Reading OUT ports for debugging

[Richard29]

Hi,

I have a FIFO which has an interface that looks something like this:

entity fifo is
    port (
    CLK                       : IN  std_logic := '0';
    DIN                       : IN  std_logic_vector(31 DOWNTO 0);
    ALMOST_EMPTY      : OUT std_logic;
    ALMOST_FULL         : OUT std_logic;
    DOUT                    : OUT std_logic_vector(31 DOWNTO 0);
    EMPTY                   : OUT std_logic;
    FULL                     : OUT std_logic;
    OVERFLOW             : OUT std_logic;
    WR_ACK                 : OUT std_logic
);
end fifo;

This interface is given and I can't change is. The thing is now, for debugging purposes, I wanna see what is written and read to/from the FIFO. In other words, ideally I would like to assign two debug the in and out values of the FIFO, ie.

      DBG_FIFO_IN    <= DIN;
      DBG_FIFO_OUT <= DOUT;

For obvious reasons, the second assignment gives me the following error message:

[exec] ERROR:HDLParsers:1401 - Object DOUT of mode OUT can not be read.

So I am wondering if there is any way how I can assing the DOUT value to my debug symbol. The interface is given, so I cant make DOUT an inout signal.

Many thanks for helpful comments!

 

[jducluzeau]

where do you add these assignement?
Inside the architecture of FIFO?

Regards,
Jerome

 

[Richard29]

No Jerome, It is in another Module where I have an instance of the FIFO and from there I wanna read somehow the
output from the FIFO. As stated earlier, the interface of the FIFO is given, I cannot change here anything.

 

[jducluzeau]

Is DOUT an output port of this other module too?

 

[Richard29]

Yes, and at some point I end up at the top level signal with the debug signal where I assign it then to the Chipscope ILA core for debugging purposes

 

[jducluzeau]

then the problem is simple.
you must use intermediate signals like this

fifo1 :fifo(...,DOUT=>dout_int;....);
DBG_FIFO_OUT <= dout_int;
DOUT<=dout_int;
In vhdl the only way you can use an output port is at left hand of an assignement.

Regards,
Jerome

 

[Richard29]

Oh yes, it is indeed easy Thanks a lot!