`timescale 1ns/1ps

`define BITS 8
module sc_decoder_fsm #(parameter BITS=8, N=11'd32)(
input                           clk, rst,
input                           in_valid,
input signed  [N-1:0][BITS-1:0] y,
input         [N-1:0]           f, 
output wire   [N-1:0]           u_cap,
output wire   [N-1:0]           v_final,
output wire                     out_valid
);


//function for fminsum calculation
function void fminsum_calc;
        input  signed [`BITS-1:0] a;
        input  signed [`BITS-1:0] b;
        output signed [`BITS-1:0] c;
        
        logic [`BITS-2:0] abs_a;
        logic [`BITS-2:0] abs_b;
        logic [`BITS-2:0] abs_c;

        abs_a = (a[`BITS-1])    ? ~a[`BITS-2:0] + 1'b1 : a[`BITS-2:0];
        abs_b = (b[`BITS-1])    ? ~b[`BITS-2:0] + 1'b1 : b[`BITS-2:0];
        abs_c = (abs_b < abs_a) ? abs_b         : abs_a;
        
        c[`BITS-1] = a[`BITS-1] ^ b[`BITS-1];
        c[`BITS-2:0] = (c[`BITS-1]) ? ~abs_c + 1'b1 : abs_c;
        
endfunction
    
//function for g-value calculation
    
function  void g_calc;
    input  signed [`BITS-1:0] a;         
    input  signed [`BITS-1:0] b;
    input u;
    output signed [`BITS:0] c;

      c = (u == 0) ? (b + a) : (b + (~a+1'b1));

endfunction

// Parameter 
localparam d = $clog2(N);

// Internal Signals
logic [N-1:0][BITS-1:0] L_in, L_out;
logic [d  :0]           temp_index_f,temp_index_g;
logic [N-1:0]           v_in, v_out;
logic [11 :0]           jL1,jL2,
                        jU1,jU2,
                        jR1,jR2,jR3;
logic ena_v,enb_v,wea_v;
logic ena_L,enb_L,wea_L;
logic [N-1:0]u;
reg signed [BITS-1:0] LRU[2];
reg [N-1:0]v;

// State Variables
logic [4:0] c_state, n_state;

//Auxiliary registers declarations
logic [d:0]  depth,depth_reg;
logic [d:0]  node,node_reg;
logic [11:0] tmp_L, tmp_L_reg, 
             tmp_R, tmp_R_reg,
             tmp_U, tmp_U_reg;

//FSM States
localparam idle        = 5'd0 , root        = 5'd1 , wait_L_logic      = 5'd2, 
           wait_L      = 5'd3 , state_L     = 5'd4 , wait_R_logic      = 5'd5, 
           wait_R      = 5'd6 , state_R     = 5'd7 , wait_U_logic      = 5'd8, 
           wait_U      = 5'd9 , state_U     = 5'd10, wait_LRU_logic    = 5'd11, 
           wait_LRU    = 5'd12, state_LRU   = 5'd13, wait_lnode_logic  = 5'd14, 
           wait_lnode  = 5'd15, state_lnode = 5'd16, wait_lstate_logic = 5'd17, 
           wait_lstate = 5'd18, state_last  = 5'd19;

//BlockRAM Instantiations
 bram_v #(  .ADDR_WIDTH(d-1),
            .DATA_WIDTH(N),
            .DEPTH(2**(d-1))) 
 bram_v_i (
            .clk(clk),.ena(ena_v),.enb(enb_v),
            .addra(depth_reg-1'b1),
            .addrb(depth_reg),
            .wea(wea_v),
            .dia(v_in),
            .dob(v_out));

bram_L #(   .ADDR_WIDTH(d-1),
            .DATA_WIDTH(N*BITS),
            .DEPTH(2**(d-1)),
            .N(N)) 
bram_L_i (
            .clk(clk),.ena(ena_L),.enb(enb_L),
            .addra(depth_reg),
            .addrb(depth_reg-1'b1),
            .wea(wea_L),
            .dia(L_in),
            .dob(L_out));

