Driver (TX) and Receiver (RX) buffers are key elements of a serial interface, as well as the connecting channel. IBIS AMI models are provided by chip vendors or their model makers to allow the interconnect channel to be optimized. They also allow you to configure the signal processing parameters for TX and RX. Gigabit signalling would not be achievable without sophisticated signal processing techniques such as pre-emphasis, equalization, etc.
IBIS-AMI models comprise the following parts.
- An AMI part for the digital signal processing.
- An analog part which describes the switching characteristics. This analog part is given in a standard (legacy) IBIS file. The actual AMI part is provided as a binary executable file in a shared library.
To configure the algorithmic model behavior within the run-time library, the model makers provide AMI parameter files (extension “.ami”) in addition to the executable files. You can edit these AMI parameter files in order to control the behavior of the algorithmic model. Output parameters can also be modified by the algorithmic model during the analysis.
The available AMI parameters and their allowed value ranges are provided in the AMI parameter file, with a set of default values. The AMI Parameters dialog provides functions to deal with the sets of parameters.
- The meaning of the AMI parameters is typically described in the relevant IBIS AMI model documentation. You must study this documentation in order to understand the correct operation modes of the IBIS AMI model.
- Some IBIS AMI models require certain termination networks or package descriptions to be included within the analog channel. Otherwise, no successful processing is possible. This may also be described in the IBIS AMI model documentation.
AMI Models: IBIS Import
IBIS AMI models can be imported into the Simulation Library from an IBIS file repository or any other location within the file system, like any other IBIS file. All associated files are automatically transferred with the IBIS file. Currently, IBIS files up to AMI V 6.1 are supported. However, not all existing AMI functions are supported yet by eCADSTAR. For example, there is a lack of available models that support the latest functionality. Unsupported functions are reported on in eCADSTAR. It is possible to import into the Simulation Library, even if the model has unsupported features.
- The Channel Characterization and Eye Pattern computation that is based on the channel's impulse response are available even when no IBIS AMI models are assigned.
- Some available IBIS-AMI models show syntax errors in the IBIS (.ibs) file, or in the AMI Parameter file (.ami) which may prevent a successful IBIS import into the Simulation Library. Some can be corrected manually without altering the model behavior, as described below. If other issues occur, then review the IBIS parser log or run the IBISCHK tool. This is available from the IBIS web page.
| Error Case | Correction | IBSCHK output |
|---|---|---|
| String Type misses “xxx”. | Insert “” around value xxx. | ERROR: The List value Fast for Type String is invalid. |
| Use of “Label” or “Labels” instead of “List_Tip” in lists. | Replace “Label” with “List_Tip”. | ERROR: Unexpected leaf Labels found. |
| Misuse of “Default” value in combination with “Format Value” definition. | Remove Format Value definition. | ERROR: Default cannot be specified when Format Value is specified. |
AMI Model Assignment
IBIS AMI models which have been imported into the Simulation Library can be assigned to Differential Pair driver and receiver buffer symbols in Electrical Editor like any other suitable buffer model. The Show AMI Models only check box in the Select Model dialog provides an AMI model filter to filter the list of models.
AMI Model Configuration
The AMI Analysis dialog provides a list of model-specific properties for both TX and RX buffers. The Property table shows the Reference name of the buffers, their Differential Pin names, as well as the assigned Buffer Model.
This table allows you to configure the AMI models in the required detail to enable successful AMI Analysis. The model configuration is mainly done by a set of specific parameters that are provided by the model maker in an AMI parameter file.
- The Property table shows the name of both model files: the AMI Executable File and the AMI Parameter File.
- The AMI Analysis dialog allows you to open the AMI Parameters, in order to view and edit the contents of the AMI parameter file.
- Click
in the AMI
Analysis dialog, Property table,
AMI Parameter Set row to launch
the AMI Parameters dialog.
The AMI-Analysis environment can accommodate different sets of AMI Parameters. However, the initial (Default) AMI Parameter Set cannot be modified. This is provided by the model maker. The AMI Parameters dialog allows you to view and edit the set of AMI Parameters. Modified AMI Parameter Sets must be re-named, and are automatically stored with the AMI buffer information. Select from the AMI Parameter Sets that are already defined in the AMI Parameters dialog. The Property table shows the selected AMI Parameter Set.
Refer to the data sheet of the AMI model for suitable model parameters. This also applies to other AMI Analysis settings which are not part of the AMI Parameter Set. For example, the Data Rate value.
Supported Run-time Environments
IBIS AMI models may be provided for different operating systems. Also, different compile environments may be required to successfully run an IBIS AMI model. In general, 32 bit and 64 bit IBIS AMI models are supported. The correct model version must be observed when an IBIS AMI model is assigned. The applied AMI Architecture is shown individually for TX and RX models in the AMI Analysis dialog, Property table.
Size of Data Sequence
The AMI Analysis processing steps in the AMI part of the RX and TX models require the incoming data stream to be limited in size. Instead of feeding the full data stream of potentially several millions of bits into the IBIS AMI models, the AMI analysis process is divided into sequences of bits. The Size of Data Sequence row in the in the AMI Analysis dialog, Property table allows you to specify the length of the data sequence on a per-model basis. The size of the data sequence is typically the product of the number of bits, and the sampling rate per bit. This therefore represents the number of data points that is handled by the IBIS AMI model in one step.
Several IBIS AMI models strictly require a certain size of data sequence. This is sometimes referred to as “block size” or “wave size”. It is important that you refer to the model documentation for this parameter, as a wrong setting may cause problems in the computation process. This may lead to an inaccurate eye pattern.
