Procedures, variables and their scope.

[Michel Bieleveld]

Hi All,

I have a problem, as far as I know procedures can change
signals/variables as long as the procedures are defined within the
scope where the variables are defined. Yet when i try to simulate my
vhdl code the ISE synthesizer gives me the following warning :

WARNING:Xst:1960 - C:/projects/redemption/ax88796.vhd line 86:
Potential simulation mismatch, variable <register_uit> declared in
block <$PROCESS1> is assigned in block <WriteReg>.

My code looks basicly like the code shown here. It seems like that the
variables within the procedure do not change the variable outside the
procedure, which is what i was hoping for.

Is there any Macro command or something in vhdl, because that is what
i am using the procedure for.

With regards,

Michel Bieleveld.


entity ax88796 is
...
end ax88796;

architecture RTL of ax88796 is
...
begin
process (nRST,CLK)
...
variable operand : std_logic_vector(15 downto 0);

procedure ReadReg(Ax_reg : in std_logic_vector(7 downto 0))is
begin
operand := B"00001110" & Ax_reg;
return_state := current_state;
next_state := st_ExRead;
end ReadReg;

begin
...

blahblah ReadReg(X"00");
...
end process;
end rtl;

 

[Mike Treseler]

I have a problem, as far as I know procedures can change
signals/variables as long as the procedures are defined within the
scope where the variables are defined.

Variables must be passed a parameters to a procedure.

It seems like that the
variables within the procedure do not change the variable outside the
procedure

If you pass the process variable, the procedure can change
its value. Variable scope is local to the procedure or process.
Pass the variable or use a signal.

-- Mike Treseler

 

[Michel Bieleveld]

But I thought the difference between (pure) functions and procedures
is that procedures can have side effects. In this case changing a
variable defined in the process from which I am calling the procedure.

<Michel Bieleveld>

 

[Mike Treseler]

But I thought the difference between (pure) functions and procedures
is that procedures can have side effects. True

In this case changing a
variable defined in the process from which I am calling the procedure.

Yes, but only if the variable is passed from process scope
to procedure scope.

-- Mike Treseler

 

[Alan Fitch]

procedure.

Yes, but only if the variable is passed from process scope
to procedure scope.

Hallo Mike,
I don't think that's correct. Michel is right, a procedure
declared
within a process can directly access variables declared within the
process,
just as it can directly access signals declared within the
architecture that
contains that process.

Regarding the original problem, Michel can you post your actual code?

regards
Alan

--
Alan Fitch
Consultant

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[Mike Treseler]

I don't think that's correct. Michel is right, a procedure
declared within a process can directly access variables declared within the
process, just as it can directly access signals declared within the
architecture that contains that process.

Sorry about that.
Yes you and Michel are right, and
I did not read his example carefully.

As long as the variable is declared before the procedure
it is directly visible to that procedure.

My comments applied to packaged procedures
that can be called from any process.

-- Mike Treseler