Split out more insns

[fpgaboy.git] / GBZ80Core.v

diff --git a/GBZ80Core.v b/GBZ80Core.v
index 1d06b12f1bfd3cd10d752cd166e0d8a195c1d9d8..f41805ac3c679aeebded8c8d2014f921fe8931c0 100644 (file)
--- a/GBZ80Core.v
+++ b/GBZ80Core.v
@@ -31,6 +31,30 @@
 `define INSN_PUSH_reg          8'b11xx0101
 `define INSN_POP_reg                   8'b11xx0001
 `define INSN_LDH_AC                    8'b111x0010     // Either LDH A,(C) or LDH (C),A
 `define INSN_PUSH_reg          8'b11xx0101
 `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_NOP                               8'b00000000
+`define INSN_RST                               8'b11xxx111
+`define INSN_RET                               8'b110x1001     // 1 = RETI, 0 = RET
+`define INSN_RETCC                     8'b110xx000
+`define INSN_CALL                              8'b11001101
+`define INSN_CALLCC                    8'b110xx100     // Not that call/cc.
+`define INSN_JP_imm                    8'b11000011
+`define INSN_JPCC_imm          8'b110xx010
+`define INSN_ALU_A             8'b00xxx111
+`define INSN_JP_HL                     8'b11101001
+`define INSN_JR_imm                    8'b00011000
+`define INSN_JRCC_imm          8'b001xx000
+`define INSN_INCDEC16          8'b00xxx011
+`define INSN_VOP_INTR          8'b11111100     // 0xFC is grabbed by the fetch if there is an interrupt pending.
+`define INSN_DI                                8'b11110011
+`define INSN_EI                                8'b11111011
+
+`define INSN_cc_NZ                     2'b00
+`define INSN_cc_Z                              2'b01
+`define INSN_cc_NC                     2'b10
+`define INSN_cc_C                              2'b11
+

 `define INSN_reg_A             3'b111
 `define INSN_reg_B             3'b000
 `define INSN_reg_C             3'b001
 `define INSN_reg_A             3'b111
 `define INSN_reg_B             3'b000
 `define INSN_reg_C             3'b001


@@ -47,14 +71,32 @@
 `define INSN_stack_BC  2'b00
 `define INSN_stack_DE  2'b01
 `define INSN_stack_HL  2'b10
 `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?
+`define INSN_alu_RLCA          3'b000
+`define INSN_alu_RRCA          3'b001
+`define INSN_alu_RLA           3'b010
+`define INSN_alu_RRA           3'b011
+`define INSN_alu_DAA           3'b100
+`define INSN_alu_CPL           3'b101
+`define INSN_alu_SCF           3'b110
+`define INSN_alu_CCF           3'b111
+

 module GBZ80Core(
        input clk,
        output reg [15:0] busaddress,   /* BUS_* is latched on STATE_FETCH. */
        inout [7:0] busdata,
 module GBZ80Core(
        input clk,
        output reg [15:0] busaddress,   /* BUS_* is latched on STATE_FETCH. */
        inout [7:0] busdata,

-       output reg buswr, output reg busrd);
+       output reg buswr, output reg busrd,
+       input irq, input [7:0] jaddr);

        
        

-       reg [1:0] state = 0;                                    /* State within this bus cycle (see STATE_*). */
-       reg [2:0] cycle = 0;                                    /* Cycle for instructions. */
+       reg [1:0] state;                                        /* State within this bus cycle (see STATE_*). */
+       reg [2:0] cycle;                                        /* Cycle for instructions. */

        
        reg [7:0] registers[11:0];
        
        
        reg [7:0] registers[11:0];
        


@@ -63,13 +105,15 @@ module GBZ80Core(
        reg [7:0] opcode;                               /* Opcode from the current machine cycle. */
        
        reg [7:0] rdata, wdata;         /* Read data from this bus cycle, or write data for the next. */
        reg [7:0] opcode;                               /* Opcode from the current machine cycle. */
        
        reg [7:0] rdata, wdata;         /* Read data from this bus cycle, or write data for the next. */

-       reg rd = 1, wr = 0, newcycle = 1;
+       reg rd, wr, newcycle;

        
        

