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

// Copyright (C) 2009 , Olivier Girard

//

// Redistribution and use in source and binary forms, with or without

// modification, are permitted provided that the following conditions

// are met:

//     * Redistributions of source code must retain the above copyright

//       notice, this list of conditions and the following disclaimer.

//     * Redistributions in binary form must reproduce the above copyright

//       notice, this list of conditions and the following disclaimer in the

//       documentation and/or other materials provided with the distribution.

//     * Neither the name of the authors nor the names of its contributors

//       may be used to endorse or promote products derived from this software

//       without specific prior written permission.

//

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE

// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,

// OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN

// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF

// THE POSSIBILITY OF SUCH DAMAGE

//

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

//

// *File Name: omsp_execution_unit.v

// 

// *Module Description:

//                       openMSP430 Execution unit

//

// *Author(s):

//              - Olivier Girard,    olgirard@gmail.com

//

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

// $Rev: 174 $

// $LastChangedBy: olivier.girard $

// $LastChangedDate: 2013-01-30 22:18:42 +0100 (Wed, 30 Jan 2013) $

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

`ifdef OMSP_NO_INCLUDE

`else

`include "openMSP430_defines.v"

`endif

module  omsp_execution_unit (

// OUTPUTs

    cpuoff,                        // Turns off the CPU

    dbg_reg_din,                   // Debug unit CPU register data input

    gie,                           // General interrupt enable

    mab,                           // Memory address bus

    mb_en,                         // Memory bus enable

    mb_wr,                         // Memory bus write transfer

    mdb_out,                       // Memory data bus output

    oscoff,                        // Turns off LFXT1 clock input

    pc_sw,                         // Program counter software value

    pc_sw_wr,                      // Program counter software write

    scg0,                          // System clock generator 1. Turns off the DCO

    scg1,                          // System clock generator 1. Turns off the SMCLK

// INPUTs

    dbg_halt_st,                   // Halt/Run status from CPU

    dbg_mem_dout,                  // Debug unit data output

    dbg_reg_wr,                    // Debug unit CPU register write

    e_state,                       // Execution state

    exec_done,                     // Execution completed

    inst_ad,                       // Decoded Inst: destination addressing mode

    inst_as,                       // Decoded Inst: source addressing mode

    inst_alu,                      // ALU control signals

    inst_bw,                       // Decoded Inst: byte width

    inst_dest,                     // Decoded Inst: destination (one hot)

    inst_dext,                     // Decoded Inst: destination extended instruction word

    inst_irq_rst,                  // Decoded Inst: reset interrupt

    inst_jmp,                      // Decoded Inst: Conditional jump

    inst_mov,                      // Decoded Inst: mov instruction

    inst_sext,                     // Decoded Inst: source extended instruction word

    inst_so,                       // Decoded Inst: Single-operand arithmetic

    inst_src,                      // Decoded Inst: source (one hot)

    inst_type,                     // Decoded Instruction type

    mclk,                          // Main system clock

    mdb_in,                        // Memory data bus input

    pc,                            // Program counter

    pc_nxt,                        // Next PC value (for CALL & IRQ)

    puc_rst,                       // Main system reset

    scan_enable                    // Scan enable (active during scan shifting)

);

// OUTPUTs

//=========

output              cpuoff;        // Turns off the CPU

output       [15:0] dbg_reg_din;   // Debug unit CPU register data input

output              gie;           // General interrupt enable

output       [15:0] mab;           // Memory address bus

output              mb_en;         // Memory bus enable

output        [1:0] mb_wr;         // Memory bus write transfer

output       [15:0] mdb_out;       // Memory data bus output

output              oscoff;        // Turns off LFXT1 clock input

output       [15:0] pc_sw;         // Program counter software value

output              pc_sw_wr;      // Program counter software write

output              scg0;          // System clock generator 1. Turns off the DCO

output              scg1;          // System clock generator 1. Turns off the SMCLK

