Re: New enable argument to analog events and NULL

Hi Dave,

I believe the regular BNF is just an empty statement after the vertical
bar, so

analog_expression_or_null ::=
     analog_expression
   |

constant_expression_or_null ::=
     analog_expression
   |

Cheers,
Marq


owner-verilog-ams@server.eda.org wrote on 02-04-2008 21:54:27:

> The syntax needs to be updated to allow for the new 'enable' argument to
> cross/above/timer.
>
>
> analog_event_functions ::= // from A.6.5
> cross ( analog_expression [ , analog_expression
> [ , constant_expression [ , constant_expression [ ,
> analog_expression ] ] ] ] )
>
>
> We are going to allow the user to use NULL arguments for the optionsthey
want
> to leave as default.
> So:
> cross(V(a) - 5, , , ,enable) ....
>
> Here detect crossings in both +ve and -ve direction using simulator
default
> expressio and time tolerances.
>
> But the NULL arg is not handled in the analog_expression or
> constant_expression
> type.
> Instead of adding extra [] to the syntax would be better to create anew
token:
>
> analog_expression_or_null ::=
>      analog_expression
>    | null
>
> constant_expression_or_null ::=
>      analog_expression
>    | null
>
> Cross then becomes:
>
> cross ( analog_expression [ , analog_expression_or_null
> [ , constant_expression_or_null [ , constant_expression_or_null [ ,
> analog_expression ] ] ] ] )
>
> Not quite sure what the convention is in BNF to specify NULL (nill
> or prehaps "").
>
> Dave
>
>
> --
> =====================================
> -- David Miller
> -- Design Technology (Austin)
> -- Freescale Semiconductor
> -- Ph : 512 996-7377 Fax: x7755
> =====================================
>
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