module grom_cpu(
input clk,
input reset,
output reg [11:0] addr,
input [7:0] data_in,
output reg [7:0] data_out,
output reg we,
output reg ioreq,
output reg hlt
);
reg[11:0] PC /* verilator public_flat */; // Program counter
reg[7:0] IR /* verilator public_flat */; // Instruction register
reg[7:0] VALUE /* verilator public_flat */; // Temp reg for storing 2nd operand
reg[3:0] CS /* verilator public_flat */; // Code segment regiser
reg[3:0] DS /* verilator public_flat */; // Data segment regiser
reg[11:0] SP /* verilator public_flat */; // Stack pointer regiser
reg[7:0] R[0:3] /* verilator public_flat */; // General purpose registers
reg[11:0] FUTURE_PC /* verilator public_flat */; // PC to jump to
localparam STATE_RESET /*verilator public_flat*/ = 5'b00000;
localparam STATE_FETCH_PREP /*verilator public_flat*/ = 5'b00001;
localparam STATE_FETCH_WAIT /*verilator public_flat*/ = 5'b00010;
localparam STATE_FETCH /*verilator public_flat*/ = 5'b00011;
localparam STATE_EXECUTE /*verilator public_flat*/ = 5'b00100;
localparam STATE_FETCH_VALUE_PREP /*verilator public_flat*/ = 5'b00101;
localparam STATE_FETCH_VALUE /*verilator public_flat*/ = 5'b00110;
localparam STATE_EXECUTE_DBL /*verilator public_flat*/ = 5'b00111;
localparam STATE_LOAD_VALUE /*verilator public_flat*/ = 5'b01000;
localparam STATE_LOAD_VALUE_WAIT /*verilator public_flat*/ = 5'b01001;
localparam STATE_ALU_RESULT_WAIT /*verilator public_flat*/ = 5'b01010;
localparam STATE_ALU_RESULT /*verilator public_flat*/ = 5'b01011;
localparam STATE_PUSH_PC_LOW /*verilator public_flat*/ = 5'b01100;
localparam STATE_JUMP /*verilator public_flat*/ = 5'b01101;
localparam STATE_RET_VALUE_WAIT /*verilator public_flat*/ = 5'b01110;
localparam STATE_RET_VALUE /*verilator public_flat*/ = 5'b01111;
localparam STATE_RET_VALUE_WAIT2 /*verilator public_flat*/ = 5'b10000;
localparam STATE_RET_VALUE2 /*verilator public_flat*/ = 5'b10001;
reg [4:0] state /* verilator public_flat */ = STATE_RESET;
reg [7:0] alu_a /* verilator public_flat */;
reg [7:0] alu_b /* verilator public_flat */;
reg [3:0] alu_op /* verilator public_flat */;
reg [1:0] RESULT_REG /* verilator public_flat */;
wire [7:0] alu_res /* verilator public_flat */;
wire alu_CF /* verilator public_flat */;
wire alu_ZF /* verilator public_flat */;
wire alu_SF /* verilator public_flat */;
reg jump;
alu alu(.clk(clk),.A(alu_a),.B(alu_b),.operation(alu_op),.result(alu_res),.CF(alu_CF),.ZF(alu_ZF),.SF(alu_SF));
always @(posedge clk)
begin
if (reset)
begin
state <= STATE_RESET;
hlt <= 0;
end
else
begin
case (state)
STATE_RESET :
begin
PC <= 12'h000;
state <= STATE_FETCH_PREP;
CS <= 4'h0;
DS <= 4'h0;
R[0] <= 8'h00;
R[1] <= 8'h00;