//output assignment
for(genvar i=0; i<N; i++)
 assign u_cap[i] = u[i];


assign v_final   = v;
assign out_valid = (n_state == state_lnode) ? 1'b1 : 1'b0;
 

// Sequential Logic - FSM State and Data Registers
always_ff@(posedge clk) 
begin
    if(rst) 
    begin
        c_state   <= idle;
        depth_reg <= 0;
        node_reg  <= 0;
        tmp_L_reg <= 0;
        tmp_R_reg <= 0;
        tmp_U_reg <= 0;
    end
    else 
    begin
        c_state   <= n_state;
        depth_reg <= depth;
        node_reg  <= node;
        tmp_L_reg <= tmp_L;
        tmp_R_reg <= tmp_R;
        tmp_U_reg <= tmp_U;
    end
end

//Combinational Logic - FSM Next State Logic
always_comb 
  begin 
    u = 0;
    v = 0;
//    depth = 0; 
    if(in_valid)
      case(c_state)
        idle: 
                begin 
                  depth = 0; node  = 0;
                  tmp_L = 0; tmp_R = 0; tmp_U = 0;
                  ena_L = 0; wea_L = 0; enb_L = 0;
                  ena_v = 0; wea_v = 0; enb_v = 0;
                  u = 0; v = 0; 
                  if(out_valid)
                    n_state = idle;
                  else
                    n_state = root;    
                end
          
        root: 
                begin
                  depth = depth_reg; 
                  node  = node_reg;
                  ena_L = 1'b1;      wea_L = 1'b1; 
                  enb_L = 0;         ena_v = 0;         
                  wea_v = 0;         enb_v = 0;     
                  
                  u = u;
                  v = v;
                  for(int k = 0; k < N; k++)
                    L_in[k] = y[k];
                  
                  n_state = wait_L_logic;
                end

        wait_L_logic: 
                begin
                  depth = depth_reg + 1'b1; node  = ((2*node_reg) + 1'b1); 
                  ena_L = 0;                wea_L = 0;
                  tmp_L = 0;                enb_L = 1'b1;
                  ena_v = 0;                wea_v = 0;
                  enb_v = 0; 
                
                  u = u;
                  v = v;
                  if(depth < d)
                    n_state = wait_L;
                  else
                    n_state = wait_LRU_logic;                                    
                end

        wait_L:    
                begin
                  u = u;
//                  depth = depth_reg;
                  n_state = state_L; 
                end

        state_L:   
                begin     
                  u = u;
                  v = v;
//                  depth = depth_reg;
                  ena_L = 1'b1; wea_L = 1'b1; enb_L = 0;
                  ena_v = 0;    wea_v = 0;    enb_v = 0;
                  
                  tmp_L = tmp_L_reg + 1'b1;
                  
                  temp_index_f = ((N/(2**(depth+1'b1))) * ((2*(node) + 1'b1) - ((2**(depth + 1'b1)) - 1'b1))); 
                  
                  jL1 = (tmp_L_reg) + temp_index_f;
                  jL2 = (tmp_L_reg) + temp_index_f + (N/(2**depth));
                  
                  fminsum_calc(L_out[jL1],L_out[jL2],L_in[jL1]); 
                                                                 
                  if(tmp_L< (N/(2**depth)))    
                    n_state = state_L;                 
                  else if(depth < d)
                    n_state = wait_L_logic;
                  else
                    n_state = wait_LRU_logic;
                end

        wait_R_logic: 
                begin
                  u = u;
                  v = v;
                  depth   = depth_reg - 1'b1; 
                  node    = node_reg + 1'b1; 
                  tmp_R   = 0;
                  n_state = wait_R;
                end                       
     
        wait_R: 
                begin
//                  depth = depth_reg;
                  ena_L = 0;wea_L = 0; enb_L = 1'b1;
                  ena_v = 0;wea_v = 0; enb_v = 1'b1;
                  u = u;
                  v = v;
                  n_state = state_R; 
                end                       
    
