What's Good About Checkpoint Restart For Digital and Mixed Circuits? It's In SPB16.2!

Checkpoint Restart for Digital and Mixed Circuits will allow PSpice users to set checkpoints while doing a transient analysis for digital and mixed circuits, saving all the transient information onto the disk and then allowing users to restart the analysis from any of the saved checkpoints.

The CheckPoint Restart feature lets you save the state of a transient simulation at different moments as Checkpoints. One can specify any of the CheckPoints as a restart point and rerun the simulation from that point thus avoiding running a long simulation from the start. Instead the user can only run simulation for the portion of time that is expected to have the outputs of interest. This feature was introduced in the SPB16.0 release for analog circuits and now with the SPB16.2 release, it also supports digital and mixed circuits.

The use model for using CheckPoints is as follows:

1. Specify the CheckPoints
2. Run the initial analysis
3. Specify the restart point
4. Restart the analysis

Specifying Checkpoints

The Save CheckPoints option can be accessed under the Transient Analysis section of the Simulation Settings.

The user must define the following for CheckPoints:

1. Simulation time interval: The interval in simulation time between two CheckPoints. The default unit is seconds(s), but you can also specify the time in all standard scale modifiers, such as microseconds (ms) and nanoseconds (ns).

2. Real time interval: The interval between two CheckPoints in real time. The default is minutes (min), but you can also specify intervals in hours (hrs).

3. Time points: Specific times when CheckPoints are created. This can be done in two ways:

    a. User defined Time Points: The user specifies the checkpoints by entering values (separated by a space or a comma) in the Time Points box.

    b. PSpice Calculated Time Points: The user specifies the time interval over which the checkpoints have to be saved and the simulator will choose specific time points.

4. Directory location: The location where CheckPoint data is stored. The default location is the transient simulation profile directory.

In case of purely digital circuits, a checkpoint will not be generated at a timepoint if there are no events. For example, if a digital circuit changes state from 0 to 1 at a specified timepoint, a checkpoint will be generated. But, if there is no transition, a checkpoint will not be generated at that timepoint. Thus, only PSpice calculated time points for saving checkpoint states is honored by the simulator.

Restarting Simulation from a saved Checkpoint

The user can restart a simulation from a saved CheckPoint after changing the design. PSpice allows you to change the following in the schematic before restarting a simulation:

a.  Component values
b.  Parameter values
c.  Simulation options
d.  CheckPoint restart options
e.  Data save options

However, the following changes cannot be made before restarting simulations:

a. Add or remove components before restarting simulation
b. Change device name or order in the circuit file
c. Change initial condition of device such as capacitor
d. Change multi-analysis options, such as temperature, parameter, or MC sweep

The user needs to point to the appropriate checkpoint directory (where he has saved the checkpoints) and the exact time point from where the simulation has to be restarted can be chosen from the drop down menu as shown above.

As always, I'm interested in your usage of this new AMS Simulator feature in the SPB16.2 release.

Jerry GenPart