R[2] <= 8'h00;
R[3] <= 8'h00;
SP <= 12'hfff;
end
STATE_FETCH_PREP :
begin
addr <= PC;
we <= 0;
ioreq <= 0;
state <= STATE_FETCH_WAIT;
end
STATE_FETCH_WAIT :
begin
// Sync with memory due to CLK
state <= (hlt) ? STATE_FETCH_PREP : STATE_FETCH;
end
STATE_FETCH :
begin
IR <= data_in;
PC <= PC + 1;
state <= STATE_EXECUTE;
end
STATE_EXECUTE :
begin
`ifdef DISASSEMBLY
$display(" PC %h R0 %h R1 %h R2 %h R3 %h CS %h DS %h SP %h ALU [%d %d %d]", PC, R[0], R[1], R[2], R[3], CS, DS, SP, alu_CF,alu_SF,alu_ZF);
`endif
if (IR[7])
begin
addr <= PC;
state <= STATE_FETCH_VALUE_PREP;
PC <= PC + 1;
end
else
begin
case(IR[6:4])
3'b000 :
begin
`ifdef DISASSEMBLY
$display("MOV R%d,R%d",IR[3:2],IR[1:0]);
`endif
R[IR[3:2]] <= R[IR[1:0]];
state <= STATE_FETCH_PREP;
end
3'b001 :
begin
alu_a <= R[0]; // first input R0
alu_b <= R[IR[1:0]];
RESULT_REG <= 0; // result in R0
alu_op <= { 2'b00, IR[3:2] };
state <= STATE_ALU_RESULT_WAIT;
`ifdef DISASSEMBLY
case(IR[3:2])
2'b00 : begin
$display("ADD R%d",IR[1:0]);
end
2'b01 : begin
$display("SUB R%d",IR[1:0]);
end
2'b10 : begin
$display("ADC R%d",IR[1:0]);
end
2'b11 : begin
$display("SBC R%d",IR[1:0]);
end
endcase
`endif
end
3'b010 :
begin
alu_a <= R[0]; // first input R0
alu_b <= R[IR[1:0]];
RESULT_REG <= 0; // result in R0
alu_op <= { 2'b01, IR[3:2] };
state <= STATE_ALU_RESULT_WAIT;
`ifdef DISASSEMBLY
case(IR[3:2])
2'b00 : begin
$display("AND R%d",IR[1:0]);
end
2'b01 : begin
$display("OR R%d",IR[1:0]);
end
2'b10 : begin
$display("NOT R%d",IR[1:0]);
end
2'b11 : begin
$display("XOR R%d",IR[1:0]);
end
endcase
`endif
end
3'b011 :
begin
RESULT_REG <= IR[1:0]; // result in REG
// CMP and TEST are not storing result
state <= IR[3] ? STATE_FETCH_PREP : STATE_ALU_RESULT_WAIT;
// CMP and TEST are having first input R0, for INC and DEC is REG
alu_a <= IR[3] ? R[0] : R[IR[1:0]];
// CMP and TEST are having second input REG, for INC and DEC is 1
alu_b <= IR[3] ? R[IR[1:0]] : 8'b00000001;
case(IR[3:2])
2'b00 : begin
`ifdef DISASSEMBLY
$display("INC R%d",IR[1:0]);
`endif
alu_op <= 4'b0000; // ALU_OP_ADD
end
2'b01 : begin
`ifdef DISASSEMBLY
$display("DEC R%d",IR[1:0]);
`endif
alu_op <= 4'b0001; // ALU_OP_SUB
end
2'b10 : begin
`ifdef DISASSEMBLY
$display("CMP R%d",IR[1:0]);
`endif
alu_op <= 4'b0001; // ALU_OP_SUB
end
2'b11 : begin
`ifdef DISASSEMBLY
$display("TST R%d",IR[1:0]);
`endif
alu_op <= 4'b0100; // ALU_OP_AND
end
endcase
end
3'b100 :
begin
if (IR[3]==0)
begin
alu_a <= R[0]; // first input R0
// no 2nd input
RESULT_REG <= 0; // result in R0
alu_op <= { 1'b1, IR[2:0] };
`ifdef DISASSEMBLY
case(IR[2:0])
3'b000 : begin
$display("SHL");
end
3'b001 : begin
$display("SHR");
end
3'b010 : begin
$display("SAL");
end
