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Annotation of gforth/arch/misc/misc.v, revision 1.2

1.2     ! pazsan      1: // Copyright (C) 1998,2000,2003 Free Software Foundation, Inc.
        !             2: 
        !             3: // This file is part of Gforth.
        !             4: 
        !             5: // Gforth is free software; you can redistribute it and/or
        !             6: // modify it under the terms of the GNU General Public License
        !             7: // as published by the Free Software Foundation; either version 2
        !             8: // of the License, or (at your option) any later version.
        !             9: 
        !            10: // This program is distributed in the hope that it will be useful,
        !            11: // but WITHOUT ANY WARRANTY; without even the implied warranty of
        !            12: // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        !            13: // GNU General Public License for more details.
        !            14: 
        !            15: // You should have received a copy of the GNU General Public License
        !            16: // along with this program; if not, write to the Free Software
        !            17: // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
        !            18: 
1.1       pazsan     19: /* Minimal Instruction Set Computer
                     20:  \ sources                 destinations
                     21: 
                     22: $0 Constant PC         $0 Constant JMP
                     23: $1 Constant PC+2       $1 Constant JS
                     24: $2 Constant PC+4       $2 Constant JZ
                     25: $3 Constant PC+6       
                     26:                        $4 Constant JC
                     27: 
                     28:  
                     29:  
                     30: $8 Constant ACCU       $8 Constant ACCU
                     31: $9 Constant SF         $9 Constant SUB
                     32: $A Constant ZF         $A Constant SUBR
                     33:                        $B Constant ADD
                     34: $C Constant CF         $C Constant XOR
                     35:                        $D Constant OR
                     36:                        $E Constant AND
                     37:                        $F Constant SHR
                     38: */
                     39: 
                     40: `define L [0:l-1]
                     41:  
                     42: module misc(clock, data, addr, csel, rw);
                     43:    parameter l=16, d=10;
                     44:    input clock;
                     45:    inout `L data;
                     46:    output `L addr;
                     47:    output csel;
                     48:    output rw;
                     49: 
                     50:    reg `L inst, dtr, accu, pc;
                     51:    reg [0:1] state;
                     52:    reg carry, zero;
                     53:    wire `L regs;
                     54:    wire alusel, cout, zout, pccond;
                     55:    wire `L alu1, alu2, aluout;
                     56:    wire [0:2] aluop;
                     57:    
                     58:    initial
                     59:     begin
                     60:        state = 0;
                     61:        pc = 'h10;
                     62:        inst = 0;
                     63:        dtr = 0;
                     64:        accu = 0;
                     65:        carry = 0;
                     66:        zero = 1;
                     67:     end
                     68:    
                     69:    assign
                     70:     rw=~&state,
                     71:     csel=~state[1] | |inst[0:l-5],
                     72:     addr = state[1] ? inst : pc,
                     73:     data = rw ? {l{1'bz}} : dtr;
                     74: 
                     75:    assign
                     76:     alusel= inst[l-4],
                     77:     pccond = ~|(inst[l-3:l-1] & ~{ carry, zero, accu[0] }),
                     78:     regs = inst[l-4] ? (|inst[l-3:l-1] ? { {(l-1){1'b0}}, pccond } : accu)
                     79:                      : aluout;
                     80:    
                     81:    always @(posedge clock)
                     82:     begin
                     83:        casez(state)
                     84:         2'bz0 : begin
                     85:            inst = data;
                     86:            pc = aluout;
                     87:         end
                     88:         2'b01 : begin
                     89:            dtr = csel ? data : regs;
                     90: //         $fwrite(2, "PC: %x : %x -( %x )->", pc-1'b1, inst, dtr);
                     91:         end
                     92:         2'b11 :
                     93:          begin
                     94:             if(~|inst[0:l-5])
                     95:              if(alusel) { carry, zero, accu } = { cout, zout, aluout };
                     96:              else
                     97:               if (pccond) pc=dtr;
                     98: //          $fwrite(2, " %x ACCU: %x\n", inst, accu);
                     99:          end
                    100:        endcase /* 2 */
                    101:        state = state + 1;
                    102:     end
                    103: 
                    104:    assign
                    105:     alu1 = &state ? accu : pc,
                    106:     alu2 = ~state[1] ? {{l{1'b0}}, 1'b1 } :
                    107:                        state[0] ? dtr : { inst[1:l-1], 1'b0 } - 1,
                    108:     aluop = &state ? inst[l-3:l-1] : 3'b011;
                    109:    
                    110:    alu #(l,d) alu0(aluop, alu1, alu2, carry, aluout, cout, zout);
                    111:    
                    112: endmodule /* misc */
                    113: 
                    114: module alu(op, in1, in2, cin, out, cout, zout);
                    115:    parameter l=16, d=10;
                    116:    input [0:2] op;
                    117:    input `L in1, in2;
                    118:    input cin;
                    119:    output `L out;
                    120:    output cout, zout;
                    121:    
                    122:    reg `L out;
                    123:    reg cout;
                    124: 
                    125:    initial
                    126:     cout = 0;
                    127:    
                    128:    always @(in1 or in2 or op)
                    129:     #d case(op)
                    130:       3'b000 : { cout, out } = { cin, in2 };
                    131:       3'b001 : { cout, out } = in1 - in2;
                    132:       3'b010 : { cout, out } = in2 - in1;
                    133:       3'b011 : { cout, out } = in1 + in2;
                    134:       3'b100 : { cout, out } = { cin, in1 ^ in2 };
                    135:       3'b101 : { cout, out } = { cin, in1 | in2 };
                    136:       3'b110 : { cout, out } = { cin, in1 & in2 };
                    137:       3'b111 : { cout, out } = { in2[l-1], cin, in2[0:l-2] };
                    138:     endcase /* 3 */
                    139: 
                    140:    assign
                    141:     zout = ~|out;
                    142:    
                    143: endmodule /* alu */