First cut at timer

[fpgaboy.git] / GBZ80Core.v

diff --git a/GBZ80Core.v b/GBZ80Core.v
index e5a7d35e16262ccfa113e892f147e39f9260adee..96e4dcd38a164996df038dca0232ab82a837e90e 100644 (file)
--- a/GBZ80Core.v
+++ b/GBZ80Core.v
@@ -26,6 +26,32 @@
 `define INSN_LD_HL_reg         8'b01110xxx
 `define INSN_LD_reg_HL         8'b01xxx110
 `define INSN_LD_reg_reg                8'b01xxxxxx
 `define INSN_LD_HL_reg         8'b01110xxx
 `define INSN_LD_reg_HL         8'b01xxx110
 `define INSN_LD_reg_reg                8'b01xxxxxx

+`define INSN_LD_reg_imm16      8'b00xx0001
+`define INSN_LD_SP_HL          8'b11111001
+`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_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


@@ -34,6 +60,30 @@
 `define INSN_reg_H             3'b100
 `define INSN_reg_L             3'b101
 `define INSN_reg_dHL   3'b110
 `define INSN_reg_H             3'b100
 `define INSN_reg_L             3'b101
 `define INSN_reg_dHL   3'b110

+`define INSN_reg16_BC  2'b00
+`define INSN_reg16_DE  2'b01
+`define INSN_reg16_HL  2'b10
+`define INSN_reg16_SP  2'b11
+`define INSN_stack_AF  2'b11
+`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,
 
 module GBZ80Core(
        input clk,


@@ -53,37 +103,48 @@ module GBZ80Core(
        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 [7:0] rdata, wdata;         /* Read data from this bus cycle, or write data for the next. */
        reg rd = 1, wr = 0, newcycle = 1;
        

-       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 = 0;
+       

        initial begin
        initial begin

-               registers[ 0] = 0;
-               registers[ 1] = 0;
-               registers[ 2] = 0;
-               registers[ 3] = 0;
-               registers[ 4] = 0;
-               registers[ 5] = 0;
-               registers[ 6] = 0;
-               registers[ 7] = 0;
-               registers[ 8] = 0;
-               registers[ 9] = 0;
-               registers[10] = 0;
-               registers[11] = 0;
+               registers[ 0] <= 0;
+               registers[ 1] <= 0;
+               registers[ 2] <= 0;
+               registers[ 3] <= 0;
+               registers[ 4] <= 0;
+               registers[ 5] <= 0;
+               registers[ 6] <= 0;
+               registers[ 7] <= 0;
+               registers[ 8] <= 0;
+               registers[ 9] <= 0;
+               registers[10] <= 0;
+               registers[11] <= 0;
+               ie <= 0;
+               rd <= 1;
+               wr <= 0;
+               newcycle <= 1;
+               state <= 0;
+               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
                        state <= `STATE_DECODE;
                end
                `STATE_DECODE: begin


@@ -92,10 +153,16 @@ module GBZ80Core(
                                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

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

+                       wr <= 0;
+                       rd <= 0;
+                       address <= 16'bxxxxxxxxxxxxxxxx;        // Make it obvious if something of type has happened.
+                       wdata <= 8'bxxxxxxxx;

                        state <= `STATE_EXECUTE;
                end
                `STATE_EXECUTE: begin
                        state <= `STATE_EXECUTE;
                end
                `STATE_EXECUTE: begin


@@ -113,7 +180,7 @@ module GBZ80Core(
                                                `EXEC_NEXTADDR_PCINC;
                                                rd <= 1;
                                        end
                                                `EXEC_NEXTADDR_PCINC;
                                                rd <= 1;
                                        end

-                               1: begin
+                               1:      begin

                                                `EXEC_INC_PC;
                                                if (opcode[5:3] == `INSN_reg_dHL) begin
                                                        address <= {registers[`REG_H], registers[`REG_L]};
                                                `EXEC_INC_PC;
                                                if (opcode[5:3] == `INSN_reg_dHL) begin
                                                        address <= {registers[`REG_H], registers[`REG_L]};


@@ -124,94 +191,715 @@ module GBZ80Core(
                                                        `EXEC_NEWCYCLE;
                                                end
                                        end
                                                        `EXEC_NEWCYCLE;
                                                end
                                        end

-                               2: begin
+                               2:      begin

                                                `EXEC_NEWCYCLE;
                                        end
                                endcase
                        end
                        `INSN_HALT: begin
                                                `EXEC_NEWCYCLE;
                                        end
                                endcase
                        end
                        `INSN_HALT: begin

