0

I wrote Arduino sketch and it works. It waits for a command and answers text on response.

enter image description here

Simultaneously, I can't get any response with command line tools.

For example, I have the following code to get temperature:

#!/bin/bash
tty=/dev/ttyUSB0
exec 4<$tty 5>$tty
stty -F $tty cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts
#stty -F $tty 9600 -echo
#printf "temp\n" >&5
echo temp >&5
read reply <&4
echo "$reply"
#tail -n 1 - <&4

It returns empty or hang under different circumstances.

Also, if I run built-in Serial Monitor, I can see responses on command lines like:

echo temp > /dev/ttyUSB0

But I see nothing with commands like tail -f /dev/ttyUSB0

What I am doing wrong?

  • I really want to say using Linux is where you going wrong, but that would be childish. :) I'm not sure if I read it right, but are you trying to connect two apps to the same console port? I wouldn't expect that to work, but I only use Windows, does that work on Linux? – Code Gorilla Oct 12 '15 at 19:41
1

Add the flag -hupcl to your stty command. That will disable the assertion of DTR which is resetting the board.

 hupcl (-hupcl)
             Stop asserting modem control (do not stop asserting modem
             control) on last close.

The first time it is run there will be a reset, since setting that flag entails opening the port, which causes a reset. So you need to add a delay long enough to get past the bootloader - minimum 2 seconds, best make it 3.

You can do that with the sleep command: sleep 3

Note that you now won't be able to upload a new sketch since you have disabled the auto-reset feature that allows you to enter the bootloader, so before uploading a new sketch you need to turn the reset back on with

stty -F $tty hupcl

If you don't disable the reset then every operation in your script that opens and then closes the serial port will trigger a reset of the board. So in summary try this:

#!/bin/bash
tty=/dev/ttyUSB0
stty -F $tty cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts -hupcl
sleep 3
echo temp >$tty
read reply <$tty
echo "$reply"
stty -F $tty hupcl
  • I was wishing to use reset feature. Why doesn't it work with it? – Dims Oct 12 '15 at 19:44
  • In that case leave the stty as it is, but just add the three second delay so it can get past the bootloader before you send your request. – Majenko Oct 12 '15 at 19:45
  • I was waiting long enough with tail -f, also I was observing directly, that Serial Monitor does see the output, while tail -f does not. – Dims Oct 12 '15 at 19:45
  • You can't read the data with two things at once - only one thing will get it. Also you have to wait before sending "temp" otherwise it just won't ever get it. – Majenko Oct 12 '15 at 19:46
  • By the way, what are exact conditions for resetting? I have 3 commands in the script, touching the port: stty, echo and read. Will it reset 3 times or only one, how to know? – Dims Oct 12 '15 at 19:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.