Insert char into array in embedded function

Hello, I am trying to send array of data to arduino through Serial Send, however due to not knowing how large records will be ( each can range from 80 to 1000) I want to separate each data with coma in order to read them in arduino ( so I can go byte by byte and whenever there is a coma I will know that that record ends) . I tried inserting them in embedded function and casting result into uint8 but I am getting error about unknown output sizes. Is there any way to do it (or maybe better way to read array od data in arduino)?

function y = fcn(a,b,c,d,e)

q=[a,',',b,',',c,',',d,',',e,'|'];

y = typecast(q,uint8);

Thanks, Tom

[Walter Roberson]

As this is an embedded function, then your a b c d e must all be numeric. Are you sure you want to do the equivalent of char() of each of them as you build q? Or do you want to format them?

If I recall correctly, support for sprintf() was not added to Coder until R2018a; as far as I could tell in previous versions the work-around was to use coder.ceval() to invoke sprintf()

[Tom]

a,b,c,d,e all will be numeric values, all I just want to do is separate them by commas in data stream. I attached screen how I would like it to be. Honestly it doesn't need to be commas, any character other than digit that is readable by arduino will do.

EDIT: Now that I think about it, is it possible to run simulation, export data to workspace and run script with them in the same time? At the end I will have the simulation of some circuit in simulink and need to somehow send measurements from it to arduino.

Answer 1

[Walter Roberson]

You would need to use coder.varsize() to declare the output string probably, and you would sprintf into it. If you are using before r2018a you might need to coder.ceval() to use sprintf.

You cannot just use char() on your values because you need to emit the printable equivalent of your values like '400' not char(400)

[Tom]

Thank you, just one more question, do you think there is an easier way to send multiple data through serial communication to arduino? I am not that really experienced in matlab and all inserting functions in C seems quite complicated.

[Walter Roberson]

If you knew the maximum and minimum range for the values and knew how many decimal points you wanted then you could do conversion to a fixed number of characters using arithmetic operations, emitting uint8 that could be sent to the serial port. With the width being fixed, a delimiter would not be needed.

But personally for more than one or two digits then I would find that to be more of a nuisance than invoking sprintf().

Simulink just isn't designed to work with characters, and because of that is sadly lacking on options for formatting characters to send to I/O ports.

[Tom]

Well, too bad. Thank you very much.

[Tom]

Well, here I am again, when trying to use coder.ceval code generator is returning error:

Cannot assign 'o' from 'coder.ceval' because the type and size of 'o' are not known. To fix, preinitialize 'o'.

My code:

function o = tostring(a,b,c,d,e) %#codegen

coder.varsize('o');

o = coder.ceval('sprintf','%.2f,%.2f,%.2f,%.2f,%.2f.',a,b,c,d,e);

I don't really understand, isn't the point of varsize is to declare that size varies?

[Walter Roberson]

You still need to define the type of 'o'

https://www.mathworks.com/help/fixedpoint/ug/defining-variable-size-data-for-code-generation.html