User`s guide

3 Working with Signals
3-92
block is called multirate when at least one input or output port has a different
frame rate than the others.
Many blocks are permanently single-rate, which means that all input and
output ports always have the same frame rate. For other blocks, the block
parameter settings determine whether the block is single-rate or multirate.
Only multirate blocks are subject to tasking latency.
Note Simulink may report an algebraic loop error if it detects a feedback loop
composed entirely of multirate blocks. To break such an algebraic loop, insert
a single-rate block with nonzero delay, such as a Unit Delay block. For more
information about algebraic loops, see “Algebraic Loops” in the Simulink
documentation.
Model Rate Type. When all ports of all blocks in a model operate at a single frame
rate, the model is called single-rate. When the model contains blocks with
differing frame rates, or at least one multirate block, the model is called
multirate. Note that Simulink prevents a single-rate model from running in
multitasking mode by generating an error.
Block Sample Mode. Many blocks can operate in either sample-based or
frame-based modes. In source blocks, the mode is usually determined by the
Samples per frame parameter; a value of 1 for this parameter indicates
sample-based mode, while a value greater than
1 indicates frame-based mode.
In nonsource blocks, the sample mode is determined by the input signal. See
Chapter 5, “DSP Block Reference,” for additional information on particular
blocks.
Predicting Tasking Latency
The specific amount of tasking latency created by a particular combination of
block parameter and simulation settings is described in the “Latency” section
of the reference page for the block in question. The following examples show
how to use Chapter 5, “DSP Block Reference,” to predict tasking latency:
•“Example: Nonzero Tasking Latency” on page 3-93
•“Example: Zero Tasking Latency” on page 3-95