I am debugging a VHDL block which has a "for loop" inside a
procedure.  Within each iteration of the for loop, a variable is
conditionally assigned.  For troubleshooting the design, I am
interested in viewing the value of the variable at specific locations
of the process.  Since the variable is re-assigned subsequently within
the process, the variable has changed state multiple times in zero
time.  I realize this rules out any viewing in a wave window.

process(clk,reset)
variable a;
variable b;
begin
    if rising_edge(clk) then
        for i in 0 to 7 loop
            if condition1  then
                a  :=  x(i);
            end if;
            b  :=  a;
            if condition2  then
                a  :=  x(i+1);
            end if;
        end for;
    end if
end process;

Here is a simple example.  Please do not recommend a different coding
style, as this is merely an attempt to illustrate the problem.  Let's
say I want to lok at the value of a (or i, for that matter) at the end
of the first if statement.  I do not want to see it after the process
completes.  I would be happy if I could insert a line of code similar
to the report command, that could display the value of a variable at
the time of execution.

Any suggestions?
Brett

On Thu, 18 Feb 2010 13:50:15 -0800 (PST)
rwdfan <brett.chaveriat@gmail.com> wrote:

> I am debugging a VHDL block which has a "for loop" inside a
> procedure.  Within each iteration of the for loop, a variable is
> conditionally assigned.  For troubleshooting the design, I am
> interested in viewing the value of the variable at specific locations
> of the process.  Since the variable is re-assigned subsequently within
> the process, the variable has changed state multiple times in zero
> time.  I realize this rules out any viewing in a wave window.
> 
> process(clk,reset)
> variable a;
> variable b;
> begin
>     if rising_edge(clk) then
>         for i in 0 to 7 loop
>             if condition1  then
>                 a  :=  x(i);
>             end if;
>             b  :=  a;
>             if condition2  then
>                 a  :=  x(i+1);
>             end if;
>         end for;
>     end if
> end process;
> 
> Here is a simple example.  Please do not recommend a different coding
> style, as this is merely an attempt to illustrate the problem.  Let's
> say I want to lok at the value of a (or i, for that matter) at the end
> of the first if statement.  I do not want to see it after the process
> completes.  I would be happy if I could insert a line of code similar
> to the report command, that could display the value of a variable at
> the time of execution.
> 
> Any suggestions?
> Brett
> 

Set a breakpoint and single step it.

-- 
Rob Gaddi, Highland Technology
Email address is currently out of order

rwdfan wrote:
> I am debugging a VHDL block which has a "for loop" inside a
> procedure.  Within each iteration of the for loop, a variable is
> conditionally assigned.  For troubleshooting the design, I am
> interested in viewing the value of the variable at specific locations
> of the process.  Since the variable is re-assigned subsequently within
> the process, the variable has changed state multiple times in zero
> time.  I realize this rules out any viewing in a wave window.

Not true.
If I name the process, I can add it by name with an "add wave" command.
However, only the final value is shown on the wave.

> I would be happy if I could insert a line of code similar
> to the report command, that could display the value of a variable at
> the time of execution.

You can do exactly that in simulation.


> Any suggestions?

With modelsim, I just say STEP at the command line,
and watch the variables as the code comes into scope.

      -- Mike Treseler

On 18 Feb., 22:50, rwdfan <brett.chaver...@gmail.com> wrote:
> I am debugging a VHDL block which has a "for loop" inside a
> procedure. =A0Within each iteration of the for loop, a variable is
> conditionally assigned. =A0For troubleshooting the design, I am
> interested in viewing the value of the variable at specific locations
> of the process. =A0Since the variable is re-assigned subsequently within
> the process, the variable has changed state multiple times in zero
> time. =A0I realize this rules out any viewing in a wave window.
>
> process(clk,reset)
> variable a;
> variable b;
> begin
> =A0 =A0 if rising_edge(clk) then
> =A0 =A0 =A0 =A0 for i in 0 to 7 loop
> =A0 =A0 =A0 =A0 =A0 =A0 if condition1 =A0then
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 a =A0:=3D =A0x(i);
> =A0 =A0 =A0 =A0 =A0 =A0 end if;
> =A0 =A0 =A0 =A0 =A0 =A0 b =A0:=3D =A0a;
> =A0 =A0 =A0 =A0 =A0 =A0 if condition2 =A0then
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 a =A0:=3D =A0x(i+1);
> =A0 =A0 =A0 =A0 =A0 =A0 end if;
> =A0 =A0 =A0 =A0 end for;
> =A0 =A0 end if
> end process;
>
> Here is a simple example. =A0Please do not recommend a different coding
> style, as this is merely an attempt to illustrate the problem. =A0Let's
> say I want to lok at the value of a (or i, for that matter) at the end
> of the first if statement. =A0I do not want to see it after the process
> completes. =A0I would be happy if I could insert a line of code similar
> to the report command, that could display the value of a variable at
> the time of execution.
>
> Any suggestions?
> Brett

Hi,
with Modelsim you also have the option to use the LIST view.
This can be expanded to show each delta cycle, and the changes of a
value in a loop should cause delta cycles.
So you should be able to see the behavior of your variable there.