-       reg [7:0] tmp;                                  /* Generic temporary reg. */
+       reg [7:0] tmp, tmp2;                    /* Generic temporary regs. */

        
        reg [7:0] buswdata;
        assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
        
        
        reg [7:0] buswdata;
        assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
        

+       reg ie, iedelay;
+       

        initial begin
                registers[ 0] <= 0;
                registers[ 1] <= 0;
        initial begin
                registers[ 0] <= 0;
                registers[ 1] <= 0;


@@ -83,29 +127,54 @@ module GBZ80Core(
                registers[ 9] <= 0;
                registers[10] <= 0;
                registers[11] <= 0;
                registers[ 9] <= 0;
                registers[10] <= 0;
                registers[11] <= 0;

+               rd <= 1;
+               wr <= 0;
+               newcycle <= 1;
+               state <= 0;
+               cycle <= 0;
+               busrd <= 0;
+               buswr <= 0;
+               busaddress <= 0;
+               ie <= 0;
+               iedelay <= 0;
+               opcode <= 0;
+               state <= `STATE_WRITEBACK;
+               cycle <= 0;

        end
 
        always @(posedge clk)
                case (state)
                `STATE_FETCH: begin
        end
 
        always @(posedge clk)
                case (state)
                `STATE_FETCH: begin

-                       if (wr)
-                               buswdata <= wdata;
-                       if (newcycle)
+                       if (newcycle) begin

                                busaddress <= {registers[`REG_PCH], registers[`REG_PCL]};
                                busaddress <= {registers[`REG_PCH], registers[`REG_PCL]};

-                       else
+                               buswr <= 0;
+                               busrd <= 1;
+                       end else begin

                                busaddress <= address;
                                busaddress <= address;

-                       buswr <= wr;
-                       busrd <= rd;
+                               buswr <= wr;
+                               busrd <= rd;
+                               if (wr)
+                                       buswdata <= wdata;
+                       end

                        state <= `STATE_DECODE;
                end
                `STATE_DECODE: begin
                        if (newcycle) begin
                        state <= `STATE_DECODE;
                end
                `STATE_DECODE: begin
                        if (newcycle) begin

-                               opcode <= busdata;
+                               if (ie && irq)
+                                       opcode <= `INSN_VOP_INTR;
+                               else
+                                       opcode <= busdata;

                                rdata <= busdata;
                                newcycle <= 0;
                                cycle <= 0;
                                rdata <= busdata;
                                newcycle <= 0;
                                cycle <= 0;

-                       end else
+                       end else begin

                                if (rd) rdata <= busdata;
                                if (rd) rdata <= busdata;

+                               cycle <= cycle + 1;
+                       end
+                       if (iedelay) begin
+                               ie <= 1;
+                               iedelay <= 0;
+                       end

                        buswr <= 0;
                        busrd <= 0;
                        wr <= 0;
                        buswr <= 0;
                        busrd <= 0;
                        wr <= 0;


@@ -122,168 +191,206 @@ module GBZ80Core(
 `define EXEC_NEWCYCLE \
        newcycle <= 1; rd <= 1; wr <= 0
                        casex (opcode)
 `define EXEC_NEWCYCLE \
        newcycle <= 1; rd <= 1; wr <= 0
                        casex (opcode)

-                       `INSN_LD_reg_imm8: begin
+                       `define EXECUTE
+                       `include "allinsns.v"
+                       `undef EXECUTE
+                       `INSN_RST: begin

                                case (cycle)
                                0:      begin
                                case (cycle)
                                0:      begin

-                                               `EXEC_INC_PC;
-                                               `EXEC_NEXTADDR_PCINC;
-                                               rd <= 1;
+                                               `EXEC_INC_PC;           // This goes FIRST in RST

                                        end
                                        end

-                               1: begin
-                                               `EXEC_INC_PC;
-                                               if (opcode[5:3] == `INSN_reg_dHL) begin
-                                                       address <= {registers[`REG_H], registers[`REG_L]};
-                                                       wdata <= rdata;
-                                                       rd <= 0;
-                                                       wr <= 1;
-                                               end else begin
-                                                       `EXEC_NEWCYCLE;
-                                               end
+                               1:      begin
+                                               wr <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
+                                               wdata <= registers[`REG_PCH];
+                                       end
+                               2:      begin
+                                               wr <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]}-2;
+                                               wdata <= registers[`REG_PCL];

