'Linux serial port listener and interpreter?

I'm using a serial device for a project, and what I'm trying to accomplish PC side, is listening for a command sent by the serial device, interpreting the query, running some code depending on the query, and transmitting back the result.

To be honest I tried out using PHP as the listener, and it works, unfortunately the infinite loop required to make the script act as a receiver, loads the CPU to 25%. So it's not really the best option.

I'm using cygwin right now, I'd like to create a bash script using linux native commands.

I can receive data by using:

cat /dev/ttyS2

And send a response with:

echo "command to send" > /dev/ttyS2

My question is, how do I make an automated listener to be able to receive and send data? The main issue I have, is actually how do I stop the cat /dev/ttyS2 command once information was received, put it into a variable which then I could compare with a switch, or a series of if else then blocks. Afterwards send back a response and start the cycle all over again?

Thanks

linuxbashserial-portcygwin


Solution 1:[1]

Is this not what you're looking for?

while read -r line < /dev/ttyS2; do
  # $line is the line read, do something with it
  # which produces $result
  echo $result > /dev/ttyS2
done

It's possible that reopening the serial device on every line has some side-effect, in which case you could try:

while read -r line; do
  # $line is the line read, do something with it
  # which produces $result
  echo $result > /dev/ttyS2
done < /dev/ttyS2

You could also move the output redirection, but I suspect you will have to turn off stdout buffering.

Solution 2:[2]

To remain fairly system independent, use a cross platform programming language: like Python, use a cross platform serial library like : pySerial and do the processing inside a script. I have used pySerial and I could run the script cross platform with almost no changes in source code. By using BASH you're limiting yourself a fair little.

Solution 3:[3]

If you use right tools, it is possible to actually have your CPU usage to be exactly 0 when your device does not have any output.

To accomplish this, you should use some higher level language (Perl, Python, C/C++ would do, but not bash) and use select loop on top of file handle of your serial device. This is an example for Perl http://perldoc.perl.org/IO/Select.html, but you can use any other language as long as it has support for select() syscall.

Sources

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Source: Stack Overflow

Solution Source
Solution 1
Solution 2 Aniket Inge
Solution 3 mvp

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