MATLAB: Do I get a data-dependency violation when using triggered subsystems inside the model in Simulink 7.2 (R2008b)

buschart;datadependencyeventfunction callloopnon-virtualsimulinkstateflowviolationvirtual

I have a Stateflow chart and a function-call subsystem in a loop inside my model (see attached model test_02.mdl). I understand that this may cause data-dependency violation as shown in documentation examples such as sl_subsys_fcncallerr4.mdl. However in my model, I am only using bus creator and bus-selector blocks in the loop. I would like to know why I get a data-dependency violation when simulating this model.

Please load the attached mat file, structForSim.mat and simulate the model.

Best Answer

The issue with this model is that the Bus Creator block is trying to combine a non-virtual bus and the function-call signal into a single bus. To accomplish this bus hierarchy, the bus-creator has to convert the non-virtual bus to a virtual bus by inserting a hidden Signal Conversion block. This operation causes Simulink to fail to resolve the data dependency in the loop, an issue similar to the one observed with the model sl_subsys_fcncallerr4.mdl.

The workaround for model test2.mdl is implemented in attached model test4.mdl and consists in avoiding signal operations between the Stateflow Chart and the Triggered Subsystem. This means the two following modifications:

1. Keep the non-virtual bus and the function-call event as separate lines in the model. These signals are not meant to be combined.

2. Place the Bus Selector block inside the Triggered subsystem, for the reasons explained in demo model sl_subsys_fcncallerr4.mdl.

Related Solutions

MATLAB: What is the difference between the Mux (Demux) and Bus Creator (Bus Selector) blocks in Simulink

This enhancement has been incorporated in Release 2008b (R2008b). For previous product releases, read below for any possible workarounds:

The main difference between mux signals and bus signals is that the components of a bus signal can include more than one data type and can be hierarchical, while the components of a mux signal must all have the same data type and cannot be hierarchical. The documentation of Composite Signals explains this distinction:

 <http://www.mathworks.com/help/releases/R2012b/simulink/composite-signals.html>

Buses can provide consistency checking with the use of a Bus Object, but muxes cannot. Please refer the following for more information:

 <http://www.mathworks.com/help/releases/R2012b/simulink/ug/using-bus-objects.html>

Buses can be realized as structures in generated code, but muxes cannot. See:

 <http://www.mathworks.com/help/releases/R2012b/simulink/slref/buscreator.html>

MathWorks strongly discourages mixing muxes and buses. For example, do not use Mux blocks as Bus Creators. See:

 <http://www.mathworks.com/help/releases/R2013a/simulink/ug/avoiding-mux-bus-mixtures.html>

The Demux block has a Bus Selector mode. For information about when to use this mode, see:

 <http://www.mathworks.com/help/releases/R2012b/simulink/slref/demux.html>

Using a Bus Selector block, you can change the order of signals. This cannot be done with a Demux block. An example is attached to this solution (bus_mux_vec.mdl). In bus_mux_vec.mdl model, the order of the two input signals going through the Bus Creator and the Bus Selector blocks has been changed. After running the model, you will see [1 2 3 4] in Scope1, not [5 6 7 8]. However, the order of the two input signals going through the Mux and Demux blocks cannot be changed, so you will always see [5 6 7 8] in Scope1. For more information on how to change the order of signals using a Bus Selector block, see:

 <http://www.mathworks.com/help/releases/R2012b/simulink/slref/busselector.html>

Although the Demux block cannot rearrange the order of muxed signals, the Signal Selector block can. See:

 <http://www.mathworks.com/help/releases/R2012b/simulink/slref/selector.html>

Bus signals that are hierarchical or include components of different data types can drive only Bus Capable blocks. See:

 <http://www.mathworks.com/help/releases/R2012b/simulink/ug/bus-capable-blocks.html>

This limitation does not apply to a mux signal as long as the Mux block inputs are vectors or vector-like. A vector-like signal is any signal that is a scalar (one-element vector), a vector, or a single-column or single-row matrix. For example, a muxed signal can drive a Gain block, while a bus cannot. See:

 <http://www.mathworks.com/help/releases/R2012b/simulink/slref/mux.html>

For a list of Simulink virtual and conditionally virtual buses, see:

 <http://www.mathworks.com/help/releases/R2012b/simulink/ug/virtual-and-nonvirtual-buses.html>

The Bus Selector block supports matrix inputs. The Demux block does not support matrix inputs unless you double click on the Demux block and check "Bus selection mode". Run the attached model, bus_mux_matrix.mdl. It should work correctly. However, if you double click on the Demux block, uncheck "Bus selection mode" and run the model, it will generate an error.

The Bus Selector block has an option labeled 'muxed output'. This option is mislabeled: the output is a Bus and should be treated as such. Refer to the Related Solution for more information on this feature.

MATLAB: Am I receiving errors when I change one of the virtual buses into a nonvirtual bus using Simulink

This enhancement has been incorporated in Release 14 Service Pack 3 (R14SP3). For previous product releases, read below for any possible workarounds:

When converting to a nonvirtual bus, all buses feeding the bus creator must have bus objects defined for them. Also if the bus you want to convert then feeds a bus creator block, that block must also output a nonvirtual bus. It is not possible to have nested buses of mixed type, virtual or nonvirtual.

Once all buses are converted appropriately, a valid update diagram will occur.

One can follow these steps in the conversion process:

1. Update the model containing the virtual buses

2. Identify bus (BUS_X) that will become non-virtual

3. Generate bus objects for that bus and all bus creators up stream from that Bus Creator

4. Populate bus objects for all bus creators upstream and the bus creator associated with BUS_X

5. Set Bus Creator associated with BUS_X to ‘output as nonvirtual’

6. Identify all Bus Creator blocks that BUS_X feeds

7. Identify all Buses to that Bus creator

8. Make sure all Buses are nonvirtual (make bus objects and set to nonvirtual for each)

9. Make the output of that Bus Creator nonvirtual (by creating bus objects)

10. Recursively do step 5 until no more Bus Creators are found, leaving behind only Bus Selectors.

11. Update diagram once again to make sure that the conversion has been successful.

Best Answer

Related Solutions

MATLAB: What is the difference between the Mux (Demux) and Bus Creator (Bus Selector) blocks in Simulink

MATLAB: Am I receiving errors when I change one of the virtual buses into a nonvirtual bus using Simulink

Related Question