// INPUTs

//=========

input               dbg_halt_st;   // Halt/Run status from CPU

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

input               dbg_reg_wr;    // Debug unit CPU register write

input         [3:0] e_state;       // Execution state

input               exec_done;     // Execution completed

input         [7:0] inst_ad;       // Decoded Inst: destination addressing mode

input         [7:0] inst_as;       // Decoded Inst: source addressing mode

input        [11:0] inst_alu;      // ALU control signals

input               inst_bw;       // Decoded Inst: byte width

input        [15:0] inst_dest;     // Decoded Inst: destination (one hot)

input        [15:0] inst_dext;     // Decoded Inst: destination extended instruction word

input               inst_irq_rst;  // Decoded Inst: reset interrupt

input         [7:0] inst_jmp;      // Decoded Inst: Conditional jump

input               inst_mov;      // Decoded Inst: mov instruction

input        [15:0] inst_sext;     // Decoded Inst: source extended instruction word

input         [7:0] inst_so;       // Decoded Inst: Single-operand arithmetic

input        [15:0] inst_src;      // Decoded Inst: source (one hot)

input         [2:0] inst_type;     // Decoded Instruction type

input               mclk;          // Main system clock

input        [15:0] mdb_in;        // Memory data bus input

input        [15:0] pc;            // Program counter

input        [15:0] pc_nxt;        // Next PC value (for CALL & IRQ)

input               puc_rst;       // Main system reset

input               scan_enable;   // Scan enable (active during scan shifting)

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

// 1)  INTERNAL WIRES/REGISTERS/PARAMETERS DECLARATION

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

wire         [15:0] alu_out;

wire         [15:0] alu_out_add;

wire          [3:0] alu_stat;

wire          [3:0] alu_stat_wr;

wire         [15:0] op_dst;

wire         [15:0] op_src;

wire         [15:0] reg_dest;

wire         [15:0] reg_src;

wire         [15:0] mdb_in_bw;

wire         [15:0] mdb_in_val;

wire          [3:0] status;

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

// 2)  REGISTER FILE

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

wire reg_dest_wr  = ((e_state==`E_EXEC) & (

                     (inst_type[`INST_TO] & inst_ad[`DIR] & ~inst_alu[`EXEC_NO_WR])  |

                     (inst_type[`INST_SO] & inst_as[`DIR] & ~(inst_so[`PUSH] | inst_so[`CALL] | inst_so[`RETI])) |

                      inst_type[`INST_JMP])) | dbg_reg_wr;

wire reg_sp_wr    = (((e_state==`E_IRQ_1) | (e_state==`E_IRQ_3)) & ~inst_irq_rst) |

                     ((e_state==`E_DST_RD) & ((inst_so[`PUSH] | inst_so[`CALL]) &  ~inst_as[`IDX] & ~((inst_as[`INDIR] | inst_as[`INDIR_I]) & inst_src[1]))) |

                     ((e_state==`E_SRC_AD) & ((inst_so[`PUSH] | inst_so[`CALL]) &  inst_as[`IDX])) |

                     ((e_state==`E_SRC_RD) & ((inst_so[`PUSH] | inst_so[`CALL]) &  ((inst_as[`INDIR] | inst_as[`INDIR_I]) & inst_src[1])));

wire reg_sr_wr    =  (e_state==`E_DST_RD) & inst_so[`RETI];

wire reg_sr_clr   =  (e_state==`E_IRQ_2);

wire reg_pc_call  = ((e_state==`E_EXEC)   & inst_so[`CALL]) |

                    ((e_state==`E_DST_WR) & inst_so[`RETI]);

wire reg_incr     =  (exec_done          & inst_as[`INDIR_I]) |

                    ((e_state==`E_SRC_RD) & inst_so[`RETI])    |

                    ((e_state==`E_EXEC)   & inst_so[`RETI]);

assign dbg_reg_din = reg_dest;

