//this is the collision detection module


module denise_collision
(
  input   clk,          // 28MHz clock
  input clk7_en,
  input  reset,          //reset
  input aga,        // aga enabled
  input   [8:1] reg_address_in,  //register adress inputs
  input   [15:0] data_in,      //bus data in
  output  [15:0] data_out,    //bus data out
  input  dblpf,        //dual playfield signal, required to support undocumented feature
  input  [7:0] bpldata,      //bitplane serial video data in
  input  [7:0] nsprite
);

//register names and adresses
parameter CLXCON  = 9'h098;
parameter CLXCON2 = 9'h10e;
parameter CLXDAT  = 9'h00e;

//local signals
reg    [15:0] clxcon;      //collision detection control register
reg   [15:0] clxcon2;     // collision reg 2
reg    [14:0] clxdat;      //collision detection data register
wire  [3:0] sprmatch;      //sprite group matches clxcon settings
wire  oddmatch;        //odd bitplane data matches clxcon settings
wire  evenmatch;        //even bitplane data matches clxcon settings

//--------------------------------------------------------------------------------------

//CLXCON register
always @(posedge clk)
  if (clk7_en) begin
    if (reset) //reset to safe value
      clxcon <= 16'h0fff;
    else if (reg_address_in[8:1] == CLXCON[8:1])
      clxcon <= data_in;
  end

always @ (posedge clk) begin
  if (clk7_en) begin
    if (reset || (reg_address_in[8:1] == CLXCON[8:1]))
      clxcon2 <= #1 16'h0000;
    else if (aga && (reg_address_in[8:1] == CLXCON2[8:1]))
      clxcon2 <= #1 data_in;
  end
end

//--------------------------------------------------------------------------------------

//generate bitplane match signal
wire [7:0] bm;
assign bm = (bpldata[7:0] ^ ~{clxcon2[1:0],clxcon[5:0]}) | (~{clxcon2[7:6],clxcon[11:6]}); // JB: playfield collision detection fix

// this is the implementation of an undocumented function in the real Denise chip, developed by Yaqube.
// trigger was the game Rotor. mentioned in WinUAE sources to be the only known game needing this feature.
// it also fixes the Spaceport instandly helicopter crash at takeoff
// and Archon-1 'sticky effect' of player sprite at the battlefield.
// the OCS mystery is cleaning up :)
assign oddmatch = bm[6] & bm[4] & bm[2] & bm[0] & (dblpf | evenmatch);
assign evenmatch = bm[7] & bm[5] & bm[3] & bm[1];

//generate sprite group match signal
/*assign sprmatch[0] = (nsprite[0] | (nsprite[1]) & clxcon[12]);*/
/*assign sprmatch[1] = (nsprite[2] | (nsprite[3]) & clxcon[13]);*/
/*assign sprmatch[2] = (nsprite[4] | (nsprite[5]) & clxcon[14]);*/
/*assign sprmatch[3] = (nsprite[6] | (nsprite[7]) & clxcon[15]);*/
assign sprmatch[0] = nsprite[0] | (nsprite[1] & clxcon[12]);
assign sprmatch[1] = nsprite[2] | (nsprite[3] & clxcon[13]);
assign sprmatch[2] = nsprite[4] | (nsprite[5] & clxcon[14]);
assign sprmatch[3] = nsprite[6] | (nsprite[7] & clxcon[15]);

//--------------------------------------------------------------------------------------

//detect collisions
wire [14:0] cl;
reg clxdat_read_del;

assign cl[0]  = evenmatch   & oddmatch;    //odd to even bitplanes
assign cl[1]  = oddmatch    & sprmatch[0];  //odd bitplanes to sprite 0(or 1)
assign cl[2]  = oddmatch    & sprmatch[1];  //odd bitplanes to sprite 2(or 3)
assign cl[3]  = oddmatch    & sprmatch[2];  //odd bitplanes to sprite 4(or 5)
assign cl[4]  = oddmatch    & sprmatch[3];  //odd bitplanes to sprite 6(or 7)
assign cl[5]  = evenmatch   & sprmatch[0];  //even bitplanes to sprite 0(or 1)
assign cl[6]  = evenmatch   & sprmatch[1];  //even bitplanes to sprite 2(or 3)
assign cl[7]  = evenmatch   & sprmatch[2];  //even bitplanes to sprite 4(or 5)
assign cl[8]  = evenmatch   & sprmatch[3];  //even bitplanes to sprite 6(or 7)
assign cl[9]  = sprmatch[0] & sprmatch[1];  //sprite 0(or 1) to sprite 2(or 3)
assign cl[10] = sprmatch[0] & sprmatch[2];  //sprite 0(or 1) to sprite 4(or 5)
assign cl[11] = sprmatch[0] & sprmatch[3];  //sprite 0(or 1) to sprite 6(or 7)
assign cl[12] = sprmatch[1] & sprmatch[2];  //sprite 2(or 3) to sprite 4(or 5)
assign cl[13] = sprmatch[1] & sprmatch[3];  //sprite 2(or 3) to sprite 6(or 7)
assign cl[14] = sprmatch[2] & sprmatch[3];  //sprite 4(or 5) to sprite 6(or 7)

wire clxdat_read = (reg_address_in[8:1]==CLXDAT[8:1]);// clxdat read

always @(posedge clk)
  if (clk7_en) begin
    clxdat_read_del <= clxdat_read;
  end

//register detected collisions
always @(posedge clk)
  if (clk7_en) begin
  //  if (reg_address_in[8:1]==CLXDAT[8:1])    //if clxdat is read, clxdat is cleared to all zero's
    if (!clxdat_read & clxdat_read_del)  //if clxdat is read, clxdat is cleared to all zero's after read
      clxdat <= 0;
    else //else register collisions
      clxdat <= clxdat[14:0] | cl[14:0];
  end

//--------------------------------------------------------------------------------------

//reading of clxdat register
assign data_out = reg_address_in[8:1]==CLXDAT[8:1] ? {1'b1,clxdat[14:0]} : 16'd0;


endmodule