Frame-Based Signals
About Frame-Based Signals
This section explains how to create an S-function that accepts
and/or produces frame-based signals. See Frame-Based Signals in
the Working with Signals section
of the Signal Processing Blockset documentation for a comprehensive
discussion of the use of frame-based signals in Simulink models.
Note
Simulating a model containing an S-function that accepts or
produces frames requires a Signal Processing Blockset product license. |
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Using Frame-Based Signals in C S-Functions
To accept or produce frame-based signals, a C MEX S-function
must perform the following tasks:
The S-function's mdlInitializeSizes callback
method must set the port frame status to FRAME_YES, FRAME_NO,
or FRAME_INHERITED for each of the S-function's
I/O ports, using the ssSetInputPortFrameData and ssSetOutputPortFrameData functions.
The frame status for a port must be set after the call to ssSetNumInputPorts and ssSetNumOutputPorts.
For example, the following code in mdlInitializeSizes specifies
that the first input port accepts a frame-based signal while the first
output port emits a sample-based signal:
ssSetNumInputPorts(S, 1);
ssSetInputPortFrameData(S, 0, FRAME_YES);
ssSetNumOutputPorts(S,1);
ssSetOutputPortFrameData(S, 0, FRAME_NO);
The S-function should specify the dimensions of the
signals that its frame-based ports accept or produce in its mdlInitializeSizes or mdlSetInputPortDimensionInfo and mdlSetOutputPortDimensionInfo callback
methods. Note that frame-based signals must be dimensioned as 2-D
arrays. For example, the following code in mdlInitializeSizes specifies
that the first frame-based input port is dynamically sized. This S-function
must then also have an mdlSetInputPortDimensionInfo callback
that sets the specific dimensions of this input port.
ssSetNumInputPorts(S, 1);
ssSetInputPortFrameData(S, 0, FRAME_YES);
ssSetInputPortMatrixDimensions(S, 0, DYNAMICALLY_SIZED, DYNAMICALLY_SIZED);
If the frame status of any of the S-function's input
ports is inherited, the S-function should define a mdlSetInputPortFrameData callback method.
The Simulink engine passes the frame status that it assigns to
the port, based on frame signal propagation rules, as an argument
to this callback method. The callback method should in turn use the ssSetInputPortFrameData function
to set the port to the assigned status if it is acceptable or signal
an error using ssSetErrorStatus if
it is not. If the frame status of other ports of the S-function depend
on the status inherited by one of its input ports, the callback method
can also use ssSetInputPortFrameData to set the
frame status of the other ports based on the status that the input
port inherits. A template for the mdlSetInputPortFrameData callback
is shown below.
#if defined(MATLAB_MEX_FILE)
#define MDL_SET_INPUT_PORT_FRAME_DATA
static void mdlSetInputPortFrameData(SimStruct *S,
int_T portIndex,
Frame_T frameData)
{
if(!frameData==FRAME_YES) {
ssSetErrorStatus(S, "Incorrect frame status");
return;
}
ssSetInputPortFrameData(S, portIndex, frameData); /* Sets frame status */
} /* end mdlSetInputPortFrameData */
#endifThe S-function's mdlOutputs method
should include code to process the signals. The macro ssGetInputPortDimensions can
be used in mdlOutputs to determine the dimensions
of dynamically sized frame-based inputs, as follows:
int *dims = ssGetInputPortDimensions(S, 0);
int frameSize = dims[0];
int numChannels = dims[1];
See the frame-based A/D converter S-function example (sfun_frmad.c) for
an example of how to create a frame-based S-function. This S-function
is one of several S-functions that manipulate frame-based signals
found in the Simulink model sfcndemo_frame.mdl.
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Using Frame-Based Signals in Level-2 M-File S-Functions
In a Level-2 M-file S-function, set the SamplingMode property
of the port to indicate if the block accepts frame-based signals,
for example:
block.InputPort(1).SamplingMode = 'Inherited';
If any of the ports inherited their sampling mode,
define a SetInputPortSamplingMode callback method
to specify the sampling mode.
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