simple but annoying message

[syedshan]

hi all,

I am getting pretty simple message which I am completely aware of and am able to completely analyze and take further steps as well.
But this time I am just fed-up...the Xilinx XST shows the warning message

WARNING:Xst:647 - Input <tr_last_cmd> is never used. This port will be preserved and left unconnected if it belongs to a top-level block or it belongs to a sub-block and the hierarchy of this sub-block is preserved.

where as the code is

...
...
tr_last_cmd : in std_logic;
...
...
if(phy_init_done = '1') then
	if(refresh_dcycle = '1') then
		cmd_cnt <= (others =>'0');	cmd_finish_reg <= '0';
	elsif(refresh_dcycle = '0') then		
	if(tr_cmd_val = '1' and tr_last_cmd ='0') then	cmd_cnt <= cmd_cnt + '1'; 
	elsif(tr_cmd_val = '1' and tr_last_cmd ='1' and cmd_finish_reg = '0') then
		cmd_cnt <= (others =>'0');		cmd_finish_reg <= '1';
	end if;

Note that this signals is one of the essential signal, hence I cannot afford that synthesizer just trim it and remove its functionality,
What I suspect is that in if else, it ignore the tr_last_cmd signal, due to logics...any idea?

- - - Updated - - -

oh...

Is it because the cmd_cnt and cmd_finis_reg are not used else where in the design, although cmd_cnt is incremented regularly, but it is never used in the design, It was just for me to count the number of commands...?
and these two signals are the only one which are being affected by the tr_last_cmd, hence it ignores the tr_last_cmd because of these signals

 

[FvM]

An input signal will be discarded if no design output signal depends on it. FPGA design compilers are pretty good in determining unused signals and you can most likely trust it.

Note that this signals is one of the essential signal, hence I cannot afford that synthesizer just trim it and remove its functionality,
What I suspect is that in if else, it ignore the tr_last_cmd signal, due to logics...any idea?

Is it because the cmd_cnt and cmd_finis_reg are not used else where in the design, although cmd_cnt is incremented regularly, but it is never used in the design, It was just for me to count the number of commands...?
and these two signals are the only one which are being affected by the tr_last_cmd, hence it ignores the tr_last_cmd because of these signals

Both statements are mutual exclusive. Either the signal is essential, then the design output must somehow depend on it. Or it's just unused and can be discarded in synthesis.