Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
?
Solved

How do I know whether my device is attached to tty?

Posted on 1997-08-20
6
Medium Priority
?
397 Views
Last Modified: 2013-12-26
I'm using AIX Ver 4.1 on IBM server.
In a C program, how do I know whether my device is attached to tty?  My device is asynchronous.

If my device is not attached, my program will hang on the following sentence : read(port, buf, 22);

I've tried using the following sentences but to no avail:
      port = open(PORT, O_RDWR | O_NODELAY);
and
     port = open(PORT, O_RDWR | O_NONBLOCK);


Thanks!


0
Comment
Question by:Rita060297
6 Comments
 
LVL 4

Accepted Solution

by:
rembo earned 60 total points
ID: 1294491


What sort of device is it?  Take a look at the man page
for the specific device and there should be an ioctl()
that you can use to determine device readiness.  The open()
system call often just sets a flag and never accesses
the device.  
0
 

Author Comment

by:Rita060297
ID: 1294492
The device is a digital clock which will send me the current time when
I send it a certain character.

I've tried ioctl with FIONREAD but I receive 0 for the number of bytes available to be read on the file descriptor when device is attached and device not attached.

Are there any alternatives?
0
 
LVL 85

Expert Comment

by:ozo
ID: 1294493
So it's a tty device?
Can you try an ioctl TIOCMGET?
Can you do a select with a timeout?

0
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

Expert Comment

by:aditya070797
ID: 1294494
I don't understand the question completely, but I think you can
try using:
----------------------------------
struct termios *termios_ptr;
...
rv = tcgetattr(port, termios_ptr);
----------------------------------
If you get an error (rv == -1) and errno is set to ENOTTY,
then the port is not a tty.
0
 

Author Comment

by:Rita060297
ID: 1294495
I tried ioctl(port, TIOCMGET, &nbyte) and received the following results :

nbyte = 70 when device attached to port
nbyte = 6 when device not attached to port

I've found out that TIOCMGET defines the following :
Gets all modem bits.  The argument to this command is a pointer to an
integer where the current state of the modem status lines is stored.
Which modem status and modem control lines are supported depends on the capabilities of the hardware and the hardware's device driver.

Question :
(1) How do I know what 70 or 6 means?
(2) Can I use 70 and 6 as a guide for deteching the attached or non-attached device?  It seems to be consistent during my numerous testing.


0
 
LVL 85

Expert Comment

by:ozo
ID: 1294496
You should be able to find the definition of the bits in /usr/include/sys/termios.h
It looks like 6 is DTR+RTS, and 0106 is DTR+RTS+CD (carrier detect)


0

Featured Post

VIDEO: THE CONCERTO CLOUD FOR HEALTHCARE

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction: Displaying information on the statusbar.   Continuing from the third article about sudoku.   Open the project in visual studio. Status bar – let’s display the timestamp there.  We need to get the timestamp from the document s…
Introduction: Finishing the grid – keyboard support for arrow keys to manoeuvre, entering the numbers.  The PreTranslateMessage function is to be used to intercept and respond to keyboard events. Continuing from the fourth article about sudoku. …
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
How can you see what you are working on when you want to see it while you to save a copy? Add a "Save As" icon to the Quick Access Toolbar, or QAT. That way, when you save a copy of a query, form, report, or other object you are modifying, you…
Suggested Courses
Course of the Month12 days, 11 hours left to enroll

580 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question