From 4d07ec3fa1b2259dd585f91a892bbdbf6cea4e4a Mon Sep 17 00:00:00 2001
From: Xiretza <xiretza@xiretza.xyz>
Date: Mon, 6 Jun 2022 15:24:49 +0200
Subject: [PATCH] vhdl: reorganize receive FSM to avoid ghdl issues

https://github.com/ghdl/ghdl/issues/2077
https://github.com/ghdl/ghdl/issues/2078
---
 vhdl/splink.vhdl | 94 +++++++++++++++++++++++++++++-------------------
 1 file changed, 57 insertions(+), 37 deletions(-)

diff --git a/vhdl/splink.vhdl b/vhdl/splink.vhdl
index be3dbc1..0b5a1da 100644
--- a/vhdl/splink.vhdl
+++ b/vhdl/splink.vhdl
@@ -34,6 +34,14 @@ architecture a of splink is
 
 	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 frame_number: unsigned(31 downto 0);
+	signal pixels_received: natural range 0 to MAX_STRAND_LEN-1;
+
+	type receive_state_t is (FRAME_NUM, STRAND_NUM, DATA, DROP);
+	signal receive_state : receive_state_t;
 begin
 	driver_gen: for i in 0 to NUM_STRANDS-1 generate
 		ws2812_inst: entity work.ws2812
@@ -61,66 +69,78 @@ begin
 
 				dout => drivers(i)
 			);
+
+		writer: process(clk)
+			type strand_store_t is array(0 to MAX_STRAND_LEN-1) of color_t;
+			variable strand_store: strand_store_t;
+		begin
+			if rising_edge(clk) then
+				led_data_arr(i).current_color <= strand_store(to_integer(unsigned(led_data_arr(i).addr)));
+
+				if udp_valid = '1' and receive_state = DATA and active_strand = i then
+					strand_store(pixels_received) := udp_data(23 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 frame_done then
+					led_data_arr(i).was_written <= '0';
+				end if;
+			end if;
+		end process;
 	end generate;
 
-	writer: process(clk)
-		type strand_store_t is array(0 to MAX_STRAND_LEN-1) of color_t;
-		type strand_stores_t is array(0 to NUM_STRANDS-1) of strand_store_t;
-		variable strand_stores: strand_stores_t;
+	process(led_data_arr)
+	begin
+		frame_done <= '1';
 
-		variable active_strand: natural range 0 to NUM_STRANDS-1;
-		variable packet_len: natural range 1 to MAX_STRAND_LEN;
-		variable frame_number: unsigned(31 downto 0);
-		variable store_counter: natural range 0 to MAX_STRAND_LEN-1;
+		for i in 0 to NUM_STRANDS-1 loop
+			if not led_data_arr(i).was_written then
+				frame_done <= '0';
+			end if;
+		end loop;
+	end process;
 
-		type receive_state_t is (FRAME_NUM, STRAND_NUM, DATA, DROP);
-		variable receive_state : receive_state_t;
+	fsm: process(clk)
 	begin
 		if rising_edge(clk) then
-			frame_done <= '0';
+			if reset then
+				receive_state <= STRAND_NUM;
+			elsif udp_valid then
+				if udp_last then
+					-- always resynchronize to start of packet
+					receive_state <= STRAND_NUM;
+				end if;
 
-			for i in 0 to NUM_STRANDS-1 loop
-				led_data_arr(i).current_color <= strand_stores(i)(to_integer(unsigned(led_data_arr(i).addr)));
-			end loop;
-
-			if udp_valid then
 				case receive_state is
 					when STRAND_NUM =>
 						-- TODO udp_length, range check with MAX_STRAND_LEN
-						packet_len := MAX_STRAND_LEN;
+						num_pixels <= MAX_STRAND_LEN;
 
 						-- FIXME bounds check
-						active_strand := to_integer(unsigned(udp_data));
+						active_strand <= to_integer(unsigned(udp_data));
 
-						receive_state := FRAME_NUM;
+						receive_state <= FRAME_NUM;
 
 					when FRAME_NUM =>
-						frame_number := unsigned(udp_data);
+						frame_number <= unsigned(udp_data);
 
-						store_counter := 0;
-						receive_state := DATA;
+						pixels_received <= 0;
+						receive_state <= DATA;
 
 					when DATA =>
-						strand_stores(active_strand)(store_counter) := udp_data(23 downto 0);
-
-						if store_counter = packet_len then
-							if udp_last then
-								--led_data_arr(active_strand).was_written <= '1';
-							else
-								-- packet too long
-								receive_state := DROP;
-							end if;
-						else
-							store_counter := store_counter + 1;
+						if pixels_received /= num_pixels - 1 then
+							pixels_received <= pixels_received + 1;
+						elsif not udp_last then
+							-- packet too long
+							receive_state <= DROP;
 						end if;
 
 					when DROP =>
 						-- wait until udp_last
 				end case;
-
-				if udp_last then
-					receive_state := STRAND_NUM;
-				end if;
 			end if;
 		end if;
 	end process;