-                               /* XXX UNIMP */
+                               `EXEC_NEWCYCLE;
+                               /* XXX Interrupts needed for HALT. */

                        end
                        `INSN_LD_HL_reg: begin
                        end
                        `INSN_LD_HL_reg: begin

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

                        end
                        `INSN_LD_reg_HL: begin
                        end
                        `INSN_LD_reg_HL: begin

-                               /* XXX UNIMP */
+                               case(cycle)
+                               0:      begin
+                                               address <= {registers[`REG_H], registers[`REG_L]};
+                                               rd <= 1;
+                                       end
+                               1:      begin
+                                               tmp <= rdata;
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEWCYCLE;
+                                       end
+                               endcase

                        end
                        `INSN_LD_reg_reg: begin
                                `EXEC_INC_PC;
                                `EXEC_NEWCYCLE;
                                case (opcode[2:0])
                        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
+                               `INSN_reg_A:    tmp <= registers[`REG_A];
+                               `INSN_reg_B:    tmp <= registers[`REG_B];
+                               `INSN_reg_C:    tmp <= registers[`REG_C];
+                               `INSN_reg_D:    tmp <= registers[`REG_D];
+                               `INSN_reg_E:    tmp <= registers[`REG_E];
+                               `INSN_reg_H:    tmp <= registers[`REG_H];
+                               `INSN_reg_L:    tmp <= registers[`REG_L];
+                               endcase
+                       end
+                       `INSN_LD_reg_imm16: begin
+                               `EXEC_INC_PC;
+                               case (cycle)
+                               0:      begin
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               1:      begin
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               2: begin `EXEC_NEWCYCLE; end

                                endcase
                        end
                                endcase
                        end

+                       `INSN_LD_SP_HL: begin
+                               case (cycle)
+                               0:      begin
+                                               tmp <= registers[`REG_H];
+                                       end
+                               1:      begin
+                                               `EXEC_NEWCYCLE;
+                                               `EXEC_INC_PC;
+                                               tmp <= registers[`REG_L];
+                                       end
+                               endcase
+                       end
+                       `INSN_PUSH_reg: begin   /* PUSH is 16 cycles! */
+                               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
+                                       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
+                                       end
+                               2:      begin /* Twiddle thumbs. */ end
+                               3:      begin
+                                               `EXEC_NEWCYCLE;
+                                               `EXEC_INC_PC;
+                                       end
+                               endcase
+                       end
+                       `INSN_POP_reg: begin    /* POP is 12 cycles! */
+                               case (cycle)
+                               0:      begin
+                                               rd <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]};
+                                       end
+                               1:      begin
+                                               rd <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]};
+                                       end
+                               2:      begin
+                                               `EXEC_NEWCYCLE;
+                                               `EXEC_INC_PC;
+                                       end
+                               endcase
+                       end
+                       `INSN_LDH_AC: 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 <= registers[`REG_A];
+                                               end
+                                       end
+                               1:      begin
+                                               `EXEC_NEWCYCLE;
+                                               `EXEC_INC_PC;
+                                       end
+                               endcase
+                       end
+                       `INSN_LDx_AHL: begin
+                               case (cycle)
+                               0:      begin
+                                               address <= {registers[`REG_H],registers[`REG_L]};
+                                               if (opcode[3]) begin    // LDx A, (HL)
+                                                       rd <= 1;
+                                               end else begin
+                                                       wr <= 1;
+                                                       wdata <= registers[`REG_A];
+                                               end
+                                       end
+                               1:      begin
+                                               `EXEC_NEWCYCLE;
+                                               `EXEC_INC_PC;
+                                       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:    tmp <= registers[`REG_A];
+                                       `INSN_reg_B:    tmp <= registers[`REG_B];
+                                       `INSN_reg_C:    tmp <= registers[`REG_C];
+                                       `INSN_reg_D:    tmp <= registers[`REG_D];
+                                       `INSN_reg_E:    tmp <= registers[`REG_E];
+                                       `INSN_reg_H:    tmp <= registers[`REG_H];
+                                       `INSN_reg_L:    tmp <= registers[`REG_L];
+                                       `INSN_reg_dHL:  tmp <= rdata;
+                                       endcase
+                               end
+                       end
+                       `INSN_ALU_A: begin
+                               `EXEC_NEWCYCLE;
+                               `EXEC_INC_PC;
+                       end
+                       `INSN_NOP: begin
+                               `EXEC_NEWCYCLE;
+                               `EXEC_INC_PC;
+                       end
+                       `INSN_RST: begin
+                               case (cycle)
+                               0:      begin
+                                               `EXEC_INC_PC;           // This goes FIRST in RST
+                                       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
+                               3:      begin
+                                               `EXEC_NEWCYCLE;
+                                               {registers[`REG_PCH],registers[`REG_PCL]} <=
+                                                       {10'b0,opcode[5:3],3'b0};
+                                       end
+                               endcase
+                       end
+                       `INSN_RET,`INSN_RETCC: begin
+                               case (cycle)
+                               0:      begin
+                                               rd <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]};
+                                       end
+                               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
+                               2:      begin
+                                               rd <= 1;
+                                               address <= {registers[`REG_SPH],registers[`REG_SPL]} + 1;
+                                       end
+                               3:      begin /* twiddle thumbs */ end
+                               4:      begin
+                                               `EXEC_NEWCYCLE;
+                                               // do NOT increment PC!
+                                       end
+                               endcase
+                       end
+                       `INSN_CALL,`INSN_CALLCC: begin
+                               case (cycle)
+                               0:      begin
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               1:      begin
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       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
+                       `INSN_JP_imm,`INSN_JPCC_imm: begin
+                               case (cycle)
+                               0:      begin
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               1:      begin
+                                               `EXEC_INC_PC;
+                                               `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
+                       `INSN_JP_HL: begin
+                               `EXEC_NEWCYCLE;
+                       end
+                       `INSN_JR_imm,`INSN_JRCC_imm: begin
+                               case (cycle)
+                               0:      begin
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEXTADDR_PCINC;
+                                               rd <= 1;
+                                       end
+                               1: begin
+                                               `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
+                               2:      begin
+                                               `EXEC_NEWCYCLE;
+                                       end
+                               endcase
+                       end
+                       `INSN_INCDEC16: begin
+                               case (cycle)
+                               0: begin
+                                               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
+                                               `EXEC_INC_PC;
+                                               `EXEC_NEWCYCLE;
+                                       end
+                               endcase
+                       end
+                       default:
+                               $stop;