                                        end
                                        end

-                               2: begin
+                               3:      begin

                                                `EXEC_NEWCYCLE;
                                                `EXEC_NEWCYCLE;

+                                               {registers[`REG_PCH],registers[`REG_PCL]} <=
+                                                       {10'b0,opcode[5:3],3'b0};

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_HALT: begin
-                               `EXEC_NEWCYCLE;
-                               /* XXX Interrupts needed for HALT. */
-                       end
-                       `INSN_LD_HL_reg: begin
+                       `INSN_RET,`INSN_RETCC: begin

                                case (cycle)
                                0:      begin
                                case (cycle)
                                0:      begin

-                                               case (opcode[2:0])
-                                               `INSN_reg_A:    begin wdata <= registers[`REG_A]; end
-                                               `INSN_reg_B:    begin wdata <= registers[`REG_B]; end
-                                               `INSN_reg_C:    begin wdata <= registers[`REG_C]; end
-                                               `INSN_reg_D:    begin wdata <= registers[`REG_D]; end
-                                               `INSN_reg_E:    begin wdata <= registers[`REG_E]; end
-                                               `INSN_reg_H:    begin wdata <= registers[`REG_H]; end
-                                               `INSN_reg_L:    begin wdata <= registers[`REG_L]; end
-                                               endcase
-                                               address <= {registers[`REG_H], registers[`REG_L]};
-                                               wr <= 1; rd <= 0;
+                                               rd <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]};

                                        end
                                        end

-                               1:      begin
-                                               `EXEC_INC_PC;
-                                               `EXEC_NEWCYCLE;
+                               1:      begin   // SPECIAL CASE: cycle does NOT increase linearly with ret!
+                                               `EXEC_INC_PC;   // cycle 1 is skipped if we are not retcc
+                                               case (opcode[4:3])
+                                               `INSN_cc_NZ:    if (registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                               `INSN_cc_Z:             if (~registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                               `INSN_cc_NC:    if (registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                               `INSN_cc_C:             if (~registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                               endcase
+                                               rd <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]};

                                        end
                                        end

-                               endcase
-                       end
-                       `INSN_LD_reg_HL: begin
-                               case(cycle)
-                               0: begin
-                                               address <= {registers[`REG_H], registers[`REG_L]};
+                               2:      begin

                                                rd <= 1;
                                                rd <= 1;

+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} + 1;

                                        end
                                        end

-                               1: begin
-                                               tmp <= rdata;
-                                               `EXEC_INC_PC;
+                               3:      begin /* twiddle thumbs */ end
+                               4:      begin

                                                `EXEC_NEWCYCLE;
                                                `EXEC_NEWCYCLE;

+                                               // do NOT increment PC!

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_LD_reg_reg: begin
-                               `EXEC_INC_PC;
-                               `EXEC_NEWCYCLE;
-                               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
-                               endcase
-                       end
-                       `INSN_LD_reg_imm16: begin
-                               `EXEC_INC_PC;
+                       `INSN_CALL,`INSN_CALLCC: begin

                                case (cycle)
                                0:      begin
                                case (cycle)
                                0:      begin

+                                               `EXEC_INC_PC;

                                                `EXEC_NEXTADDR_PCINC;
                                                rd <= 1;
                                        end
                                1:      begin
                                                `EXEC_NEXTADDR_PCINC;
                                                rd <= 1;
                                        end
                                1:      begin

+                                               `EXEC_INC_PC;

                                                `EXEC_NEXTADDR_PCINC;
                                                rd <= 1;
                                        end
                                                `EXEC_NEXTADDR_PCINC;
                                                rd <= 1;
                                        end

-                               2: begin `EXEC_NEWCYCLE; end
+                               2:      begin
+                                               `EXEC_INC_PC;
+                                               if (!opcode[0]) // i.e., is callcc
+                                                       /* We need to check the condition code to bail out. */
+                                                       case (opcode[4:3])
+                                                       `INSN_cc_NZ:    if (registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_Z:             if (~registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_NC:    if (registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_C:             if (~registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                                       endcase
+                                       end
+                               3:      begin
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+                                               wdata <= registers[`REG_PCH];
+                                               wr <= 1;
+                                       end
+                               4:      begin
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+                                               wdata <= registers[`REG_PCL];
+                                               wr <= 1;
+                                       end
+                               5:      begin
+                                               `EXEC_NEWCYCLE; /* do NOT increment the PC */
+                                       end

