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Observer icel
Registered: ‎11-19-2007

Keep getting warnings that I/O is never used, port will be preserved and left unconnected.



I'm trying to synthesize my code which is a hardware wrapper between two other VHDL source codes but I keep getting the following warning:


Input /Output<input/output_name> 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.


I believe it is caused by the way i coded my processes. One example is shown below. The full source code is attached.


 process (DMA_SEL,DMA_RENi,DMA_WENi,clk)
    if     DMA_SEL = x"0" then
            input_1_en <= DMA_RENi;
    else     input_1_en <= 'Z';
    end if;
    if     DMA_SEL = x"1" then
            input_2_en <= DMA_RENi;
    else     input_2_en <= 'Z';
    end if;
    if     DMA_SEL = x"2" then
            input_3_en <= DMA_RENi;
    else     input_3_en <= 'Z';
    end if;
    if        DMA_SEL = x"0" then
            output_1_en <= DMA_WENi;
    else    output_1_en <= 'Z';
    end if;

    if        DMA_SEL = x"1" then
            output_2_en <= DMA_WENi;
    else    output_2_en <= 'Z';
    end if;
end process;


I've tried seperating all the if-endif into different process but it still showed the same issue. 

Can someone guide me on how should i solve this issue?


The hardware wrapper connects a DMA controller and a component with  3 inputs and 2 outputs. The DMA controller will read or write into the I/Os  from/to a inout bus depending on the DMA channel selected and DMA direction.

DMA channel 0 - input 1, output 1

DMA channel 1 - input 2, output 2

DMA channel 2 - input 3

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1 Reply
Observer johndap
Registered: ‎03-31-2009

Re: Keep getting warnings that I/O is never used, port will be preserved and left unconnected.

I suspect it is because you aren't connecting the output of DMA channel 2.  Either connect that to an otherwise unused signal or ignore the warning. 




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