                        endcase
                        state <= `STATE_WRITEBACK;
                end
                `STATE_WRITEBACK: begin
                        casex (opcode)
                        endcase
                        state <= `STATE_WRITEBACK;
                end
                `STATE_WRITEBACK: begin
                        casex (opcode)

-                               `INSN_LD_reg_imm8:
-                                       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;
+                       `INSN_LD_reg_imm8:
+                               case (cycle)
+                               0:      begin end
+                               1:      case (opcode[5:3])
+                                       `INSN_reg_A:    begin registers[`REG_A] <= rdata; end
+                                       `INSN_reg_B:    begin registers[`REG_B] <= rdata; end
+                                       `INSN_reg_C:    begin registers[`REG_C] <= rdata; end
+                                       `INSN_reg_D:    begin registers[`REG_D] <= rdata; end
+                                       `INSN_reg_E:    begin registers[`REG_E] <= rdata; end
+                                       `INSN_reg_H:    begin registers[`REG_H] <= rdata; end
+                                       `INSN_reg_L:    begin registers[`REG_L] <= rdata; end
+                                       `INSN_reg_dHL:  begin /* Go off to cycle 2 */ end
+                                       endcase
+                               2:      begin end
+                               endcase
+                       `INSN_HALT: begin
+                               /* Nothing needs happen here. */
+                               /* XXX Interrupts needed for HALT. */
+                       end
+                       `INSN_LD_HL_reg: begin
+                               /* Nothing of interest here */
+                       end
+                       `INSN_LD_reg_HL: begin
+                               case (cycle)
+                               0:      begin end
+                               1:      begin
+                                               case (opcode[5:3])
+                                               `INSN_reg_A:    registers[`REG_A] <= tmp;
+                                               `INSN_reg_B:    registers[`REG_B] <= tmp;
+                                               `INSN_reg_C:    registers[`REG_C] <= tmp;
+                                               `INSN_reg_D:    registers[`REG_D] <= tmp;
+                                               `INSN_reg_E:    registers[`REG_E] <= tmp;
+                                               `INSN_reg_H:    registers[`REG_H] <= tmp;
+                                               `INSN_reg_L:    registers[`REG_L] <= tmp;
+                                               endcase
+                                       end
+                               endcase
+                       end
+                       `INSN_LD_reg_reg: begin
+                               case (opcode[5:3])
+                               `INSN_reg_A:    registers[`REG_A] <= tmp;
+                               `INSN_reg_B:    registers[`REG_B] <= tmp;
+                               `INSN_reg_C:    registers[`REG_C] <= tmp;
+                               `INSN_reg_D:    registers[`REG_D] <= tmp;
+                               `INSN_reg_E:    registers[`REG_E] <= tmp;
+                               `INSN_reg_H:    registers[`REG_H] <= tmp;
+                               `INSN_reg_L:    registers[`REG_L] <= tmp;
+                               endcase
+                       end
+                       `INSN_LD_reg_imm16: begin
+                               case (cycle)
+                               0:      begin /* */ end
+                               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
+                                       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
+                                       end
+                               endcase
+                       end
+                       `INSN_LD_SP_HL: begin
+                               case (cycle)
+                               0:      registers[`REG_SPH] <= tmp;
+                               1: registers[`REG_SPL] <= tmp;
+                               endcase
+                       end
+                       `INSN_PUSH_reg: begin   /* PUSH is 16 cycles! */
+                               case (cycle)
+                               0:      {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                               {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+                               1:      {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                               {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+                               2:      begin /* type F */ end
+                               3:      begin /* type F */ end
+                               endcase
+                       end
+                       `INSN_POP_reg: begin    /* POP is 12 cycles! */
+                               case (cycle)
+                               0:      {registers[`REG_SPH],registers[`REG_SPL]} <=
+                                               {registers[`REG_SPH],registers[`REG_SPL]} + 1;
+                               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;
+                                       end
+                               2:      begin
+                                               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;

