From 5d6df0219be2bc1a4bfab8b2c106f4ba25e9f4d3 Mon Sep 17 00:00:00 2001
From: Markus Koch <markus@notsyncing.net>
Date: Sat, 28 Aug 2021 14:22:28 +0200
Subject: [PATCH] phy: rx: Introduce simple glitch filter

---
 trashernet/trashernet_phy.vhd | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/trashernet/trashernet_phy.vhd b/trashernet/trashernet_phy.vhd
index 2e085f2..d5c2293 100644
--- a/trashernet/trashernet_phy.vhd
+++ b/trashernet/trashernet_phy.vhd
@@ -37,9 +37,10 @@ begin
 
 	receiver : block
 		-- Signal conditioning
-		signal rx      : std_logic;
-		signal rx_last : std_logic;
-		signal rx_edge : std_logic;
+		signal rx             : std_logic;
+		signal rx_last        : std_logic;
+		signal rx_last_static : std_logic;
+		signal rx_edge        : std_logic;
 
 		-- Bit recovery
 		signal bit_value : std_logic;
@@ -61,11 +62,23 @@ begin
 				data_out => rx
 			);
 
-		-- Edge detector for RX
-		rx_last <= '0' when rst
-		           else rx when rising_edge(clk)
-		         ;
-		rx_edge <= rx_last xor rx;
+		-- Edge detector for RX (+glitch filter)
+		edgedet : process(clk, rst) is
+		begin
+			if rst then
+				rx_last        <= '0';
+				rx_last_static <= '0';
+				rx_edge        <= '0';
+
+			elsif rising_edge(clk) then
+				rx_edge <= '0';
+				if (rx_last = rx) then
+					rx_edge        <= rx_last_static xor rx;
+					rx_last_static <= rx;
+				end if;
+				rx_last <= rx;
+			end if;
+		end process edgedet;
 
 		demanchestizer : block
 			-- Transition detector