Subject: Re: Parameter Interface Bugs?? Clarification?? Enhancement??
From: Stuart Sutherland (stuart@sutherland-hdl.com)
Date: Wed Jan 09 2002 - 11:15:55 PST
I think the only correct answer in regards to the current 1364-2001
standard is that the syntax for the placement of commas and semicolons
should exactly match the syntax of port declarations with the port list. I
believe that is #7 in Cliff's long list of examples. The requirement to
have " ;, " in the parameter list, as in #3, is inconsistent with the ANSI
C style port lists, and should be documented as an errata in the current
1364-2001 BNF.
As for the inclusion of localparams in the module parameter list, that
should be postponed for a consideration in a future revision to the
standard. Perhaps it could be added with SystemVerilog, or perhaps in
1364-200x, or perhaps not at all. In any case, I feel it is not an errata
in the current BNF.
Stu
At 10:45 AM 1/9/2002, Clifford E. Cummings wrote:
>Precedence: bulk
>
>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
>//*****************************************************************//
>// Cliff Cummings Phone: 503-641-8446 //
>// Sunburst Design, Inc. FAX: 503-641-8486 //
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Stuart Sutherland Sutherland HDL Inc.
stuart@sutherland-hdl.com 22805 SW 92nd Place
phone: 503-692-0898 Tualatin, OR 97062
www.sutherland-hdl.com
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