After a lot of head scratching, sending messages to this list and
even suspecting a bug in DU I've finally figured out why I was having
trouble doing I/O on my serial device. (See original post below).
It was all because of a silly little mistake in my code. I apologize
to those who wasted their time reading and/or responding to my messages.
Here's the bug: in my routine that opens the device I had a line like
this:
if (fd = open(...) >= 0)
return(fd)
The ">=" has precedence over "=" so the inequality was performed first,
always resulting in 1, so fd was always one. Later in my code, I was
doing my ioctl's and fstat's on an fd of 1, or stdout! Thus the results
I describe below occured.
Thank you to those who tried in vain to help me, especially Tom Blinn
who went far beyond the call of duty.
Regards,
Mike
------------------- Original question -------------------
managers:
As promised in my previous summary, here is my 3rd question about
my problem controlling a device connected to the serial port. Here's
a recap: I am trying to use ioctl() calls to control a device (a barcode
reader) connected to my serial port. I am able to open() /dev/tty01 and
change the port settings with ioctl()'s. However when I change port
settings it seems to affect my terminal, not the connection to the device.
For example, when I turn off echo, characters no longer appear at my
prompt when I type.
One experiment I've tried is to look at the major and minor device
numbers of the devie and /dev/tty before and after opening, using stat()
and fstat(). BTW, the "ace" serial port driver (major # 35) is configured
for tty01. Before opening, tty01 and tty have a major/minor pair of 35/1
and 1/0 respectively, as would be expected. However, after opening each
device, the major/minor pair becomes 6/4 for both devices. This happens
to be the same pair as my terminal device /dev/ttyp4.
Does anyone have any clue why, after opening, I am getting access to
the terminal rather than to the actual physical device? Is there some
sort of terminal or serial port configuration I don't know about?
Thanks,
Mike
P.S. An addendum to my previous summary: One reason I became confused
about the appropriate driver for my serial port was that there is no
man page for the ace driver. There are man pages for the scc and iscc
drivers however. There is a man page for ace in DU 4.0. Someone has
emailed it to me.
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Michael Galuza
DeJarnette Research Systems mgaluza_at_dejarnette.com
401 Washington Ave Suite 700 Voice: +1(410)583-0680 x691
Towson, MD 21204 Fax: +1(410)583-0696
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----------------------------------------------------------------------
Michael Galuza
DeJarnette Research Systems mgaluza_at_dejarnette.com
401 Washington Ave Suite 700 Voice: +1(410)583-0680 x691
Towson, MD 21204 Fax: +1(410)583-0696
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Received on Tue Jul 02 1996 - 17:03:43 NZST