`include "cpu_pkg.svh"

import cpu_pkg::*;

module cpu (
    input  logic clk_i,
    input  logic nreset_i,

    output logic [15:0] address_o,
    input  logic [ 7:0] rdata_i,
    output logic        we_o,
    output logic [ 7:0] wdata_o
);

    state_t   state;

    logic     alu_op_valid;
    alu_op_t  alu_op;
    op_src_t  op_src;
    op_dest_t op_dest;
    adr_src_t adr_src;
    logic     reg_write_alu;

    logic [ 7:0] alu_operand;

    logic [ 7:0] rega;
    logic [ 7:0] regf;

    logic [15:0] pc;
    logic [15:0] sp;
    logic [15:0] hl;

    logic instr_valid;
    logic instr_undef;

    logic [ 7:0] operand8;
    logic [15:0] operand16;

    reg8_t       reg8_wselect;
    logic        reg8_we;
    logic [ 7:0] reg8_wdata;
    reg16_t      reg16_wselect;
    logic        reg16_we;
    logic [15:0] reg16_wdata;
    reg8_t       reg8_rselect;
    reg16_t      reg16_rselect;
    reg16_t      reg16_rselect2;
    logic [ 7:0] reg8_rdata;
    logic [15:0] reg16_rdata;
    logic [15:0] reg16_rdata2;
    alu16_op_t   alu16_op;
    logic [ 7:0] alu_out8;
    logic [15:0] alu_out16;

    control control_inst (
        .clk_i         (clk_i),
        .nreset_i      (nreset_i),
        .rdata_i       (rdata_i),
        .state_o       (state),
        .f_i           (regf),
        .pc_o          (pc),
        .sp_o          (sp),
        .alu_op_valid_o(alu_op_valid),
        .alu_op_o      (alu_op),
        .reg_write_alu_o(reg_write_alu),
        .op_src_o      (op_src),
        .op_dest_o     (op_dest),
        .instr_valid_o (instr_valid),
        .instr_undef_o (instr_undef),
        .operand8_o    (operand8),
        .operand16_o   (operand16),
        .reg8_dest_o   (reg8_wselect),
        .reg8_src_o    (reg8_rselect),
        .alu16_op_o    (alu16_op),
        .reg16_src_o   (reg16_rselect),
        .reg16_dest_o  (reg16_wselect),
        .memory_we_o   (we_o),
        .adr_src_o     (adr_src)
    );

    alu alu_inst (
        .clk_i         (clk_i),
        .nreset_i      (nreset_i),
        .alu_op_valid_i(alu_op_valid),
        .alu_op_i      (alu_op),
        .operand_i     (alu_operand),
        .inx8_i        (operand8[5:3]), // Used for bit/set/res
        .a_o           (rega),
        .f_o           (regf),
        .alu16_op_i    (alu16_op),
        .inx16_i       (reg16_rdata2),
        .iny16_i       (reg16_rdata),
        .out8_o        (alu_out8),
        .out16_o       (alu_out16)
    );

    registers registers_inst (
        .clk_i   (clk_i),
        .nreset_i(nreset_i),

        .reg8_wselect_i (reg8_wselect),
        .reg8_we_i      (reg8_we),
        .reg8_wdata_i   (reg8_wdata),
        .reg16_wselect_i(reg16_wselect),
        .reg16_we_i     (reg16_we),
        .reg16_wdata_i  (reg16_wdata),
        .reg8_rselect_i (reg8_rselect),
        .reg8_rdata_o   (reg8_rdata),
        .reg16_rselect_i(reg16_rselect),
        .reg16_rdata_o  (reg16_rdata),
        .reg16_rselect2_i(reg16_rselect2),
        .reg16_rdata2_o  (reg16_rdata2),
        .hl_o            (hl)
    );

    assign alu_operand = (op_src == OP_SRC_A)        ? rega       :
                         (op_src == OP_SRC_OPERAND8) ? operand8   :
                         (op_src == OP_SRC_REG8)     ? reg8_rdata :
                         (op_src == OP_SRC_MEMORY)   ? rdata_i    :
                                                       'X;

    assign reg8_we       = instr_valid & (op_dest == OP_DEST_REG8);
    assign reg8_wdata    = reg_write_alu ? alu_out8 : alu_operand;
    assign reg16_we      = instr_valid & (op_dest == OP_DEST_REG16);
    assign reg16_wdata   = (op_src == OP_SRC_OPERAND16) ? operand16 : alu_out16;
    assign reg16_rselect2 = reg16_wselect;

    assign address_o = (adr_src == ADR_SRC_HL)        ? hl                  :
                       (adr_src == ADR_SRC_REG8)      ? {8'hFF, reg8_rdata} :
                       (adr_src == ADR_SRC_REG16)     ? reg16_rdata         :
                       (adr_src == ADR_SRC_OPERAND8)  ? {8'hFF, operand8}   :
                       (adr_src == ADR_SRC_OPERAND16) ? operand16           :
                                                        pc;
    assign wdata_o   = (op_dest == OP_DEST_MEMORY) ? alu_operand :
                                                     rega; // ldi/ldd hl, a use the normal control paths for HL

endmodule : cpu