Brainfuck implementation in Verilog

bf.v

module bf;
    reg [7:0] mem [0:255];
    reg [7:0] mp = 0;
    reg [2:0] code [0:255];
    reg [7:0] ip = 0;
    reg [7:0] stack [0:255];
    reg [7:0] sp = 0;
    reg [2:0] state = 0;

    reg clk = 0;

    reg [7:0] next = 0;
    reg [2:0] opcode = 0;

    integer STDOUT = 32'h8000_0001;

    always @(posedge clk) begin
        case (state)
            0: begin // fetch
                opcode = code[ip];
                state <= 1;
            end
            1: begin // decode + execute
                if (next) begin
                    if (opcode == 3'b110) next++; // [
                    if (opcode == 3'b111) next--; // ]
                end
                else case(opcode)
                    3'b010: $fwrite(STDOUT, "%c", mem[mp]);  // .
                    3'b100: mp++; // >
                    3'b101: mp--; // <
                    3'b110: begin // [
                        if (mem[mp] == 0) begin
                            next = 1;
                        end else begin
                            stack[sp] = ip;
                            sp++;
                        end
                    end
                    3'b111: begin // ]
                        if (mem[mp] != 0) begin
                            ip = stack[sp - 1];
                        end else begin
                            sp--;
                        end
                    end
                endcase
                state <= 2;
            end
            2: begin // write back
                case (opcode)
                    3'b000: mem[mp]++; // +
                    3'b001: mem[mp]--; // -
                    3'b011: mem[mp] = 0; // , (I don't know how to get input from stdin in verilog lol)
                endcase
                state <= 3;
            end
            3: begin
                ip++;
                state <= 0;
                if (ip == 0) $finish;
            end
        endcase
    end

    integer i;
    initial begin
        for (i = 0; i < 255; i++) mem[i] = 0;
        for (i = 0; i < 255; i++) code[i] = 0;
        for (i = 0; i < 255; i++) stack[i] = 0;
        $readmemh("program.hex", code);
    end

    always #1 clk = ~clk;
endmodule