`define REG_A 0 `define REG_B 1 `define REG_C 2 `define REG_D 3 `define REG_E 4 `define REG_F 5 `define REG_H 6 `define REG_L 7 `define REG_SPH 8 `define REG_SPL 9 `define REG_PCH 10 `define REG_PCL 11 `define FLAG_Z 8'b10000000 `define FLAG_N 8'b01000000 `define FLAG_H 8'b00100000 `define FLAG_C 8'b00010000 `define STATE_FETCH 2'h0 `define STATE_DECODE 2'h1 `define STATE_EXECUTE 2'h2 `define STATE_WRITEBACK 2'h3 `define INSN_LD_reg_imm8 8'b00xxx110 `define INSN_HALT 8'b01110110 `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_CALL 8'b11001101 `define INSN_JP_imm 8'b11000011 `define INSN_JPCC_imm 8'b110xx010 `define INSN_ALU_A 8'b00xxx111 `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_D 3'b010 `define INSN_reg_E 3'b011 `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, output reg [15:0] busaddress, /* BUS_* is latched on STATE_FETCH. */ inout [7:0] busdata, output reg buswr, output reg busrd); reg [1:0] state = 0; /* State within this bus cycle (see STATE_*). */ reg [2:0] cycle = 0; /* Cycle for instructions. */ reg [7:0] registers[11:0]; reg [15:0] address; /* Address for the next bus operation. */ 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 [7:0] tmp, tmp2; /* Generic temporary regs. */ reg [7:0] buswdata; assign busdata = buswr ? buswdata : 8'bzzzzzzzz; reg ie = 0; 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; ie <= 0; rd <= 1; wr <= 0; newcycle <= 1; state <= 0; cycle <= 0; end always @(posedge clk) case (state) `STATE_FETCH: begin if (newcycle) begin busaddress <= {registers[`REG_PCH], registers[`REG_PCL]}; buswr <= 0; busrd <= 1; end else begin busaddress <= address; buswr <= wr; busrd <= rd; if (wr) buswdata <= wdata; end state <= `STATE_DECODE; end `STATE_DECODE: begin if (newcycle) begin opcode <= busdata; rdata <= busdata; newcycle <= 0; cycle <= 0; end else begin if (rd) rdata <= busdata; cycle <= cycle + 1; end 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 `define EXEC_INC_PC \ {registers[`REG_PCH], registers[`REG_PCL]} <= {registers[`REG_PCH], registers[`REG_PCL]} + 1 `define EXEC_NEXTADDR_PCINC \ address <= {registers[`REG_PCH], registers[`REG_PCL]} + 1 `define EXEC_NEWCYCLE \ newcycle <= 1; rd <= 1; wr <= 0 casex (opcode) `INSN_LD_reg_imm8: begin case (cycle) 0: begin `EXEC_INC_PC; `EXEC_NEXTADDR_PCINC; rd <= 1; 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 end 2: begin `EXEC_NEWCYCLE; end endcase end `INSN_HALT: begin `EXEC_NEWCYCLE; /* XXX Interrupts needed for HALT. */ end `INSN_LD_HL_reg: begin 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 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]) `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 `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: begin 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]} + 1; end 2: begin /* twiddle thumbs */ end 3: begin `EXEC_NEWCYCLE; // do NOT increment PC! end endcase end `INSN_CALL: 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; 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 default: $stop; endcase state <= `STATE_WRITEBACK; end `STATE_WRITEBACK: begin casex (opcode) `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 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 end 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 `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 `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 `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: begin case (cycle) 0: begin /* type F */ end 1: registers[`REG_PCL] <= rdata; 2: registers[`REG_PCH] <= rdata; 3: begin {registers[`REG_SPH],registers[`REG_SPL]} <= {registers[`REG_SPH],registers[`REG_SPL]} + 2; if (opcode[4]) /* RETI */ ie <= 1; end endcase end `INSN_CALL: 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 default: $stop; endcase state <= `STATE_FETCH; end endcase endmodule