omsp_register_file register_file_0 (

// OUTPUTs

    .cpuoff       (cpuoff),       // Turns off the CPU

    .gie          (gie),          // General interrupt enable

    .oscoff       (oscoff),       // Turns off LFXT1 clock input

    .pc_sw        (pc_sw),        // Program counter software value

    .pc_sw_wr     (pc_sw_wr),     // Program counter software write

    .reg_dest     (reg_dest),     // Selected register destination content

    .reg_src      (reg_src),      // Selected register source content

    .scg0         (scg0),         // System clock generator 1. Turns off the DCO

    .scg1         (scg1),         // System clock generator 1. Turns off the SMCLK

    .status       (status),       // R2 Status {V,N,Z,C}

// INPUTs

    .alu_stat     (alu_stat),     // ALU Status {V,N,Z,C}

    .alu_stat_wr  (alu_stat_wr),  // ALU Status write {V,N,Z,C}

    .inst_bw      (inst_bw),      // Decoded Inst: byte width

    .inst_dest    (inst_dest),    // Register destination selection

    .inst_src     (inst_src),     // Register source selection

    .mclk         (mclk),         // Main system clock

    .pc           (pc),           // Program counter

    .puc_rst      (puc_rst),      // Main system reset

    .reg_dest_val (alu_out),      // Selected register destination value

    .reg_dest_wr  (reg_dest_wr),  // Write selected register destination

    .reg_pc_call  (reg_pc_call),  // Trigger PC update for a CALL instruction

    .reg_sp_val   (alu_out_add),  // Stack Pointer next value

    .reg_sp_wr    (reg_sp_wr),    // Stack Pointer write

    .reg_sr_clr   (reg_sr_clr),   // Status register clear for interrupts

    .reg_sr_wr    (reg_sr_wr),    // Status Register update for RETI instruction

    .reg_incr     (reg_incr),     // Increment source register

    .scan_enable  (scan_enable)   // Scan enable (active during scan shifting)

);

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

// 3)  SOURCE OPERAND MUXING

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

// inst_as[`DIR]    : Register direct.   -> Source is in register

// inst_as[`IDX]    : Register indexed.  -> Source is in memory, address is register+offset

// inst_as[`INDIR]  : Register indirect.

// inst_as[`INDIR_I]: Register indirect autoincrement.

// inst_as[`SYMB]   : Symbolic (operand is in memory at address PC+x).

// inst_as[`IMM]    : Immediate (operand is next word in the instruction stream).

// inst_as[`ABS]    : Absolute (operand is in memory at address x).

// inst_as[`CONST]  : Constant.

wire src_reg_src_sel    =  (e_state==`E_IRQ_0)                    |

                           (e_state==`E_IRQ_2)                    |

                          ((e_state==`E_SRC_RD) & ~inst_as[`ABS]) |

                          ((e_state==`E_SRC_WR) & ~inst_as[`ABS]) |

                          ((e_state==`E_EXEC)   &  inst_as[`DIR] & ~inst_type[`INST_JMP]);

wire src_reg_dest_sel   =  (e_state==`E_IRQ_1)                    |

                           (e_state==`E_IRQ_3)                    |

                          ((e_state==`E_DST_RD) & (inst_so[`PUSH] | inst_so[`CALL])) |

                          ((e_state==`E_SRC_AD) & (inst_so[`PUSH] | inst_so[`CALL]) & inst_as[`IDX]);

wire src_mdb_in_val_sel = ((e_state==`E_DST_RD) &  inst_so[`RETI])                     |

                          ((e_state==`E_EXEC)   & (inst_as[`INDIR] | inst_as[`INDIR_I] |

                                                   inst_as[`IDX]   | inst_as[`SYMB]    |

                                                   inst_as[`ABS]));

wire src_inst_dext_sel =  ((e_state==`E_DST_RD) & ~(inst_so[`PUSH] | inst_so[`CALL])) |

                          ((e_state==`E_DST_WR) & ~(inst_so[`PUSH] | inst_so[`CALL]   |

                                                    inst_so[`RETI]));

wire src_inst_sext_sel =  ((e_state==`E_EXEC)   &  (inst_type[`INST_JMP] | inst_as[`IMM] |

                                                    inst_as[`CONST]      | inst_so[`RETI]));

assign op_src = src_reg_src_sel     ?  reg_src    :

                src_reg_dest_sel    ?  reg_dest   :

                src_mdb_in_val_sel  ?  mdb_in_val :

                src_inst_dext_sel   ?  inst_dext  :

                src_inst_sext_sel   ?  inst_sext  : 16'h0000;

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

// 4)  DESTINATION OPERAND MUXING

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

// inst_ad[`DIR]    : Register direct.