Have a nice simulation
  Eilert

backhus wrote:
> On 18 Feb., 22:50, rwdfan <brett.chaver...@gmail.com> wrote:
>> I am debugging a VHDL block which has a "for loop" inside a
>> procedure.  Within each iteration of the for loop, a variable is
>> conditionally assigned.  For troubleshooting the design, I am
>> interested in viewing the value of the variable at specific locations
>> of the process.  Since the variable is re-assigned subsequently within
>> the process, the variable has changed state multiple times in zero
>> time.  I realize this rules out any viewing in a wave window.
>>
>> process(clk,reset)
>> variable a;
>> variable b;
>> begin
>>     if rising_edge(clk) then
>>         for i in 0 to 7 loop
>>             if condition1  then
>>                 a  :=  x(i);
>>             end if;
>>             b  :=  a;
>>             if condition2  then
>>                 a  :=  x(i+1);
>>             end if;
>>         end for;
>>     end if
>> end process;
>>
>> Here is a simple example.  Please do not recommend a different coding
>> style, as this is merely an attempt to illustrate the problem.  Let's
>> say I want to lok at the value of a (or i, for that matter) at the end
>> of the first if statement.  I do not want to see it after the process
>> completes.  I would be happy if I could insert a line of code similar
>> to the report command, that could display the value of a variable at
>> the time of execution.
>>
>> Any suggestions?
>> Brett
> 
> Hi,
> with Modelsim you also have the option to use the LIST view.
> This can be expanded to show each delta cycle, and the changes of a
> value in a loop should cause delta cycles.
> So you should be able to see the behavior of your variable there.
> 
> Have a nice simulation
>   Eilert

As others say, setting breakpoints is very convenient.

If your variable is of a scalar type (for instance INTEGER), you can do

report INTEGER'IMAGE(a);

If it's a more complex type, you can write to standard output, e.g.

write(L, s);
writeline(OUTPUT, L);

regards
Alan

P.S. VHDL 2008 adds implicit to_string functions for one dimensional 
arrays of character literals, but for earlier versions you could use 
ieee.std_logic_textio to write out standard logic vectors.

-- 
Alan Fitch
Senior Consultant

Doulos � Developing Design Know-how
VHDL * Verilog * SystemVerilog * SystemC * PSL * Perl * Tcl/Tk * Project 
Services

Doulos Ltd. Church Hatch, 22 Marketing Place, Ringwood, Hampshire, BH24 
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------------------------------------------------------------------------

This message may contain personal views which are not the views of 
Doulos, unless specifically stated.

On Thu, 18 Feb 2010 23:45:34 -0800 (PST), backhus wrote:

>with Modelsim you also have the option to use the LIST view.
>This can be expanded to show each delta cycle, and the changes of a
>value in a loop should cause delta cycles.

Really?  If that's true, then VHDL is far too much like
Verilog for my taste :-)
-- 
Jonathan Bromley

"backhus" <goouse99@googlemail.com> wrote in message 
news:25cd1a09-6b67-40ac-99fa-31e793c23470@q16g2000yqq.googlegroups.com...
On 18 Feb., 22:50, rwdfan <brett.chaver...@gmail.com> wrote:
<snip>
>
>Hi,
>with Modelsim you also have the option to use the LIST view.
>This can be expanded to show each delta cycle, and the changes of a
>value in a loop should cause delta cycles.

Just a side note, the waveform window is much easier for looking at Delta 
cycles, this is supported in 6.5x and later.

Hans
www.ht-lab.com


>So you should be able to see the behavior of your variable there.
>
>Have a nice simulation
>  Eilert 

>I am debugging a VHDL block which has a "for loop" inside a
> procedure.  Within each iteration of the for loop, a variable is
> conditionally assigned.  For troubleshooting the design, I am
> interested in viewing the value of the variable at specific locations
> of the process.  Since the variable is re-assigned subsequently within
> the process, the variable has changed state multiple times in zero
> time.  I realize this rules out any viewing in a wave window.

I assume this is a ModelSim issue.

Just set up a signal to mirror all variables.

Use two or more signals to take care of your
zero time issue. Perhaps put a flag signal
in each of your if statements. You should be
able to see anything reasonable.

Brad Smallridge
AiVision

On Feb 19, 1:45=A0am, backhus <goous...@googlemail.com> wrote:
>
> This can be expanded to show each delta cycle, and the changes of a
> value in a loop should cause delta cycles.
> So you should be able to see the behavior of your variable there.

Jonathan eluded to this, but here's another hint:

Delta cycles occur at suspensions of processes. Thus the iterations of
a loop in a process (so long as the loop does not contain a wait
statement) do not generate delta cycles.

I suppose you could insert "wait for 0 ns;" inside the loop, and it
would generate delta cycles for each loop iteration.

Like Mike and others, I use breakpoints, single-stepping, etc., or I
use a report/assert statement.

Andy