                                                endcase
                                                endcase

-                                       2: cycle <= 0;
+                                       end
+                               endcase
+                       end
+                       `INSN_LDH_AC: begin
+                               case (cycle)
+                               0:      begin /* Type F */ end
+                               1:      if (opcode[4])
+                                               registers[`REG_A] <= rdata;
+                               endcase
+                       end
+                       `INSN_LDx_AHL: begin
+                               case (cycle)
+                               0:      begin /* Type F */ end
+                               1:      begin
+                                               if (opcode[3])
+                                                       registers[`REG_A] <= rdata;
+                                               {registers[`REG_H],registers[`REG_L]} <=
+                                                       opcode[4] ? // if set, LDD, else LDI
+                                                       ({registers[`REG_H],registers[`REG_L]} - 1) :
+                                                       ({registers[`REG_H],registers[`REG_L]} + 1);
+                                       end
+                               endcase
+                       end
+                       `INSN_ALU8: begin
+                               if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
+                                       /* Sit on our asses. */
+                               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 */ 1'b0,
+                                                         /* 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
+                                       `INSN_alu_ADC: begin
+                                               registers[`REG_A] <=
+                                                       registers[`REG_A] + tmp + {7'b0,registers[`REG_F][4]};
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] + tmp + {7'b0,registers[`REG_F][4]}) == 0) ? 1'b1 : 1'b0,
+                                                         /* N */ 1'b0,
+                                                         /* H */ (({1'b0,registers[`REG_A][3:0]} + {1'b0,tmp[3:0]} + {4'b0,registers[`REG_F][4]}) >> 4 == 1) ? 1'b1 : 1'b0,
+                                                         /* C */ (({1'b0,registers[`REG_A]} + {1'b0,tmp} + {8'b0,registers[`REG_F][4]}) >> 8 == 1) ? 1'b1 : 1'b0,
+                                                         registers[`REG_F][3:0]
+                                                       };
+                                       end
+                                       `INSN_alu_SUB: begin
+                                               registers[`REG_A] <=
+                                                       registers[`REG_A] - tmp;
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] - tmp) == 0) ? 1'b1 : 1'b0,
+                                                         /* N */ 1'b1,
+                                                         /* 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
+                                       `INSN_alu_SBC: begin
+                                               registers[`REG_A] <=
+                                                       registers[`REG_A] - (tmp + {7'b0,registers[`REG_F][4]});
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] - (tmp + {7'b0,registers[`REG_F][4]})) == 0) ? 1'b1 : 1'b0,
+                                                         /* N */ 1'b1,
+                                                         /* H */ (({1'b0,registers[`REG_A][3:0]} - ({1'b0,tmp[3:0]} + {4'b0,registers[`REG_F][4]})) >> 4 == 1) ? 1'b1 : 1'b0,
+                                                         /* C */ (({1'b0,registers[`REG_A]} - ({1'b0,tmp} + {8'b0,registers[`REG_F][4]})) >> 8 == 1) ? 1'b1 : 1'b0,
+                                                         registers[`REG_F][3:0]
+                                                       };
+                                       end
+                                       `INSN_alu_AND: begin
+                                               registers[`REG_A] <=
+                                                       registers[`REG_A] & tmp;
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] & tmp) == 0) ? 1'b1 : 1'b0,
+                                                         3'b010,
+                                                         registers[`REG_F][3:0]
+                                                       };
+                                       end
+                                       `INSN_alu_OR: begin
+                                               registers[`REG_A] <=
+                                                       registers[`REG_A] | tmp;
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] | tmp) == 0) ? 1'b1 : 1'b0,
+                                                         3'b000,
+                                                         registers[`REG_F][3:0]
+                                                       };
+                                       end
+                                       `INSN_alu_XOR: begin
+                                               registers[`REG_A] <=
+                                                       registers[`REG_A] ^ tmp;
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] ^ tmp) == 0) ? 1'b1 : 1'b0,
+                                                         3'b000,
+                                                         registers[`REG_F][3:0]
+                                                       };
+                                       end
+                                       `INSN_alu_CP: begin
+                                               registers[`REG_F] <=
+                                                       { /* Z */ ((registers[`REG_A] - tmp) == 0) ? 1'b1 : 1'b0,
+                                                         /* N */ 1'b1,
+                                                         /* 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
                                        endcase

