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

// Copyright (C) 2001 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, write to the Free Software Foundation,

// Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

//

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

//

// *File Name: omsp_mem_backbone.v

// 

// *Module Description:

//                       Memory interface backbone (decoder + arbiter)

//

// *Author(s):

//              - Olivier Girard,    olgirard@gmail.com

//

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

// $Rev: 34 $

// $LastChangedBy: olivier.girard $

// $LastChangedDate: 2009-12-29 20:10:34 +0100 (Tue, 29 Dec 2009) $

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

`include "timescale.v"

`include "openMSP430_defines.v"

module  omsp_mem_backbone (

// OUTPUTs

    dbg_mem_din,                    // Debug unit Memory data input

    dmem_addr,                      // Data Memory address

    dmem_cen,                       // Data Memory chip enable (low active)

    dmem_din,                       // Data Memory data input

    dmem_wen,                       // Data Memory write enable (low active)

    eu_mdb_in,                      // Execution Unit Memory data bus input

    fe_mdb_in,                      // Frontend Memory data bus input

    fe_pmem_wait,                   // Frontend wait for Instruction fetch

    per_addr,                       // Peripheral address

    per_din,                        // Peripheral data input

    per_wen,                        // Peripheral write enable (high active)

    per_en,                         // Peripheral enable (high active)

    pmem_addr,                      // Program Memory address

    pmem_cen,                       // Program Memory chip enable (low active)

    pmem_din,                       // Program Memory data input (optional)

    pmem_wen,                       // Program Memory write enable (low active) (optional)

// INPUTs

    dbg_halt_st,                    // Halt/Run status from CPU

    dbg_mem_addr,                   // Debug address for rd/wr access

    dbg_mem_dout,                   // Debug unit data output

    dbg_mem_en,                     // Debug unit memory enable

    dbg_mem_wr,                     // Debug unit memory write

    dmem_dout,                      // Data Memory data output

    eu_mab,                         // Execution Unit Memory address bus

    eu_mb_en,                       // Execution Unit Memory bus enable

    eu_mb_wr,                       // Execution Unit Memory bus write transfer

    eu_mdb_out,                     // Execution Unit Memory data bus output

    fe_mab,                         // Frontend Memory address bus

    fe_mb_en,                       // Frontend Memory bus enable

    mclk,                           // Main system clock

    per_dout,                       // Peripheral data output

    pmem_dout,                      // Program Memory data output

    puc                             // Main system reset

);

// OUTPUTs

//=========

output        [15:0] dbg_mem_din;   // Debug unit Memory data input

output [`DMEM_MSB:0] dmem_addr;     // Data Memory address

output               dmem_cen;      // Data Memory chip enable (low active)

output        [15:0] dmem_din;      // Data Memory data input

output         [1:0] dmem_wen;      // Data Memory write enable (low active)

output        [15:0] eu_mdb_in;     // Execution Unit Memory data bus input

output        [15:0] fe_mdb_in;     // Frontend Memory data bus input

output               fe_pmem_wait;  // Frontend wait for Instruction fetch

output         [7:0] per_addr;      // Peripheral address

output        [15:0] per_din;       // Peripheral data input

output         [1:0] per_wen;       // Peripheral write enable (high active)

output               per_en;        // Peripheral enable (high active)

output [`PMEM_MSB:0] pmem_addr;     // Program Memory address

output               pmem_cen;      // Program Memory chip enable (low active)

output        [15:0] pmem_din;      // Program Memory data input (optional)

output         [1:0] pmem_wen;      // Program Memory write enable (low active) (optional)

// INPUTs

//=========

input                dbg_halt_st;   // Halt/Run status from CPU

input         [15:0] dbg_mem_addr;  // Debug address for rd/wr access

input         [15:0] dbg_mem_dout;  // Debug unit data output

input                dbg_mem_en;    // Debug unit memory enable

input          [1:0] dbg_mem_wr;    // Debug unit memory write

input         [15:0] dmem_dout;     // Data Memory data output

input         [14:0] eu_mab;        // Execution Unit Memory address bus

input                eu_mb_en;      // Execution Unit Memory bus enable

input          [1:0] eu_mb_wr;      // Execution Unit Memory bus write transfer

input         [15:0] eu_mdb_out;    // Execution Unit Memory data bus output

input         [14:0] fe_mab;        // Frontend Memory address bus

input                fe_mb_en;      // Frontend Memory bus enable

input                mclk;          // Main system clock

input         [15:0] per_dout;      // Peripheral data output

input         [15:0] pmem_dout;     // Program Memory data output

input                puc;           // Main system reset

//=============================================================================

// 1)  DECODER

//=============================================================================

// RAM Interface

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

// Execution unit access

wire               eu_dmem_cen   = ~(eu_mb_en & (eu_mab>=(`DMEM_BASE>>1)) &

                                                (eu_mab<((`DMEM_BASE+`DMEM_SIZE)>>1)));

wire        [15:0] eu_dmem_addr  = eu_mab-(`DMEM_BASE>>1);

// Debug interface access

wire               dbg_dmem_cen  = ~(dbg_mem_en & (dbg_mem_addr[15:1]>=(`DMEM_BASE>>1)) &

                                                  (dbg_mem_addr[15:1]<((`DMEM_BASE+`DMEM_SIZE)>>1)));

wire        [15:0] dbg_dmem_addr = dbg_mem_addr[15:1]-(`DMEM_BASE>>1);

