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

//                                                              //

//  Register Bank for Amber Core                                //

//                                                              //

//  This file is part of the Amber project                      //

//  http://www.opencores.org/project,amber                      //

//                                                              //

//  Description                                                 //

//  Contains 37 32-bit registers, 16 of which are visible       //

//  ina any one operating mode. Registers use real flipflops,   //

//  rather than SRAM. This makes sense for an FPGA              //

//  implementation, where flipflops are plentiful.              //

//                                                              //

//  Author(s):                                                  //

//      - Conor Santifort, csantifort.amber@gmail.com           //

//                                                              //

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

//                                                              //

// Copyright (C) 2010 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 a23_register_bank (

input                       i_clk,

input                       i_fetch_stall,

input       [1:0]           i_mode_idec,            // user, supervisor, irq_idec, firq_idec etc.

                                                    // Used for register writes

input       [1:0]           i_mode_exec,            // 1 periods delayed from i_mode_idec

                                                    // Used for register reads

input       [3:0]           i_mode_rds_exec,        // Use one-hot version specifically for rds, 

                                                    // includes i_user_mode_regs_store

input                       i_user_mode_regs_load,

input                       i_firq_not_user_mode,

input       [3:0]           i_rm_sel,

input       [3:0]           i_rds_sel,

input       [3:0]           i_rn_sel,

input                       i_pc_wen,

input       [14:0]          i_reg_bank_wen,

input       [23:0]          i_pc,                   // program counter [25:2]

input       [31:0]          i_reg,

input       [3:0]           i_status_bits_flags,

input                       i_status_bits_irq_mask,

input                       i_status_bits_firq_mask,

output      [31:0]          o_rm,

output reg  [31:0]          o_rs,

output reg  [31:0]          o_rd,

output      [31:0]          o_rn,

output      [31:0]          o_pc

);

`include "a23_localparams.v"

`include "a23_functions.v"

// User Mode Registers

reg  [31:0] r0  = 32'hdead_beef;

reg  [31:0] r1  = 32'hdead_beef;

reg  [31:0] r2  = 32'hdead_beef;

reg  [31:0] r3  = 32'hdead_beef;

reg  [31:0] r4  = 32'hdead_beef;

reg  [31:0] r5  = 32'hdead_beef;

reg  [31:0] r6  = 32'hdead_beef;

reg  [31:0] r7  = 32'hdead_beef;

reg  [31:0] r8  = 32'hdead_beef;

reg  [31:0] r9  = 32'hdead_beef;

reg  [31:0] r10 = 32'hdead_beef;

reg  [31:0] r11 = 32'hdead_beef;

reg  [31:0] r12 = 32'hdead_beef;

reg  [31:0] r13 = 32'hdead_beef;

reg  [31:0] r14 = 32'hdead_beef;

reg  [23:0] r15 = 24'hc0_ffee;

wire  [31:0] r0_out;

wire  [31:0] r1_out;

wire  [31:0] r2_out;

wire  [31:0] r3_out;

wire  [31:0] r4_out;

wire  [31:0] r5_out;

wire  [31:0] r6_out;

wire  [31:0] r7_out;

wire  [31:0] r8_out;

wire  [31:0] r9_out;

wire  [31:0] r10_out;

wire  [31:0] r11_out;

wire  [31:0] r12_out;

wire  [31:0] r13_out;

wire  [31:0] r14_out;

wire  [31:0] r15_out_rm;

wire  [31:0] r15_out_rm_nxt;

wire  [31:0] r15_out_rn;

wire  [31:0] r8_rds;

wire  [31:0] r9_rds;

wire  [31:0] r10_rds;

wire  [31:0] r11_rds;

wire  [31:0] r12_rds;

wire  [31:0] r13_rds;

wire  [31:0] r14_rds;

// Supervisor Mode Registers

reg  [31:0] r13_svc = 32'hdead_beef;

reg  [31:0] r14_svc = 32'hdead_beef;

// Interrupt Mode Registers

reg  [31:0] r13_irq = 32'hdead_beef;

reg  [31:0] r14_irq = 32'hdead_beef;

// Fast Interrupt Mode Registers

reg  [31:0] r8_firq  = 32'hdead_beef;

reg  [31:0] r9_firq  = 32'hdead_beef;

reg  [31:0] r10_firq = 32'hdead_beef;

reg  [31:0] r11_firq = 32'hdead_beef;

reg  [31:0] r12_firq = 32'hdead_beef;

reg  [31:0] r13_firq = 32'hdead_beef;

reg  [31:0] r14_firq = 32'hdead_beef;

wire        usr_exec;

wire        svc_exec;

wire        irq_exec;

wire        firq_exec;

wire        usr_idec;

wire        svc_idec;

wire        irq_idec;

wire        firq_idec;

