Sample Times in Subsystems
Subsystems fall into two categories: triggered and non-triggered. For triggered
subsystems, in general, the subsystem gets its sample time from the triggering signal.
One exception occurs when you use a Trigger block to create a triggered subsystem. If you set the block
Trigger type to function-call
and the Sample time type to
becomes active. In this case, you specify the sample time of the
Trigger block, which in turn, establishes the sample time of the
There are four non-triggered subsystems:
Simulink® calculates the sample times of virtual and enabled subsystems based on the respective sample times of their contents.
The atomic subsystem is a special case in that the subsystem block has a
SystemSampleTime parameter. Moreover, for a sample time other
than the default value of –1, the blocks inside the atomic subsystem can have only a
Inf, –1, or the identical (discrete) value of the subsystem
SampleTime parameter. If the atomic subsystem is left as
inherited, Simulink calculates the block sample time in the same manner as the virtual and
enabled subsystems. However, the main purpose of the subsystem
SampleTime parameter is to allow for the simultaneous
specification of a large number of blocks, within an atomic subsystem, that are all set
to inherited. To obtain the sample time set on an atomic subsystem, use this command at
the command prompt:
Finally, the sample time of the action subsystem is set by the If block or the Switch Case block.
For non-triggered subsystems where blocks have different sample rates, Simulink returns the Compiled Sample Time for the subsystem as a cell array of all
the sample rates present in the subsystem. To see this, use the
get_param command at MATLAB prompt.