Subject: [IBIS] Sticky problem in [Driver Schedule]
From: Mirmak, Michael (michael.mirmak@intel.com)
Date: Fri Apr 18 2003 - 16:38:21 PDT
All,
We have just noted a strange issue when using the [Driver Schedule] keyword.
The specification clearly states that, for a "top-level" model under [Driver Schedule], keywords such as [Pulldown], [Rising Waveform], [Ramp], etc. are ignored. [Power Clamp] and [GND Clamp], however, are not (they would be ignored in the scheduled buffers).
In order to ensure a minimum of issues with tool interpretations of [Driver Schedule], I recently created a model which uses a top-level Model_type of "Input," while using scheduled models of "Open_source," "Open_sink," etc. An input-only top-level model is not explicitly prohibited by the specification, and, indeed, the parser flagged no errors or warnings with this construction.
Unfortunately, many tools, especially those for which users must explicitly create input stimulus nodes, will probably not be able to use this kind of construction successfully (where, for example, do you tie the input stimulus from the core on an input-only top-level buffer model?).
At this point, I can only conclude that a clarification BIRD should be written to add restrictions on the Model_type of [Driver Schedule] models. A parser bug would be inappropriate, since the parser is faithfully following the language of the specification.
Any thoughts?
- Michael Mirmak, Intel Corp.
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