Re: Minutes: Ex1

wow... sure wish I could attend and participate.. 
jbd

 Jonathan David
j.david@ieee.org
jb_david@yahoo.com
http://ieee-jbdavid.blogspot.com
Mobile 408 390 2425



----- Original Message ----
From: Kevin Cameron <Kevin.Cameron@truecircuits.com>
To: verilog-ams@eda.org
Sent: Saturday, November 8, 2008 1:01:52 PM
Subject: Re: Minutes: Ex1


[Sorry I missed the call]

Folks who are not familiar with how analog/ms simulators work should note that
the it is actually sampled rather than continuous. The simulator will
attempt to evaluate future state as far ahead as possible for a given
start state, and will step through conditions unless they are
specifically mentioned in "cross" statements. This is mostly required
for efficiency since automatically stepping to exactly where (say) "V(a) < 10.0 mV" changes
may cause unnecessarily short timesteps.

Signals in Verilog-AMS are both analog and digital: at any given time a
wire has both an analog value and a digital value. The automatic
insertion of A to D converters in Verilog-AMS means that in any context
the digital value of a signal "x" and its analog representation "V(x)"
should be in sync (if the conversion code is written correctly). This
is a feature of the language which allows "plug & play" of analog
and digital modules without incurring timing errors.

@cross is both digital and analog in that it is evaluated in analog to
stop at the right time but you can perform digital functions in the
@cross block since it happens at a discrete time.

Kev.

Anand Himyanshu wrote: 
.... 
 
Discussion on
examples followed. 
 
Ex 1: 
Ken asked the
question whether V(a) < 10.0 mV goes from false to true in
continuous time or
digital time? There was some discussion on this. Himyanshu mentioned
that in the
example, the transition was envisioned with ideal semantics in
continuous time.
Ken mentioned that the value of the expression is Boolean. Value of the
expression at 'Time Zero' was also discussed. Dejan mentioned that the
property
could be rewritten using past time. John asked there were questions
about the
interpretation of past time at Time Zero. It was felt that 'past or
negative time' needs to be discussed more, but for this example we had
thought
about future time. Since there was no governing event and in the
example we
avoided the use of ##0 and instead used #0. 
 
Is 'c' signal
digital or analog signal? Himyanshu mentioned it could be viewed as a
digital
signal. John mentioned it could be either and no claims were being made
whether it was digital or analog, as long as the values are available
in the
continuous time domain. Ken mentioned that if 'c' is digital then at
every
increment of the digital simulator its value is defined. It needs to be
mapped
(aliased?) to analog domain or vice versa. There was a good deal of
discussion
on digital and analog values and how they interacted with each other
within an
AMS simulator.
 
Ken asked another
question, Is @cross, digital or analog? John mentioned we had not
thought about
it and assumed ideal semantics. It was mentioned that @cross behaved
differently
depending upon whether it was digital or analog and that needs to be
taken into
account.
 


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