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Reading data from a serial port

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Operating Systems Linux Debian Reading data from a serial port
# 1  
Old 10-03-2014
Reading data from a serial port
Dear List -

I am trying to capture data from a serial port and write it to a file.
Code:
/var/www$ cat /dev/ttyS0 > scale_value.html 
cat: /dev/ttyS0: Device or resource busy 

/var/www#  cat /proc/tty/driver/serial 
serinfo:1.0 driver revision: 

0: uart:16550A port:000003F8 irq:4 tx:90 rx:270 brk:2 RTS|CTS|DTR|DSR|CD 
1: uart:16550A port:00001C90 irq:17 tx:19 rx:0 CTS|DSR|CD 
2: uart:unknown port:000003E8 irq:4 
3: uart:unknown port:000002E8 irq:3 

/var/www# cat /proc/interrupts 
           CPU0       CPU1 
  0:         42          0   IO-APIC-edge      timer 
  1:          3          0   IO-APIC-edge      i8042 
  4:         74         89   IO-APIC-edge      serial 
  6:          2          1   IO-APIC-edge      floppy 
  8:          0          1   IO-APIC-edge      rtc0 
  9:          1          2   IO-APIC-fasteoi   acpi 
 12:          5          0   IO-APIC-edge      i8042 
 16:     148679     155632   IO-APIC-fasteoi   uhci_hcd:usb1, uhci_hcd:usb4, ehci_hcd:usb7 
 17:          9          8   IO-APIC-fasteoi   uhci_hcd:usb2, uhci_hcd:usb5, i801_smbus 
 18:        131        143   IO-APIC-fasteoi   uhci_hcd:usb3, ehci_hcd:usb6, uhci_hcd:usb8 
 40:   54993721          0  HPET_MSI-edge      hpet2 
 41:          0   53507648  HPET_MSI-edge      hpet3 
 42:    1041026     920449   PCI-MSI-edge      eth0 
 43:     524549     476624   PCI-MSI-edge      ahci 
 44:         11          9   PCI-MSI-edge      mei_me 
 45:      46800      46570   PCI-MSI-edge      i915 
 46:       1488       1583   PCI-MSI-edge      snd_hda_intel 
NMI:      37245      37177   Non-maskable interrupts 
LOC:         16         12   Local timer interrupts 
SPU:          0          0   Spurious interrupts 
PMI:      37245      37177   Performance monitoring interrupts 
IWI:     258822     264271   IRQ work interrupts 
RTR:          0          0   APIC ICR read retries 
RES:    5271209    5278411   Rescheduling interrupts 
CAL:        433        693   Function call interrupts 
TLB:    2917013    2903216   TLB shootdowns 
TRM:          0          0   Thermal event interrupts 
THR:          0          0   Threshold APIC interrupts 
MCE:          0          0   Machine check exceptions 
MCP:       1061       1061   Machine check polls 
ERR:          0 
MIS:          0 

/dev/ttyS1, Line 1, UART: 16550A, Port: 0x1c90, IRQ: 17 
    Baud_base: 115200, close_delay: 50, divisor: 0 
    closing_wait: none 
    Flags: spd_normal skip_test 

/var/www#  setserial /dev/ttyS0 -a 
/dev/ttyS0, Line 0, UART: 16550A, Port: 0x03f8, IRQ: 4 
    Baud_base: 115200, close_delay: 50, divisor: 0 
    closing_wait: 3000 
    Flags: spd_normal skip_test

How do I get rid of the busy message?

TIA

Ethan

Moderator's Comments:
Mod Comment Please use code tags next time for your code and data. Thanks
# 2  
Old 10-03-2014
Mayhap it IS busy? What be the output of lsof /dev/ttyS0?
# 3  
Old 10-03-2014
The IRQ of your serial port hasn't been relevant for about 20 years.

Depending on how your serial port is configured, it may expect RTS/CTS or DTR/DSR handshaking before it will communicate(i.e. will consider the connection 'closed' when certain control lines aren't just right). You can configure this with stty. I think this turns it off.

Code:
stty -f /dev/ttyS0 -crtscts -cdtrdsr

This User Gave Thanks to Corona688 For This Post:
jim mcnamara
# 4  
Old 10-04-2014
Thanks RudiC


Code:
lsof /dev/ttyS0
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
screen 28323 root 6u CHR 4,64 0t0 1119 /dev/ttyS0

The output is from scale which transmits via a rs232 link.

I can see the output on the screen, in ASCII characters.
# 5  
Old 10-04-2014
Quote:
Originally Posted by Meow613
I can see the output on the screen, in ASCII characters.
That, obviously, would be what has it open.

Close that screen session.
# 6  
Old 10-04-2014
Thanks Corona688

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

No screen program running
# 7  
Old 10-05-2014
Sometimes a serial transfer can be a RPITA...
There is usually a buffer of _at_least_ 256 bytes to fill first, so........
........try this sequence of events as a starter test mode from root TO assume a 3 wire system only:-
(RTS and CTS should be ignored using the below.)
Code:
1) Close down your terminal completely and do a reboot of your machine.
2) In root mode open up a new terminal then...
3) Number 4) below is optional...
4) chmod 666 /dev/ttyS0
5) Check the status of your /dev/ttyS0
6) Note that your stty might need -f instead of -F and may already be at 9600bps...
7) stty -F /dev/ttyS0
8) Set up the on board serial I/O to 9600bps and RAW data transfer, in my case, for PCLinuxOS and Debian.
9) Again note that your stty might need -f instead of -F ...
10) stty -F /dev/ttyS0 9600
11) stty -F /dev/ttyS0 raw
12) Finally, again check the status of your /dev/ttyS0
13) And again, note that your stty might need -f instead of -F ...
14) stty -F /dev/ttyS0
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.

Hope this works for you...
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