splink/vhdl/splink.vhdl

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

use work.ws2812_pkg.color_t;
use work.ws2812_pkg.colors_vector;

entity splink is
	generic (
		NUM_STRANDS : positive;
		MAX_STRAND_LEN : positive := 256
	);
	port (
		clk : in std_logic;
		reset : in std_logic;

		udp_length : in std_logic_vector(15 downto 0);
		udp_valid : in std_logic;
		udp_last : in std_logic;
		udp_data : in std_logic_vector(31 downto 0);

		frame_number : out unsigned(31 downto 0);

		drivers : out std_logic_vector(NUM_STRANDS-1 downto 0)
	);
end entity;

architecture a of splink is
	constant BITS_PER_LED: natural := 24;

	signal led_addr : std_logic_vector(7 downto 0);
	signal led_data_a : std_logic_vector(BITS_PER_LED * NUM_STRANDS - 1 downto 0);
	signal led_data_b : std_logic_vector(BITS_PER_LED * NUM_STRANDS - 1 downto 0);
	signal led_data : std_logic_vector(BITS_PER_LED * NUM_STRANDS - 1 downto 0);
	signal led_colors : colors_vector(NUM_STRANDS-1 downto 0);

	signal active_strand: natural range 0 to NUM_STRANDS-1;
	signal num_pixels: natural range 1 to MAX_STRAND_LEN;
	signal current_frame: unsigned(31 downto 0);
	signal pixels_received: natural range 0 to MAX_STRAND_LEN-1;

	signal run : std_logic;
	signal sender_done : std_logic;

	-- "PIXL"
	constant MAGIC_NUMBER : std_logic_vector(31 downto 0) := x"5049584c";
	-- magic + frame num + strand num (4 bytes each)
	constant HEADER_LEN : natural := 12;

	type receive_state_t is (MAGIC, FRAME_NUM, STRAND_NUM, DATA, DROP);
	constant RESET_STATE : receive_state_t := MAGIC;
	signal receive_state : receive_state_t;

	type bank_t is (BANK_A, BANK_B);
	signal output_bank : bank_t;
begin
	ws2812_inst: entity work.ws2812_parallel
		generic map (
			NUM_DRIVERS => NUM_STRANDS,
			NUM_LEDS => MAX_STRAND_LEN,
			COLOR_ORDER => "GRB",
			T_CLK => 12.5 ns,

			T0H => 0.35 us,
			T0L => 0.9 us,
			T1H => 0.7 us,
			T1L => 0.55 us,

			T_RES => 100 us
		)
		port map (
			n_reset => not reset,
			clk     => clk,
			run     => run,
			done    => sender_done,

			led_addr => led_addr,

			led_colors => led_colors,

			dout => drivers
		);

	process(led_data)
		function make_color(data_in: std_logic_vector(BITS_PER_LED-1 downto 0)) return color_t is
		begin
			return (
				red => data_in(23 downto 16),
				green => data_in(15 downto 8),
				blue => data_in(7 downto 0)
			);
		end function;
	begin
		for i in 0 to NUM_STRANDS-1 loop
			led_colors(i) <= make_color(led_data((i+1) * BITS_PER_LED - 1 downto i * BITS_PER_LED));
		end loop;
	end process;

	-- memory inference help
	with output_bank select led_data <=
		led_data_a when BANK_A,
		led_data_b when BANK_B;

	fsm: process(clk)
		type strand_buffer_t is array(0 to MAX_STRAND_LEN-1) of std_logic_vector(BITS_PER_LED * NUM_STRANDS - 1 downto 0);

		variable strand_buffer_a : strand_buffer_t;
		variable strand_buffer_b : strand_buffer_t;

		variable received_strands : std_logic_vector(NUM_STRANDS-1 downto 0);
		variable input_bank : bank_t;
	begin
		if rising_edge(clk) then
			led_data_a <= strand_buffer_a(to_integer(unsigned(led_addr)));
			led_data_b <= strand_buffer_b(to_integer(unsigned(led_addr)));

			if (and received_strands) and sender_done then
				output_bank <= input_bank;
				run <= '1';

				case input_bank is
					when BANK_A => input_bank := BANK_B;
					when BANK_B => input_bank := BANK_A;
				end case;
				frame_number <= current_frame;
				received_strands := (others => '0');
			else
				run <= '0';
			end if;

			if reset then
				received_strands := (others => '0');
				receive_state <= RESET_STATE;
			elsif udp_valid then
				if udp_last then
					-- always resynchronize to start of packet
					receive_state <= RESET_STATE;
				end if;

				case receive_state is
					when MAGIC =>
						if udp_data /= MAGIC_NUMBER then
							receive_state <= DROP;
						elsif (unsigned(udp_length) - HEADER_LEN) / 4 > MAX_STRAND_LEN then
							receive_state <= DROP;
						else
							num_pixels <= (to_integer(unsigned(udp_length)) - HEADER_LEN) / 4;
							receive_state <= STRAND_NUM;
						end if;

					when STRAND_NUM =>
						if unsigned(udp_data) >= NUM_STRANDS then
							receive_state <= DROP;
						else
							active_strand <= to_integer(unsigned(udp_data));
							receive_state <= FRAME_NUM;
						end if;

					when FRAME_NUM =>
						if not (or received_strands) then
							current_frame <= unsigned(udp_data);
						elsif current_frame /= unsigned(udp_data) then
							current_frame <= unsigned(udp_data);
							received_strands := (others => '0');
						end if;

						pixels_received <= 0;
						receive_state <= DATA;

					when DATA =>
						if pixels_received /= num_pixels - 1 then
							pixels_received <= pixels_received + 1;
						elsif udp_last then
							received_strands(active_strand) := '1';
						else
							-- packet too long
							receive_state <= DROP;
						end if;

					when DROP =>
						-- wait until udp_last
				end case;
			end if;

			-- workaround for ghdl#2078
			if reset = '0' and udp_valid = '1' and receive_state = DATA then
				if input_bank = BANK_A then
					strand_buffer_a(pixels_received)((active_strand+1) * BITS_PER_LED - 1 downto active_strand * BITS_PER_LED) := udp_data(23 downto 0);
				else
					strand_buffer_b(pixels_received)((active_strand+1) * BITS_PER_LED - 1 downto active_strand * BITS_PER_LED) := udp_data(23 downto 0);
				end if;
			end if;
		end if;
	end process;
end architecture;