3'b011 : begin
$display("SAR");
end
3'b100 : begin
$display("ROL");
end
3'b101 : begin
$display("ROR");
end
3'b110 : begin
$display("RCL");
end
3'b111 : begin
$display("RCR");
end
endcase
`endif
state <= STATE_ALU_RESULT_WAIT;
end
else
begin
if (IR[2]==0)
begin
`ifdef DISASSEMBLY
$display("PUSH R%d",IR[1:0]);
`endif
addr <= SP;
we <= 1;
ioreq <= 0;
data_out <= R[IR[1:0]];
SP <= SP - 1;
state <= STATE_FETCH_PREP;
end
else
begin
`ifdef DISASSEMBLY
$display("POP R%d",IR[1:0]);
`endif
addr <= SP + 1;
we <= 0;
ioreq <= 0;
RESULT_REG <= IR[1:0];
SP <= SP + 1;
state <= STATE_LOAD_VALUE_WAIT;
end
end
end
3'b101 :
begin
`ifdef DISASSEMBLY
$display("LOAD R%d,[R%d]", IR[3:2], IR[1:0]);
`endif
addr <= { DS, R[IR[1:0]] };
we <= 0;
ioreq <= 0;
RESULT_REG <= IR[3:2];
state <= STATE_LOAD_VALUE_WAIT;
end
3'b110 :
begin
`ifdef DISASSEMBLY
$display("STORE [R%d],R%d", IR[3:2], IR[1:0]);
`endif
addr <= { DS, R[IR[3:2]] };
we <= 1;
ioreq <= 0;
data_out <= R[IR[1:0]];
state <= STATE_FETCH_PREP;
end
3'b111 :
begin
// Special instuctions
case(IR[3:2])
2'b00 : begin
CS <= R[IR[1:0]][3:0];
state <= STATE_FETCH_PREP;
`ifdef DISASSEMBLY
$display("MOV CS,R%d",IR[1:0]);
`endif
end
2'b01 : begin
DS <= R[IR[1:0]][3:0];
state <= STATE_FETCH_PREP;
`ifdef DISASSEMBLY
$display("MOV DS,R%d",IR[1:0]);
`endif
end
2'b10 : begin
case(IR[1:0])
2'b00 : begin
`ifdef DISASSEMBLY
$display("PUSH CS");
`endif
addr <= SP;
we <= 1;
ioreq <= 0;
data_out <= { 4'b0000, CS};
SP <= SP - 1;
state <= STATE_FETCH_PREP;
end
2'b01 : begin
`ifdef DISASSEMBLY
$display("PUSH DS");
`endif
addr <= SP;
we <= 1;
ioreq <= 0;
data_out <= { 4'b0000, DS};
SP <= SP - 1;
state <= STATE_FETCH_PREP;
end
2'b10 : begin
`ifdef DISASSEMBLY
$display("Unused opcode");
`endif
end
2'b11 : begin
`ifdef DISASSEMBLY
$display("Unused opcode");
`endif
end
endcase
state <= STATE_FETCH_PREP;
end
2'b11 : begin
case(IR[1:0])
2'b00 : begin
`ifdef DISASSEMBLY
$display("Unused opcode");
`endif
state <= STATE_FETCH_PREP;
end
2'b01 : begin
`ifdef DISASSEMBLY
$display("Unused opcode");
`endif
state <= STATE_FETCH_PREP;
end
2'b10 : begin
`ifdef DISASSEMBLY
$display("RET");
`endif
addr <= SP + 1;
we <= 0;
ioreq <= 0;
SP <= SP + 1;
state <= STATE_RET_VALUE_WAIT;
end
2'b11 : begin
hlt <= 1;
`ifdef DISASSEMBLY
$display("HALT");
`endif
state <= STATE_FETCH_PREP;
end
endcase
end
endcase
end
endcase
end
end
STATE_FETCH_VALUE_PREP :
begin
// Sync with memory due to CLK
state <= STATE_FETCH_VALUE;
end
STATE_FETCH_VALUE :
begin
VALUE <= data_in;
state <= STATE_EXECUTE_DBL;
end
STATE_EXECUTE_DBL :
begin
case(IR[6:4])
3'b000 :
begin
if (IR[3]==0)
begin
case(IR[2:0])
3'b000 :
begin
`ifdef DISASSEMBLY
$display("JMP %h ",{ CS, VALUE[7:0] });
