insn_alu8.v

   1 `ifdef EXECUTE
   2         `INSN_ALU8,`INSN_ALU8IMM: begin
   3                 if ((opcode[7:6] == 2'b11) && (cycle == 0)) begin       // alu8imm
   4                         `EXEC_INC_PC
   5                         `EXEC_READ(`_PC + 1)
   6                 end else if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0))
   7                         `EXEC_READ(`_HL)
   8                 else begin
   9                         `EXEC_NEWCYCLE
  10                         `EXEC_INC_PC
  11                         case (opcode[2:0])
  12                         `INSN_reg_A:    tmp <= `_A;
  13                         `INSN_reg_B:    tmp <= `_B;
  14                         `INSN_reg_C:    tmp <= `_C;
  15                         `INSN_reg_D:    tmp <= `_D;
  16                         `INSN_reg_E:    tmp <= `_E;
  17                         `INSN_reg_H:    tmp <= `_H;
  18                         `INSN_reg_L:    tmp <= `_L;
  19                         `INSN_reg_dHL:  tmp <= rdata;
  20                         endcase
  21                 end
  22         end
  23 `endif
  24
  25 `ifdef WRITEBACK
  26         `INSN_ALU8,`INSN_ALU8IMM: begin
  27                 if (((opcode[2:0] == `INSN_reg_dHL) || (opcode[7:6] == 2'b11)) && (cycle == 0)) begin
  28                         /* Sit on our asses. */
  29                 end else begin          /* Actually do the computation! */
  30                         case (opcode[5:3])
  31                         `INSN_alu_ADD: begin
  32                                 `_A <= `_A + tmp;
  33                                 `_F <=  { /* Z */ ((`_A + tmp) == 8'b0) ? 1'b1 : 1'b0,
  34                                           /* N */ 1'b0,
  35                                           /* H */ (({1'b0,`_A[3:0]} + {1'b0,tmp[3:0]}) >> 4 == 1) ? 1'b1 : 1'b0,
  36                                           /* C */ (({1'b0,`_A} + {1'b0,tmp}) >> 8 == 1) ? 1'b1 : 1'b0,
  37                                           `_F[3:0]
  38                                         };
  39                         end
  40                         `INSN_alu_ADC: begin
  41                                 `_A <= `_A + tmp + {7'b0,`_F[4]};
  42                                 `_F <=  { /* Z */ ((`_A + tmp + {7'b0,`_F[4]}) == 8'b0) ? 1'b1 : 1'b0,
  43                                           /* N */ 1'b0,
  44                                           /* H */ (({1'b0,`_A[3:0]} + {1'b0,tmp[3:0]} + {4'b0,`_F[4]}) >> 4 == 1) ? 1'b1 : 1'b0,
  45                                           /* C */ (({1'b0,`_A} + {1'b0,tmp} + {8'b0,`_F[4]}) >> 8 == 1) ? 1'b1 : 1'b0,
  46                                           `_F[3:0]
  47                                         };
  48                         end
  49                         `INSN_alu_SUB: begin
  50                                 `_A <= `_A - tmp;
  51                                 `_F <=  { /* Z */ (`_A == tmp) ? 1'b1 : 1'b0,
  52                                           /* N */ 1'b1,
  53                                           /* H */ (tmp[3:0] > `_A[3:0]) ? 1'b1 : 1'b0,
  54                                           /* C */ (tmp > `_A) ? 1'b1 : 1'b0,
  55                                           `_F[3:0]
  56                                         };
  57                         end
  58                         `INSN_alu_SBC: begin
  59                                 `_A <= `_A - (tmp + {7'b0,`_F[4]});
  60                                 `_F <=  { /* Z */ ((`_A - (tmp + {7'b0,`_F[4]})) == 8'b0) ? 1'b1 : 1'b0,
  61                                           /* N */ 1'b1,
  62                                           /* H */ (({1'b0,tmp[3:0]} + {4'b0,`_F[4]}) > {1'b0,`_A[3:0]}) ? 1'b1 : 1'b0,
  63                                           /* C */ (({1'b0,tmp} + {8'b0,`_F[4]}) > {1'b0,`_A[7:0]}) ? 1'b1 : 1'b0,
  64                                           `_F[3:0]
  65                                         };
  66                         end
  67                         `INSN_alu_AND: begin
  68                                 `_A <= `_A & tmp;
  69                                 `_F <=  { /* Z */ ((`_A & tmp) == 0) ? 1'b1 : 1'b0,
  70                                           3'b010,
  71                                           `_F[3:0]
  72                                         };
  73                         end
  74                         `INSN_alu_OR: begin
  75                                 `_A <= `_A | tmp;
  76                                 `_F <=  { /* Z */ ((`_A | tmp) == 0) ? 1'b1 : 1'b0,
  77                                           3'b000,
  78                                           `_F[3:0]
  79                                         };
  80                         end
  81                         `INSN_alu_XOR: begin
  82                                 `_A <= `_A ^ tmp;
  83                                 `_F <=  { /* Z */ ((`_A ^ tmp) == 0) ? 1'b1 : 1'b0,
  84                                           3'b000,
  85                                           `_F[3:0]
  86                                         };
  87                         end
  88                         `INSN_alu_CP: begin
  89                                 `_F <=  { /* Z */ (`_A == tmp) ? 1'b1 : 1'b0,
  90                                           /* N */ 1'b1,
  91                                           /* H */ (tmp[3:0] > `_A[3:0]) ? 1'b1 : 1'b0,
  92                                           /* C */ (tmp > `_A) ? 1'b1 : 1'b0,
  93                                           `_F[3:0]
  94                                         };
  95                         end
  96                         default:
  97                                 $stop;
  98                         endcase
  99                 end
 100         end
 101 `endif