how to know while loop number of iteration ?

[jojo26]

hey there ,
so in my code i need to know how many times a while loop was excuted (i don't know the number of iteration in advance and i should know it in a division algorithm )
how to know the value of I outside the process in the following example ?

  process (r,b)
    variable I :integer :=0 ;
    begin
    
   WHILE (x > b) LOOP 
 x <= r+b ;
I:=I+1 ;

END LOOP ;
end process;

i'm a newbie please help me and excuse my english

 

[dpaul]

3 comments after a casual glance.....
1. You are doing a comparison between x and b but have not included x in the sensitivity list.
2. Avoid using 'while' loop (if this piece is used for non-synth part of the design, then ok with while loop)
3. I am assuming 'I' is storing the no. of iterations. So declare it as signal and then use it accordingly if you want to use it in another process.

 

[jojo26]

3 comments after a casual glance.....
1. You are doing a comparison between x and b but have not included x in the sensitivity list.
2. Avoid using 'while' loop (if this piece is used for non-synth part of the design, then ok with while loop)
3. I am assuming 'I' is storing the no. of iterations. So declare it as signal and then use it accordingly if you want to use it in another process.

thanks a lot,i'm sorry for making such horrible mistakes,i need to synthesis this code,i'm going to do a number of repeated substraction until i reach a certain condition (for example a>b ..) so can you give me a suggestion in whish structure should i use to do that,knowing that i'm dealing with signed numbers thanks a looot !

 

[ads-ee]

thanks a lot,i'm sorry for making such horrible mistakes,i need to synthesis this code,i'm going to do a number of repeated substraction until i reach a certain condition (for example a>b ..) so can you give me a suggestion in whish structure should i use to do that,knowing that i'm dealing with signed numbers thanks a looot !

Counters (along with terminal count compares) are typically used in hardware designs to determine how many times you do something.

 

[KlausST]

Hi,

i'm going to do a number of repeated substraction until i reach a certain condition

define the (valid) ranges for "x", "r" and "b".

***
imagine "r" = 0.
then neither "x" nor "b" will be changed in your loop.
--> the loop will be infinite.

Klaus

 

[FvM]

The code can't be synthesized anyway due to unconstraint iteration count.

I presume it's based on the popular misunderstanding that an iteration loop defines a sequence in time. But it's only sequentially executed in simulation. In synthesis it instantiates parallel logic. Because the iteration count can't be determined at compile time, it's dropping a synthesis error.

In cases where you actually want to generate parallel logic by an iteration construct, the compiler must know how many instances. A for next loop will tell this by its fixed range.

As ads-ee explained, a sequential divider will use a loop counter and a clock. Under circumstances you can define a parallel divider by an iteration construct. But it would be better generated in a hierarchical structural description.

 

[jojo26]

can you recommand any book or tutorials that can help me understand how a design work on hardware ? when it can be synthesizable and when not and why ? i feel like it's hard to write VHDL with my basic electronics knowlege
i'm so grateful,thanks for your answers
regards jojo