Can a bus be an IN/OUT variable with partial assignment in the resultant generated code

How do you make the Simulink generated C Code update a single item from a bus without re-assigning the whole bus?

I have a model which takes in a bus with many elements and updates a single entry in the bus which is then output. The output is routed to the next model block for additional computations.

I am trying to compile this atomic model into a stand-alone ERT library. I setup the input and output parameters to be pass-by-reference but can't find anything that would let the generator treat the input and output variables as one.

When the generated *_step function ends, it assigns all of the output entries to the input values which is essentially:

(*pParam) = (*pParam);

I am trying to get Matlab to write-back the computed value into the input bus for it to be sent on its merry way.

Answer 1

[John]

The model has to be setup in 3 places in order to ensure that a bus structure is treated as a pass-through element.

1. Ensure that the inport is set to NOT "Output as nonvirtual bus"
2. Manually configure model interface per Combining I/O Arguments to have the outport to be combined with the inport as pointer arguments.
3. Add a signal conversion block from virtual to nonvirtual before the bus assignment block.

This will create efficient C code where the C structure is passed in as a pointer and then modified without making any extra copies of the input bus structure.

[amit shelke]

Hello John

The link you have given in above answer is not working (Combining I/O Arguments) Can you provide the updated link

Answer 2

[John]

Instead of using a bus input, if I use a named data store and data store read/write blocks, the generated code will take in the data store reference as part of the model parameters (as a pointer) and only update the specific entries listed in the data store write block.

While this is good for the C code that is generated, this makes the block design at the next level up completely obfuscated where the referenced model has no inputs or outputs.