// inst_ad[`IDX]    : Register indexed.

// inst_ad[`SYMB]   : Symbolic (operand is in memory at address PC+x).

// inst_ad[`ABS]    : Absolute (operand is in memory at address x).

wire dst_inst_sext_sel  = ((e_state==`E_SRC_RD) & (inst_as[`IDX] | inst_as[`SYMB] |

                                                   inst_as[`ABS]))                |

                          ((e_state==`E_SRC_WR) & (inst_as[`IDX] | inst_as[`SYMB] |

                                                   inst_as[`ABS]));

wire dst_mdb_in_bw_sel  = ((e_state==`E_DST_WR) &   inst_so[`RETI]) |

                          ((e_state==`E_EXEC)   & ~(inst_ad[`DIR] | inst_type[`INST_JMP] |

                                                    inst_type[`INST_SO]) & ~inst_so[`RETI]);

wire dst_fffe_sel       =  (e_state==`E_IRQ_0)  |

                           (e_state==`E_IRQ_1)  |

                           (e_state==`E_IRQ_3)  |

                          ((e_state==`E_DST_RD) & (inst_so[`PUSH] | inst_so[`CALL]) & ~inst_so[`RETI]) |

                          ((e_state==`E_SRC_AD) & (inst_so[`PUSH] | inst_so[`CALL]) & inst_as[`IDX]) |

                          ((e_state==`E_SRC_RD) & (inst_so[`PUSH] | inst_so[`CALL]) & (inst_as[`INDIR] | inst_as[`INDIR_I]) & inst_src[1]);

wire dst_reg_dest_sel   = ((e_state==`E_DST_RD) & ~(inst_so[`PUSH] | inst_so[`CALL] | inst_ad[`ABS] | inst_so[`RETI])) |

                          ((e_state==`E_DST_WR) &  ~inst_ad[`ABS]) |

                          ((e_state==`E_EXEC)   &  (inst_ad[`DIR] | inst_type[`INST_JMP] |

                                                    inst_type[`INST_SO]) & ~inst_so[`RETI]);

assign op_dst = dbg_halt_st        ? dbg_mem_dout  :

                dst_inst_sext_sel  ? inst_sext     :

                dst_mdb_in_bw_sel  ? mdb_in_bw     :

                dst_reg_dest_sel   ? reg_dest      :

                dst_fffe_sel       ? 16'hfffe      : 16'h0000;

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

// 5)  ALU

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

wire exec_cycle = (e_state==`E_EXEC);

omsp_alu alu_0 (

// OUTPUTs

    .alu_out      (alu_out),      // ALU output value

    .alu_out_add  (alu_out_add),  // ALU adder output value

    .alu_stat     (alu_stat),     // ALU Status {V,N,Z,C}

    .alu_stat_wr  (alu_stat_wr),  // ALU Status write {V,N,Z,C}

// INPUTs

    .dbg_halt_st  (dbg_halt_st),  // Halt/Run status from CPU

    .exec_cycle   (exec_cycle),   // Instruction execution cycle

    .inst_alu     (inst_alu),     // ALU control signals

    .inst_bw      (inst_bw),      // Decoded Inst: byte width

    .inst_jmp     (inst_jmp),     // Decoded Inst: Conditional jump

    .inst_so      (inst_so),      // Single-operand arithmetic

    .op_dst       (op_dst),       // Destination operand

    .op_src       (op_src),       // Source operand

    .status       (status)        // R2 Status {V,N,Z,C}

);

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

// 6)  MEMORY INTERFACE

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

// Detect memory read/write access

wire        mb_rd_det = ((e_state==`E_SRC_RD) & ~inst_as[`IMM])       |

                        ((e_state==`E_EXEC)   &  inst_so[`RETI])      |

                        ((e_state==`E_DST_RD) & ~inst_type[`INST_SO]

