RE: [sv-bc] Attributes taking runtime constants?

It should be added that the 1364-2005 standard allows a constant
expression to include certain built-in system functions as well.

Shalom


> -----Original Message-----
> From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On
> Behalf Of Steven Sharp
> Sent: Thursday, February 02, 2006 8:54 PM
> To: sv-bc@eda.org; stacey.secatch@xilinx.com
> Subject: Re: [sv-bc] Attributes taking runtime constants?
> 
> 
> >From: "Stacey Secatch" <stacey.secatch@xilinx.com>
> 
> >The 3.1a spec does not include this, and at this time, I have
> no
> >access to the IEEE preliminary versions.
> 
> Attributes were added in the IEEE Std 1364-2001 Verilog
> standard,
> not in SystemVerilog.
> 
> 
> >Has there been any work into allowing attributes to take
> values
> >from a runtime constant such as a generate variable or a
> parameter
> >rather than only fixed constants?
> 
> Genvars and parameters are not runtime constants; they are
> elaboration-time constants.  I assume that what you meant was
> that they are constants that are not set at parse-time, but can
> be set differently for different instances at elaboration time.
> 
> The standard allows attributes to be set to expressions that
> include
> such elaboration-time constants.  I proposed this specifically
> to
> allow attributes to be set to values that are different for
> different
> instances, or are propagated down through the design hierarchy.
> This
> avoided the need to add complicated extensions to attributes
> themselves
> to accomplish the same thing, which was being proposed.
> 
> 
> >But I may want "foo" to be changable passed on parameters, or
> >it's location in a generate block. The following code is a
> compile
> >error:
> >
> >localparam my_attr_str = "foo";
> >(* my_attr = my_attr_str *)
> 
> This is legal Verilog according to the standard, though that
> does
> not guarantee that all implementations will support it.  I am
> aware
> of tools that only allow setting attributes to constant
> literals,
> which is a subset of the full feature.
> 
> 
> Steven Sharp
> sharp@cadence.com