Warning of Xst:2677

[Sudeep Vhdl-Rookie]

I am getting a warning of My Array is not connecting to the block.
when i test bench it i am getting 'U's.


WARNING:Xst:2677 - Node <COUNT_3_0> of sequential type is unconnected
in block <MemMod2d>.


Sample code:
architecture Behavioral of MemMod2d is
type MEM1 is array (0 to 255) of STD_LOGIC_VECTOR (7 downto 0); -- 1d
x 1d
signal COUNT: MEM1;

begin

DataIn: process (pixdata,clk,Reset_Frame)

begin
if (Reset_Frame = '1') then

if (clk'event and clk = '0') then
For i in 0 to 255 Loop
if (pixdata = i) then
COUNT (i) <= COUNT (i)+ "1";

end loop;
end if;
end if;


end process DataIn;

 

[Andy Peters]

I am getting a warning of My Array is not connecting to the block.
when i test bench it i am getting 'U's.

WARNING:Xst:2677 - Node <COUNT_3_0> of sequential type is unconnected
in block <MemMod2d>.

Oy! Where to begin ...

Sample code:
architecture Behavioral of MemMod2d is
type MEM1 is array (0 to 255) of STD_LOGIC_VECTOR (7 downto 0); -- 1d
x 1d
signal COUNT: MEM1;

begin
DataIn: process (pixdata,clk,Reset_Frame)
begin
if (Reset_Frame = '1') then
if (clk'event and clk = '0') then
For i in 0 to 255 Loop
if (pixdata = i) then
COUNT (i) <= COUNT (i)+ "1";
end loop;
end if;
end if;
end process DataIn;

Let's see ... first of all, XST is probably as confused by your code
as I am. pixdata shouldn't be on the sensitivity list if your intent
is to build synchronous logic (looks like you want an array of
counters). Also, the falling clock edge shouldn't be inside the
Reset_Frame "if" block.

Finally, nothing ever properly initializes COUNT. Think about the
statement:

COUNT(i) <= COUNT(i) + "1";

I don't see anything that loads a value into any of the elements of
COUNT(i), so of course when you first use it, COUNT(i) has the value
"UUUUUUUU". Adding 1 to "UUUUUUUU" is still "UUUUUUUUU."

-a

 

[Jonathan Bromley]

Sample code:

architecture Behavioral of MemMod2d is
type MEM1 is array (0 to 255) of STD_LOGIC_VECTOR (7 downto 0);
signal COUNT: MEM1;
begin
DataIn: process (pixdata,clk,Reset_Frame)
begin
if (Reset_Frame = '1') then
if (clk'event and clk = '0') then
For i in 0 to 255 Loop
if (pixdata = i) then
COUNT (i) <= COUNT (i)+ "1";
end loop;
end if;
end if;
end process DataIn;

I totally agree with everything Andy Peters said.

A few other points:

(1)
Try using only 2-space indents. It makes the code far
easier to read.

(2)
Is this to gather an image histogram? If so, you should question
whether 8-bit counters are wide enough. Images often have many
thousands of pixels of the same colour - especially saturated white
or black. Your counters will wrap round from 255 to 0, giving
confusing results. You already have a lot of counters; increasing
their width to perhaps 12 bits would not be a huge overhead.

(3)
I suspect it's wrong for Reset_Frame to be in the sensitivity list.
Surely you have a *synchronous* frame reset signal?

(4)
How are you planning on getting data *out* of the counters?
--
Jonathan Bromley, Consultant

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[vipinlal]

hope this helps..
vhdlguru.blogspot.com/2010/03/synthesis-warning-node-of-sequential.html