Martin,
Maybe I need to rearrange my example,
as I intended it as multiple changes on the same signal (y) rather than
multiple transitions using the same argument (x1). So the same story applies
to:
analog
y = transition(x1, 5n, 5n);
analog begin
y = transition(x2, 15n, 5n);
y = transition(x3, 10n, 5n);
end
The notable differences should be in the delay, not in the expression argument.
Cheers,
Marq
Marq Kole
Competence Leader Robust Design
Research
NXP Semiconductors
"Martin O'Leary" <oleary@cadence.com>
23-01-2007 15:40
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To
| "Marq Kole" <marq.kole@nxp.com>
"verilog-ams" <verilog-ams@eda-stds.org>
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cc
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Subject
| RE: transition function
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Classification
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Marq,
I believe this refers to muliple
changes (transitions) on a single signal feed to a transition operator
over time not to multiple transition operators with the same signal as
argument.
The examples do however bring
up interesting questions about race conditions around analog variable assignment.
Thanks,
--Martin
From: owner-verilog-ams@eda.org [mailto:owner-verilog-ams@eda.org]
On Behalf Of Marq Kole
Sent: Tuesday, January 23, 2007 2:06 AM
To: verilog-ams
Subject: transition function
All,
Transition functions can introduce ambiguities on signals that have multiple
transitions defined for them. According to section 4.4.9 of the Verilog-AMS
2.2 LRM:
“With different delays, it is possible for a new transition to be specified
before a previously specified transition starts. The transition function
handles this by deleting any transitions which would follow a newly scheduled
transition. A transition function can have an arbitrary number of transitions
pending.”
Consequently, it seems to me that when a new transition is applied to a
signal that already has a transition pending then the new transition is
added to the transition function if the new delay is larger, but any existing
transition with a larger delay would be removed.
However, if the transitions are applied in different concurrent analog
constructs the order of evaluation of these analog constructs becomes important.
Would there be any problem with assigning all transitions defined on a
signal, unless the transitions are assigned in a single analog block? So:
analog
y = transition(x1, 5n, 5n);
analog begin
y = transition(x1, 10n, 5n);
y = transition(x2, 15n, 5n);
end
Would have all three transitions pending for signal y, independent of the
order of evaluation of the two analog blocks, and:
analog
y = transition(x1, 5n, 5n);
analog begin
y = transition(x2, 15n, 5n);
y = transition(x1, 10n, 5n);
end
Would only have the transitions from signal x1 pending, as the transition
from signal x2 in the second analog block is deleted per section 4.4.9
as the second transition from signal x1 has a shorter delay. Again, independent
of the order of evaluation of the two analog blocks.
The above approach would keep the concurrency of multiple analog blocks,
while at the same time being backwards compatible with the Verilog-AMS
2.2 LRM. The only alternative I see is to disallow transitions from multiple
analog blocks. Any other suggestions?
Cheers,
Marq
Marq Kole
Competence Leader Robust Design
Research
NXP Semiconductors
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Received on Tue Jan 23 06:54:21 2007