// Copyright 2021 cpu-dev
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

module cpu(clock, reset, instr, pc, rd_data, rs_data, mem_w_en, mem_r_data, int_req, int_en, int_vec, reg_w_en);
    input clock;
    input reset;
    input [7:0] instr;
    input int_req;
    input [7:0] int_en;
    input [7:0] int_vec;

    output [7:0] pc;
    reg [7:0] ret_addr;
    output [7:0] rd_data, rs_data;
    output mem_w_en;
    input [7:0] mem_r_data;
    reg flag;
    reg [7:0] pc;
    
    wire [3:0] opcode;
    wire [1:0] rd_a, rd_a_p, rs_a, rs_a_p;
    wire [3:0] imm;

    output reg_w_en;
    wire [7:0] reg_w_data;
    wire [7:0] reg_w_data_p;
    wire [7:0] reg_w_data_p_p;
    wire [7:0] reg_w_imm;

    wire reg_reg_mem_w_sel;
    wire reg_alu_w_sel;

    wire [3:0] alu_ctrl;
    wire [7:0] alu_out;

    wire flag_w_en;

    wire imm_en;
    wire ih_il_sel;

    wire jmp_en, je_en;
    wire ret;

    reg intr_en = 1'b0;
    reg _flag;

    decoder decoder(instr, opcode, rs_a_p, rd_a_p, imm);

    main_controller main_controller(opcode, rd_a_p, reg_w_en, mem_w_en, reg_reg_mem_w_sel, reg_alu_w_sel, flag_w_en, imm_en, ih_il_sel, jmp_en, je_en, ret);
    alu_controller alu_controller(opcode, alu_ctrl);

    regfile regfile(rd_a, rs_a, reg_w_data, reg_w_en, rd_data, rs_data, clock, intr_en);

    assign rd_a = imm_en ? 2'b11 : rd_a_p;
    assign rs_a = imm_en ? 2'b11 : rs_a_p;

    assign reg_w_data_p_p = reg_reg_mem_w_sel ? mem_r_data : rs_data;
    assign reg_w_data_p = reg_alu_w_sel ? alu_out : reg_w_data_p_p;
    assign reg_w_imm = ih_il_sel ? {imm, rs_data[3:0]} : {rs_data[7:4], imm};
    assign reg_w_data = imm_en ? reg_w_imm : reg_w_data_p;

    alu alu(rd_data, rs_data, alu_ctrl, alu_out);

    always @(posedge clock) begin
        if(ret) begin
            flag <= _flag;
        end else if(je_en) begin
            flag <= 0;
        end else if(flag_w_en) begin
            flag <= alu_out;
        end else begin
            flag <= flag;
        end
    end

    always @(posedge clock) begin
        if(ret) begin
            intr_en <= 1'b0;
        end else if(int_req && int_en[0]) begin
				intr_en <= 1'b1;
        end
    end

    always @(posedge clock) begin
        if(int_req == 1'b1 && int_en[0]) begin
            if(jmp_en) begin
                ret_addr <= rs_data;
            end else if(je_en && flag) begin
                ret_addr <= rs_data;
            end else begin
                ret_addr <= pc + 1;
            end
        end else begin
            ret_addr <= ret_addr;
        end
    end

    always @(posedge reset) begin
        ret_addr<= 8'h00;
        flag    <= 1'b0;
        pc      <= 8'h00;
        intr_en <= 1'b0;
        _flag   <= 1'b0;
    end 

    always @(posedge clock) begin
        if(int_req && int_en[0]) begin
            _flag <= flag;
            pc <= int_vec;
        end else if(ret) begin
            pc <= ret_addr;
        end else if(jmp_en) begin
            pc <= rs_data;
        end else if(je_en) begin
            if(flag) begin
                pc <= rs_data;
            end else begin
                pc <= pc + 1;
            end
        end else begin
            pc <= pc + 1;
        end
    end
endmodule