Subject: Parameter Interface Bugs?? Clarification?? Enhancement??
From: Clifford E. Cummings (cliffc@sunburst-design.com)
Date: Wed Jan 09 2002 - 10:45:49 PST
Hi, All -
This is a separate email thread to discuss parameter interface bugs,
enhancements, etc.
In a separate thread, there is a discussion about whether or not localparam
would be a valuable addition to a parameter list. One of the stronger
arguments against adding localparam to a parameter interface is that a
localparam cannot be modified during instantiation; therefore, it is not
really part of an interface. An argument in favor is that the calculation
of a localparam may be necessary before making ANSI-port declarations.
If we do decide to add localparams to a parameter interface, a reasonable
restriction may be to require all localparam declarations to be placed
after all parameter declarations in a parameter interface.
Opinion and vote (please indicate which of the following parameter
interface forms that you believe are or should be legal in Verilog-2001 or
SystemVerilog (the BNF does not support some of these and it requires
others that did not seem to be intended - oops!)
(1) module mymodule #(parameter DEPTH=16; parameter WIDTH=8) (...) //
semicolons between parameters
(2) module mymodule #(parameter DEPTH=16; parameter WIDTH=8;) (...) //
semicolons after all parameters, including the last parameter
(3) module mymodule #(parameter DEPTH=16;, parameter WIDTH=8;) (...) //
semicolons after all parameters and commas after semicolons between parameters
(4) module mymodule #(parameter DEPTH=16, parameter WIDTH=8) (...) //
commas between parameters / parameter keyword repeated
(5) module mymodule #(parameter DEPTH=16, WIDTH=8) (...) // commas between
all parameter assignments / only one parameter keyword
(6) module mymodule #(parameter DEPTH=16, WIDTH=8;) (...) // commas between
all parameter assignments / only one parameter keyword
(7) module mymodule #(parameter DEPTH=16, AWIDTH=8; parameter BWIDTH=8)
(...) // commas between parameter lists but a semicolon to separate another
parameter keyword in the list
(8) module mymodule #(DEPTH=16, AWIDTH=8, BWIDTH=8) (...) // commas between
parameter assignments but no parameter keyword / the #(...) syntax
indicates parameters
(9) module mymodule #(parameter AWIDTH=8, BWIDTH=8; localparam
YWIDTH=AWIDTH+BWIDTH; parameter DEPTH=16) (...) // mixture of semicolon
separated parameter and localparam declarations
(10) module mymodule #(parameter DEPTH=16, AWIDTH=8, BWIDTH=8; localparam
YWIDTH=AWIDTH+BWIDTH) (...) // both parameters and localparams permitted
but all localparams must follow all parameter declarations
(11) module mymodule #(DEPTH=16, AWIDTH=8, BWIDTH=8; localparam
YWIDTH=AWIDTH+BWIDTH) (...) // both parameters and localparams permitted
but all localparams must follow all parameter declarations. Parameter
keyword not required.
(12) module mymodule #(parameter DEPTH=16; localparam AWIDTH=clogb2(DEPTH))
(...) // both parameter and localparam permitted. All localparams must
follow all parameter declarations. The localparam calls the ceiling of the
log-base-2 (clogb2) constant function to calculate the address width
(AWIDTH) for the specified DEPTH.
(13) module mymodule #(DEPTH=16; localparam AWIDTH=clogb2(DEPTH)) (...) //
both parameter and localparam permitted. All localparams must follow all
parameter declarations. The parameter keyword is not required. The
localparam calls the ceiling of the log-base-2 (clogb2) constant function
to calculate the address width (AWIDTH) for the specified DEPTH.
I believe the following is true:
Legal per the BNF: (3) (6)
Illegal per the BNF: (1) (2) (4) (5) (7) (8) (9) (10) (11) (12) (13)
Legal per the documentation (see first example of section 12.2): (5)
Intended legal per the documentation(??): (1) (7)
Not legal per the documentation (no known examples in the Standard): (2)
(3) (4) (6) (8) (9) (10) (11) (12) (13)
Cliff would like these to be legal: (1) (5) (7) (8) (10) (11) (12) (13)
(The #(...) notation and adding the keyword parameter now seems to be
redundant)
Cliff does not want these to be legal: (2) (3) (4) (6) (9)
Legal(by mistake?) (but Cliff would not like these to be legal): (3) (6)
I would like to see opinions from other BTF, VSG and SystemVerilog
participants.
I wish I had been more thorough about parameters and localparams during the
IEEE process.
Regards - Cliff
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