                                              & ~inst_mov);

wire        mb_wr_det = ((e_state==`E_IRQ_1)  & ~inst_irq_rst)        |

                        ((e_state==`E_IRQ_3)  & ~inst_irq_rst)        |

                        ((e_state==`E_DST_WR) & ~inst_so[`RETI])      |

                         (e_state==`E_SRC_WR);

wire  [1:0] mb_wr_msk =  inst_alu[`EXEC_NO_WR]  ? 2'b00 :

                        ~inst_bw                ? 2'b11 :

                         alu_out_add[0]         ? 2'b10 : 2'b01;

assign      mb_en     = mb_rd_det | mb_wr_det;

assign      mb_wr     = ({2{mb_wr_det}}) & mb_wr_msk;

// Memory address bus

assign      mab       = alu_out_add[15:0];

// Memory data bus output

reg  [15:0] mdb_out_nxt;

`ifdef CLOCK_GATING

wire        mdb_out_nxt_en  = (e_state==`E_DST_RD) |

                              (((e_state==`E_EXEC) & ~inst_so[`CALL]) |

                                (e_state==`E_IRQ_0) | (e_state==`E_IRQ_2));

wire        mclk_mdb_out_nxt;

omsp_clock_gate clock_gate_mdb_out_nxt (.gclk(mclk_mdb_out_nxt),

                                        .clk (mclk), .enable(mdb_out_nxt_en), .scan_enable(scan_enable));

`else

wire        mclk_mdb_out_nxt = mclk;

`endif

always @(posedge mclk_mdb_out_nxt or posedge puc_rst)

  if (puc_rst)                                        mdb_out_nxt <= 16'h0000;

  else if (e_state==`E_DST_RD)                        mdb_out_nxt <= pc_nxt;

`ifdef CLOCK_GATING

  else                                                mdb_out_nxt <= alu_out;

`else

  else if ((e_state==`E_EXEC & ~inst_so[`CALL]) |

           (e_state==`E_IRQ_0) | (e_state==`E_IRQ_2)) mdb_out_nxt <= alu_out;

`endif

assign      mdb_out = inst_bw ? {2{mdb_out_nxt[7:0]}} : mdb_out_nxt;

// Format memory data bus input depending on BW

reg        mab_lsb;

always @(posedge mclk or posedge puc_rst)

  if (puc_rst)    mab_lsb <= 1'b0;

  else if (mb_en) mab_lsb <= alu_out_add[0];

assign mdb_in_bw  = ~inst_bw ? mdb_in :

                     mab_lsb ? {2{mdb_in[15:8]}} : mdb_in;

// Memory data bus input buffer (buffer after a source read)

reg         mdb_in_buf_en;

always @(posedge mclk or posedge puc_rst)

  if (puc_rst)  mdb_in_buf_en <= 1'b0;

  else          mdb_in_buf_en <= (e_state==`E_SRC_RD);

reg         mdb_in_buf_valid;

always @(posedge mclk or posedge puc_rst)

  if (puc_rst)               mdb_in_buf_valid <= 1'b0;

  else if (e_state==`E_EXEC) mdb_in_buf_valid <= 1'b0;

  else if (mdb_in_buf_en)    mdb_in_buf_valid <= 1'b1;

reg  [15:0] mdb_in_buf;

`ifdef CLOCK_GATING

wire        mclk_mdb_in_buf;

omsp_clock_gate clock_gate_mdb_in_buf (.gclk(mclk_mdb_in_buf),

                                       .clk (mclk), .enable(mdb_in_buf_en), .scan_enable(scan_enable));

`else

wire        mclk_mdb_in_buf = mclk;

`endif

always @(posedge mclk_mdb_in_buf or posedge puc_rst)

  if (puc_rst)            mdb_in_buf <= 16'h0000;

`ifdef CLOCK_GATING

  else                    mdb_in_buf <= mdb_in_bw;

`else

  else if (mdb_in_buf_en) mdb_in_buf <= mdb_in_bw;

`endif

assign mdb_in_val = mdb_in_buf_valid ? mdb_in_buf : mdb_in_bw;

endmodule // omsp_execution_unit

`ifdef OMSP_NO_INCLUDE

`else

`include "openMSP430_undefines.v"

`endif