Warning:Xst:382 - Register A is equivalent to B

[mag]

Hello

During synthesis of the code belove I have recieved two warnings:
----
Mapping all equations...
Building and optimizing final netlist ...
WARNING:Xst:382 - Register Mtrien_rx_minus is equivalent to Mtrien_rx_plus
Found area constraint ratio of 100 (+ 5) on block ways, actual ratio is 0.
WARNING:Xst:382 - Register Mtrien_rx_minus is equivalent to Mtrien_rx_plus
----

This code I wrote specially for 2-way signals "rx_minus" , "rx_plus" (that
is why it includes 2 processes). When the signal is = '1' then in the first
process those signals <= 'Z' and then they are inputs in the second process
(I did'n find better solution for this).

Ok, about the warning... Is the synthesis tool tying "rx_minus" , "rx_plus"
together? Both signals look the same but are not the same of course...

have you got any solution/explanation?

--- ---------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;

entity ways is
port(
rst, clk : in std_logic;

rx_minus, rx_plus : inout std_logic;

Receiving_Data : in std_logic;
tx_minus_OUT, tx_plus_OUT : in std_logic;
rx_minus_input, rx_plus_input : out std_logic
);
end ways;

architecture arch_ways of ways is
begin
process(clk, Receiving_Data)
begin
if rising_edge(clk) then
if rst = '1' then

rx_minus <= 'Z';
rx_plus <= 'Z';

else

if Receiving_Data = '0' then
rx_minus <= tx_minus_OUT;
rx_plus <= tx_plus_OUT;

else

rx_minus <= 'Z';
rx_plus <= 'Z';

end if;
end if;
end if;

end process;

process(clk, Receiving_Data, rx_minus, rx_plus)
begin
if rising_edge(clk) then
if rst = '1' then
rx_minus_input <= '1';
rx_plus_input <= '1';
else

if Receiving_Data = '1' then
rx_minus_input <= rx_minus;
rx_plus_input <= rx_plus;
end if;
end if;
end if;
end process;

end architecture;

 

[Andy Peters]

Hello

During synthesis of the code belove I have recieved two warnings:
----
Mapping all equations...
Building and optimizing final netlist ...
WARNING:Xst:382 - Register Mtrien_rx_minus is equivalent to Mtrien_rx_plus
Found area constraint ratio of 100 (+ 5) on block ways, actual ratio is 0.
WARNING:Xst:382 - Register Mtrien_rx_minus is equivalent to Mtrien_rx_plus
----

This code I wrote specially for 2-way signals "rx_minus" , "rx_plus" (that
is why it includes 2 processes). When the signal is = '1' then in the first
process those signals <= 'Z' and then they are inputs in the second process
(I did'n find better solution for this).

Ok, about the warning... Is the synthesis tool tying "rx_minus" , "rx_plus"
together? Both signals look the same but are not the same of course...

have you got any solution/explanation?

architecture arch_ways of ways is
begin
process(clk, Receiving_Data)

First -- why is Receiving_Data on your sensitivity list? Re-read the
synthesis tool documents.

begin
if rising_edge(clk) then
if rst = '1' then

rx_minus <= 'Z';
rx_plus <= 'Z';

Think Hardware. What real flipflop lets you assign Hi-Z to its input
and then clock that through?

else

if Receiving_Data = '0' then
rx_minus <= tx_minus_OUT;
rx_plus <= tx_plus_OUT;

else

rx_minus <= 'Z';
rx_plus <= 'Z';

Same comment about assigning Hi-Z here.

end if;
end if;
end if;

end process;

process(clk, Receiving_Data, rx_minus, rx_plus)

Again, why the other stuff on the sensitivity list?

begin
if rising_edge(clk) then
if rst = '1' then
rx_minus_input <= '1';
rx_plus_input <= '1';
else
if Receiving_Data = '1' then
rx_minus_input <= rx_minus;
rx_plus_input <= rx_plus;
end if;
end if;
end if;
end process;

end architecture;

I think your problem is that you've confused the synthesis tool. You
need to come up with logic that creates output enables for your
bidirectional signals and use them in continuous assignments.

-a