    // Write Enables from execute stage

assign usr_idec  =  i_user_mode_regs_load || i_mode_idec == USR;

assign svc_idec  = !i_user_mode_regs_load && i_mode_idec == SVC;

assign irq_idec  = !i_user_mode_regs_load && i_mode_idec == IRQ;

// pre-encoded in decode stage to speed up long path

assign firq_idec = i_firq_not_user_mode;

    // Read Enables from stage 1 (fetch)

assign usr_exec  = i_mode_exec == USR;

assign svc_exec  = i_mode_exec == SVC;

assign irq_exec  = i_mode_exec == IRQ;

assign firq_exec = i_mode_exec == FIRQ;

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

// Register Update

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

always @ ( posedge i_clk )

    if (!i_fetch_stall)

        begin

        r0       <=  i_reg_bank_wen[0 ]              ? i_reg : r0;

        r1       <=  i_reg_bank_wen[1 ]              ? i_reg : r1;

        r2       <=  i_reg_bank_wen[2 ]              ? i_reg : r2;

        r3       <=  i_reg_bank_wen[3 ]              ? i_reg : r3;

        r4       <=  i_reg_bank_wen[4 ]              ? i_reg : r4;

        r5       <=  i_reg_bank_wen[5 ]              ? i_reg : r5;

        r6       <=  i_reg_bank_wen[6 ]              ? i_reg : r6;

        r7       <=  i_reg_bank_wen[7 ]              ? i_reg : r7;

        r8       <= (i_reg_bank_wen[8 ] && !firq_idec) ? i_reg : r8;

        r9       <= (i_reg_bank_wen[9 ] && !firq_idec) ? i_reg : r9;

        r10      <= (i_reg_bank_wen[10] && !firq_idec) ? i_reg : r10;

        r11      <= (i_reg_bank_wen[11] && !firq_idec) ? i_reg : r11;

        r12      <= (i_reg_bank_wen[12] && !firq_idec) ? i_reg : r12;

        r8_firq  <= (i_reg_bank_wen[8 ] &&  firq_idec) ? i_reg : r8_firq;

        r9_firq  <= (i_reg_bank_wen[9 ] &&  firq_idec) ? i_reg : r9_firq;

        r10_firq <= (i_reg_bank_wen[10] &&  firq_idec) ? i_reg : r10_firq;

        r11_firq <= (i_reg_bank_wen[11] &&  firq_idec) ? i_reg : r11_firq;

        r12_firq <= (i_reg_bank_wen[12] &&  firq_idec) ? i_reg : r12_firq;

        r13      <= (i_reg_bank_wen[13] &&  usr_idec)  ? i_reg : r13;

        r14      <= (i_reg_bank_wen[14] &&  usr_idec)  ? i_reg : r14;

        r13_svc  <= (i_reg_bank_wen[13] &&  svc_idec)  ? i_reg : r13_svc;

        r14_svc  <= (i_reg_bank_wen[14] &&  svc_idec)  ? i_reg : r14_svc;

        r13_irq  <= (i_reg_bank_wen[13] &&  irq_idec)  ? i_reg : r13_irq;

        r14_irq  <= (i_reg_bank_wen[14] &&  irq_idec)  ? i_reg : r14_irq;

        r13_firq <= (i_reg_bank_wen[13] &&  firq_idec) ? i_reg : r13_firq;

        r14_firq <= (i_reg_bank_wen[14] &&  firq_idec) ? i_reg : r14_firq;

        r15      <=  i_pc_wen                          ?  i_pc : r15;

        end

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

// Register Read based on Mode

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

assign r0_out = r0;

assign r1_out = r1;

assign r2_out = r2;

assign r3_out = r3;

assign r4_out = r4;

assign r5_out = r5;

assign r6_out = r6;

assign r7_out = r7;

assign r8_out  = firq_exec ? r8_firq  : r8;

assign r9_out  = firq_exec ? r9_firq  : r9;

assign r10_out = firq_exec ? r10_firq : r10;

assign r11_out = firq_exec ? r11_firq : r11;

assign r12_out = firq_exec ? r12_firq : r12;

assign r13_out = usr_exec ? r13      :

                 svc_exec ? r13_svc  :

                 irq_exec ? r13_irq  :

                          r13_firq ;

assign r14_out = usr_exec ? r14      :

                 svc_exec ? r14_svc  :

                 irq_exec ? r14_irq  :

                          r14_firq ;

assign r15_out_rm     = { i_status_bits_flags,

                          i_status_bits_irq_mask,

                          i_status_bits_firq_mask,

                          r15,

                          i_mode_exec};

assign r15_out_rm_nxt = { i_status_bits_flags,

                          i_status_bits_irq_mask,

                          i_status_bits_firq_mask,

                          i_pc,

                          i_mode_exec};

assign r15_out_rn     = {6'd0, r15, 2'd0};

