doc: Add circuit diagram

README.MD

@@ -17,10 +17,15 @@ When writing it, the following were the main design philosophies:
 
 ## Hardware
 
-TBD. TL;DR:
+![Circuit Diagram](doc/circuit.svg)
 
-* RX: Use resistors behind Ethernet magnetics to reduce Ethernet RX voltage levels (0 +-2.5V) to LVPECL voltage levels (1.65V +-400mV). Or LVDS if your FPGA can't handle LVPECL.
-* TX: Meh, a series current limiting resistor is good enough.
+* RX: Use resistors behind Ethernet magnetics to reduce Ethernet RX voltage levels (0 +-2.5V) to LVPECL voltage levels (1.65V +-400mV). Or LVDS if your FPGA can't handle LVPECL. Also, pull up/down resistors help to avoid glitchy behavior with no cable connected or little data activity.
+* TX: Meh, a series current limiting resistor is good enough. Drive two outputs differentially to increase the voltage swing. (Technically not true antivalent signals as there's also the "off" state with both disabled.)
+
+Notes:
+
+* The RX pull up/downs are probably not the best idea, and fixable in a better way. But for now, this shall work -- and suffice!
+* On the TX side, I'm grossly overloading the drivers. A line driver would probably be a good idea. Or you can just parallel multiple outputs ;D
 
 ## License
 

trashernet/trashernet_phy.vhd

@@ -128,7 +128,9 @@ begin
 
 			-- Bit recovery
 			type demanchestization_state_t is (SYNC, DATA, ERROR);
-			signal demanchestization_state : demanchestization_state_t;
+			signal demanchestization_state              : demanchestization_state_t;
+			constant DEMANCHESTIZATION_MIN_SYNC_CNT_MAX : integer := (4 * 8) - 1; -- 4 good sync bytes
+			signal demanchestization_min_sync_cnt       : integer range 0 to DEMANCHESTIZATION_MIN_SYNC_CNT_MAX;
 		begin
 			-- Detects spacing of transitions
 			transition_detector : process(clk, rst) is
@@ -200,21 +202,30 @@ begin
 			bit_recovery : process(clk, rst) is
 			begin
 				if rst then
-					demanchestization_state <= SYNC;
-					bit_stb                 <= '0';
-					phy_out.rx_active       <= '0';
-					phy_out.rx_error        <= '0';
+					demanchestization_state        <= SYNC;
+					bit_stb                        <= '0';
+					phy_out.rx_active              <= '0';
+					phy_out.rx_error               <= '0';
+					demanchestization_min_sync_cnt <= DEMANCHESTIZATION_MIN_SYNC_CNT_MAX;
 				elsif rising_edge(clk) then
 					bit_stb          <= '0';
 					phy_out.rx_error <= '0';
 
+					if (bit_ev = TOGGLE) and (demanchestization_min_sync_cnt /= 0) then
+						demanchestization_min_sync_cnt <= demanchestization_min_sync_cnt - 1;
+					elsif (bit_ev = KEEP) or (bit_ev = ERROR) then
+						demanchestization_min_sync_cnt <= DEMANCHESTIZATION_MIN_SYNC_CNT_MAX;
+					end if;
+
 					if (bit_ev /= NONE) then
 						case demanchestization_state is
 							when SYNC =>
 								if (bit_ev = KEEP) then
-									bit_value               <= '1';
-									demanchestization_state <= DATA;
-									phy_out.rx_active       <= '1';
+									if demanchestization_min_sync_cnt = 0 then
+										bit_value               <= '1';
+										demanchestization_state <= DATA;
+										phy_out.rx_active       <= '1';
+									end if;
 								end if;
 							when DATA => -- @suppress: Condition outside of case allows to exit this state
 								bit_value <= not bit_value when bit_ev = TOGGLE else bit_value;
@@ -225,7 +236,7 @@ begin
 					end if;
 
 					if (bit_ev = ERROR) then
-						phy_out.rx_error        <= '1';
+						phy_out.rx_error        <= '1' when (demanchestization_state = DATA) else '0';
 						demanchestization_state <= ERROR;
 					end if;