Function 'webread' not supported for code generation Matlab - ThingSpeak - Raspberry Pi

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Vinicio Moya 2021-6-25

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https://ww2.mathworks.cn/matlabcentral/answers/865605-function-webread-not-supported-for-code-generation-matlab-thingspeak-raspberry-pi

评论： Vinicio Moya 2021-6-29

Hello everybody!

I need to use a Raspberry Pi that get data from a ThingSpeak channel in a standalone configuration, but the problem is that functions ThingSpeakRead and webread are not supported. What can I do?

 direccion=['https://api.thingspeak.com/channels/' chId '/feeds.json?api_key=' Read '&results=' cPoints];
 datos=webread(direccion);
Function 'webread' not supported for code generation

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Answer 1

Vinicio Moya 2021-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/865605-function-webread-not-supported-for-code-generation-matlab-thingspeak-raspberry-pi#answer_736283

在 MATLAB Online 中打开

Finally the solution adopted was: https://www.mathworks.com/matlabcentral/answers/467879-how-do-i-write-to-a-thingspeak-channel-from-a-raspberry-pi-via-code-deployed-using-the-matlab-coder.

 commandStr =  [ 'sudo curl  -s "https://api.thingspeak.com/update.json?api_key=' sprintf('%s', Write) '&field1=' sprintf( '%f', dato1 ) ' &field2=' sprintf( '%f', dato2) ' &field3=' sprintf( '%f', dato3) ' &field4=' sprintf( '%f', dato4) ' " ' ];
 response = system(mypi, commandStr);

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Answer 2

Denis Gurchenkov 2021-6-29

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Yes, you are right, webread() does not support code generation. As a workaround, you can use coder.ceval functon to call a hand-written C function that opens the connection, reads and decodes the data, and returns the data back to MATLAB code. It is a bit complicated : you would need to maintain two branches in your MATLAB code, one for normal MATLAB execution, the other one for Raspberry Pi, and use coder.target to switch between those.

In order to impelment the C fucntion that does the http read, you can use one of the opensource free HTTP libraries that are available (libcurl is availalbe on raspberry pi?). An alternative is to just invoke curl using system() command. Would this approach work for you?