| DSP Blockset | |
Additional Settings for Discrete-Time Simulations. It is worthwhile to know how the other solver options available in Simulink affect discrete-time signals. In particular, you should be aware of the properties of discrete-time signals under the following settings:
When the Fixed-step MultiTasking solver is selected, discrete signals in Simulink most accurately model the prototypical discrete signal described in Discrete-Time Signals. In particular, when these settings are in effect, discrete signals are undefined between sample times. Simulink generates an error when operations attempt to reference the undefined region of a signal, as, for example, when signals with different sample rates are added.
To perform cross-rate operations like the addition of two signals with different sample rates, you must explicitly convert the two signals to a common sample rate. There are several blocks provided for precisely this purpose in the Signal Operations and Multirate Filters libraries. See Converting Sample Rates and Frame Rates for more information. By requiring explicit rate conversions for cross-rate operations in discrete mode, Simulink helps you to identify sample rate conversion issues early in the design process.
When the Variable-step solver is selected, discrete time signals remain defined between sample times, just as in the Fixed-step SingleTasking setting previously described in Recommended Settings for Discrete-Time Simulations. In this mode, cross-rate operations are allowed by Simulink.
In the Fixed-step Auto setting, Simulink automatically selects a tasking mode (single-tasking or multitasking) that is best suited to the model. See Simulink Tasking Mode for a description of the criteria that Simulink uses to make this decision. For the typical model containing multiple rates, Simulink selects the multitasking mode.
| | Recommended Settings for Discrete-Time Simulations | Cross-Rate Operations in Variable-Step and Fixed-Step SingleTasking Modes | |