-- ***************************************************************************
-- ***************************************************************************
-- Copyright 2013(c) Analog Devices, Inc.
--  Author: Lars-Peter Clausen <lars-peter.clausen@analog.com>
-- 
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-- ***************************************************************************

library ieee;
use ieee.std_logic_1164.all;

entity i2s_tx is
	generic(
		C_SLOT_WIDTH	: integer := 24;	-- Width of one Slot
		C_NUM		: integer := 1
	);
	port(
		clk		: in  std_logic; 	-- System clock 
		resetn		: in  std_logic; 	-- System reset
		enable		: in  Boolean;		-- Enable TX

		bclk		: in  std_logic;	-- Bit Clock
		channel_sync	: in  std_logic;	-- Channel Sync
		frame_sync	: in  std_logic;	-- Frame Sync
		sdata		: out std_logic_vector(C_NUM - 1 downto 0);	-- Serial Data Output

		ack		: out std_logic;	-- Request new Slot Data
		stb		: in std_logic;	-- Request new Slot Data
		data		: in  std_logic_vector(C_SLOT_WIDTH-1 downto 0) 	-- Slot Data in
	);
end i2s_tx;

architecture Behavioral of i2s_tx is
	type mem is array (0 to C_NUM - 1) of std_logic_vector(31 downto 0);
	signal data_int : mem;
	signal reset_int : Boolean;
	signal enable_int : Boolean;

	signal bit_sync : std_logic;
	signal channel_sync_int : std_logic;
	signal frame_sync_int : std_logic;
	signal channel_sync_int_d1 : std_logic;

	signal bclk_d1 : std_logic;
begin

	reset_int <= resetn = '0' or not enable;

	process (clk)
	begin
		if rising_edge(clk) then
			if resetn = '0' then
				bclk_d1 <= '0';
				channel_sync_int_d1 <= '0';
			else
				bclk_d1 <= bclk;
				channel_sync_int_d1 <= channel_sync_int;
			end if;
	    end if;
	end process;

	bit_sync <= (bclk xor bclk_d1) and not bclk;
	channel_sync_int <= channel_sync and bit_sync;
	frame_sync_int <= frame_sync and bit_sync;

	ack <= '1' when channel_sync_int_d1 = '1' and enable_int else '0';

	gen: for i in 0 to C_NUM - 1 generate

	serialize_data: process(clk)
	begin
		if rising_edge(clk) then
			if reset_int then
				data_int(i)(31 downto 0) <= (others => '0');
			elsif bit_sync = '1' then
				if channel_sync_int = '1' then
					data_int(i)(31 downto 32-C_SLOT_WIDTH) <= data;
					data_int(i)(31-C_SLOT_WIDTH downto 0) <= (others => '0');
				else
					data_int(i) <= data_int(i)(30 downto 0) & '0';
				end if;
			end if;
		end if;
	end process serialize_data;
	sdata(i) <= data_int(i)(31) when enable_int else '0';

	end generate;

	enable_sync: process (clk)
	begin
		if rising_edge(clk) then
			if reset_int then
				enable_int <= False;
			else
				if enable and frame_sync_int = '1' and stb = '1' then
					enable_int <= True;
				elsif not enable then
					enable_int <= False;
				end if;
			end if;
		end if;
	end process;

end Behavioral;