`endif
jump = 1;
end
3'b001 :
begin
`ifdef DISASSEMBLY
$display("JC %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_CF==1);
end
3'b010 :
begin
`ifdef DISASSEMBLY
$display("JNC %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_CF==0);
end
3'b011 :
begin
`ifdef DISASSEMBLY
$display("JM %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_SF==1);
end
3'b100 :
begin
`ifdef DISASSEMBLY
$display("JP %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_SF==0);
end
3'b101 :
begin
`ifdef DISASSEMBLY
$display("JZ %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_ZF==1);
end
3'b110 :
begin
`ifdef DISASSEMBLY
$display("JNZ %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_ZF==0);
end
3'b111 :
begin
`ifdef DISASSEMBLY
$display("Unused opcode %h",IR);
`endif
jump = 0;
end
endcase
if (jump)
begin
PC <= { CS, VALUE[7:0] };
addr <= { CS, VALUE[7:0] };
we <= 0;
ioreq <= 0;
end
state <= STATE_FETCH_PREP;
end
else
begin
case(IR[2:0])
3'b000 :
begin
`ifdef DISASSEMBLY
$display("JR %h ", PC + {VALUE[7],VALUE[7],VALUE[7],VALUE[7],VALUE[7:0]} );
`endif
jump = 1;
end
3'b001 :
begin
`ifdef DISASSEMBLY
$display("JRC %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_CF==1);
end
3'b010 :
begin
`ifdef DISASSEMBLY
$display("JRNC %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_CF==0);
end
3'b011 :
begin
`ifdef DISASSEMBLY
$display("JRM %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_SF==1);
end
3'b100 :
begin
`ifdef DISASSEMBLY
$display("JRP %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_SF==0);
end
3'b101 :
begin
`ifdef DISASSEMBLY
$display("JRZ %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_ZF==1);
end
3'b110 :
begin
`ifdef DISASSEMBLY
$display("JRNZ %h ",{CS, VALUE[7:0] });
`endif
jump = (alu_ZF==0);
end
3'b111 :
begin
`ifdef DISASSEMBLY
$display("Unused opcode %h",IR);
`endif
jump = 0;
end
endcase
if (jump)
begin
PC <= PC + {VALUE[7],VALUE[7],VALUE[7],VALUE[7],VALUE[7:0]};
addr <= PC + {VALUE[7],VALUE[7],VALUE[7],VALUE[7],VALUE[7:0]};
we <= 0;
ioreq <= 0;
end
state <= STATE_FETCH_PREP;
end
end
3'b001 :
begin
`ifdef DISASSEMBLY
$display("JUMP %h ",{ IR[3:0], VALUE[7:0] });
`endif
PC <= { IR[3:0], VALUE[7:0] };
addr <= { IR[3:0], VALUE[7:0] };
we <= 0;
ioreq <= 0;
state <= STATE_FETCH_PREP;
end
3'b010 :
begin
`ifdef DISASSEMBLY
$display("CALL %h ",{ IR[3:0], VALUE[7:0] });
`endif
FUTURE_PC <= { IR[3:0], VALUE[7:0] };
addr <= SP;
we <= 1;
ioreq <= 0;
data_out <= { 4'b0000, PC[11:8]};
SP <= SP - 1;
state <= STATE_PUSH_PC_LOW;
end
3'b011 :
begin
`ifdef DISASSEMBLY
$display("MOV SP,%h ",{ IR[3:0], VALUE[7:0] });
`endif
SP <= { IR[3:0], VALUE[7:0] };
state <= STATE_FETCH_PREP;