        state_R:
                begin
//                  depth = depth_reg;
                  u = u;
                  v = v; 
                  ena_L = 1'b1; wea_L = 1'b1; enb_L = 0;
                  ena_v = 0;    wea_v = 0;    enb_v = 0;
                  
                  tmp_R = tmp_R_reg + 1'b1;
                  temp_index_f = ((N/(2**(depth + 1'b1))) * ((2*(node) + 1'b1) -((2**(depth + 1'b1)) - 1'b1)));
                  temp_index_g = ((N/(2**(depth + 1'b1))) * ((2*(node - 1'b1) + 1'b1)-((2**(depth + 1'b1)) -  1'b1)));
                  
                  jR1 = (tmp_R_reg) + temp_index_g;
                  jR2 = (tmp_R_reg) + temp_index_g + (N/(2**depth));
                  jR3 = (tmp_R_reg) + temp_index_f;
                  
                  g_calc(L_out[jR1],L_out[jR2],v_out[jR1],L_in[jR3]);
                        
                  if(tmp_R < (N/(2**depth)))    
                    n_state = state_R;
                  else if(node == ((2**d) - 2)) 
                    n_state = wait_lnode_logic;
                  else if(depth == d)
                    n_state = wait_LRU_logic;
                  else 
                    n_state = wait_L_logic;                                               
                end                   
                            
        wait_U_logic: 
                begin
                  depth = depth_reg - 1'b1; 
                  node  = (node_reg - 2) >> 1; 
                  tmp_U = 0;
                  u = u;
                  v = v;
                  n_state = wait_U;
                end                       
    
        wait_U:
                begin
 //                 depth = depth_reg;
                  ena_L = 0; wea_L = 0; enb_L = 0;
                  ena_v = 0; wea_v = 0; enb_v = 1'b1; 
 
                  n_state = state_U; 
                end                        
    
        state_U:
                begin
//                  depth = depth_reg;
                  ena_L = 0; ena_v =1'b1; enb_L = 0;
                  wea_L = 0; wea_v =1'b1; enb_v = 0;
                  u = u;
                  v = v;
                  tmp_U        = tmp_U_reg+1'b1;
                  temp_index_f = ((N/(2**(depth))) * ((2*node + 1'b1) - ((2**(depth)) - 1'b1))); 
                  
                  jU1 = (tmp_U_reg) + temp_index_f;
                  jU2 = (tmp_U_reg) + temp_index_f + (N/(2**(depth)));
                  
                  v_in[jU1] = v_out[jU1] ^ v_out[jU2]; 
                  v_in[jU2] = v_out[jU2]; 
                                    
                  if(tmp_U < (N/(2**(depth)))) 
                    n_state = state_U;
                  else if(depth > 0 && ~node[0])  
                    n_state = wait_U_logic;                          
                  else if(depth > 0 && node!=0)
                    n_state = wait_R_logic;
                  else              
                    n_state = wait_lstate_logic;         
                end 
    
        wait_LRU_logic: 
                begin
                  u = u;
                  v = v;
 //                 depth = depth_reg; 
                  node  = (node_reg - 1'b1) >> 1;
                
                  n_state = wait_LRU;
                end                         
    
        wait_LRU: 
                begin
 //                 depth = depth_reg;
                  u = u;
                  v = v;
                  ena_L = 0; wea_L = 0; enb_L = 1'b1;
                  ena_v = 0; wea_v = 0; enb_v = 0; 
                  
                  n_state = state_LRU; 
                end                                                            
 
        state_LRU:  
                begin
//                  depth = depth_reg;
                  ena_L = 0; ena_v = 1'b1;  
                  enb_v = 0; wea_v = 1'b1;
                  wea_L = 0; enb_L = 0; 
                  v = v;
                  temp_index_f = ((N/(2**(depth))) * ((2*node + 1'b1) - ((2**(depth)) - 1'b1)));
                  
                  fminsum_calc(L_out[temp_index_f],L_out[temp_index_f + 1],LRU[0]);
                  
