ieee.numeric_std?

[Kim Enkovaara]

Weng Tianxiang wrote:

Another question is unanswered:

Why unsigned/signed cannot be used in top layer? and why the signals in
the top layer must be std_logic and std_logic_vector?

Usually synthesis creates a toplevel that has only std_logic* signals. And if
you want to simulate netlist without any extra wrappers, it's easiest to use
std_logic also at the RTL top level symbol.

In asics sometimes you still need the wrappers, because the io-pads are done during
the netlist generation in many flows. In that case RTL toplevel does not yet have
three state drivers and simulation wrapper is needed to match the netlist
functionality.

--Kim

 

[Mike Treseler]

Eric Smith wrote:

Reto Zimmermann wrote:

The reason why not to use integer is that it is defined as a 32 bit
signed vector.

No, it isn't. It is defined as an integer with a range of at least
-2147483647 to +2147483647.

That's the spec, but a top integer port
has to default to something for synthesis,
if no range is specified.

That something is a 32 bit signed vector
for all synthesis tools I know of.

-- Mike Treseler

 

[Eric Smith]

Reto Zimmermann wrote:

The reason why not to use integer is that it is defined as a 32 bit
signed vector.

I wrote:

No, it isn't. It is defined as an integer with a range of at least
-2147483647 to +2147483647.

Mike Treseler wrote:

That's the spec, but a top integer port has to default to something
for synthesis, if no range is specified.
That something is a 32 bit signed vector for all synthesis tools I
know of.

As soon as you start depending on using an integer type and having it
syntheisze to a 32-bit signed vector, someone somewhere will release
a synthesis tool that produced a 64-bit vector, or a 37-bit vector,
or soemthing else that meets the spec but isn't what you expect.

If you want a 32-bit vector, write it that way. Don't count on
behavior that is implementation-specific.

 

[Mike Treseler]

Eric Smith wrote:

If you want a 32-bit vector, write it that way. Don't count on
behavior that is implementation-specific.

I agree.
Reto was advocating not using integers.
I was explaining where the length 32 came from.

-- Mike Treseler