-                               `INSN_HALT: begin
-                                       /* XXX UNIMP */

                                end
                                end

-                               `INSN_LD_HL_reg: begin
-                                       /* XXX UNIMP */
+                       end
+                       `INSN_ALU_A: begin
+                               case(opcode[5:3])
+                               `INSN_alu_RLCA: begin
+                                       registers[`REG_A] <= {registers[`REG_A][6:0],registers[`REG_A][7]};
+                                       registers[`REG_F] <= {registers[`REG_F][7:5],registers[`REG_A][7],registers[`REG_F][3:0]};

                                end
                                end

-                               `INSN_LD_reg_HL: begin
-                                       /* XXX UNIMP */
+                               `INSN_alu_RRCA: begin
+                                       registers[`REG_A] <= {registers[`REG_A][0],registers[`REG_A][7:1]};
+                                       registers[`REG_F] <= {registers[`REG_F][7:5],registers[`REG_A][0],registers[`REG_F][3:0]};

                                end
                                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
+                               `INSN_alu_RLA: begin
+                                       registers[`REG_A] <= {registers[`REG_A][6:0],registers[`REG_F][4]};
+                                       registers[`REG_F] <= {registers[`REG_F][7:5],registers[`REG_A][7],registers[`REG_F][3:0]};
+                               end
+                               `INSN_alu_RRA: begin
+                                       registers[`REG_A] <= {registers[`REG_A][4],registers[`REG_A][7:1]};
+                                       registers[`REG_F] <= {registers[`REG_F][7:5],registers[`REG_A][0],registers[`REG_F][3:0]};
+                               end
+                               `INSN_alu_CPL: begin
+                                       registers[`REG_A] <= ~registers[`REG_A];
+                                       registers[`REG_F] <= {registers[`REG_F][7],1'b1,1'b1,registers[`REG_F][4:0]};
+                               end
+                               `INSN_alu_SCF: begin
+                                       registers[`REG_F] <= {registers[`REG_F][7:5],1,registers[`REG_F][3:0]};

                                end
                                end

+                               `INSN_alu_CCF: begin
+                                       registers[`REG_F] <= {registers[`REG_F][7:5],~registers[`REG_F][4],registers[`REG_F][3:0]};
+                               end
+                               endcase
+                       end
+                       `INSN_NOP: begin /* NOP! */ end
+                       `INSN_RST: begin
+                               case (cycle)
+                               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
+                       end
+                       `INSN_RET,`INSN_RETCC: begin
+                               case (cycle)
+                               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
+                       `INSN_CALL,`INSN_CALLCC: begin
+                               case (cycle)
+                               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
+                       `INSN_JP_imm,`INSN_JPCC_imm: begin
+                               case (cycle)
+                               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
+                       `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)
+                               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
+                       `INSN_INCDEC16: begin
+                               case (cycle)
+                               0:      {tmp,tmp2} <= {tmp,tmp2} +
+                                               (opcode[3] ? 16'hFFFF : 16'h0001);
+                               1: begin
+                                               case (opcode[5:4])
+                                               `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
+                                       end
+                               endcase
+                       end
+                       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