end
3'b100 :
begin
`ifdef DISASSEMBLY
$display("IN R%d,[0x%h]",IR[1:0], VALUE);
`endif
ioreq <= 1;
we <= 0;
addr <= { 4'b0000, VALUE };
RESULT_REG <= IR[1:0];
state <= STATE_LOAD_VALUE_WAIT;
end
3'b101 :
begin
`ifdef DISASSEMBLY
$display("OUT [0x%h],R%d",VALUE,IR[1:0]);
`endif
ioreq <= 1;
we <= 1;
addr <= { 4'b0000, VALUE };
data_out <= R[IR[1:0]];
state <= STATE_FETCH_PREP;
end
3'b110 :
begin
// Special instuctions
case(IR[1:0])
2'b00 : begin
`ifdef DISASSEMBLY
$display("MOV CS,0x%h",VALUE);
`endif
CS <= VALUE[3:0];
state <= STATE_FETCH_PREP;
end
2'b01 : begin
`ifdef DISASSEMBLY
$display("MOV DS,0x%h",VALUE);
`endif
DS <= VALUE[3:0];
state <= STATE_FETCH_PREP;
end
2'b10 : begin
`ifdef DISASSEMBLY
$display("Unused opcode %h",IR);
`endif
state <= STATE_FETCH_PREP;
end
2'b11 : begin
`ifdef DISASSEMBLY
$display("Unused opcode %h",IR);
`endif
state <= STATE_FETCH_PREP;
end
endcase
end
3'b111 :
begin
case(IR[3:2])
2'b00 : begin
`ifdef DISASSEMBLY
$display("MOV R%d,0x%h",IR[1:0],VALUE);
`endif
R[IR[1:0]] <= VALUE;
state <= STATE_FETCH_PREP;
end
2'b01 : begin
`ifdef DISASSEMBLY
$display("LOAD R%d,[0x%h]",IR[1:0], {DS, VALUE});
`endif
addr <= { DS, VALUE };
we <= 0;
ioreq <= 0;
RESULT_REG <= IR[1:0];
state <= STATE_LOAD_VALUE_WAIT;
end
2'b10 : begin
`ifdef DISASSEMBLY
$display("STORE [0x%h],R%d", {DS, VALUE}, IR[1:0]);
`endif
addr <= { DS, VALUE };
we <= 1;
ioreq <= 0;
data_out <= R[IR[1:0]];
state <= STATE_FETCH_PREP;
end
2'b11 : begin
`ifdef DISASSEMBLY
$display("Unused opcode %h",IR);
`endif
state <= STATE_FETCH_PREP;
end
endcase
end
endcase
end
STATE_LOAD_VALUE_WAIT :
begin
// Sync with memory due to CLK
state <= STATE_LOAD_VALUE;
end
STATE_LOAD_VALUE :
begin
R[RESULT_REG] <= data_in;
we <= 0;
state <= STATE_FETCH_PREP;
end
STATE_ALU_RESULT_WAIT :
begin
state <= STATE_ALU_RESULT;
end
STATE_ALU_RESULT :
begin
R[RESULT_REG] <= alu_res;
state <= STATE_FETCH_PREP;
end
STATE_PUSH_PC_LOW :
begin
addr <= SP;
we <= 1;
ioreq <= 0;
data_out <= PC[7:0];
SP <= SP - 1;
state <= STATE_JUMP;
end
STATE_JUMP :
begin
`ifdef DISASSEMBLY
$display("Jumping to %h",FUTURE_PC);
`endif
PC <= FUTURE_PC;
state <= STATE_FETCH_PREP;
end
STATE_RET_VALUE_WAIT :
begin
// Sync with memory due to CLK
state <= STATE_RET_VALUE;
end
STATE_RET_VALUE :
begin
FUTURE_PC <= { 4'b0000, data_in };
we <= 0;
state <= STATE_RET_VALUE_WAIT2;
addr <= SP + 1;
we <= 0;
ioreq <= 0;
SP <= SP + 1;
end
STATE_RET_VALUE_WAIT2 :
begin
// Sync with memory due to CLK
state <= STATE_RET_VALUE2;
end
STATE_RET_VALUE2 :
begin
FUTURE_PC <= FUTURE_PC | ({ 4'b0000, data_in } << 8);
we <= 0;
state <= STATE_JUMP;
end
default :
begin
state <= STATE_FETCH_PREP;
end
endcase
end
end
endmodule