module RISCcore (
  input rst,
  input clk,
  output reg [31:0] pc,
  output reg [31:0] next_pc,
  output wire [31:0] instr
);


//PC
always @(posedge clk) begin 
  if(rst) begin
    pc <= 32'h0;
    next_pc <= 32'h4;
  end
  else begin 
    next_pc <= taken_br ? br_tgt_pc : (pc + 32'h4);
    pc <= next_pc;
  end
end

//IMem
reg [31:0] imem [0:255];

initial begin
  $readmemh("program.hex", imem);
end

assign instr = imem[pc[31:2]];

//Decoder

wire isUType = ((instr[6:0] == 7'b0110111) || (instr[6:0] == 7'b0010111));
wire isIType = ((instr[6:0] == 7'b0000011) || (instr[6:0] == 7'b0000111) || (instr[6:0] == 7'b0010011) || (instr[6:0] == 7'b0011011) || (instr [6:0] == 7'b1100111));
wire isRType = ((instr[6:0] == 7'b0101111) || (instr[6:0] == 7'b0110011) || (instr[6:0] == 7'b0111011) || (instr[6:0] == 7'b0110011));
wire isSType = ((instr[6:0] == 7'b0100011) || (instr[6:0] == 7'b0100111));
wire isBType = (instr[6:0] == 7'b1100011);
wire isJType = (instr[6:0] == 7'b1101111);

wire [4:0] rs1 = instr[19:15];
wire [4:0] rs2 = instr[24:20];
wire [4:0] rd = instr[11:7];

wire rs2Valid = (isRType || isSType || isBType);
wire rs1Valid = (~isUType && ~isJType);
wire rdValid = (~isSType && ~isBType);

wire [3:0] funct3 = instr[14:12];
wire [6:0] funct7 = instr[31:25];

wire funct3Valid = rs1Valid;
wire funct7Valid = isRType;

wire [31:0] Iimm = {{21{instr[31]}}, {instr[30:25]}, {instr[24:20]}};
wire [31:0] Simm = {{21{instr[31]}}, {instr[30:25]}, {instr[11:7]}};
wire [31:0] Bimm = {{20{instr[31]}}, {instr[7]}, {instr[30:25]}, {instr[11:8]}, 1'b0};
wire [31:0] Uimm = {{instr[31]}, {instr[30:20]}, {instr[19:12]}, {12{1'b0}};
wire [31:0] Jimm = {{12{instr[31]}}, {instr[19:12]}, {instr[20]}, {instr[30:25]}, {instr[24:21]}, 1'b0};

//Instructions

isBEQ = (funct3 == 3'b000 && isBType);
isBNE = (funct3 == 3'b001 && isBType);
isBLT = (funct3 == 3'b100 && isBType);
isBGE = (funct3 == 3'b101 && isBType);
isBLTU = (funct3 == 3'b110 && isBType);
isBGEU = (funct3 == 3'b111 && isBType);

isADDI = (funct3 == 3'b000 && isIType);

isADD = (funct7[5] == 1'b0 && isRType);

isLW = (funct3 == 3'b010 && isIType);
isSW = (funct3 == 3'b010 && isSType);

//Register file

wire rf_wr_en;
wire [4:0] rf_wr_index;
wire [31:0] rf_wr_data;
wire rf_rd_en1, rf_rd_en2;
wire [4:0] rf_rd_index1, rf_rd_index2;

wire rf_rd_data1, rf_rd_data2;

wire src1_value, src2_value;

assign rf_rd_en1 = rs1Valid;
assign rf_rd_en2 = rs2Valid;

assign rf_rd_index1 = rs1;
assign rf_rd_index2 = rs2;

assign [31:0] src1_value = {31{rf_rd_data1}};
assign [31:0] src2_value = {31{rf_rd_data2}};

/* Maybe write logic ?
assign rf_wr_en = 1'b0;
assign rf_wr_index = 5'b0;
assign rf_wr_data = 32'b0;
Disabled */

// ALU FOR ADD, ADDI 
wire [31:0] alu_result = 32'b0;
wire [31:0] alu_op2 = isADDI ? Iimm : src2_value;

assign alu_result = (isADDI || isADD) ? (src1_value + alu_op2) : 32'b0;

//ALU Register file connect
/*
assign rf_wr_data = alu_result;
assign rf_wr_en = rdValid && (isADD || isADDI);
assign rf_wr_index = rd;
*/

//x0 support adding 
assign rf_wr_data = rf_wr_en ? alu_result : 32'b0;
assign rf_wr_en = rdValid && (isADD || isADDI) && (rd != 5'b0);
assign rf_wr_index = rd;

//Branch
if(isBType) begin 
  wire taken_br = (isBEQ ? src1_value == src2_value : 1'b0) ||
    (isBNE ? src1_value != src2_value : 1'b0) ||
    (isBLT ? ((src1_value < src2_value) ^ (src1_value[31] != src2_value[31])) : 1'b0) ||
    (isBGE ? ((src1_value >= src2_value) ^ (src1_value[31] != src2_value)) : 1'b0) ||
    (isBLTU ? src1_value < src2_value : 1'b0) ||
    (isBGEU ? src1_value >= src2_value : 1'b0);
  wire [31:0] br_tgt_pc = next_pc + Bimm;
end 


endmodule