loop in VHDL

Altera_Forum · ‎07-11-2012

Hi, I have a question. now there are 3 vector connect with AND gate like this:

C(3)<= A(4) and B(3)

C(2)<= A(4)and A(3)and B(2)

C(1)<= A(4)and A(3)andA(2)and B(1)

C(0)<= A(4)and A(3)andA(2)andA(1)B(0)

How can I use loop to describe it?

Altera_Forum · ‎07-11-2012

Do you want to write generic code or do you simply want to use a

loop construct on the actual code you've posted?

Using a loop construct on your actual code will make it worse imho.

Altera_Forum · ‎07-11-2012

with generic code, like:

C(n-1)<= A(n) and B(n-1)

C(n-2)<= A(n)and A(n-1)and B(n-2)

......

C(0)<= A(n)and A(n-1)......and A(1)B(0).

upstair is a example for n=4

Altera_Forum · ‎07-11-2012

--- Quote Start ---

Do you want to write generic code or do you simply want to use a

loop construct on the actual code you've posted?

Using a loop construct on your actual code will make it worse imho.

--- Quote End ---

with generic code, like:

C(n-1)<= A(n) and B(n-1)

C(n-2)<= A(n)and A(n-1)and B(n-2)

......

C(0)<= A(n)and A(n-1)......and A(1)B(0).

upstair is a example for n=4

Altera_Forum · ‎07-11-2012

--- Quote Start ---

with generic code, like:

C(n-1)<= A(n) and B(n-1)

C(n-2)<= A(n)and A(n-1)and B(n-2)

......

C(0)<= A(n)and A(n-1)......and A(1)B(0).

upstair is a example for n=4

--- Quote End ---

BTW: What does A(1)B(1) mean?

Altera_Forum · ‎07-11-2012

Try something like that

for   i in 0      to n - 1 loop
  for j in i + 2  to n     loop
    a_res :=  a(j) and a(j - 1);
  end loop;
  c(i)  <=  a_res and b(i);
end loop;

But be aware that it's untested code.

You've to verify it. :)

edit:

That's definitely not it! :(

But I think you've to use nested loops...

Altera_Forum · ‎07-12-2012

I think something like that would do the trickfor i in 0 to n - 1 loop a_res := a(n); for j in i + 1 to n - 1 loop a_res := a_res and a(j); end loop; c(i) <= a_res and b(i); end loop;Yes the nested loops ides is the right one, you just need to initialize the variable and use it recursively in the inside loop. Don't forget to declare the variable in the process.