----------------------------------------------------------------------------------
-- Company:             Tek15 Solutions
-- Engineer:            Matt Lewis
--
-- Create Date:     14:22:35 01/20/2018
-- Design Name:         V2FPGA Serial Module
-- Module Name:     Serial - Behavioral
-- Project Name:        Vermonster DRSSTC Controller
-- Target Devices:  -undetermined-
-- Description:         FPGA-based dual-resonant solid-state Tesla coil
--                          controller designed for the Vermonster DRSSTC
-- Revision:            2
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity Serial is
    port (
        CLK_50MHz: IN STD_LOGIC;
        RX: IN STD_LOGIC;
        TX: OUT STD_LOGIC
    );
end Serial;

architecture Behavioral of Serial is

begin

-- 9600 baud = 9600 bits/sec
-- 1 bit time = 1000ms/9600 = 104.2us
-- 1/2 bit time = 52.1us
-- 1 tick = 1/50000000Hz = 20ns
-- Ticks per bit: 104.2us/20ns = 5210 ticks
-- Ticks per half bit: 52.1us/20ns = 2605 ticks

-- Data Stream:
-- BYTE0
-- |BIT7|BIT6|  BIT5|   BIT4|   BIT3|   BIT2|   BIT1|   BIT0|
-- |STRT|R/W ||_____________FEATURE______________|
-- BYTE1
-- |BIT7|BIT5| BIT5| BIT4|  BIT3|   BIT2|   BIT1|   BIT0|
--  |________________VALUE (WRITE)________________|

RxBytes: process(CLK_50MHz)

    variable RxByte0: STD_LOGIC_VECTOR(7 downto 0) := (others => '0');  -- Received byte 0
    variable RxByte1: STD_LOGIC_VECTOR(7 downto 0) := (others => '0');  --  Received byte 1
    variable RxBegun: STD_LOGIC := '0';                 --  Receive sequence started
    variable RxFinished: STD_LOGIC := '1';              --  Receive sequence finished
    variable CurrentByte: INTEGER RANGE 0 TO 1;             --  Current byte being received
    variable Counter: INTEGER RANGE 0 TO 7815;      --  Counter for baud generator (1.5 bits max @ 50MHz)
    variable BitCount: INTEGER RANGE 0 TO 128;      --  Counter for number of bits received. Should not exceed 16 per cmd string

begin
    if (rising_edge(CLK_50MHz)) then                        -- If CLK_50MHz is rising
        if (RX = '0') then                                  --  If RX input is low (start bit detected)
            if (RxBegun = '0') then                         --          If receive has not yet begun
                RxBegun := '1';                             --              Begin receive
                RxFinished := '0';                          --              Receive not yet finished

                -- Byte0 --

                BitCount := BitCount + 1;                   --              Increment number of bits received
                RxByte0(7) := '0';                          --              Load '0' into Byte0 BIT7 (start bit)
                if (Counter < 7815) then                    --              Count 1.5 bit times to sample center of BIT6
                    Counter := Counter + 1;
                else                                                --              If ready for BIT6
                    Counter := 0;                               --                  Reset time counter
                    RxByte0(6) := RX;                           --                  Load value on RX pin into Byte0 BIT6 (R/W)
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT5
                    Counter := Counter + 1;
                else                                                --              If ready for BIT5
                    Counter := 0;                               --                  Reset time counter
                    RxByte0(5) := RX;                           --                  Load value on RX pin into Byte0 BIT5
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT4
                    Counter := Counter + 1;
                else                                                --              If ready for BIT4
                    Counter := 0;                               --                  Reset time counter
                    RxByte0(4) := RX;                           --                  Load value on RX pin into Byte0 BIT4
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT3
                    Counter := Counter + 1;
                else                                                --              If ready for BIT3
                    Counter := 0;                               --                  Reset time counter
                    RxByte0(3) := RX;                           --                  Load value on RX pin into Byte0 BIT3
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT2
                    Counter := Counter + 1;
                else                                                --              If ready for BIT2
                    Counter := 0;                               --                  Reset time counter
                    RxByte0(2) := RX;                           --                  Load value on RX pin into Byte0 BIT2
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT1
                    Counter := Counter + 1;
                else                                                --              If ready for BIT1
                    Counter := 0;                               --                  Reset time counter
                    RxByte0(1) := RX;                           --                  Load value on RX pin into Byte0 BIT1
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT0
                    Counter := Counter + 1;
                else                                                --              If ready for BIT0
                    Counter := 0;                               --                  Reset time counter
                    RxByte0(0) := RX;                           --                  Load value on RX pin into Byte0 BIT0
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;

                -- Byte1 --

                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT7
                    Counter := Counter + 1;
                else                                                --              If ready for BIT7
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(7) := RX;                           --                  Load value on RX pin into Byte1 BIT7
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT6
                    Counter := Counter + 1;
                else                                                --              If ready for BIT6
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(6) := RX;                           --                  Load value on RX pin into Byte1 BIT6
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT5
                    Counter := Counter + 1;
                else                                                --              If ready for BIT5
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(5) := RX;                           --                  Load value on RX pin into Byte1 BIT5
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT4
                    Counter := Counter + 1;
                else                                                --              If ready for BIT4
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(4) := RX;                           --                  Load value on RX pin into Byte1 BIT4
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT3
                    Counter := Counter + 1;
                else                                                --              If ready for BIT3
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(3) := RX;                           --                  Load value on RX pin into Byte1 BIT3
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT2
                    Counter := Counter + 1;
                else                                                --              If ready for BIT2
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(2) := RX;                           --                  Load value on RX pin into Byte1 BIT2
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT1
                    Counter := Counter + 1;
                else                                                --              If ready for BIT1
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(1) := RX;                           --                  Load value on RX pin into Byte1 BIT1
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                end if;
                if (Counter < 5210) then                    --              Count 1 bit time to sample center of BIT0
                    Counter := Counter + 1;
                else                                                --              If ready for BIT0
                    Counter := 0;                               --                  Reset time counter
                    RxByte1(0) := RX;                           --                  Load value on RX pin into Byte1 BIT0 (Stop bit)
                    BitCount := BitCount + 1;               --                  Increment number of bits received
                    RxBegun := '0';                         --                  Receive finished
                end if;

                -- Error check --
                if (BitCount /= 16) then                    --              If wrong number of bits detected
                    RxByte0 := (others => '0');         --                  Clear RxByte0
                    RxByte1 := (others => '0');         --                  Clear RxByte1
                else                                                --              If data valid
                    BitCount := 0;                              --                  Reset bit counter
                    RxFinished := '1';                      --                  Receive is finished
                end if;
            end if;
        end if;
    end if;
end process RxBytes;

end Behavioral;