Out of range on type real?

I'm trying to scale some reals in a test bench, however I'm getting an
out of range error:

<SNIP>

signal srefloat_unscale : real;
signal simfloat_unscale : real;
signal srefloat_test : real;
signal simfloat_test : real;

begin
....
....
....
scaleresult_proc: process(srefloat_unscale, simfloat_unscale)
begin
srefloat_test <= srefloat_unscale*2.0**7;
simfloat_test <= simfloat_unscale*2.0**7;
-- srefloat_test <= srefloat_unscale;
-- simfloat_test <= simfloat_unscale;
end process scaleresult_proc;
</SNIP>

In ModelSim:

VSIM> run
# ** Fatal: (vsim-3421) Value -1.#INF is out of range 1e+308 to
-1e+308.

What gives? Is the scale factor I'm multiplying by somehow causing an
overflow in the floating point? srefloat_unscale and simfloat_unscale
are both reals between -1 and +1 (normalized fixed point), so the
result should be anywhere from -128 to +128 after scaling.

Thanks,
-Brandon

Brandon

initialise the real variables and proceed.

Neo

uninitialized objects get 'left value of their type.

in this case, the real signals get most -ive value
i.e. -1e+308. When this is multiplied, it overflows.

btw, NCVHDL has an option "-initzero" to initialize
all "integer" and "time" type objects (signals,variables,
generics) in the design to 0 (instead of 'left).
so if this is what you desire, you don't have to
explicitly set for objects of these types.

Thanks.
-Amit.


Brandon wrote:
> I'm trying to scale some reals in a test bench, however I'm getting an
> out of range error:
>
> <SNIP>
>
> signal srefloat_unscale : real;
> signal simfloat_unscale : real;
> signal srefloat_test : real;
> signal simfloat_test : real;
>
> begin
> ...
> ...
> ...
> scaleresult_proc: process(srefloat_unscale, simfloat_unscale)
> begin
> srefloat_test <= srefloat_unscale*2.0**7;
> simfloat_test <= simfloat_unscale*2.0**7;
> -- srefloat_test <= srefloat_unscale;
> -- simfloat_test <= simfloat_unscale;
> end process scaleresult_proc;
> </SNIP>
>
> In ModelSim:
>
> VSIM> run
> # ** Fatal: (vsim-3421) Value -1.#INF is out of range 1e+308 to
> -1e+308.
>
> What gives? Is the scale factor I'm multiplying by somehow causing an
> overflow in the floating point? srefloat_unscale and simfloat_unscale
> are both reals between -1 and +1 (normalized fixed point), so the
> result should be anywhere from -128 to +128 after scaling.
>
> Thanks,
> -Brandon
>

Amit Dua

I tried the above advice, but it did not seem to help.

I think the problem is because the signals are connected to output
ports of the entity that converts my fixed point binary to real:
<SNIP>

architecture behavioral_ar of my_tb is
....
signal srefloat_unscale : real := 0.0;
signal simfloat_unscale : real := 0.0;
signal srefloat_test : real := 0.0;
signal simfloat_test : real := 0.0;
....

begin
sreConvert_ins : entity work.fxdbin2fpdec_g(behavioral_ar)
generic map (dwidth => DWIDTH_C)
port map (fxdbin => sre, fpdec => srefloat_unscale);

simConvert_ins : entity work.fxdbin2fpdec_g(behavioral_ar)
generic map (dwidth => DWIDTH_C)
port map (fxdbin => sim, fpdec => simfloat_unscale);
....
scaleresult_proc: process(srefloat_unscale, simfloat_unscale)
begin
srefloat_test <= srefloat_unscale*2.0**7;
simfloat_test <= simfloat_unscale*2.0**7;
end process scaleresult_proc;

end behavioral_ar;
</SNIP>

Is there anyway around this? I'm also using ModelSim, so ncvhdl
compiler properties are not an option.

Brandon

Did you also initialize the input in the entity declaration?
e.g.
entity dbbl is
port (x : in real :=0.0 ; y : out real);
end dbbl;

Egbert Molenkamp

"Brandon" <> wrote in message
news: oups.com...
>I tried the above advice, but it did not seem to help.
>
> I think the problem is because the signals are connected to output
> ports of the entity that converts my fixed point binary to real:
> <SNIP>
>
> architecture behavioral_ar of my_tb is
> ...
> signal srefloat_unscale : real := 0.0;
> signal simfloat_unscale : real := 0.0;
> signal srefloat_test : real := 0.0;
> signal simfloat_test : real := 0.0;
> ...
>
> begin
> sreConvert_ins : entity work.fxdbin2fpdec_g(behavioral_ar)
> generic map (dwidth => DWIDTH_C)
> port map (fxdbin => sre, fpdec => srefloat_unscale);
>
> simConvert_ins : entity work.fxdbin2fpdec_g(behavioral_ar)
> generic map (dwidth => DWIDTH_C)
> port map (fxdbin => sim, fpdec => simfloat_unscale);
> ...
> scaleresult_proc: process(srefloat_unscale, simfloat_unscale)
> begin
> srefloat_test <= srefloat_unscale*2.0**7;
> simfloat_test <= simfloat_unscale*2.0**7;
> end process scaleresult_proc;
>
> end behavioral_ar;
> </SNIP>
>
> Is there anyway around this? I'm also using ModelSim, so ncvhdl
> compiler properties are not an option.
>

Egbert Molenkamp