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BIRD ID#:        96
ISSUE TITLE:     [Model Spec] and [Receiver Thresholds] Ordering
REQUESTER:       Randy Wolff, Micron Technology, Inc.
DATE SUBMITTED:  December 29, 2004
DATE ACCEPTED BY IBIS OPEN FORUM: February 18, 2005 

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STATEMENT OF THE ISSUE:

At present, the IBIS 4.1 specification does not clearly state that any
specific ordering of the [Model Spec] and [Receiver Thresholds] keywords
should be maintained following all the subparameters of a model.  Also, 
there is no language to indicate that these keywords must be specified
before other keywords of a model.

The IBIS 4.1 parser currently issues an error unless [Model Spec] is specified
immediately after all the subparameters of a model and before the other
keywords of a model.  An error is also issued unless [Receiver Thresholds] is 
specified immediately after all the subparameters of a model and before the 
other keywords of a model except [Model Spec].  The changes below will align
the specification with parser behavior.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:

Changes are noted in the relevant sections below by |* lines.

In section 6, under [Model Spec], replace:
| Usage Rules:  [Model Spec] must follow all other subparameters under the 
|               [Model] keyword.

with:
|* Usage Rules:  [Model Spec] must follow all subparameters under the [Model] 
|*               keyword and precede all other keywords of a model.


Under [Receiver Thresholds], replace:
| Usage Rules:  The [Receiver Thresholds] keyword is valid if the model type
|               includes any reference to input or I/O.  For single ended
|               receivers the Vinh_ac, Vinh_dc, Vinl_ac, Vinh_dc, Vth and
|               Tslew_ac subparameters are required and override the Vinh,
|               Vinl, Vinh+/- and Vinl+/- subparameters declared under the 
|               [Model] or [Model Spec] keywords.  For single ended receivers
|               the Vth_min, Vth_max, Threshold_sensitivity and
|               Reference_supply subparameters are optional.  However, if 
|               the Threshold_sensitivity subparameter is present then the 
|               Reference_supply subparameter must also be present.

with:
|* Usage Rules:  [Receiver Thresholds] must follow all subparameters under
|*               the [Model] keyword and precede all other keywords of a
|*               model except [Model Spec]. 
|*
|*               The [Receiver Thresholds] keyword is valid if the model type
|               includes any reference to input or I/O.  For single ended
|               receivers the Vinh_ac, Vinh_dc, Vinl_ac, Vinh_dc, Vth and
|               Tslew_ac subparameters are required and override the Vinh,
|               Vinl, Vinh+/- and Vinl+/- subparameters declared under the 
|               [Model] or [Model Spec] keywords.  For single ended receivers
|               the Vth_min, Vth_max, Threshold_sensitivity and
|               Reference_supply subparameters are optional.  However, if 
|               the Threshold_sensitivity subparameter is present then the 
|               Reference_supply subparameter must also be present.

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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION

It was discovered that the IBIS 4.1 parser assumes specific ordering and
placement of the [Model Spec] and [Receiver Thresholds] keywords within a
model statement.  However, the IBIS 4.1 specification does not clearly state
any of these requirements.  This BIRD will align the specification with
parser behavior and remove any ambiguity in the specification.

Having the [Model Spec] keyword immediately following the subparameters of a
model provides grouping of the same and new subparameters in typ-min-max
format.  The [Receiver Thresholds] keyword also contains subparameter type
data, so it is desirable for it to be positioned in the same manner.
  

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ANY OTHER BACKGROUND INFORMATION:


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