// RAM Interface

wire [`DMEM_MSB:0] dmem_addr     = ~dbg_dmem_cen ? dbg_dmem_addr[`DMEM_MSB:0] : eu_dmem_addr[`DMEM_MSB:0];

wire               dmem_cen      =  dbg_dmem_cen & eu_dmem_cen;

wire         [1:0] dmem_wen      = ~(dbg_mem_wr | eu_mb_wr);

wire        [15:0] dmem_din      = ~dbg_dmem_cen ? dbg_mem_dout : eu_mdb_out;

// ROM Interface

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

parameter          PMEM_OFFSET   = (16'hFFFF-`PMEM_SIZE+1);

// Execution unit access (only read access are accepted)

wire               eu_pmem_cen   = ~(eu_mb_en & ~|eu_mb_wr & (eu_mab>=(PMEM_OFFSET>>1)));

wire        [15:0] eu_pmem_addr  = eu_mab-(PMEM_OFFSET>>1);

// Front-end access

wire               fe_pmem_cen   = ~(fe_mb_en & (fe_mab>=(PMEM_OFFSET>>1)));

wire        [15:0] fe_pmem_addr  = fe_mab-(PMEM_OFFSET>>1);

// Debug interface access

wire               dbg_pmem_cen  = ~(dbg_mem_en & (dbg_mem_addr[15:1]>=(PMEM_OFFSET>>1)));

wire        [15:0] dbg_pmem_addr = dbg_mem_addr[15:1]-(PMEM_OFFSET>>1);

// ROM Interface (Execution unit has priority)

wire [`PMEM_MSB:0] pmem_addr     = ~dbg_pmem_cen ? dbg_pmem_addr[`PMEM_MSB:0] :

                                   ~eu_pmem_cen  ? eu_pmem_addr[`PMEM_MSB:0]  : fe_pmem_addr[`PMEM_MSB:0];

wire               pmem_cen      =  fe_pmem_cen & eu_pmem_cen & dbg_pmem_cen;

wire         [1:0] pmem_wen      = ~dbg_mem_wr;

wire        [15:0] pmem_din      =  dbg_mem_dout;

wire               fe_pmem_wait  = (~fe_pmem_cen & ~eu_pmem_cen);

// Peripherals

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

wire         dbg_per_en    =  dbg_mem_en & (dbg_mem_addr[15:9]==7'h00);

wire         eu_per_en     =  eu_mb_en   & (eu_mab[14:8]==7'h00);

wire   [7:0] per_addr      =  dbg_mem_en ? dbg_mem_addr[8:1] : eu_mab[7:0];

wire  [15:0] per_din       =  dbg_mem_en ? dbg_mem_dout      : eu_mdb_out;

wire   [1:0] per_wen       =  dbg_mem_en ? dbg_mem_wr        : eu_mb_wr;

wire         per_en        =  dbg_mem_en ? dbg_per_en        : eu_per_en;

reg   [15:0] per_dout_val;

always @ (posedge mclk or posedge puc)

  if (puc)      per_dout_val <= 16'h0000;

  else          per_dout_val <= per_dout;

// Frontend data Mux

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

// Whenever the frontend doesn't access the ROM,  backup the data

// Detect whenever the data should be backuped and restored

reg         fe_pmem_cen_dly;

always @(posedge mclk or posedge puc)

  if (puc)     fe_pmem_cen_dly <=  1'b0;

  else         fe_pmem_cen_dly <=  fe_pmem_cen;

wire fe_pmem_save    = ( fe_pmem_cen & ~fe_pmem_cen_dly) & ~dbg_halt_st;

wire fe_pmem_restore = (~fe_pmem_cen &  fe_pmem_cen_dly) |  dbg_halt_st;

reg  [15:0] pmem_dout_bckup;

always @(posedge mclk or posedge puc)

  if (puc)               pmem_dout_bckup     <=  16'h0000;

  else if (fe_pmem_save) pmem_dout_bckup     <=  pmem_dout;

// Mux between the ROM data and the backup

reg         pmem_dout_bckup_sel;

always @(posedge mclk or posedge puc)

  if (puc)                  pmem_dout_bckup_sel <=  1'b0;

  else if (fe_pmem_save)    pmem_dout_bckup_sel <=  1'b1;

  else if (fe_pmem_restore) pmem_dout_bckup_sel <=  1'b0;

assign fe_mdb_in = pmem_dout_bckup_sel ? pmem_dout_bckup : pmem_dout;

// Execution-Unit data Mux

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

// Select between peripherals, RAM and ROM

reg [1:0] eu_mdb_in_sel;

always @(posedge mclk or posedge puc)

  if (puc)  eu_mdb_in_sel <= 2'b00;

  else      eu_mdb_in_sel <= {~eu_pmem_cen, per_en};

// Mux

assign      eu_mdb_in      = eu_mdb_in_sel[1] ? pmem_dout    :

                             eu_mdb_in_sel[0] ? per_dout_val : dmem_dout;

// Debug interface  data Mux

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

// Select between peripherals, RAM and ROM

reg [1:0] dbg_mem_din_sel;

always @(posedge mclk or posedge puc)

  if (puc)  dbg_mem_din_sel <= 2'b00;

  else      dbg_mem_din_sel <= {~dbg_pmem_cen, dbg_per_en};

// Mux

assign      dbg_mem_din  = dbg_mem_din_sel[1] ? pmem_dout    :

                           dbg_mem_din_sel[0] ? per_dout_val : dmem_dout;

endmodule // omsp_mem_backbone

`include "openMSP430_undefines.v"