insn_alu8.v

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