NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/sys/sun/misc/6222

Text File | 1993-01-11 | 1.4 KB | 32 lines

Newsgroups: comp.sys.sun.misc
Path: sparky!uunet!haven.umd.edu!darwin.sura.net!mlb.semi.harris.com!sloth.mlb.semi.harris.com!pjp
From: [e-mail] (Pat J. Pinchera)
Subject: How do I Detect Pending Data on a Serial Port?
Date: Mon, 11 Jan 1993 21:58:18 GMT
Nntp-Posting-Host: sloth.mlb.semi.harris.com
Organization: Interface & Control Systems, Inc., Melbourne FL
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I've openend up the serial port (/dev/tty[ab]) on my Sun IPC using the
'open' command. I get back a file descriptor.  How can I detect if there
is any data ready for reading, i.e. a Peek?

I've tried ioctl(fd, I_PEEK, arg) but this really only applies to
STREAMS, not File Descriptors.  Then I tried ioctl(fd, FIONREAD, &num),
but this is supposed to apply to 'files' per the filio man page. Note
that both of these calls seemed to work in a simple C test program, but
when I tried to use them in my big C++ project, they both returned -1
and set errno to ENOTTY, which means the specified request does not
apply to the kind of object I specified in 'fd'.

Does anyone know how to do this? I want to be able to tell if there's
data there without actually doing the read, because that would 'consume'
the data. Reply here or e-mail.  If this goes like my last couple of
posts, I'll suddenly discover the answer in about 2 hours :-)

Thanks,
Pat