         (sdram_resetn       ),

          .aempty             (                   ),

          .empty              (wrdatafifo_empty   ),

          .rd_en              (wrdatafifo_rd      ),

          .rd_data            ({sdr_wr_en_n,

                                sdr_wr_data}      )

     );

// synopsys translate_off

always @(posedge wb_clk_i) begin

  if (wrdatafifo_full == 1'b1 && wrdatafifo_wr == 1'b1)  begin

     $display("ERROR:%m WRITE DATA FIFO WRITE OVERFLOW");

  end

end

always @(posedge sdram_clk) begin

   if (wrdatafifo_empty == 1'b1 && wrdatafifo_rd == 1'b1) begin

      $display("ERROR:%m WRITE DATA FIFO READ OVERFLOW");

   end

end

// synopsys translate_on

// -------------------------------------------------------------------

//  READ DATA FIFO

//  ------------------------------------------------------------------

wire    rd_eop; // last read indication

// Read FIFO write generation, when ever SDRAM controller issues the read

// valid signal

wire    rddatafifo_wr = sdr_rd_valid;

// Read FIFO read generation, when ever ack is generated along with read

// request.

// Note: Ack generation is already accounted the write FIFO Not Empty

//       condition

wire    rddatafifo_rd = wb_ack_o & !wb_we_i;

//-------------------------------------------------------------------------

// Async Read FIFO

// This block handles the clock domain change over + Read data from SDRAM

// controller to Application layer.

//  Note: 

//    1. READ DATA FIFO depth is kept small, assuming that Sys-CLock > SDRAM Clock

//       READ DATA + EOP

//    2. EOP indicate, last transfer of Burst Read Access. use-full for future

//       Tag handling per burst

//

// ------------------------------------------------------------------------

    async_fifo #(.W(dw+1), .DP(4), .WR_FAST(1'b0), .RD_FAST(1'b1) ) u_rddatafifo (

       // Write Path , SDRAM clock domain

          .wr_clk             (sdram_clk          ),

          .wr_reset_n         (sdram_resetn       ),

          .wr_en              (rddatafifo_wr      ),

          .wr_data            ({sdr_last_rd,

                                sdr_rd_data}      ),

          .afull              (                   ),

          .full               (rddatafifo_full    ),

       // Read Path , SYS clock domain

          .rd_clk             (wb_clk_i           ),

          .rd_reset_n         (!wb_rst_i          ),

          .empty              (rddatafifo_empty   ),

          .aempty             (                   ),

          .rd_en              (rddatafifo_rd      ),

          .rd_data            ({rd_eop,

                                wb_dat_o}         )

     );

// synopsys translate_off

always @(posedge sdram_clk) begin

  if (rddatafifo_full == 1'b1 && rddatafifo_wr == 1'b1)  begin

     $display("ERROR:%m READ DATA FIFO WRITE OVERFLOW");

  end

end

always @(posedge wb_clk_i) begin

   if (rddatafifo_empty == 1'b1 && rddatafifo_rd == 1'b1) begin

      $display("ERROR:%m READ DATA FIFO READ OVERFLOW");

   end

end

// synopsys translate_on

endmodule