LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.NUMERIC_STD.ALL;
use std.textio.all; --  Imports the standard textio package.

use work.utils_pkg.all;
use work.spi_types.all;

ENTITY spi_tx IS
	Generic
	(
		word_width	: natural := 32
	);
	Port
	(
		rst			: in  STD_LOGIC;
		clk			: in  STD_LOGIC;
		cmd_vld		: in  STD_LOGIC;
		cmd_ack		: out STD_LOGIC;
		cmd			: in  cmd_t;
		din_vld		: in  STD_LOGIC;
		din_re		: out STD_LOGIC;
		din			: in  unsigned(word_width-1 downto 0);
		shift_en	: in  STD_LOGIC;
		data_out	: out STD_LOGIC;
		clk_out		: out STD_LOGIC
		
	);
END spi_tx;

ARCHITECTURE behavior OF spi_tx IS

	type state_t is (idle, prepare, shift, finish);

	signal xfer_count			: unsigned(NextExpBaseTwo(XFER_SIZE_MAX)-1 downto 0);
	signal data_count			: unsigned(NextExpBaseTwo(XFER_SIZE_MAX)-1 downto 0);
	signal word_count			: unsigned(NextExpBaseTwo(XFER_SIZE_MAX)-1 downto 0);
	signal cmd_reg				: cmd_t;	
	signal state				: state_t;
	signal state_next			: state_t;
	signal cmd_reg_we			: std_logic;
	signal xfer_count_en		: std_logic;
	signal data_count_en		: std_logic;
	signal xfer_count_busy		: std_logic;
	signal data_count_busy		: std_logic;
	signal clk_en				: std_logic;
	
--------------------------------------------------------------------------
begin

	clk_out		<= clk and clk_en;
	
--------------------------------------------------------------------------
proc_state_next:
process(clk)
begin
	if rising_edge(clk) then
		if rst = '1' then
			state	<= idle;
		else
			state	<= state_next;
		end if;
	end if;
end process;

proc_fsm:
process(state, cmd_vld, xfer_count_busy)
begin
	state_next		<= state;
	cmd_reg_we		<= '0';
	cmd_ack			<= '0';
	xfer_count_en	<= '0';
	data_count_en	<= '0';
	clk_en			<= '0';
	case state is
	
	when idle =>
		cmd_ack		<= cmd_vld;
		if cmd_vld = '1' then
			cmd_reg_we	<= '1';
			state_next	<= prepare;
		end if;

	when prepare =>
		xfer_count_en	<= '1';
		data_count_en	<= '1';
		state_next	<= shift;
		
	when shift =>
		clk_en			<= '1';
		xfer_count_en	<= '1';
		data_count_en	<= '1';
		if xfer_count_busy = '0' then
			state_next	<= finish;
		end if;

	when finish =>
		state_next	<= idle;

	when others =>
		state_next	<= idle;

	end case;	
end process;

process(clk)
begin
	if rising_edge(clk) then
		if xfer_count_en = '0' then
			xfer_count			<= cmd.xfer_size;
			xfer_count_busy		<= '0';
		elsif shift_en = '1' then
			if xfer_count /= to_unsigned(0, xfer_count'length) then
				xfer_count_busy		<= '1';
				xfer_count			<= xfer_count - 1;
			else
				xfer_count_busy		<= '0';
			end if;
		end if;
	end if;
end process;

process(clk)
begin
	if rising_edge(clk) then
		din_re	<= '0';
		if data_count_en = '0' then
			word_count			<= to_unsigned(0, word_count'length);
			data_count			<= cmd.data_size;
			data_count_busy		<= '0';
		elsif shift_en = '1' then
			if word_count /= to_unsigned(0, word_count'length) then
				word_count			<= word_count - 1;
			else
				din_re				<= '1';
				word_count			<= to_unsigned(word_width, word_count'length);
			end if;
			if data_count /= to_unsigned(1, data_count'length) then
				data_count_busy		<= '1';
				data_count			<= data_count - 1;
			else
				data_count_busy		<= '0';
			end if;
		end if;
	end if;
end process;

end behavior;