Reading data from a serial port


 
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Operating Systems Linux Debian Reading data from a serial port
# 8  
Old 10-05-2014
Quote:
Originally Posted by Meow613
Thanks Corona688

Code:
cat < /dev/ttyS0 > myfile
bash: /dev/ttyS0: Device or resource busy

No screen program running
Run lsof again. There might be an orphaned process or something. If screen can read it, so can you, it's not special.
# 9  
Old 10-05-2014
Thank you Coorona688

Code:
root@meow:/home/ethan#  lsof /dev/ttyS0
COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
screen  3871 root    6u   CHR   4,64      0t0 1119 /dev/ttyS0

---------- Post updated at 03:58 PM ---------- Previous update was at 03:29 PM ----------

Thanks Corona668

Here is some more info -
Code:
root@meow:/home/ethan# cat < /dev/ttyS0 > myfile
^Z
[1]+  Stopped                 cat < /dev/ttyS0 > myfile
root@meow:/home/ethan# locate myfile
/home/ethan/myfile
root@meow:/home/ethan# cat myfile
root@meow:/home/ethan# cat < /dev/ttyS0 > myfile
^Z
[2]+  Stopped                 cat < /dev/ttyS0 > myfile
root@meow:/home/ethan# chown ethan:ethan myfile
root@meow:/home/ethan# cat < /dev/ttyS0 > myfile
^C
root@meow:/home/ethan# cat myfile
root@meow:/home/ethan# ls -l myfile
-rw-r--r-- 1 ethan ethan 0 Oct  5 15:54 myfile
root@meow:/home/ethan# chmod 777 myfile
root@meow:/home/ethan# ls -l myfile
-rwxrwxrwx 1 ethan ethan 0 Oct  5 15:54 myfile
root@meow:/home/ethan# cat < /dev/ttyS0 > myfile
^Z
[3]+  Stopped                 cat < /dev/ttyS0 > myfile
root@meow:/home/ethan# cat myfile

TIA
# 10  
Old 10-06-2014
Quote:
Originally Posted by Meow613
Thank you Coorona688

Code:
root@meow:/home/ethan#  lsof /dev/ttyS0
COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
screen  3871 root    6u   CHR   4,64      0t0 1119 /dev/ttyS0

Kill that screen session, for good this time, and don't open another. You cannot print it to the screen and expect anything else to be able to open it.
# 11  
Old 10-06-2014
Thanks wisecracker -

Code:
root@meow:/home/ethan# stty -F /dev/ttyS0
speed 9600 baud; line = 0;
-brkint -imaxbel
root@meow:/home/ethan#  stty -F /dev/ttyS0 raw
root@meow:/home/ethan# stty -F /dev/ttyS0
speed 9600 baud; line = 0;
min = 1; time = 0;
-brkint -icrnl -imaxbel
-opost
-isig -icanon


15) Now start printing, (blocks of?), characters to the terminal window... 
16) cat < /dev/ttyS0 17) It might take a second or so to fill your 
default serial buffer and may display a 256 byte  burst on each access so be aware.

"Now start printing, (blocks of?), characters to the terminal window.."
How??

TIA
# 12  
Old 10-07-2014
What do you mean how?

If the value being read from the serial port is 0, (zero), then the cursor will not move.
Until the value changes from 33 to 126 you will not see anything printed but the cursor __might__ move by one space.

What is connected to the serial port, /dev/ttyS0?
Does it allow raw transfer? (e.g. Arduino.)

If nothing is connected then obtain a loopback plug as a test piece and plug it into the port.

Once set up and with a loopback plug connected use this untested line:-
Code:
printf "Some text to display" > /dev/ttyS0

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