                                endcase
                        end
                                endcase
                        end

-                       `INSN_LD_SP_HL: begin
+                       `INSN_JP_imm,`INSN_JPCC_imm: begin

                                case (cycle)
                                0:      begin
                                case (cycle)
                                0:      begin

-                                               tmp <= registers[`REG_H];
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;

                                        end
                                1:      begin
                                        end
                                1:      begin

-                                               `EXEC_NEWCYCLE;

                                                `EXEC_INC_PC;
                                                `EXEC_INC_PC;

-                                               tmp <= registers[`REG_L];
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               2:      begin
+                                               `EXEC_INC_PC;
+                                               if (!opcode[0]) begin   // i.e., JP cc,nn
+                                                       /* We need to check the condition code to bail out. */
+                                                       case (opcode[4:3])
+                                                       `INSN_cc_NZ:    if (registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_Z:             if (~registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_NC:    if (registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_C:             if (~registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                                       endcase
+                                               end
+                                       end
+                               3:      begin
+                                               `EXEC_NEWCYCLE;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_PUSH_reg: begin   /* PUSH is 16 cycles! */
+                       `INSN_JP_HL: begin
+                               `EXEC_NEWCYCLE;
+                       end
+                       `INSN_JR_imm,`INSN_JRCC_imm: begin

                                case (cycle)
                                case (cycle)

-                               0: begin
-                                               wr <= 1;
-                                               address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
-                                               case (opcode[5:4])
-                                               `INSN_stack_AF: wdata <= registers[`REG_A];
-                                               `INSN_stack_BC: wdata <= registers[`REG_B];
-                                               `INSN_stack_DE: wdata <= registers[`REG_D];
-                                               `INSN_stack_HL: wdata <= registers[`REG_H];
-                                               endcase
+                               0:      begin
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;

                                        end
                                1: begin
                                        end
                                1: begin

-                                               wr <= 1;
-                                               address <= {registers[`REG_SPH],registers[`REG_SPL]}-1;
-                                               case (opcode[5:4])
-                                               `INSN_stack_AF: wdata <= registers[`REG_F];
-                                               `INSN_stack_BC: wdata <= registers[`REG_C];
-                                               `INSN_stack_DE: wdata <= registers[`REG_E];
-                                               `INSN_stack_HL: wdata <= registers[`REG_L];
-                                               endcase
+                                               `EXEC_INC_PC;
+                                               if (opcode[5]) begin    // i.e., JP cc,nn
+                                                       /* We need to check the condition code to bail out. */
+                                                       case (opcode[4:3])
+                                                       `INSN_cc_NZ:    if (registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_Z:             if (~registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_NC:    if (registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                                       `INSN_cc_C:             if (~registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+                                                       endcase
+                                               end

                                        end
                                        end

-                               2:      begin /* TWIDDLE OUR FUCKING THUMBS! */ end
-                               3: begin
+                               2:      begin

                                                `EXEC_NEWCYCLE;
                                                `EXEC_NEWCYCLE;

-                                               `EXEC_INC_PC;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_POP_reg: begin    /* POP is 12 cycles! */
+                       `INSN_INCDEC16: begin

                                case (cycle)
                                0: begin
                                case (cycle)
                                0: begin

-                                               rd <= 1;
-                                               address <= {registers[`REG_SPH],registers[`REG_SPL]};
+                                               case (opcode[5:4])
+                                               `INSN_reg16_BC: begin
+                                                       tmp <= registers[`REG_B];
+                                                       tmp2 <= registers[`REG_C];
+                                               end
+                                               `INSN_reg16_DE: begin
+                                                       tmp <= registers[`REG_D];
+                                                       tmp2 <= registers[`REG_E];
+                                               end
+                                               `INSN_reg16_HL: begin
+                                                       tmp <= registers[`REG_H];
+                                                       tmp2 <= registers[`REG_L];
+                                               end
+                                               `INSN_reg16_SP: begin
+                                                       tmp <= registers[`REG_SPH];
+                                                       tmp2 <= registers[`REG_SPL];
+                                               end
+                                               endcase

                                        end
                                1: begin
                                        end
                                1: begin

