MATLAB: Using printf/scanf in External Mode Simulation

Embedded Coder

I am generating an executable from my model for External Mode simulation that I will run on a target machine and connect to from my host computer. The executable has "printf" and "scanf" statements included in it to monitor its error status and provide yes/no inputs, for example:

1) “X is doing Y”

2) “Do you accept [y/N]:"

The documentation states that "printf" and "scanf" statements are supported for External Mode simulation:

https://www.mathworks.com/help/releases/R2018b/ecoder/ug/_bp6h8fr-1.html#bvmievw

"External mode simulations support the use of printf calls to display error and information messages from the target program."

However, these messages are displayed in the console on the target. Right now, we have to SSH to the console on the target to interact with the "printf" and "scanf" statements. Is there a way for the input/output of these statements to show up in Simulink on the host computer?

Best Answer

There is unfortunately not a way to interact with printf/scanf statements directly from Simulink. These functions are supported in the generated code, but they only provide interaction through the console where the executable is running.

You can still interact with the External mode execution directly from Simulink using tunable parameters, dashboard blocks, and instrumentation blocks (e.g. displays, scopes, to workspace, etc.). See the supported features here:

https://www.mathworks.com/help/rtw/ug/set-up-and-use-hosttarget-communication-channel.html

How you choose to use these blocks depends on your use case. For your application, it sounds like a viable approach would be to have a "status" output from the S-function blocks, which might be a code that corresponds to "X is doing Y". You may also consider using a Manual Switch block for "y/n" inputs.

A different approach you may consider is printing output to a file instead of printing to the console. However, this may not satisfy your use case if you want to deploy to a separate target (i.e. not running the executable on the host).

As a final workaround you may connect to the console running the executable via SSH, as mentioned.

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MATLAB: How to run the Real-Time Windows Target simulation from the command line or a MATLAB file

You can use the SET_PARAM function to connect and simulate your target model from the MATLAB command line or a MATLAB file. See the following example for the steps necessary to simulate your model:

1. First, you need to change the simulation mode of a model from 'normal' to 'external'. You can do this with the following command:

set_param('model_name','SimulationMode','external')

2. Second, you need to connect to the target. You can do this with the following command:

set_param('model_name','SimulationCommand','connect');

3. Now, you need to run the code:

set_param('model_name','SimulationCommand','start');

4. To stop the real time code:

set_param('model_name','SimulationCommand','stop');

5. And finally, to disconnect from the target:

set_param('model_name','SimulationCommand','disconnect');

For more information on simulating from the command line, please refer to the Simulink User's Guide.

MATLAB: How to use “mexPrintf” for simulation and “printf” for code generation in a MATLAB Function Block using coder.ceval

You can use the "MATLAB_MEX_FILE" C preprocessor macro in your custom C code to determine whether you are compiling for a MEX target. For example, you can use this macro to define a custom "printOutput" function:

#include <stdio.h>
#include <stdlib.h>
#ifdef MATLAB_MEX_FILE
#include "mex.h"
#endif
void printOutput(const char* str);
#ifdef MATLAB_MEX_FILE
// Use the mexPrintf function
void printOutput(const char* str) {
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}
#else
// Use the standard C printf function
void printOutput(const char* str) {
    printf(str);
}
#endif

This function is defined to call "mexPrintf" when compiled for a MEX and "printf" otherwise.

Best Answer

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