Hi,
I’d
like to add a proposal that is somewhat related to Item n/a 10:
(10)
ANSI style ports and parameters - allow either comma or semicolon
separators
(slide 36)
It can
either be a separate item to vote on, or combined with n/a 10.
When
generating or transforming Verilog code, it is common to iterate over a
list of
items such as port declarations or connections. Currently in such
cases,
the generation code must take into account whether an item is the first
or last
when deciding whether to insert a comma between items. This is
annoying
all on its own, but is especially problematic when generating code that
may be
conditionally parsed:
module foo (
`ifdef NEED_PORT_A
input a,
`endif
`ifdef NEED_PORT_B
input b
`endif
);
endmodule
module bar();
foo foo (
`ifdef NEED_PORT_A
.a(a),
`endif
`ifdef NEED_PORT_B
.b(b)
`endif
);
endmodule
If NEED_PORT_A
is defined but NEED_PORT_B isn’t, then you get syntax errors. You
can try to use leading commas instead:
module foo (
`ifdef NEED_PORT_A
input a
`endif
`ifdef NEED_PORT_B
, input b
`endif
);
endmodule
module bar();
foo foo (
`ifdef NEED_PORT_A
.a(a)
`endif
`ifdef NEED_PORT_B
, .b(b)
`endif
);
endmodule
But now
if NEED_PORT_A is undefined and NEED_PORT_B is defined, you get
different
syntax errors. It’s actually quite difficult to write legal code
for all 4 cases (especially given the absence of a `if or `ifeq in the
preprocessor.) Add more ports and things get exponentially worse.
However,
if you allow trailing commas, then it’s possibly to generate “safe”
code in all cases, and also it’s no longer necessary to detect the
first
or last item as a special case.
So the
proposal is to allow trailing commas at the end of named connection
lists and
ANSI-Style port declaration lists:
list_of_port_connections ::=
ordered_port_connection
{ , ordered_port_connection
}
|
named_port_connection { , named_port_connection
} { , }
list_of_port_declarations ::=
( [ {
attribute_instance} ansi_port_declaration
{ , {
attribute_instance}
ansi_port_declaration } { , } ] )
This
becomes somewhat more important if you also consider Mantis 210, that
would
extend generate functionality to these same lists. In that case, you
have
to decide what form of separator / terminator is needed for the
generated ports
/ connections.
An
alternative to the proposed enhancement would continue to restrict use
of comma
as a port / connection item _separator_ and add the option of
using
semicolon as a port / connection item _terminator_.
~ Dave
// David
A. Gates, Ph.D. 408.749.4497
// Director,
RTL Center of Expertise
//
Fellow, Design Automation
// Advanced Micro Devices www.amd.com
//
Less talk, more action.