-                                               rd <= 1;
-                                               address <= {registers[`REG_SPH],registers[`REG_SPL]};
-                                       end
-                               2: begin
-                                               `EXEC_NEWCYCLE;

                                                `EXEC_INC_PC;
                                                `EXEC_INC_PC;

+                                               `EXEC_NEWCYCLE;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_LDH_AC: begin
+                       `INSN_VOP_INTR: begin

                                case (cycle)
                                0:      begin
                                case (cycle)
                                0:      begin

-                                               address <= {8'hFF,registers[`REG_C]};
-                                               if (opcode[4]) begin    // LD A,(C)
-                                                       rd <= 1;
-                                               end else begin
-                                                       wr <= 1;
-                                                       wdata <= {8'hFF,registers[`REG_A]};
-                                               end
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+                                               wdata <= registers[`REG_PCH];
+                                               wr <= 1;

                                        end
                                        end

-                               1: begin
+                               1:      begin
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+                                               wdata <= registers[`REG_PCL];
+                                               wr <= 1;
+                                       end
+                               2:      begin

                                                `EXEC_NEWCYCLE;
                                                `EXEC_NEWCYCLE;

-                                               `EXEC_INC_PC;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

+                       `INSN_DI: begin
+                               `EXEC_NEWCYCLE;
+                               `EXEC_INC_PC;
+                       end
+                       `INSN_EI: begin
+                               `EXEC_NEWCYCLE;
+                               `EXEC_INC_PC;
+                       end

                        default:
                                $stop;
                        endcase
                        default:
                                $stop;
                        endcase


@@ -291,170 +398,114 @@ module GBZ80Core(
                end
                `STATE_WRITEBACK: begin
                        casex (opcode)
                end
                `STATE_WRITEBACK: begin
                        casex (opcode)

-                       `INSN_LD_reg_imm8:
+                       `define WRITEBACK
+                       `include "allinsns.v"
+                       `undef WRITEBACK
+                       `INSN_RST: begin

                                case (cycle)
                                case (cycle)

-                               0: cycle <= 1;
-                               1: case (opcode[5:3])
-                                       `INSN_reg_A:    begin registers[`REG_A] <= rdata; cycle <= 0; end
-                                       `INSN_reg_B:    begin registers[`REG_B] <= rdata; cycle <= 0; end
-                                       `INSN_reg_C:    begin registers[`REG_C] <= rdata; cycle <= 0; end
-                                       `INSN_reg_D:    begin registers[`REG_D] <= rdata; cycle <= 0; end
-                                       `INSN_reg_E:    begin registers[`REG_E] <= rdata; cycle <= 0; end
-                                       `INSN_reg_H:    begin registers[`REG_H] <= rdata; cycle <= 0; end
-                                       `INSN_reg_L:    begin registers[`REG_L] <= rdata; cycle <= 0; end
-                                       `INSN_reg_dHL:  cycle <= 2;
-                                       endcase
-                               2: cycle <= 0;
+                               0:      begin /* type F */ end
+                               1:      begin /* type F */ end
+                               2:      begin /* type F */ end
+                               3:      {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                               {registers[`REG_SPH],registers[`REG_SPL]}-2;

                                endcase
                                endcase

-                       `INSN_HALT: begin
-                               /* Nothing needs happen here. */
-                               /* XXX Interrupts needed for HALT. */

                        end
                        end

-                       `INSN_LD_HL_reg: begin
+                       `INSN_RET,`INSN_RETCC: begin

                                case (cycle)
                                case (cycle)

