RE: [sv-bc] time unit specification

Hi, Mark.
 
I understand it this way:
 
The most basic form of this is something like the following:
 
module a;
..
endmodule
 
`timescale 1ns/1ns
module b;
..
endmodule
 
In this example, module b has a timescale specified whereas module a
does not. In many, if not in all tools, this causes an error to be
generated.
 
If module b did not have a timescale specified, then both a and b would
use the tool default. But once any of the modules has a timescale
explicitly specified, then all of them must have an explicit timescale
either specified or inherited.
 
Shalom


________________________________

	From: owner-sv-bc@server.eda.org
[mailto:owner-sv-bc@server.eda.org] On Behalf Of Mark Hartoog
	Sent: Wednesday, November 19, 2008 9:42 PM
	To: sv-bc@server.eda.org
	Subject: [sv-bc] time unit specification
	
	

	In section 3.14.2.3 of the P1800-2009 draft 7a LRM is says:

	 

	<quote>

	If a timeunit is not specified within a module, program,
package, or interface definition, then the time unit

	shall be determined using the following rules of precedence:

	a) If the module or interface definition is nested, then the
time unit shall be inherited from the enclosing

	module or interface (programs and packages cannot be nested).

	b) Else, if a `timescale directive has been previously specified
(within the compilation unit), then

	the time unit shall be set to the units of the last `timescale
directive.

	c) Else, if the compilation-unit scope specifies a time unit
(outside all other declarations), then the time

	unit shall be set to the time units of the compilation unit.

	d) Else, the default time unit shall be used.

	....

	It shall be an error if some design elements have a time unit
and precision specified and others do not.

	</quote>

	 

	If all design elements with no other time unit/precision
specification use the default time unit, how can you have a design
element with no time unit/precision specified? 

	 

	Does this mean that it is an error for some design elements to
use the default and other design elements to have different time
unit/precision specified? Or is it impossible for this error to occur?


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