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Having trouble installing a piece of hardware? Want to know if that peripheral is compatible with Linux?


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Old 12-29-2005, 02:08 PM   #1
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Registered: Aug 2004
Distribution: Slackware
Posts: 22

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serial port stays open after app. closes

I have a VS840 multimeter, and i found some code for PC readouts, through rs232 port

the source:
or you can find it at: (it's the same code)

the program reads out the measurings right, but the problem is that you can only stop it with C-c

after that if you run the prog. again, it doesnt read anything until a reboot.
setserial said that the port was in use

is there a way to manually close an open serial port? or another way to stop the program that would close the port (there is a close_serial function, but it is not used)?

it is boring if I have to make 20 reading to reboot my pc 20 times.

thank you for any help given
Old 12-30-2005, 11:28 PM   #2
Registered: May 2004
Posts: 552

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As root type this command to find out which application is using the serial port.

lsof /dev/ttyS0

Here's an example output, my ups daemon is on the first port.
upsd    2668 root    3u   CHR   4,64       681 /dev/ttyS0
There's another possibility, the application may be using some kind of lock file that isn't cleaned up when you ctrl-c it but gets removed when you reboot. Some programs create a file (maybe in /var/lock) and if the file exists it won't reopen the serial port even though no one is actually using the port.
Old 12-31-2005, 11:49 AM   #3
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Registered: Aug 2004
Distribution: Slackware
Posts: 22

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lsof /dev/ttyS0 doesnt output anything
there is no lock file specified in the program, and none exists for the serial port on the pc

still.. after a reboot, i start the program and it outputs me data, when i stop it, and then rerun it again, it doesnt do anything. unplugging and replugging the cables doesnt help, so does not turning off/on the meter
Old 12-31-2005, 01:16 PM   #4
Registered: May 2004
Posts: 552

Rep: Reputation: 31
Do you have the source code to the application?
Also, just try runing the lsof command from a different terminal while your application is also running and see if it prints out the name of your application.
Then when you ctrl-C the app does lsof stop listing the application?


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