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BIRD ID#:        107
ISSUE TITLE:     Update to Algorithmic Modeling API (AMI) Support in IBIS
REQUESTER:       Todd Westerhoff, SiSoft and Zhen Mu, Cadence Design Systems
DATE SUBMITTED:  April 3, 2008
DATE REVISED:    
DATE ACCEPTED BY IBIS OPEN FORUM:  PENDING

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STATEMENT OF THE ISSUE:

The waveform input to a TX AMI_Getwave call and the filtering function to be
performed by the AMI_Getwave call were ambiguous.  The analysis flow when an 
AMI model contained filtering in both the AMI_Init and AMI_Getwave calls was 
not clearly stated.  These issues were causing simulation differences when 
the same TX model was run in different IBIS-AMI toolkits.

The existing text did not make it clear that the AMI model was responsible for
deallocating memory used for AMI_parameters_out.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:


The following paragraph:

|
| 3.2.2.1 wave
| ============
|
| A vector of a time domain waveform, sampled uniformly at an interval
| specified by the ‘sample_interval’ specified during the init call.  The
| wave is both input and output.  The EDA platform provides the wave.  The
| algorithmic model is expected to modify the waveform in place.
|
| Depending on the EDA platform and the analysis/simulation method chosen,
| the input waveform could include many components.  For example, the input
| waveform could include:
|

shall be modified as follows:

|
| 3.2.2.1 wave 
| ============
|
| A vector of a time domain waveform, sampled uniformly at an interval
| specified by the ‘sample_interval’ specified during the init call. The
| wave is both input and output. The EDA platform provides the wave. 
| The algorithmic model is expected to modify the waveform in place by 
| applying a filtering behavior, for example, an equalization function,
| being modeled in the AMI_Getwave call.
|
| Depending on the EDA platform and the analysis/simulation method chosen,
| the input waveform could include many components.  For example, the input
| waveform could include:
|

------------------------------------------------------------------------------

The following paragraph:

|              Reserved Parameters:
|
|              Init_Returns_Impulse, GetWave_Exists, Max_Init_Aggressors and
|              Ignore_Bits


shall be modified as follows:

|              Reserved Parameters:
|
|              Init_Returns_Impulse, Use_Init_Output, GetWave_Exists, 
|              Max_Init_Aggressors and Ignore_Bits


------------------------------------------------------------------------------


The following paragraph:

| 3.1.2.6 AMI_parameters (_in and _out)
| =====================================
|
| Memory for AMI_parameters_in is allocated and de-allocate by the EDA.  The
| memory pointed to by AMI_parameters_out is allocated and by the model. 


shall be modified as follows:

| 3.1.2.6 AMI_parameters (_in and _out)
| =====================================
|
| Memory for AMI_parameters_in is allocated and de-allocated by the EDA platform. The 
| memory pointed to by AMI_parameters_out is allocated and de-allocated by the model. 

------------------------------------------------------------------------------

Add the following paragraph after Init_Returns_Impulse

| 			   Use_Init_Output:
|
|			   Use_Init_Output is of usage Info and type Boolean.  When Use_Init_Output 
|			   is set to "True", the effects of the AMI_Init and AMI_Getwave calls are
|                          chained together in the EDA platform by convolving the impulse response 
|                          returned by AMI_Init with the input waveform. The resulting waveform 
|                          is then presented to the AMI_Getwave call.  
|
|                          If Use_Init_Output is set to "False", the EDA platform will present the 
|                          input waveform directly to the AMI_Getwave call (i.e. without convolving 
|                          the waveform with the impulse response returned by AMI_Init).
|
|                          The algorithmic model is expected to modify the waveform in place.
|  
|			   The default value for this parameter is "True", instructing the EDA tool
|			   to use the output impulse response from the AMI_Init function 
|			   when creating the input waveform presented to the AMI_Getwave function.
|
|                          If Use_Init_Output is False, GetWave_Exists must be True.


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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION

Comparisons of simulation results from the reference toolkits revealed differences that were due
to different assumptions about the input waveform presented at a TX AMI_Getwave call, and the 
relationship of the outputs from AMI_Init and AMI_Getwave calls.  Further discussion identified 
two different styles of modeling were possible and should be supported.  In the default case, the
AMI_Init and AMI_Getwave calls represent filtering performed by sequential stages of a device, and
the results should therefore be chained together.  In the second case, the AMI_Init and AMI_Getwave 
calls each represent the overall device.  For example, the AMI_Init call could provide an LTI model 
for the device while the AMI_Getwave call provides a time-varying model.  In this case, results from
the AMI_Init and AMI_Getwave calls should be treated as independent.

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ANY OTHER BACKGROUND INFORMATION:

The thoughts captured in this BIRD were discussed at the April 1, 2008 meeting of the 
IBIS ATM Task Group.  A slide presentation of this material is available as
IBIS_ATM_BIRD_Update_040108.pdf

in the following web directory:

http://www.eda.org/pub/ibis/macromodel_wip/archive/20080401/toddwesterhoff/IBIS-AMI%20Correlation%20and%20BIRD%20Update/
(http://tinyurl.com/28ouvx)
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