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[SOLVED] unconstrained array error, need help

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sed_y

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hi,
I made simple Gray code to implement gray code increment circuit as
Code: 
library ieee;
use ieee.std_logic_1164.all;

entity graycode_inc is 
generic( n:natural := 3);
port( g: in std_logic_vector(n-1 downto 0);
      gn : out std_logic_vector(n-1 downto 0)
		);
end graycode_inc;

architecture behav of graycode_inc is
begin
 with g select 
    gn <=             "001" when "000",
	                 "011" when "001",
			 "010" when "011",
			 "110" when "010",
			 "111" when "110",
			 "101" when "111",
			 "100" when "101",
			 "000" when others;
end behav;

however, i get error:
Code: 
Selector (Signal 'g' of type std_logic_vector) is an unconstrained array
1) how is it unconstrained when it was constrained through generic.
2) if do something like this
Code: 
port( g: in std_logic_vector(2 downto 0);
      gn : out std_logic_vector(n-1 downto 0)
		);
it works fine.but, shouldn't compiler complain for gn as being unconstrained too?
any help?
 

1. what happens when g is set to 2? 4? 16? That is why g is unconstrained. Inside the graycode_inc entity g is unconstrained. The 3 value you gave it is just a default that gets used when it is instantiated without a specific value, so n at the moment is not any specific value.

2. Yes. If it doesnt compain when its compiled, it will complain when you try and run/synthesis it when n is something other than 3.
 

hi tricky,
the same code is working now, and is synthesized properly too. I don't know why xilinx did that.

sedy
 

use this code

library ieee;
use ieee.std_logic_1164.all;

entity graycode_inc is
generic(
n :integer := 3
);
port(
g: in std_logic_vector(n-1 downto 0);
gn : out std_logic_vector(n-1 downto 0)
);
end graycode_inc;

architecture behav of graycode_inc is
begin

gn <= "001" when g = "000" else
"011" when g = "001" else
"010" when g = "011" else
"110" when g = "010" else
"111" when g = "110" else
"101" when g = "111" else
"100" when g = "101" else
"000";
end behav;
 

Hamed - your code is identical to the OP's code. Changing N to integer makes no difference, because if n is anything other than 3 the code will fail.

But with your code making n an integer, someone could set n to -1, and you'd have null arrays, and you'd get rid of the whole thing.

a natural makes more sense.
 

TrickyDicky said:
Hamed - your code is identical to the OP's code. Changing N to integer makes no difference, because if n is anything other than 3 the code will fail.

But with your code making n an integer, someone could set n to -1, and you'd have null arrays, and you'd get rid of the whole thing.

a natural makes more sense.
Click to expand...

TrickyDicky - I know that but I only editted above code that can be synthesized. If some one need complete code should use for loop and compare section inside loop using parameters.
 

Naturals can be synthesised, you didnt need to change it to an integer.
 

TrickyDicky said:
Naturals can be synthesised, you didnt need to change it to an integer.
Click to expand...

I didn't changed natural into integer for synthesizablity I replaced "with select" by "when else" for synthesize error that mentioned above.because I write most of my codes(some variables) with integer it was a copy paste from my modules.

---------- Post added at 06:24 ---------- Previous post was at 06:18 ----------

I didn't changed natural into integer for synthesizablity I replaced "with select" by "when else" for synthesize error that mentioned above.because I write most of my codes(some variables) with integer it was a copy paste from my modules.
 

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