How Can I pass an open serialport-handle to a parallel worker?

Hello everyone,

I'm still figuring out parallel workers and am obviously not very good at them.

Background:

I'm talking to a TI Microcontroller which controlls a stepper motor + rotary encoder via a Serialport. This works as script AND in an app aswell. As long as this remains single-threaded everything works fine.

Goal:

I would like to be able to send the configuration commands via the "main script" or "app" BUT I also want to be able to read a pre-set amount of bytes over the same serial port in parallel. While this measurement takes place, no other commands need to be sent by matlab.

Problem:

I can't get it to work. Either no Data is returned at all or I'm getting errors, that serialport-specific functions are undefined

Tried:

1. parfor-loop | no results returned
2. https://de.mathworks.com/matlabcentral/answers/372772-how-can-i-pass-a-tcpip-handle-to-a-parfeval-worker | undefined function 'read'

Current Test-Script:

clear all
close all
clc
% Start Parallel Pool
parpool(2);

% Open and configure Serialport at COM5
SERIAL = serialport("COM5",115200,"Timeout",1);
configureTerminator(SERIAL,0); 

% Create a parpool-Constant with the Serialport-Handle
cSERIAL = parallel.pool.Constant(SERIAL);

% Measure P,V,D in parallel worker
job = parfeval(gcp(),@STEPPER_DEST,3,cSERIAL, 10);
fetchOutputs(job);

delete(gcp('nocreate'));

With the external function being:

function [Position, Geschwindigkeit, Richtung] = STEPPER_DEST(s,Zeit_s)
% Convert time s to ms
Zeit_ms = Zeit_s *1000;

% Create Measuring Vectors
Position        = zeros(1, Zeit_ms); 
Geschwindigkeit = zeros(1, Zeit_ms); 
Richtung        = zeros(1, Zeit_ms);

for i=1:Zeit_ms
    Position(1,i)           = double(read(s,1,"int32")) * 0.18;
    Geschwindigkeit(1,i)    = double(read(s,1,"uint32"))* 18;
    Richtung(1,i)           = read(s,1,"int8");
end

end

Answer 1

[Thomas Falch]

You need to use the function handle version of parallel.pool.Constant (which is what https://www.mathworks.com/matlabcentral/answers/372772-how-can-i-pass-a-tcpip-handle-to-a-parfeval-worker does).

Instead of opening the serial port on the client, and then sending it with the Constant to the worker (which will not work), the function handle version sends a function handle to the worker, which will run on the worker, and open the serial port on the worker.

In other words, something like:

function s = openSerialPort()

s = serialport("COM5",115200, "Timeout", 1);

configureTerminator(s, 0);

end

cSerial = parallel.pool.Constant(@openSerialPort)

% Rest of the code unchanged