Viewing intermediate variable value within a process in ModelSim
rwdfan
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
Rob Gaddi
Set a breakpoint and single step it.
--
Rob Gaddi, Highland Technology
Email address is currently out of order
Mike Treseler
> 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
backhus
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
Alan Fitch
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
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------------------------------------------------------------------------
This message may contain personal views which are not the views of
Doulos, unless specifically stated.
Jonathan Bromley
>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
HT-Lab
"backhus" <goou...@googlemail.com> wrote in message
news:25cd1a09-6b67-40ac...@q16g2000yqq.googlegroups.com...<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
Brad Smallridge
> 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
Andy
>
> 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