                  u[(2*node)+2-N] = (f[(2*node)+2-N]) ? 0 : ((LRU[0][BITS-1]) ? 1 : 0);
                  
                  g_calc(L_out[temp_index_f],L_out[temp_index_f+1],u[(2*node)+2-N],LRU[1]);
                  
                  u[(2*node)+3-N] = (f[(2*node)+3-N]) ? 0 : ((LRU[1][BITS-1]) ? 1 : 0);
                  
                  v_in[temp_index_f]   = u[(2*node)+2-N] ^ u[(2*node)+3-N];
                  v_in[temp_index_f+1] = u[(2*node)+3-N];                                                       
                    
                  if(node[0])               
                    n_state = wait_R_logic;                                 
                  else                          
                    n_state = wait_U_logic;
                end  
    
        wait_lnode_logic:  
                begin
                  u = u;
                  v = v;
                  depth = depth_reg + 1'b1; node = node_reg;
                
                  n_state = wait_lnode;
                end                         
    
        wait_lnode:        
                begin
//                  depth = depth_reg;
                  u = u;
                  v = v;
                  ena_L = 0; wea_L = 0; enb_L = 1'b1;
                  ena_v = 0; wea_v = 0; enb_v = 0; 
                  
                  n_state = state_lnode; 
                end 
    
        state_lnode:
                begin
//                  depth = depth_reg;
                  u = u;
                  v = v;  
                  ena_L = 0;    wea_L = 0;    enb_L = 0;
                  ena_v = 1'b1; wea_v = 1'b1; enb_v = 0;
                  
                  temp_index_f = ((N/(2**(depth))) * ((2*node + 1'b1) - ((2**(depth)) - 1'b1)));
                  
                  fminsum_calc(L_out[temp_index_f],L_out[temp_index_f+1],LRU[0]);
                  
                  u[(2*node)+2-N] = (f[(2*node)+2-N]) ? 0 : ((LRU[0][BITS-1]) ? 1'b1 : 0);
                  
                  g_calc(L_out[temp_index_f],L_out[temp_index_f+1],u[(2*node)+2-N],LRU[1]);
                  
                  u[(2*node)+3-N] = (f[(2*node)+3-N]) ? 0 : ((LRU[1][BITS-1]) ? 1'b1 : 0);   
                  
                  v_in[temp_index_f]   = u[(2*node)+2-N] ^ u[(2*node)+3-N];
                  v_in[temp_index_f+1] = u[(2*node)+3-N];                                                    
                  
                  n_state = wait_U_logic; 
                end 
    
        wait_lstate_logic: 
                begin
                  u = u;
                  v = v;
//                  depth = depth_reg;  
                  node  = node_reg;
                
                  n_state = wait_lstate;
                end                         
    
        wait_lstate:   
                begin
//                  depth = depth_reg;
                  u = u;
                  v = v;
                  ena_L = 0; wea_L = 0; enb_L = 1'b1;
                  ena_v = 0; wea_v = 0; enb_v = 0; 
            
                  n_state = state_last; 
                end
    
        state_last:  
                begin
//                  depth = depth_reg;
                  u = u;
                  ena_L = 0;    wea_L = 0;    enb_L = 0;
                  ena_v = 1'b1; wea_v = 1'b1; enb_v = 0;
                  
                  v     = v_out;
                  
                  n_state = idle;
                end
        default: 
                begin
                  u = 0;
                  v = 0;
                  depth = 0; node  = 0;
                  tmp_L = 0; tmp_R = 0; tmp_U = 0;
                  ena_L = 0; wea_L = 0; enb_L = 0;
                  ena_v = 0; wea_v = 0; enb_v = 0;

                  n_state = idle;
                end                                            
      endcase  
    else    
      begin
       u = 0;
       v = 0;
       depth   = 0; node  = 0;
       tmp_L   = 0; tmp_R = 0; tmp_U = 0;
       ena_L   = 0; wea_L = 0; enb_L = 0;
       ena_v   = 0; wea_v = 0; enb_v = 0;
       n_state = idle;                    
      end
  end
endmodule