-                               0: cycle <= 1;
-                               1: cycle <= 0;
-                               endcase
-                       end
-                       `INSN_LD_reg_HL: begin
-                               case (cycle)
-                               0:      cycle <= 1;
-                               1:      begin
-                                               case (opcode[5:3])
-                                               `INSN_reg_A:    begin registers[`REG_A] <= tmp; end
-                                               `INSN_reg_B:    begin registers[`REG_B] <= tmp; end
-                                               `INSN_reg_C:    begin registers[`REG_C] <= tmp; end
-                                               `INSN_reg_D:    begin registers[`REG_D] <= tmp; end
-                                               `INSN_reg_E:    begin registers[`REG_E] <= tmp; end
-                                               `INSN_reg_H:    begin registers[`REG_H] <= tmp; end
-                                               `INSN_reg_L:    begin registers[`REG_L] <= tmp; end
-                                               endcase
-                                               cycle <= 0;
+                               0:      if (opcode[0])  // i.e., not RETCC
+                                               cycle <= 1;     // Skip cycle 1; it gets incremented on the next round.
+                               1: begin /* Nothing need happen here. */ end
+                               2:      registers[`REG_PCL] <= rdata;
+                               3:      registers[`REG_PCH] <= rdata;
+                               4:      begin
+                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                                       {registers[`REG_SPH],registers[`REG_SPL]} + 2;
+                                               if (opcode[4] && opcode[0])     /* RETI */
+                                                       ie <= 1;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_LD_reg_reg: begin
-                               case (opcode[5:3])
-                               `INSN_reg_A:    begin registers[`REG_A] <= tmp; end
-                               `INSN_reg_B:    begin registers[`REG_B] <= tmp; end
-                               `INSN_reg_C:    begin registers[`REG_C] <= tmp; end
-                               `INSN_reg_D:    begin registers[`REG_D] <= tmp; end
-                               `INSN_reg_E:    begin registers[`REG_E] <= tmp; end
-                               `INSN_reg_H:    begin registers[`REG_H] <= tmp; end
-                               `INSN_reg_L:    begin registers[`REG_L] <= tmp; end
-                               endcase
-                       end
-                       `INSN_LD_reg_imm16: begin
+                       `INSN_CALL,`INSN_CALLCC: begin

                                case (cycle)
                                case (cycle)

-                               0:      cycle <= 1;
-                               1:      begin
-                                               case (opcode[5:4])
-                                               `INSN_reg16_BC: registers[`REG_C] <= rdata;
-                                               `INSN_reg16_DE: registers[`REG_E] <= rdata;
-                                               `INSN_reg16_HL: registers[`REG_L] <= rdata;
-                                               `INSN_reg16_SP: registers[`REG_SPL] <= rdata;
-                                               endcase
-                                               cycle <= 2;
-                                       end
-                               2: begin
-                                               case (opcode[5:4])
-                                               `INSN_reg16_BC: registers[`REG_B] <= rdata;
-                                               `INSN_reg16_DE: registers[`REG_D] <= rdata;
-                                               `INSN_reg16_HL: registers[`REG_H] <= rdata;
-                                               `INSN_reg16_SP: registers[`REG_SPH] <= rdata;
-                                               endcase
-                                               cycle <= 0;
+                               0:      begin /* type F */ end
+                               1:      tmp <= rdata;   // tmp contains newpcl
+                               2:      tmp2 <= rdata;  // tmp2 contains newpch
+                               3:      begin /* type F */ end
+                               4:      registers[`REG_PCH] <= tmp2;
+                               5: begin
+                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                                       {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+                                               registers[`REG_PCL] <= tmp;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_LD_SP_HL: begin
+                       `INSN_JP_imm,`INSN_JPCC_imm: begin

                                case (cycle)
                                case (cycle)

-                               0: begin
-                                               cycle <= 1;
-                                               registers[`REG_SPH] <= tmp;
-                                       end
-                               1: begin
-                                               cycle <= 0;
-                                               registers[`REG_SPL] <= tmp;
-                                       end
+                               0:      begin /* type F */ end
+                               1:      tmp <= rdata;   // tmp contains newpcl
+                               2:      tmp2 <= rdata;  // tmp2 contains newpch
+                               3:      {registers[`REG_PCH],registers[`REG_PCL]} <=
+                                               {tmp2,tmp};

                                endcase
                        end
                                endcase
                        end

-                       `INSN_PUSH_reg: begin   /* PUSH is 16 cycles! */
+                       `INSN_JP_HL: begin
+                               {registers[`REG_PCH],registers[`REG_PCL]} <=
+                                       {registers[`REG_H],registers[`REG_L]};
+                       end
+                       `INSN_JR_imm,`INSN_JRCC_imm: begin

                                case (cycle)
                                case (cycle)

