`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company:
// Engineer: Chris Seto
//
// Create Date:    14:14:30 01/23/2011
// Design Name:
// Module Name:    PPM
// Project Name:   PPM Decoder
// Target Devices:
// Tool versions:
// Description: An I2C PPM decoder
//
// Dependencies: I2C Slave
//
// Revision:
// Revision 0.01 - File Created
// Additional Comments:
//
//////////////////////////////////////////////////////////////////////////////////
module PPM(
  Clk,
  SDA,
  SCL,
  PPMIN
);

input Clk;
inout SDA;
input SCL;
input PPMIN;

wire [7:0] I2C_Out;
wire [7:0] I2C_In;
wire [7:0] I2C_Addr;
wire I2C_WEn;
reg UsClk;
reg [4:0] MclkDiv_Count;
reg [15:0] Channel[7:0];
reg [2:0] ChannelSelect = 0;
reg LastPosition = 0;
reg [15:0] CurrentCount = 0;

i2cSlave u_i2cSlave(
  .clk(Clk),
  .rst(0),
  .sda(SDA),
  .scl(SCL),
  .Out(I2C_Out),
  .In(I2C_In),
  .Addr(I2C_Addr),
  .WEn(I2C_WEn)
);

//assign I2C_In = (I2C_Addr[0]==0)?Channel[I2C_Addr[7:1]][7:0]:Channel[I2C_Addr[7:1]][15:8];

if (I2C_Addr[0]==0) begin
    assign I2C_In = Channel[I2C_Addr[7:1]][7:0];
end
else begin
    assign I2C_In = Channel[I2C_Addr[7:1]][15:8];
end

// 1us counter
always @(posedge Clk) begin
  if (MclkDiv_Count==25) begin
    MclkDiv_Count <= 5'h00;
     UsClk <= !UsClk;
  end
  else
    MclkDiv_Count <= MclkDiv_Count+1;
end

// Process the PPM signal
always @(posedge UsClk) begin
    LastPosition <= PPMIN;

    if ((PPMIN==1) & (LastPosition==0))
    begin
        if (CurrentCount > 2500) begin
            CurrentCount = 0;
            ChannelSelect = 0;
        end
        else begin
            Channel[ChannelSelect] = CurrentCount;
            CurrentCount = 0;
            ChannelSelect = ChannelSelect + 1;
        end
    end
    else begin
        CurrentCount = CurrentCount + 1;
    end
end

endmodule