How to use MATLAB to control an endless python script on Raspberry Pi using a TCP connection?

I have a Raspberry Pi model 2 B running Raspbian 11 (bullseye) on which my python script is regulating the voltage of a power supply, therefore running in a while loop for as long as the experiments last. I want to initialize this "instrument" from a MATLAB script and be able to send messages to the Raspberry Pi throughout the experiment. So far, I have the MATLAB Support Package for Raspberry Pi Hardware and the Instrument Control Toolbox installed. I use

r = raspi('ip_RPi','username','password');

to connect to the Pi, and then I start a tcp server with

t = tcpserver('ip_Computer',4000);

The python script connects to the server using socket.socket(). Now, I want to start the script on the Raspberry Pi using the 'system' function:

system(r,['export DISPLAY=:0' ' ; ' '~/.venv/Controller/bin/python3 ~/Controller/main.py &']);

The Raspberry Pi has a display and main.py starts a gui, therefore I export 'DISPLAY=:0' to show the gui on the Raspberry Pi screen. When ssh'ing into the Pi and running the script from terminal everything works.

The issue I'm having is that the '&' symbol in the system-call does not result in the MATLAB script to continue, instead it is busy until the script is no longer running. But since the script is not supposed to stop, I never reach the part of my MATLAB script where I read and write to the client using functions like:

function setT(tcp,T)

L = strcat('t ',string(T));

write(tcp,L);

end

I have looked into the batch function from the Parallel Computing Toolbox in order to run something like:

j = batch('init2',0,{r,['export DISPLAY=:0' ' ; ' '~/.venv/Controller/bin/python3 ~/Controller/main.py &']});

with the init2.m script:

function init2(r,command)

system(r,command);

end

I get this error message, however:

> j

j =

Job

Properties:

ID: 31

Type: independent

Username: leouh

State: finished

SubmitDateTime: 25-Apr-2022 13:50:25

StartDateTime: 25-Apr-2022 13:50:38

Running Duration: 0 days 0h 0m 4s

NumThreads: 1

AutoAttachFiles: true

Auto Attached Files: List files

AttachedFiles: {}

AutoAddClientPath: true

AdditionalPaths: 27 paths

Associated Tasks:

Number Pending: 0

Number Running: 0

Number Finished: 1

Task ID of Errors: [1]

Task ID of Warnings: [1]

Task with properties:

ID: 1

State: finished

Function: @parallel.internal.cluster.executeFunction

Parent: Job 31

StartDateTime: 25-Apr-2022 13:50:38

Running Duration: 0 days 0h 0m 3s

Error: Undefined function 'execute' for input arguments of type 'double'.

Error Stack: init2 (line 3)

Warnings: List warnings

>> diary(j)

--- Start Diary ---

Warning: The following error was caught while executing 'onCleanup' class destructor:

Undefined function 'dataIntegrate' for input arguments of type 'string'.

Error in raspi.internal.DataUtilityHelper/dataIntegrateAll

Error in raspi>@()dataIntegrateAll(obj,obj.RaspiImpl.DataUtility,true) (line 1220)

c = onCleanup(@() dataIntegrateAll(obj, obj.RaspiImpl.DataUtility, true));

Error in onCleanup/delete (line 80)

obj.task();

Error in raspi/processInternal (line 1218)

try

Error in raspi/system (line 193)

output = processInternal(obj, false, false, varargin{:});

Error in init2 (line 3)

system(r,command);

Error in parallel.internal.cluster.executeFunction (line 31)

feval(fcn, fcnArgsIn{:});

Error in parallel.internal.evaluator.evaluateWithNoErrors (line 16)

feval(fcn, args{:});

Error in parallel.internal.evaluator.CJSStreamingEvaluator/evaluate (line 41)

[out, errOut] = parallel.internal.evaluator.evaluateWithNoErrors( fcn, nOut, args );

Error in dctEvaluateTask>iEvaluateTask/nEvaluateTask (line 377)

[output, errOutput, cellTextOutput{end+1}] = evaluator.evaluate(fcn, nOut, args);

Error in dctEvaluateTask>iEvaluateTask (line 175)

nEvaluateTask();

Error in dctEvaluateTask (line 81)

[resultsFcn, taskPostFcn, taskEvaluatedOK, isAsyncTask] = iEvaluateTask(job, task, runprop);

Error in distcomp_evaluate_filetask_core>iDoTask (line 154)

dctEvaluateTask(postFcns, finishFcn);

Error in distcomp_evaluate_filetask_core (line 52)

iDoTask(handlers, postFcns);

> In raspi/processInternal (line 1218)

In raspi/system (line 193)

In init2 (line 3)

In parallel.internal.cluster.executeFunction (line 31)

In parallel.internal.evaluator.evaluateWithNoErrors (line 16)

In parallel.internal.evaluator/CJSStreamingEvaluator/evaluate (line 41)

In dctEvaluateTask>iEvaluateTask/nEvaluateTask (line 377)

In dctEvaluateTask>iEvaluateTask (line 175)

In dctEvaluateTask (line 81)

In distcomp_evaluate_filetask_core>iDoTask (line 154)

In distcomp_evaluate_filetask_core (line 52)

--- End Diary ---

>>

I have tried to print the module 'r' in the init2.m script:

function init2(r,command)

r

system(r,command);

end

And I get the following output:

>> diary(j)

--- Start Diary ---

r =

raspi with properties:

DeviceAddress: ''

Port:

BoardName: ''

AvailableLEDs: {}

AvailableDigitalPins: []

AvailableSPIChannels: {}

AvailableI2CBuses: {}

AvailableWebcams: {}

I2CBusSpeed:

Supported peripherals

along with the same error message as before. It seems to me that the raspi module is not properly passed to the function. The function correctly runs if I just do

init2(r,['export DISPLAY=:0' ' ; ' '~/.venv/Controller/bin/python3 ~/Controller/main.py &'])

but then I still have the issue that MATLAB is busy until main.py is no longer running.

Do you have any suggestions on what I can do to make either the system() with '&' or the batch() work? Or other possible solutions to the issue that MATLAB is busy until the python script has finished?

Thank you in advance!

[Leo Uhre Jakobsen]

Here is the main.py script:

% python packages
import threading

% our scripts
import ui
import loop
import globals

globals.initialize_variables()

% create threads
ui_thread = ui.ui()
main_loop_thread = loop.loop()

% start threads
ui_thread.start()
main_loop_thread.start()

exit()

I have used % instead of # here for the syntax to be correct with the code input syntax

[Alvaro]

Based on Walter's answer, your use of & should allow your call to return while the processing continues on your Raspberry Pi.

https://www.mathworks.com/matlabcentral/answers/342602-how-do-i-get-system-command-to-not-wait-for-raspberry-pi-to-reply#answer_269127

Have you tried printing a message or doing some other check on your Raspberry Pi while executing that script in the background?

Alternatively, the asker in that question does not use the & when calling batch. This should send the calling process to a MATLAB worker in the background of your client but not your Pi.