-                               0: begin
-                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
-                                                       {registers[`REG_SPH],registers[`REG_SPL]} - 1;
-                                               cycle <= 1;
-                                       end
-                               1:      begin
-                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
-                                                       {registers[`REG_SPH],registers[`REG_SPL]} - 1;
-                                               cycle <= 2;
-                                       end
-                               2:      cycle <= 3;
-                               3:      cycle <= 0;
+                               0:      begin /* type F */ end
+                               1:      tmp <= rdata;
+                               2: {registers[`REG_PCH],registers[`REG_PCL]} <=
+                                               {registers[`REG_PCH],registers[`REG_PCL]} +
+                                               {tmp[7]?8'hFF:8'h00,tmp};

                                endcase
                        end
                                endcase
                        end

-                       `INSN_POP_reg: begin    /* POP is 12 cycles! */
+                       `INSN_INCDEC16: begin

                                case (cycle)
                                case (cycle)

-                               0:      begin
-                                               cycle <= 1;
-                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
-                                                       {registers[`REG_SPH],registers[`REG_SPL]} + 1;
-                                       end
-                               1:      begin
-                                               case (opcode[5:4])
-                                               `INSN_stack_AF: registers[`REG_F] <= rdata;
-                                               `INSN_stack_BC: registers[`REG_C] <= rdata;
-                                               `INSN_stack_DE: registers[`REG_E] <= rdata;
-                                               `INSN_stack_HL: registers[`REG_L] <= rdata;
-                                               endcase
-                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
-                                                       {registers[`REG_SPH],registers[`REG_SPL]} + 1;
-                                               cycle <= 2;
-                                       end
-                               2:      begin
+                               0:      {tmp,tmp2} <= {tmp,tmp2} +
+                                               (opcode[3] ? 16'hFFFF : 16'h0001);
+                               1: begin

                                                case (opcode[5:4])
                                                case (opcode[5:4])

-                                               `INSN_stack_AF: registers[`REG_A] <= rdata;
-                                               `INSN_stack_BC: registers[`REG_B] <= rdata;
-                                               `INSN_stack_DE: registers[`REG_D] <= rdata;
-                                               `INSN_stack_HL: registers[`REG_H] <= rdata;
+                                               `INSN_reg16_BC: begin
+                                                       registers[`REG_B] <= tmp;
+                                                       registers[`REG_C] <= tmp2;
+                                               end
+                                               `INSN_reg16_DE: begin
+                                                       registers[`REG_D] <= tmp;
+                                                       registers[`REG_E] <= tmp2;
+                                               end
+                                               `INSN_reg16_HL: begin
+                                                       registers[`REG_H] <= tmp;
+                                                       registers[`REG_L] <= tmp2;
+                                               end
+                                               `INSN_reg16_SP: begin
+                                                       registers[`REG_SPH] <= tmp;
+                                                       registers[`REG_SPL] <= tmp2;
+                                               end

                                                endcase
                                                endcase

-                                               cycle <= 0;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

-                       `INSN_LDH_AC: begin
+                       `INSN_VOP_INTR: begin

                                case (cycle)
                                case (cycle)

-                               0:      cycle <= 1;
-                               1: begin
-                                               cycle <= 0;
-                                               if (opcode[4])
-                                                       registers[`REG_A] <= rdata;
+                               0:      begin end
+                               1:      begin end
+                               2:      begin
+                                               ie <= 0;
+                                               {registers[`REG_PCH],registers[`REG_PCL]} <=
+                                                       {8'b0,jaddr};
+                                               {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                                       {registers[`REG_SPH],registers[`REG_SPL]} - 2;

                                        end
                                endcase
                        end
                                        end
                                endcase
                        end

+                       `INSN_DI: ie <= 0;
+                       `INSN_EI: iedelay <= 1;
+                       default:
+                               $stop;

                        endcase
                        state <= `STATE_FETCH;
                end
                endcase
 endmodule
                        endcase
                        state <= `STATE_FETCH;
                end
                endcase
 endmodule

-
-`timescale 1ns / 1ps
-module TestBench();
-       reg clk = 0;
-       wire [15:0] addr;
-       wire [7:0] data;
-       wire wr, rd;
-       reg [7:0] rom [2047:0];
-       
-       initial $readmemh("rom.hex", rom);
-       always #10 clk <= ~clk;
-       GBZ80Core core(
-               .clk(clk),
-               .busaddress(addr),
-               .busdata(data),
-               .buswr(wr),
-               .busrd(rd));
-       assign data = rd ? rom[addr] : 8'bzzzzzzzz;
-endmodule