Added UART_RX_CTRL file.

Author: Carlos-Morales-Diaz

vhdl/UART_RX_CTRL.vhd

@@ -0,0 +1,128 @@
+-- ClariFi
+-- Part: XC7A35TICSG324-1L 
+-- UART_RX_CTRL - Utilizes the Arty A7's USB-UART Bridge (Serial Port)
+-- Serialization information:
+-- 		TXD -> Pin A9
+-- 		RXD -> Pin D10
+-- 		115200 Baud Rate
+-- 		8 Data Bits, LSB First
+-- 		1 Stop Bit
+-- 		No parity
+-- Data needs to be sampled at a rate of at least 115200*8 = 921.600 KHz
+-- A 100 MHz clock is expected. We sample in the middle of a bit data.
+
+library ieee;
+use ieee.std_logic_1164.ALL;
+use ieee.numeric_std.all;
+ 
+entity UART_RX_CTRL is
+	generic (
+		CLKS_PER_BIT : integer := 868 -- 868 = round(100MHz / 115200)
+	);
+	port (
+		CLK		: in  std_logic;
+		RST 	: in std_logic;
+		UART_RX : in  std_logic;
+		RX_DONE : out std_logic;
+		DATA	: out std_logic_vector(7 downto 0)
+	);
+end UART_RX_CTRL;
+
+architecture BHV of UART_RX_CTRL is
+ 
+  type state_type is (S_START, S_START_BIT, S_DATA_BITS, S_STOP_BIT, S_DONE);
+  signal state : state_type := S_START;
+ 
+  signal r_UART_RX : std_logic := '0';
+  signal r_r_UART_RX   : std_logic := '0';
+   
+  signal r_Bit_Counter : integer range 0 to CLKS_PER_BIT-1 := 0;
+  signal r_Bit_Index : integer range 0 to 7 := 0;  -- 8 Bits Total
+  signal r_RX_Byte   : std_logic_vector(7 downto 0) := (others => '0');
+  signal r_RX_DONE     : std_logic := '0';
+   
+begin 
+	process (CLK)
+	begin
+		if rising_edge(CLK) then
+			-- Dual-flop synchronizer to stabilize incoming signal (data)
+			r_UART_RX <= UART_RX;
+			r_r_UART_RX <= r_UART_RX;
+			 
+		  case state is
+	 
+			when S_START =>
+			  r_RX_DONE     <= '0';
+			  r_Bit_Counter <= 0;
+			  r_Bit_Index <= 0;
+	 
+			  if (r_r_UART_RX = '0') then -- falling_edge(r_r_UART_RX) then -- Start bit transitioned from '1' to '0'
+				state <= S_START_BIT;
+			  end if;
+			  state <= S_START;
+	 
+			-- Sample half bit later to make sure it's still low
+			when S_START_BIT =>
+			  if r_Bit_Counter = (CLKS_PER_BIT-1)/2 then
+				if r_r_UART_RX = '0' then
+				  r_Bit_Counter <= 0;  -- Reset the counter
+				  state   <= S_DATA_BITS; -- We are receiving data
+				else
+				  state   <= S_START; -- Start bit was not held low long enough
+				end if;
+			  else
+				r_Bit_Counter <= r_Bit_Counter + 1;
+				state   <= S_START_BIT;
+			  end if;
+	 
+			   
+			-- Sample data after CLKS_PER_BIT-1 clock cycles
+			when S_DATA_BITS =>
+			  if r_Bit_Counter < CLKS_PER_BIT-1 then
+				r_Bit_Counter <= r_Bit_Counter + 1;
+				state   <= S_DATA_BITS;
+			  else
+				r_Bit_Counter            <= 0;
+				r_RX_Byte(r_Bit_Index) <= r_r_UART_RX;
+				 
+				-- Loop back until all 8 bits have been added to r_RX_Byte
+				if r_Bit_Index < 7 then
+				  r_Bit_Index <= r_Bit_Index + 1;
+				  state   <= S_DATA_BITS;
+				else
+				  r_Bit_Index <= 0;
+				  state   <= S_STOP_BIT;
+				end if;
+			  end if;
+	 
+	 
+			-- Receive last bit, 1 stop bit. 
+			when S_STOP_BIT =>
+			  -- Check stop bit after CLKS_PER_BIT-1 clock cycles
+			  if r_Bit_Counter < CLKS_PER_BIT-1 then
+				r_Bit_Counter <= r_Bit_Counter + 1;
+				state   <= S_STOP_BIT;
+			  else
+				r_RX_DONE     <= '1';
+				r_Bit_Counter <= 0;
+				state   <= S_DONE;
+			  end if;
+	 
+					   
+			-- Wait 1 cycle before going back to S_START
+			when S_DONE =>
+			  state <= S_START;
+			  r_RX_DONE   <= '0';
+	 
+			-- Should never be reached
+			when others =>
+			  state <= S_START;
+	 
+		  end case;
+    end if;
+  end process;
+ 
+  RX_DONE   <= r_RX_DONE;
+  DATA <= r_RX_Byte;
+   
+end BHV;