DCD

DCD

Post by Robert L. Caryl, Jr » Thu, 22 Jan 1998 04:00:00



I am working on some communications stuff for XENIX (yeah, yeah, I know)
and I need a way to be able to tell if the modem
has lost carrier during file transmission.  I found a data structure in
/usr/include/sys/tty.h called "tty" (duh!).  It contains a variable
which is commented to be the serial line status byte.  This byte,
according to documentation, contains a carrier detect flag that
can be both read and set.  Unfortunately, the documentation doesn't
mention how to access this data.  I have been told to use
"ioctl", but there is no documented command parameter for ioctl that
allows use of a pointer to this structure as a parameter to
ioctl.

I appear to SOL, but I thought maybe there is someone out there who
would know about an undocumented feature of ioctl.
The version of XENIX is 2.3.4.

Thanks in advance for any help.


 
 
 

DCD

Post by Robert Li » Thu, 22 Jan 1998 04:00:00



Quote:>--------------33C5633D6EB63AFD8AB46212
>Content-Type: text/plain; charset=us-ascii
>Content-Transfer-Encoding: 7bit

Please turn off the inclusion of the HTML version of your posting.
The ASCII version is fine.

Quote:>I am working on some communications stuff for XENIX (yeah, yeah, I know)
>and I need a way to be able to tell if the modem
>has lost carrier during file transmission.  I found a data structure in

THis is better covered in comp.unix.sco.programmer.   It is, in fact,
a FAQ in that group.

        http://www.dgii.com/cgi-bin/scoprgfaq/faq.pl

Go to the bottom, search for "DCD".

--


 
 
 

1. DCD Drops, then DTR Drops, Want to Increase Delay (SLIP)

I'm having an occasional problem on my SLIP connection that causes DCD
(incoming) to drop out momentarily.

When this happens, Linux drops DTR in response, and the connection
gets broken.  Generally it happens only once in several hours, though
sometimes it will happen several times in a row over a space of an
hour before it will settle down.

What I would like to do is increase the delay between the time Linux
detects lost DCD and the time it drops DTR ... would like to increase
it to around a second or so.

If someone could direct me to the portion of the code that monitors
DCD and drops DTR, I can take care of the rest.  But I've looked all
through /usr/src/linux/ ..... (I forget the rest of the path to
serial.c), grepped on things like DCD and DTR in as much of the rest
of the source as I can find, and don't see where it's happening.

Linux version is 0.99.15, Slackware 1.1.2, using agetty in inittab to
open up the serial ports (for some reason I was not able to get getty
or getty_ps to do what I needed, probably just a config or RTFM
problem, but in any case agetty works fine).

Any assistance or pointers gratefully accepted.

 . . . . . ep

2. SRM

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