System Concepts
Simulink External Mode
External mode requires a communications interface to pass external
parameters. On the receiving end, the same communications protocol
must be used to accept new parameter values and insert them in the
proper memory locations for use by the real-time application. In some Real-Time Workshop targets
such as Tornado/VME targets, the communications interface uses TCP/IP
protocol. In the case of a Real-Time Windows Target application,
the host computer also serves as the target computer. Therefore, only
a virtual device driver is needed to exchange parameters between the MATLAB environment, Simulink memory
space, and memory that is accessible by the real-time application.
Signal acquisition — You can capture and display signals
from your real-time application while it is running. Signal data is
retrieved from the real-time application and displayed in the same Simulink Scope
blocks you used for simulating your model.
Parameter tuning — You can change parameters in your Simulink block
diagram and have the new parameters passed automatically to the real-time
application. Simulink external mode changes parameters in your
real-time application while it is running in real time.
Note that if you open a source block to change parameters, the
simulation will pause while the block dialog box is open. You must
close the dialog by clicking OK, which will
resume the simulation.
As a user of Real-Time Windows Target rapid prototyping software,
you will find that the requirements for setup are minimal. You start
by enabling external mode. You then choose the Real-Time Workshop
system target file from the Configuration Parameters dialog Real-Time
Workshop tab. The MEX-file interface is automatically selected
when you choose the target file. Then, after you have built the real-time
application, you are ready for external mode operation.
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Data Buffers and Transferring Data
At each sample interval of the real-time application, Simulink software
stores contiguous data points in memory until a data buffer is filled.
Once the data buffer is filled, Simulink software suspends data
capture while the data is transferred back to the MATLAB environment
through Simulink external mode. Your real-time application, however,
continues to run. Transfer of data is less critical than maintaining
deterministic real-time updates at the selected sample interval. Therefore,
data transfer runs at a lower priority in the remaining CPU time after
model computations are performed while waiting for another interrupt
to trigger the next model update.
Data captured within one buffer is contiguous. When a buffer
of data has been transferred, it is immediately plotted in a Simulink Scope
block, or it can be saved directly to a MAT-file using the data archiving
feature of the Simulink external mode.
With data archiving, each buffer of data can be saved to its
own MAT-file. The MAT-file names can be automatically incremented,
allowing you to capture and automatically store many data buffers.
Although points within a buffer are contiguous, the time required
to transfer data back to the Simulink software forces an intermission
for data collection until the entire buffer has been transferred and
may result in lost sample points between data buffers.
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