RE: [vhdl-200x] Update to proposal for arbitrary integers

Why not come up with a way to define a resolved integer type to handle this
type of thing?  A resolved real type would be handy as well.  This is what
the resolved type of std_logic does to std_ulogic - correct?  Why not extent
resolve types or resolution functions to cover all root types?
 
Regards,
 
Scott D. Hoy
E-mail: sdhoy@verizon.net
 

  _____  

From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of
Daniel Kho
Sent: Monday, October 13, 2014 10:29 PM
To: vhdl-200x@eda.org
Subject: Re: [vhdl-200x] Update to proposal for arbitrary integers


Hi Martin,

Thanks for this. One thing that has been bothering me quite often these days
is that integers, booleans, bits (and possibly other types from the
std.standard package) do not have the concept of resolution.


While I support the idea of having a completely-unconstrained
universal_integer type, I still would like to have the ability to assign an
"invalid" or "undriven" value to an integer. Like this:


signal i: integer;
...

begin

    i <= NaN;


where NaN is an invalid value for an integer. I find myself needing the
ability to assign integers to an invalid / undriven state, during
initialisation/reset for example, or when I would want to have a driver
explicitly "release" the bus, while have another driver drive it.


In the past, I tried writing resolution functions for integers to do exactly
this, but found my solution inadequate as I need to reserve a valid integer,
e.g. x"ffff_ffff" to act as my invalid/undriven integer. I find that when
writing such resolution functions, I do need checks against an undriven
state. For std_logic, we already have the function "is_x" (and I also have
my own "is_01") which we could use when resolving std_ulogic type signals.
But for integer and boolean types, I can't think of a way to do the same
thing as an "is_x" function would for std_logic. My dirty hack was just to
reserve a very large integer to act as my invalid value.


My opinion is that it would be great if we can do similar things with
integers, booleans, and bits. It is often easier to design using these
datatypes than with std_logic(_vector).

What do you think?


Best regards,
Daniel


On 10 October 2014 19:07, Martin.J Thompson <Martin.J.Thompson@trw.com>
wrote:


Hi all,


After the discussions in the last telecon, I have updated the Arbitrary
Integers page:

 

http://www.eda-twiki.org/cgi-bin/view.cgi/P1076/ArbitraryIntegers

 

In summary, the proposal is to

 

.         Expose universal_integer as a completely unconstrained integer
type, (and possibly make INTEGER a constrained subtype of this.  Each tool
will constrain the INTEGER to the range it currently provides for backwards
compatibility.)

.         Create universal_integer'high and 'low

.         Allow logical and shift operations on universal_integers

.         Question: should conversions between UNIVERSAL_INTEGER and INTEGER
be implicit or explicit?

 

Any comments you have will be gratefully received as always :)

 

Thanks,

Martin



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