// rds outputs

assign r8_rds  = i_mode_rds_exec[OH_FIRQ] ? r8_firq  : r8;

assign r9_rds  = i_mode_rds_exec[OH_FIRQ] ? r9_firq  : r9;

assign r10_rds = i_mode_rds_exec[OH_FIRQ] ? r10_firq : r10;

assign r11_rds = i_mode_rds_exec[OH_FIRQ] ? r11_firq : r11;

assign r12_rds = i_mode_rds_exec[OH_FIRQ] ? r12_firq : r12;

assign r13_rds = i_mode_rds_exec[OH_USR]  ? r13      :

                 i_mode_rds_exec[OH_SVC]  ? r13_svc  :

                 i_mode_rds_exec[OH_IRQ]  ? r13_irq  :

                                            r13_firq ;

assign r14_rds = i_mode_rds_exec[OH_USR]  ? r14      :

                 i_mode_rds_exec[OH_SVC]  ? r14_svc  :

                 i_mode_rds_exec[OH_IRQ]  ? r14_irq  :

                                            r14_firq ;

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

// Program Counter out

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

assign o_pc = r15_out_rn;

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

// Rm Selector

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

assign o_rm = i_rm_sel == 4'd0  ? r0_out  :

              i_rm_sel == 4'd1  ? r1_out  :

              i_rm_sel == 4'd2  ? r2_out  :

              i_rm_sel == 4'd3  ? r3_out  :

              i_rm_sel == 4'd4  ? r4_out  :

              i_rm_sel == 4'd5  ? r5_out  :

              i_rm_sel == 4'd6  ? r6_out  :

              i_rm_sel == 4'd7  ? r7_out  :

              i_rm_sel == 4'd8  ? r8_out  :

              i_rm_sel == 4'd9  ? r9_out  :

              i_rm_sel == 4'd10 ? r10_out :

              i_rm_sel == 4'd11 ? r11_out :

              i_rm_sel == 4'd12 ? r12_out :

              i_rm_sel == 4'd13 ? r13_out :

              i_rm_sel == 4'd14 ? r14_out :

                                  r15_out_rm ;

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

// Rds Selector

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

always @*

    case (i_rds_sel)

       4'd0  :  o_rs = r0_out  ;

       4'd1  :  o_rs = r1_out  ;

       4'd2  :  o_rs = r2_out  ;

       4'd3  :  o_rs = r3_out  ;

       4'd4  :  o_rs = r4_out  ;

       4'd5  :  o_rs = r5_out  ;

       4'd6  :  o_rs = r6_out  ;

       4'd7  :  o_rs = r7_out  ;

       4'd8  :  o_rs = r8_rds  ;

       4'd9  :  o_rs = r9_rds  ;

       4'd10 :  o_rs = r10_rds ;

       4'd11 :  o_rs = r11_rds ;

       4'd12 :  o_rs = r12_rds ;

       4'd13 :  o_rs = r13_rds ;

       4'd14 :  o_rs = r14_rds ;

       default: o_rs = r15_out_rn ;

    endcase

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

// Rd Selector

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

always @*

    case (i_rds_sel)

       4'd0  :  o_rd = r0_out  ;

       4'd1  :  o_rd = r1_out  ;

       4'd2  :  o_rd = r2_out  ;

       4'd3  :  o_rd = r3_out  ;

       4'd4  :  o_rd = r4_out  ;

       4'd5  :  o_rd = r5_out  ;

       4'd6  :  o_rd = r6_out  ;

       4'd7  :  o_rd = r7_out  ;

       4'd8  :  o_rd = r8_rds  ;

       4'd9  :  o_rd = r9_rds  ;

       4'd10 :  o_rd = r10_rds ;

       4'd11 :  o_rd = r11_rds ;

       4'd12 :  o_rd = r12_rds ;

       4'd13 :  o_rd = r13_rds ;

       4'd14 :  o_rd = r14_rds ;

       default: o_rd = r15_out_rm_nxt ;

    endcase

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

// Rn Selector

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

assign o_rn = i_rn_sel == 4'd0  ? r0_out  :

              i_rn_sel == 4'd1  ? r1_out  :

              i_rn_sel == 4'd2  ? r2_out  :

              i_rn_sel == 4'd3  ? r3_out  :

              i_rn_sel == 4'd4  ? r4_out  :

              i_rn_sel == 4'd5  ? r5_out  :

              i_rn_sel == 4'd6  ? r6_out  :

              i_rn_sel == 4'd7  ? r7_out  :

              i_rn_sel == 4'd8  ? r8_out  :

              i_rn_sel == 4'd9  ? r9_out  :

              i_rn_sel == 4'd10 ? r10_out :

              i_rn_sel == 4'd11 ? r11_out :

              i_rn_sel == 4'd12 ? r12_out :

              i_rn_sel == 4'd13 ? r13_out :

              i_rn_sel == 4'd14 ? r14_out :

                                  r15_out_rn ;

endmodule