Our first ALU operation -- ADD

[fpgaboy.git] / GBZ80Core.v

diff --git a/GBZ80Core.v b/GBZ80Core.v
index b7994ae3ce4fea35f6d54ed170c8385bdf8d4e59..0cdefa546c112fb204503bc5e17a6848e9136639 100644 (file)
--- a/GBZ80Core.v
+++ b/GBZ80Core.v
@@ -32,6 +32,7 @@
 `define INSN_POP_reg                   8'b11xx0001
 `define INSN_LDH_AC                    8'b111x0010     // Either LDH A,(C) or LDH (C),A
 `define INSN_LDx_AHL                   8'b001xx010     // LDD/LDI A,(HL) / (HL),A
+`define INSN_ALU8                              8'b10xxxxxx     // 10 xxx yyy
 
 `define INSN_reg_A             3'b111
 `define INSN_reg_B             3'b000
@@ -49,6 +50,15 @@
 `define INSN_stack_BC  2'b00
 `define INSN_stack_DE  2'b01
 `define INSN_stack_HL  2'b10
+`define INSN_alu_ADD           3'b000
+`define INSN_alu_ADC           3'b001
+`define INSN_alu_SUB           3'b010
+`define INSN_alu_SBC           3'b011
+`define INSN_alu_AND           3'b100
+`define INSN_alu_XOR           3'b101
+`define INSN_alu_OR            3'b110
+`define INSN_alu_CP            3'b111          // Oh lawd, is dat some CP?
+
 module GBZ80Core(
        input clk,
        output reg [15:0] busaddress,   /* BUS_* is latched on STATE_FETCH. */
@@ -303,6 +313,26 @@ module GBZ80Core(
                                        end
                                endcase
                        end
+                       `INSN_ALU8: begin
+                               if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
+                                       // fffffffff fuck your shit, read from (HL) :(
+                                       rd <= 1;
+                                       address <= {registers[`REG_H], registers[`REG_L]};
+                               end else begin
+                                       `EXEC_NEWCYCLE;
+                                       `EXEC_INC_PC;
+                                       case (opcode[2:0])
+                                       `INSN_reg_A:    begin tmp <= registers[`REG_A]; end
+                                       `INSN_reg_B:    begin tmp <= registers[`REG_B]; end
+                                       `INSN_reg_C:    begin tmp <= registers[`REG_C]; end
+                                       `INSN_reg_D:    begin tmp <= registers[`REG_D]; end
+                                       `INSN_reg_E:    begin tmp <= registers[`REG_E]; end
+                                       `INSN_reg_H:    begin tmp <= registers[`REG_H]; end
+                                       `INSN_reg_L:    begin tmp <= registers[`REG_L]; end
+                                       `INSN_reg_dHL:  begin tmp <= rdata; end
+                                       endcase
+                               end
+                       end
                        default:
                                $stop;
                        endcase
@@ -467,6 +497,28 @@ module GBZ80Core(
                                        end
                                endcase
                        end
+                       `INSN_ALU8: begin
+                               if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
+                                       /* Sit on our asses. */
+                                       cycle <= 1;
+                               end else begin          /* Actually do the computation! */
+                                       case (opcode[5:3])
+                                       `INSN_alu_ADD: begin
+                                               registers[`REG_A] <=
+                                                       registers[`REG_A] + tmp;
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] + tmp) == 0) ? 1'b1 : 1'b0,
+                                                         /* N */ 0,
+                                                         /* H */ (({1'b0,registers[`REG_A][3:0]} + {1'b0,tmp[3:0]}) >> 4 == 1) ? 1'b1 : 1'b0,
+                                                         /* C */ (({1'b0,registers[`REG_A]} + {1'b0,tmp}) >> 8 == 1) ? 1'b1 : 1'b0,
+                                                         registers[`REG_F][3:0]
+                                                       };
+                                       end
+                                       default:
+                                               $stop;
+                                       endcase
+                               end
+                       end
                        endcase
                        state <= `STATE_FETCH;
                end