fix: work around ghdl#2102

https://github.com/ghdl/ghdl/issues/2102

vhdl/splink.vhdl

@@ -29,25 +29,18 @@ 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);
 
-	type led_data_t is record
-		was_written : std_logic;
-	end record;
-
-	type led_data_arr_t is array(0 to NUM_STRANDS-1) of led_data_t;
-	signal led_data_arr : led_data_arr_t;
-
 	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 clear_write_flags : std_logic;
-
-	signal all_strands_written : std_logic;
-	signal some_strands_written : std_logic;
+	signal sender_done : std_logic;
 
 	-- "PIXL"
 	constant MAGIC_NUMBER : std_logic_vector(31 downto 0) := x"5049584c";
@@ -57,6 +50,9 @@ architecture a of splink is
 	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 (
@@ -70,12 +66,13 @@ begin
 			T1H => 0.7 us,
 			T1L => 0.55 us,
 
-			T_RES => 80 us
+			T_RES => 100 us
 		)
 		port map (
 			n_reset => not reset,
 			clk     => clk,
 			run     => run,
+			done    => sender_done,
 
 			led_addr => led_addr,
 
@@ -84,61 +81,55 @@ begin
 			dout => drivers
 		);
 
-	driver_gen: for i in 0 to NUM_STRANDS-1 generate
-		writer: process(clk)
-			type strand_store_t is array(0 to MAX_STRAND_LEN-1) of color_t;
-			variable strand_store: strand_store_t;
+	process(led_data)
+		function make_color(data_in: std_logic_vector(BITS_PER_LED-1 downto 0)) return color_t is
 		begin
-			if rising_edge(clk) then
-				led_colors(i) <= strand_store(to_integer(unsigned(led_addr)));
-
-				if udp_valid = '1' and receive_state = DATA and active_strand = i then
-					strand_store(pixels_received) := (
-						red => udp_data(23 downto 16),
-						green => udp_data(15 downto 8),
-						blue => udp_data(7 downto 0)
-					);
-
-					if pixels_received = num_pixels - 1 and udp_last = '1' then
-						led_data_arr(i).was_written <= '1';
-					end if;
-				end if;
-
-				if clear_write_flags then
-					led_data_arr(i).was_written <= '0';
-				end if;
-			end if;
-		end process;
-	end generate;
-
-	process(led_data_arr)
+			return (
+				red => data_in(23 downto 16),
+				green => data_in(15 downto 8),
+				blue => data_in(7 downto 0)
+			);
+		end function;
 	begin
-		all_strands_written <= '1';
-		some_strands_written <= '0';
-
 		for i in 0 to NUM_STRANDS-1 loop
-			if led_data_arr(i).was_written then
-				some_strands_written <= '1';
-			else
-				all_strands_written <= '0';
-			end if;
+			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
-			clear_write_flags <= '0';
-			run <= '0';
+			led_data_a <= strand_buffer_a(to_integer(unsigned(led_addr)));
+			led_data_b <= strand_buffer_b(to_integer(unsigned(led_addr)));
 
-			if all_strands_written then
-				frame_number <= current_frame;
-				clear_write_flags <= '1';
+			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
-				clear_write_flags <= '1';
+				received_strands := (others => '0');
 				receive_state <= RESET_STATE;
 			elsif udp_valid then
 				if udp_last then
@@ -150,13 +141,11 @@ begin
 					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
-							if (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;
+							num_pixels <= (to_integer(unsigned(udp_length)) - HEADER_LEN) / 4;
+							receive_state <= STRAND_NUM;
 						end if;
 
 					when STRAND_NUM =>
@@ -168,11 +157,11 @@ begin
 						end if;
 
 					when FRAME_NUM =>
-						if not some_strands_written then
+						if not (or received_strands) then
 							current_frame <= unsigned(udp_data);
 						elsif current_frame /= unsigned(udp_data) then
 							current_frame <= unsigned(udp_data);
-							clear_write_flags <= '1';
+							received_strands := (others => '0');
 						end if;
 
 						pixels_received <= 0;
@@ -181,7 +170,9 @@ begin
 					when DATA =>
 						if pixels_received /= num_pixels - 1 then
 							pixels_received <= pixels_received + 1;
-						elsif not udp_last then
+						elsif udp_last then
+							received_strands(active_strand) := '1';
+						else
 							-- packet too long
 							receive_state <= DROP;
 						end if;
@@ -190,6 +181,20 @@ begin
 						-- wait until udp_last
 				end case;
 			end if;
+
+			-- workaround for ghdl#2078
+			if reset = '0' and udp_valid = '1' and receive_state = DATA then
+				-- workaround for ghdl#2102
+				for i in 0 to NUM_STRANDS-1 loop
+					if i = active_strand then
+						if input_bank = BANK_A then
+							strand_buffer_a(pixels_received)((i+1) * BITS_PER_LED - 1 downto i * BITS_PER_LED) := udp_data(23 downto 0);
+						else
+							strand_buffer_b(pixels_received)((i+1) * BITS_PER_LED - 1 downto i * BITS_PER_LED) := udp_data(23 downto 0);
+						end if;
+					end if;
+				end loop;
+			end if;
 		end if;
 	end process;
 end architecture;