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Parameter Tuning and Monitoring
You can change program parameters from the host and monitor data with Scope blocks while the program executes using Simulink external mode. You can also monitor program outputs using the StethoScope data analysis tool.
Using Simulink external mode or StethoScope allows you to change model parameters in your program, and to analyze the results of these changes, in real time.
External Mode
Simulink external mode provides a mechanism to download new parameter values to the executing program and to monitor signals in your model. In this mode, the external link MEX-file sends a vector of new parameter values to the real-time program via the network connection. These new parameter values are sent to the program whenever you make a parameter change without requiring a new code generation or build iteration.
You can use the BlockIOSignals code generation option to monitor signals in VxWorks. See Interfacing Parameters and Signals for further information and example code.
The real-time program (executing on the VxWorks target) runs a low priority task that communicates with the external link MEX-file and accepts the new parameters as they are passed into the program.
Communication between Simulink and the real-time program is accomplished using the sockets network API. This implementation requires an Ethernet network that supports TCP/IP. See External Mode for more information on external mode.
Changes to the block diagram structure (for example, adding or removing blocks) require generation of model and execution of the build process.
Configuring VxWorks to Use Sockets
If you want to use Simulink external mode with your VxWorks program, you must configure your VxWorks kernel to support sockets by including the INCLUDE_NET_INIT, INCLUDE_NET_SHOW, and INCLUDE_NETWORK options in your VxWorks image. For more information on configuring your kernel, see the VxWorks Programmer's Guide.
Before using external mode, you must ensure that VxWorks can properly respond to your host over the network. You can test this by using the host command
Configuring Simulink to Use Sockets
Simulink external mode uses a MEX-file to communicate with the VxWorks system. The MEX-file is
where * is a host-dependent MEX-file extension. See External Mode for more information.
To use external mode with VxWorks, specify ext_comm as the MEX-file for external interface in the External Target Interface dialog box (accessed from the External Mode Control Panel). In the MEX-file arguments field you must specify the name of the VxWorks target system and, optionally, the verbosity and TCP port number. Verbosity can be 0 (the default) or 1 if extra information is desired. The TCP port number ranges from 256 to 65535 (the default is 17725). If there is a conflict with other software using TCP port 17725, you can change the port that you use by editing the third argument of the MEX-file for external interface on the External Target Interface dialog box. The format for the MEX-file arguments field is
For example, this picture shows the External Target Interface dialog box configured for a target system called halebopp with default verbosity and the port assigned to 18000.
StethoScope
With StethoScope, you can access the output of any block in the model (in the real-time program) and display this data on a host. Signals are installed in StethoScope by the real-time program using the BlockIOSignals data structure (See Interfacing Parameters and Signals for information on BlockIOSignals), or interactively from the WindSh while the real-time program is running. To use StethoScope interactively, see the StethoScope User's Manual.
To use StethoScope you must specify certain options with the build command. See Code Generation Options for information on these options.
Run-Time Structure
The real-time program executes on the VxWorks target while Simulink and StethoScope execute on the same or different host workstations. Simulink and StethoScope require tasks on the VxWorks target to handle communication.
This diagram illustrates the structure of a VxWorks application using Simulink external mode and StethoScope.
Figure 12-2: The Run-Time Structure
The program creates VxWorks tasks to run on the real-time system: one communicates with Simulink, the others execute the model. StethoScope creates its own tasks to collect data.
Host Processes
There are two processes running on the host side that communicate with the real-time program:
VxWorks Tasks
You can run the real-time program in either singletasking or multitasking mode. The code for both modes is located in
Real-Time Workshop compiles and links rt_main.c with the model code during the build process.
Singletasking. By default, the model is run as one task, tSingleRate. This may actually provide the best performance (highest base sample rate) depending on the model.
The tSingleRate task runs at the base rate of the model and executes all necessary code for the slower sample rates. Execution of the tSingleRate task is normally blocked by a call to the VxWorks semTake routine. When a clock interrupt occurs, the interrupt service routine calls the semGive routine, which causes the semTake call to return. Once enabled, the tSingleRate task executes the model code for one time step. The loop then waits at the top by again calling semTake. For more information about the semTake and semGive routines, refer to the VxWorks Reference Manual. By default, it runs at a relatively high priority (30), which allows it to execute without interruption from background system activity.
Multitasking. Optionally, the model can run as multiple tasks, one for each sample rate in the model:
tBaseRate -- This task executes the components of the model code run at the base (highest) sample rate. By default, it runs at a relatively high priority (30), which allows it to execute without interruption from background system activity.
tRaten -- The program also spawns a separate task for each additional sample rate in the system. These additional tasks are named tRate1, tRate2, ..., tRaten, where n is slowest sample rate in the system. The priority of each additional task is one lower than its predecessor (tRate1 has a lower priority than tBaseRate).
Supporting Tasks.. If you select external mode and/or StethoScope during the build process, these tasks will also be created:
t Extern -- This task implements the server side of a socket stream connection that accepts data transferred from Simulink to the real-time program. In this implementation, tExtern waits for a message to arrive from Simulink. When a message arrives, tExtern retrieves it and modifies the specified parameters accordingly.
tExtern runs at a lower priority than tRaten, the lowest priority model task. The source code for tExtern is located in matlabroot/rtw/c/src/ext_svr.c.
tScopeDaemon and tScopeLink -- StethoScope provides its own VxWorks tasks to enable real-time data collection and display. In singletasking mode, tSingleRate collects signals; in multitasking mode, tBaseRate collects them. Both perform the collection on every base time step. The StethoScope tasks then send the data to the host for display when there is idle time, that is, when the model is waiting for the next time step to occur. rt_main.c starts these tasks if they are not already running.
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