RE: percent codes for analyses (was: Feb 8 2007 minutes)

All,

First, a word of warning: in C/C++ for multiple character percent codes 
the base code is at the back of the sequence, the other characters are 
merely modifiers. The problem is that if you don't do this and you want 
the percent code to be followed directly by a normal character sequence 
you don't know where the percent code ends and the normal character 
sequence starts. So if you want to use %a for analysis, you'd have to 
think of some of the leftover characters as modiers. Unless you always 
want a multi-character code, but there is no precendent for that -- in any 
language that supports printf-like functionality!

This whole dealing with special percent codes in the first argument of 
$fopen() appears to me as quite awkward. It will change the definition of 
$fopen in a way that has no advantages for digital Verilog or 
SystemVerilog. I expect a lot of users will try to give additional 
arguments as though it was a full fledged printf-like functionality. Once 
you start thinking about different values to be returned by the various %a 
codes you will likely run into implementation dependent ways of retrieving 
the data.

If I'm allowed to make another suggestion: we currently support string 
parameters in Verilog-AMS. Can't we also support local string parameters 
and define a system function that does a $sformat() that outputs a value 
for a string parameter or string localparam? As a suggestion:

$pformat( format_string, args...)

where the return value is an initializer for a string parameter or string 
localparam. Additionally retrieve the name of the analysis using a 
specific system task, say $analysis_name. Then it could be used as:

localparam string dump_name = $pformat("dump.%s.txt", $analysis_name);

analog
  $fopen(dump_name);

The advantages are that you do not have to change the definition of $fopen 
-- as the proposed extension is much more for analog than for 
mixed-signal, let alone digital, the side effects on digital Verilog and 
SystemVerilog are less if we just add a system function. Next to that, we 
do not have to use the %a or a multi character code, but can better take 
this (global) information from the $analysis_name system task and use 
optional arguments for this system task to get different or more 
information.

$analysis_name returns the name of the analysis, or if the simulator does 
not support naming of analyses the analysis type plus an ordinal, e.g. 
"dc1".
$analysis_name("name") is equivalent to $analysis_name -- "name" is the 
default argument.
$analysis_name("type") returns the analysis type. The type name is taken 
from the possible arguments for the analysis() function (LRM 2.2, section 
4) to achieve optimal portability.
$analysis_name("simulator") returns the name of the simulator.
$analysis_name("user") returns the name of the process owner.
etc.

There is a parallel with the $simparam() system function, but while that 
function always returns a real, this function will always return a string 
value. The standard should give a minimal set of arguments that must be 
supported while allowing additional implementation dependent ones.

Cheers,
Marq


Marq Kole
Competence Leader Robust Design

Research
NXP Semiconductors


owner-verilog-ams@server.eda.org wrote on 12-02-2007 21:46:25:

> Geoffrey, Kevin, Jonathan
> thanks for your input.
> Comments below.
> --Martin 
> 
> -----Original Message-----
> From: owner-verilog-ams@eda.org [mailto:owner-verilog-ams@eda.org] On
> Behalf Of Geoffrey.Coram
> Sent: Monday, February 12, 2007 4:52 AM
> Cc: verilog-ams
> Subject: percent codes for analyses (was: Feb 8 2007 minutes)
> 
> Martin O'Leary wrote:
> > 
> > * Add percentage codes for analysis that can be used to uniquely name 
> > a file generated by an analysis.
> > It a file is not uniquely name, it will be overwritten if there are 
> > multiple analysis opening, closing and writing to the file.
> 
> Let's be sure that SV is going to go along with this; there are only 26
> percent codes, and most of them are already used.  We don't want SV to
> assign a different meaning.
> 
> What does this code look like?  If I put "results_%a" to I get files
> like "results_dc" "results_ac" ...
> 
> oleary>My take that we should use multiple character percentage codes in
> order to avoid conflict with the SV standard or reserving too much of
> the name space. They would all start with '%a' or '%A' - a/A for AMS.
> e.g. %aa for analysis, %as for simulator name, etc ...
> As suggested %a and %r would then need to be reserved for use by
> Verilog-AMS only.
> This I hope would address 
> 1) the risk of SV and Verilog-AMS coming into conflict
> 2) allow a mechanism for the Verilog-AMS to expand the percentage code
> capabilities easily
> 3) consumming too much of percentage code name space.
> 
> 
> Or are the names more like the temporary filenames generated by the C
> function "tmpnam"?
> 
> On one hand, it would be nice to know that dc results are in
> "results_dc"; on the other, I don't want the results of the second dc
> analysis in a single netlist to overwrite those of the first dc
> analysis.
> 
> Some simulators have names for the analysis, eg "dc1" in this:
> dc1 dc start=0 stop=5
> Will the percent code use this name?  On one hand, this would give good
> control to the user; on the other hand, it may be inappropriate to
> dictate this for the simulator in an HDL manual.
> 
> oleary>The file would be named after the analysis name (ie. dc1 ) not
> the analysis type (dc).
> I believe many simulators already have some kind of analysis
> naming/tagging scheme if only to determine the name of the different
> transient output waveform files when multiple transient analyses are
> being conducted.
> 
> -Geoffrey
> 
> 
> Codes used in Verilog 1364-2005:
> b,c,d,e,f,g,h, ,l,m, ,o, ,s,t,u,v, ,z
> 
> C uses i,n,p,x in some implementations, though %i looks to the same as
> %d; %x is "unsigned hex" in C, whereas %h is "hex" in Verilog.  Also, %u
> is "unsigned decimal"
> in C, but "unformatted 2-value" in Verilog.  (%p is for a pointer. %n is
> strange: printf outputs nothing but instead stores back into the
> corresponding argument the number of characters printed so far.)
> 
> I don't see any new ones in 1800-2005.  AMS uses %r.
> 
> That leaves: a,j,k,q,w,y  %a sure would be nice for analysis ...
> 
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